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Exposure to Estradiol before but Not during Acquisition of LiCl-Induced Conditioned Taste Avoidance Accelerates Extinction
Hormones and Behavior 41, 297–305 (2002) doi:10.1006/hbeh.2002.1774, available online at http://www.idealibrary.com on
Exposure to Estradiol before but Not during Acquisition of LiCl-Induced Conditioned Taste Avoidance Accelerates Extinction Kathleen C. Chambers 1 and Unja L. Hayes Department of Psychology, University of Southern California, Los Angeles, California 90089 Received February 13, 2001; revised May 24, 2001; accepted October 15, 2001
Estradiol accelerates extinction of LiCl-induced conditioned taste avoidance when it is present continuously before and during acquisition. We have suggested that the effect of estradiol on extinction is due to its illnessassociated, rather than learning-associated, properties. If this were the case, then one would expect estradiol to act before but not during acquisition. This expectation is based on previous work showing attenuation of learned taste avoidance when rats are given distal preexposure (greater than 24 h before conditioning) or proximal preexposure (less than 24 h before conditioning) to the illness-inducing agent LiCl before acquisition of a LiClinduced conditioned taste avoidance. In three separate experiments, estradiol was administered during three different time periods via subcutaneous implantation of a 10-mm estradiol-filled capsule. In each experiment, the extinction of estradiol-treated females was compared to that of females implanted with empty capsules. In the first experiment, female rats were given distal exposure to estradiol before acquisition. Capsules were implanted 11 days before acquisition and were removed 2 days before acquisition. In the second experiment, female rats were given proximal exposure to estradiol before acquisition. Capsules were implanted 2.5 h before LiCl was paired with a sucrose solution and were removed 16.5 h later. In the third experiment, female rats were given exposure to estradiol during acquisition. Capsules were implanted at the same time as LiCl administration and were removed 18 h later. The only estradiol-treated females to show accelerated extinction were those given distal preexposure to estradiol in Experiment 1. These data do not support a learning-associated hypothesis and only partially support an illnessassociated hypothesis. The failure to find accelerated extinction following proximal preexposure may reflect an inappropriate choice of the parameters used in the
1 To whom correspondence and reprint requests should be addressed. E-mail: [email protected].
0018-506X/02 $35.00 © 2002 Elsevier Science (USA) All rights reserved.
experiment or a difference in the stimulus properties of LiCl and estradiol that allow each to serve as conditioning and preexposure agents in conditioned taste avoidance paradigms. Extinction of a LiCl-induced conditioned taste avoidance is accelerated when estradiol is present before and during acquisition. In the study that demonstrated this effect, exposure to estradiol was given continuously via a subcutaneously implanted capsule during a period that started 8 days before acquisition and continued until 3 days after acquisition. © 2002 Elsevier Science (USA)
Daily extinction tests were initiated a week later and were conducted in the absence of estradiol (Yuan and Chambers, 1999a). Two hypotheses have been suggested to account for this effect of estradiol, an illnessassociated and a learning-associated hypothesis. We raised the possibility that the illness-inducing properties of estradiol could account for the accelerated extinction (Chambers and Yuan, 1990; Yuan and Chambers, 1999a, 1999b). LiCl is a putative illness-inducing agent and it has been suggested that supraphysiological levels of estradiol induce an illness that parallels that of LiCl (DeBeun, Jansen, Smeets, Niesing, Slangen, and Van de Poll, 1991; Gustavson and Gustavson, 1987; Gustavson, Gustavson, Young, Pumariega, and Nicolaus, 1989). Both estradiol and LiCl are known to produce nausea and vomiting in humans (Goodman and Gilman, 1975; Schou, 1968). In addition, both can be used as an illness-inducing agent to produce conditioned taste aversion, defined as a decrease in consumption of the taste stimulus and a shift in the hedonic evaluation of the taste stimulus, as measured by decreases in ingestive and increases in aversive orofacial and somatic responses when the taste stimulus is place directly on the tongue. Different dosages and concentrations of LiCl and different administration routes induce conditioned
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taste avoidance as well as decreases in ingestive and increases in aversive taste reactivity behaviors (Breslin, Spector, and Grill, 1992; Eckel and Ossenkopp, 1996; Nachman and Ashe, 1973). Estradiol in different forms, doses, and routes of administration can induce conditioned taste avoidance when paired with a novel flavor in rats, mice, and humans (Bernstein, Courtney, and Braget, 1986; De Beun et al., 1991; De Beun, Peeters, and Broekkamp, 1993; Ganesan and Simpkins, 1990, 1991; Gustavson and Gustavson, 1986, 1987; Gustavson et al., 1989; Gustavson, Reinarz, Gustavson, and Pumariega, 1988; Merwin and Doty, 1994; Miele, Rosellini, and Svare, 1988; Nicolaus, Farmer, Gustavson and Gustavson, 1989; Nicolaus, Herrera, Nicolaus, and Gustavson, 1989; Peeters, Smets, and Broekkamp, 1992; Rice, Lopez, and Garcia, 1987; Yuan and Chambers, 1999b). It also can produce conditioned negative shifts in palatability after it has been paired with a novel sweet taste solution (Ossenkopp, Rabi, and Eckel, 1996). Illness inducing agents have not only been used as conditioning agents in conditioned taste avoidance paradigms but as preexposure agents (Berman and Cannon, 1974; Braveman, 1975; Cannon, Baker, and Berman, 1977; Gamzu, 1977). It is well known that exposure to an illness-inducing agent before pairing a novel taste stimulus with either the same illness-inducing agent (termed an intraagent) or a different illness-inducing agent (termed an interagent) will attenuate expression of taste avoidance. For example, when LiCl is injected 8, 5, and 2 days before acquisition of conditioned taste avoidance induced by LiCl, radiation, or ethanol, the taste avoidance is attenuated (Rabin, Hunt, and Lee, 1989). Two different kinds of preacquisition exposure regimens in which LiCl is both the preexposure agent and the conditioning agent have been described. Remote or distal preexposure is characterized as taking place 24 h or more before conditioning and proximal preexposure is given less than 24 h before conditioning (Domjan, 1978). The distal preexposure regimen that successfully attenuates taste avoidance is varied, e.g., 1 preexposure given 1 day before acquisition, 8 daily preexposures starting 9 days before acquisition, or 6 preexposures every 4th day starting 25 days before acquisition (Cannon, Berman, Baker, and Atkinson, 1975; Holman, 1976; Riley, Jacobs, and LoLordo, 1976). For proximal preexposure, animals are exposed to LiCl minutes to hours before acquisition. Taste avoidance has been shown to be attenuated when LiCl is given 30, 110, 180, 270, and 360 minutes before access to a taste solution and the subsequent conditioning administration of LiCl (Domjan, 1978; Domjan and
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Best, 1977; Domjan and Gemberling, 1980). An important defining characteristic of preexposure disruption is that the preexposure agent must be present before acquisition or extinction, not during. In the experiment mentioned above, estradiol was present both before and during acquisition (Yuan and Chambers, 1999a). The presence of estradiol before acquisition may have served as an interagent disrupter and consequently led to an accelerated extinction. We also raised the possibility that estradiol disrupts a learning-associated process by reducing the effectiveness of LiCl during acquisition (Yuan and Chambers, 1999a). There is some evidence to suggest that increases in blood pressure can serve as an aversive stimulus to induce conditioned taste avoidance. Vasopressin produces increases in blood pressure and it induces conditioned taste avoidance (Ettenberg, van der Kooy, Le Moal, Koob, and Bloom, 1983). However, vasopressin-induced learned avoidance can be prevented by pretreatment with an antagonist that completely blocks the increase in blood pressure induced by the subcutaneous injection of vasopressin. In addition, conditioned taste avoidance cannot be induced by the vasopressin analogue, dDAVP, which has no vasopressor effects (Bluthe, Dantzer, Mormede, and Le Moal, 1985). LiCl also raises arterial blood pressure, but estradiol lowers it (Brosnihan, Moriguchi, Nakamoto, Dean, Ganten, and Ferrario, 1994; Hulman, Brodsky, Miller, Donnelly, Helms, and Falkner, 1996; Manwaring, Morfis, Diamond, and Howes, 2000; O’Connor, Cheng, and North, 1987). Thus the net effect of combining estradiol and LiCl may be a reduction in the illness efficacy of LiCl and consequently accelerated extinction of conditioned taste avoidance. The following experiments were designed to determine whether extinction is accelerated when estradiol is present before acquisition of a LiCl-induced conditioned taste avoidance, which would be consistent with an illness-associated hypothesis, or whether extinction is accelerated when estradiol is present at the time of LiCl administration, which would be consistent with a learning-associated hypothesis.
METHODS Subjects The subjects were adult female Fischer 344 rats (Simonsen Laboratories, Gilroy, CA). The vivarium in which the rats were quartered was temperature (21– 22°C), humidity (51%), and light controlled (a 12:12
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hour light/dark cycle with lights on at 1000 and lights off at 2200). The rats were housed in pairs in solid bottom cages (58 ⫻ 38 cm) that had wood chips as bedding material. Testing was done in the home cage but a stainless steel divider was placed in the middle of each cage to separate each pair of rats during behavioral testing. During avoidance testing, water was available 23 h a day and a sucrose solution was available for 1 h. In previous studies, we found that rats given similar drinking schedules are essentially nondeprived (Brownson, Sengstake, and Chambers, 1994; Chambers, Sengstake, Brownson, and Westfahl, 1993; Sengstake and Chambers, 1979; Sengstake, Chambers, and Thrower, 1978). When water as well as sucrose was available during the 1- or 2-h test period, most rats drank 2– 4 ml of water both before and after conditioning. Preparation of Estradiol-Filled Capsules Estradiol-treated groups were implanted with capsules that contained crystalline estradiol (Steraloids, Wilton, NH) and untreated groups received capsules that were empty. The Silastic capsules had inside diameters of 0.157 cm and outside diameters of 0.318 cm and both ends of each capsule were sealed with silicone type A Silastic adhesive. The length of the filled or empty portion of the capsule was 10 mm and the length of each sealed end was 1 mm.
postacquisition recovery period, and extinction tests. All solutions used during testing were stored under refrigeration and they were given to the rats at the beginning of the dark portion of the light/dark cycle. Each day during preconditioning, the water bottle of each rat was replaced with one cylinder containing chilled tap water. After 1 h, the cylinder was replaced with the regular water bottle. Preconditioning rats with cold water just after the lights switch off increases the likelihood that nondeprived rats will drink the novel sucrose solution during acquisition. On acquisition day, the water bottle of each rat was replaced with one cylinder containing a 10% sucrose solution, (w/v, 0.29 M). One hour later, the amount of sucrose consumption was recorded and the cylinder was removed. Each rat was removed from its cage, injected with a LiCl solution (0.15 M, 10 ml/kg of body weight), returned to its cage, and then its regular water bottle was returned. Daily extinction tests were initiated 2 (Experiment 1) or 3 (Experiments 2 and 3) days after acquisition. Extinction tests were conducted in the same manner as the acquisition test except no LiCl injections were given. For Experiment 3A, each rat was given one extinction test daily for 8 days. For all of the other experiments, each rat was given one extinction test daily for 14 days. Those rats that had not regained their acquisition day consumption by the 14th test were given additional daily extinction tests until they did or until 5 more extinction tests had been given.
Surgical Procedures Ovariectomies and implantation of Silastic capsules were performed while the rats were under halothane anesthesia (Halocarbon Laboratories, River Edge, NJ). The halothane was vaporized (Fluotec 3) and mixed with oxygen by a Fraser Harlake VMC small animal inhalation anesthesia machine (Datex-Ohmeda, Madison, WI). This gas mixture was delivered to each rat through a nose cone. The percent of halothane in the gas mixture was maintained between 1.5 and 2.0 and the oxygen flow rate was maintained between 3.5 and 4.0 l/min. Ovariectomies included bilateral incisions of the skin and muscles (1 to 2 cm from midline and anterior to the hip) and removal of the ovaries. The Silastic capsules were implanted subcutaneously at the nape of the neck. Conditioned Taste Avoidance Procedure The conditioned taste avoidance procedure included preconditioning tests, an acquisition test, a
Experimental Design Experiment 1: Distal Preexposure. Twenty females were randomly assigned to one of two groups: empty capsule (n ⫽ 10) or estradiol-filled capsule (n ⫽ 10). The experimental procedure was divided into the following six periods: ovariectomy and capsule implantation (day 1), preconditioning (days 2–9), capsule removal and recovery (days 10 –11), acquisition (day 12), postacquisition recovery (day 13), and extinction tests (days 14 –27). The capsules were implanted at the same time the females were ovariectomized and they were removed the day following the last preconditioning test. Experiment 2: Proximal Preexposure. Nineteen females were randomly assigned to one of two groups: empty capsule (n ⫽ 9) or estradiol-filled capsule (n ⫽ 10). The experimental procedure was divided into the following six periods: ovariectomy (day 1), preconditioning (days 2–11), capsule implantation and acquisition (day 12), capsule removal (day 13), postacquisi-
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tion recovery (day 14), and extinction tests (days 15– 28). Capsules were implanted approximately 1.5 h before access to sucrose, which was 2.5 h before LiCl injection, and they were removed 18 h later. Experiment 3: During Acquisition. Females were randomly assigned to one of two groups: empty capsule (n ⫽ 10 in Part A and n ⫽ 6 in Part B) or estradiol-filled capsule (n ⫽ 8 in Part A and n ⫽ 6 in Part B). The experimental procedure was divided into the following six periods: ovariectomy (day 1), preconditioning (days 2–9), acquisition and capsule implantation (day 10), capsule removal (day 11), postacquisition recovery (day 12), and extinction tests (days 13–20). Capsules were implanted immediately after access to a sucrose solution and at the same time that LiCl was injected. They were removed 18 h later. Statistical Analyses Acquisition was assessed by using a two-factor (groups ⫻ tests) analysis of variance (ANOVA) with repeated measures on tests to analyze the amount of sucrose consumed across the acquisition and first extinction test. Extinction was assessed in two ways. A two-factor (groups ⫻ tests) ANOVA with repeated measures on tests was used to analyze the amount of sucrose consumed across all of the extinction tests. The number of daily tests to reach 100% of acquisition day consumption levels (extinction criterion) was determined and these values were analyzed with independent t tests.
RESULTS Experiment 1: Distal Preexposure The results showed that extinction was accelerated in females given distal exposure to estradiol before acquisition (see Fig. 1). The estradiol-treated females extinguished in 13.5 days and the untreated females extinguished in 18.2 days. Sucrose consumption for all animals in both groups decreased across the acquisition and first extinction test and the extent of the decrease was similar for both groups (F(1, 18) ⫽ 96.91, P ⬍ 0.001 for test main effect). All animals increased their consumption of sucrose during extinction but the estradiol-treated females consumed more sucrose and showed a greater rate of increase in consumption across the 14 extinction tests than the untreated females (F(13, 234) ⫽ 10.80, P ⬍ 0.001 for tests main effect; F(1, 18) ⫽ 5.29, P ⫽ 0.033 for group
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FIG. 1. Mean (⫾SE) sucrose consumption (ml) during acquisition (ACQ) and extinction tests (E1–E14) for gonadectomized female rats implanted with an estradiol-filled Silastic capsule (E, n ⫽ 10) or an empty capsule (O, n ⫽ 10) before acquisition of a LiCl-induced conditioned taste avoidance. Capsules were implanted 11 days before acquisition and were removed 2 days before acquisition (distal preexposure). *Mean sucrose consumption and rate of increase in consumption across extinction tests was significantly greater and mean number of days to regain acquisition day consumption levels was significantly less than for the O group, P ⱕ 0.05.
main effect, F(13, 234) ⫽ 2.13, P ⫽ 0.013 for interaction effect, T(18) ⫽ 2.11, P ⫽ 0.049 for extinction criterion). Experiment 2: Proximal Preexposure The results showed that extinction was not significantly accelerated in females given proximal exposure to estradiol before acquisition (see Fig. 2). The estradiol-treated females extinguished in 12.3 days and the untreated females extinguished in 15.2 days. Sucrose consumption for all animals in both groups decreased across the acquisition and first extinction test and the extent of the decrease was similar for both groups (F(1, 17) ⫽ 58.95, P ⬍ 0.001 for test main effect). All animals increased their consumption of sucrose during extinction and the amount of sucrose consumed and rate of increase in consumption across the 14 extinction tests was similar for both groups (F(13, 221) ⫽ 19.84, P ⬍ 0.001 for test main effect). Experiment 3: During Acquisition For both experiments, the results showed that extinction was not accelerated in females exposed to estradiol during acquisition (see Fig. 3). The estradioltreated females extinguished in 6.3 days in Part A and 17.3 days in Part B and the untreated females extin-
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FIG. 2. Mean (⫾SE) sucrose consumption (ml) during acquisition (ACQ) and extinction tests (E1–E14) for gonadectomized female rats implanted with an estradiol-filled Silastic capsule (E, n ⫽ 10) or an empty capsule (O, n ⫽ 9) before acquisition of a LiCl-induced conditioned taste avoidance. Capsules were implanted 2.5 hours before pairing LiCl with a sucrose solution and were removed 15.5 h later (proximal preexposure). No significant overall differences were found.
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After 1 h, the levels are 759.6 pg/ml and after 6 h, they are 464.2 pg/ml (Yuan and Chambers, 1999b). These data suggest that both estradiol and LiCl reached peak blood levels at about the same time. The extinction rates of the untreated females in experiment 3A were faster than those of the untreated females in Experiments 1 and 2 (means for extinction criterion ⫽ 4.8, 18.2, and 15.2 days, respectively. The same was true of the estradiol treated females in Experiment 3A (means for extinction criterion ⫽ 6.3, 13.5, and 12.3). Because the animal supplier, age and sex of the rats, housing conditions, batch of sucrose and LiCl, and experimenter were the same for all of the experiments, variations in these factors cannot account for the differences in extinction rates. We occasionally have found that an entire batch of ani-
guished in 4.8 days in Part A and 14.3 days in Part B. Sucrose consumption for all animals in both groups decreased across the acquisition and first extinction test and the extent of the decrease was similar for both groups (F(1, 16) ⫽ 139.22, P ⬍ 0.001 in Part A and F(1, 10) ⫽ 78.77, P ⬍ 0.001 in Part B for test main effect). All animals increased their consumption of sucrose during extinction and the amount of sucrose consumed and rate of increase in consumption across the 14 extinction tests was similar for both groups (F(7, 112) ⫽ 13.72, P ⬍ 0.001 in Part A and F(13, 130) ⫽ 8.62, P ⬍ 0.001 in Part B for test main effect).
DISCUSSION Learning-Associated Hypothesis The presence of estradiol during LiCl illness did not accelerate extinction of a conditioned taste avoidance. It is unlikely that the failure to find accelerated extinction in the estradiol treated females of both experiments was due to inappropriate timing of the administration of estradiol and LiCl. Plasma lithium levels reach their peak 30 min after administration (Morrison, Pritchard, Brande, and Aguanns, 1971). In a pilot study, we found that serum blood levels of estradiol increase to a mean of 748 pg/ml (n ⫽ 4, range ⫽ 394 –1049 pg/ml) 30 min after implantation of a 10 mm estradiol-filled capsule in Fischer 344 female rats.
FIG. 3. Mean (⫾SE) sucrose consumption (ml) during acquisition (ACQ) and extinction tests (E1–E8 in A and E1–E14 in B) for gonadectomized female rats implanted with an estradiol-filled Silastic capsule (E, n ⫽ 8 for A and n ⫽ 6 for B) or an empty capsule (O, n ⫽ 10 for A and n ⫽ 6 for B) during acquisition of a LiCl-induced conditioned taste avoidance. Capsules were implanted at the same time as LiCl administration and were removed 18 h later. No significant overall differences were found.
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mals in a study extinguish either more quickly or more slowly than is typical. However, in subsequent replications of these studies, we have found that this variability does not alter the results, that is, the relative differences between groups remains the same. This also was the case for experiment 3. The extinction rates in experiment 3B were more typical of what is observed under our testing conditions, and as was true for experiment 3A, the presence of estradiol during LiCl illness did not accelerate extinction of a conditioned taste avoidance. If estradiol acted on some learning process, then one would have expected it to accelerate extinction when it was present at the time of association between the sucrose solution and the stimulus effects of LiCl. However, in Experiment 3, there was a tendency for the estradiol treated females in both experiments to consume less, rather than more, sucrose during most of the extinction tests and to increase sucrose consumption at a slower rate. Estradiol treated females consumed significantly less sucrose on the first extinction test in Experiment 3A and there was a tendency for them to consume less on extinction test 3 in both Experiments 3A and 3B (T(16) ⫽ 2.23, P ⫽ 0.04, T(16) ⫽ 1.86, P ⫽ 0.08 and T(10) ⫽ 3.87, P ⫽ 0.003, respectively). The tendency for estradiol to strengthen a conditioned taste avoidance when combined with LiCl is consistent with studies of the effect of combining LiCl with other illness-inducing agents. For example, subthreshold doses of LiCl and radiation, that alone do not produce conditioned taste avoidance, can induce avoidance when both are given (Rabin, Hunt, and Lee, 1987). Illness-Associated Hypothesis Distal preexposure. Extinction of a LiCl-induced conditioned taste avoidance was accelerated when rats were given distal preexposure to estradiol in Experiment 1. This result is consistent with an illnessassociated hypothesis. Elevated blood levels of estradiol cannot account for the accelerated extinction at the time of acquisition. The results of Experiment 3 show that elevated estradiol levels during acquisition do not produce accelerated extinction. Further, blood levels of estradiol fall rapidly after removal of a 10 mm capsule; they are at baseline within 2 hours after removal (Karsch, Dierschke, Weick, Yamaji, Hotchkiss, and Knobil, 1973; Legan, Coon, and Karsch, 1975). Since the acquisition trial was given 2 days after capsule removal, this suggests that estradiol levels were not elevated at the time of acquisition.
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Proximal preexposure. When rats were given proximal preexposure to estradiol in Experiment 2, extinction of a LiCl-induced conditioned taste avoidance was not accelerated. This result is not consistent with an illness-associated hypothesis. It is worth noting, however, that there was a tendency for estradioltreated females to consume more sucrose during extinction than untreated females; this difference was significant on extinction day 8 (T(17) ⫽ 2.29, P ⫽ 0.03). It is unlikely that the failure to find a significant proximal effect is tied to the prolonged presence of estradiol (18 h) after LiCl administration. The biological effects of lithium are determined by its bioavailable concentration since it is neither protein bound or metabolized by any means (Schou, 1968). Investigators who have consumed lithium, report that lithium illness lasts about 2 h and that within 10 –20 minutes of the peak illness sensations, which are correlated with the peak lithium concentration in the blood, the symptoms subside (Trautner, Morris, Noack, and Gershon, 1955). In rats that have been injected intraperitoneally with four different concentrations of LiCl, plasma lithium levels reach their peak 30 min after administration, regardless of dose, and decrease to half of the peak level in 1–2 h (Morrison et al., 1971). Quantified descriptions using reduced activity and reduced water intake as indices of LiCl-induced illness, indicate that the greatest effects occur 15 to 60 min after administration (Barker and Smith, 1974; Nachman, 1963). This suggests that in at least some of the proximal preexposure studies, LiCl from the preexposure administration was still in the circulatory system and still having its greatest illness effect at the time of the conditioning administration. Yet, rather than having an additive effect, the preexposure administration had an attenuating effect on learned taste avoidance. There are two other explanations that might account for the failure to find a proximal preexposure effect. First, the dose of estradiol may not have been high enough. When LiCl is used as both the preexposure and conditioning agent, the higher the preexposure dose of LiCl, the greater the attenuation of learned taste avoidance in both distal and proximal preexposure situations (Cannon et al., 1975; Domjan, 1978). If the dose of estradiol in the present study was not high enough, then this would further suggest that proximal preexposure requires a higher dose to produce an effect than distal preexposure. In addition, it would suggest that proximal preexposure did not contribute to the acceleration of extinction found when estradiol was present both before and during acquisition (Yuan
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and Chambers, 1999a). A second possibility is that for the dose of estradiol used, the amount of time exposed to estradiol before acquisition was not long enough to produce a proximal preexposure effect. In the proximal preexposure study, the rats were exposed to estradiol for only 2.5 h before conditioning with LiCl. Perhaps a longer period of exposure to estradiol before conditioning would have produced accelerated extinction. All of the evidence. There is a considerable amount of evidence supporting the hypothesis that the acceleration of extinction of a LiCl-induced conditioned taste avoidance when estradiol is present before and during extinction can be accounted for by its illness-inducing properties. First, subcutaneous implantation of a 10 mm estradiol-filled capsule can induce conditioned taste avoidance after pairing it with a novel sucrose solution (Yuan and Chambers, 1999b). Second, the results of Experiment 1 show that distal preexposure to estradiol, administered subcutaneously via a 10 mm capsule, accelerates extinction of a LiCl-induced conditioned taste avoidance. Third, comparisons of the temporal characteristics of estradiol and LiCl indicate that these agents can serve as mutual distal interagents before acquisition. Distal preexposure to estradiol weakens acquisition and accelerates extinction of conditioned taste avoidance induced by estradiol as well as LiCl (De Beun et al., 1993; Merwin and Doty, 1994). Distal preexposure to LiCl attenuates acquisition of both a LiCl-induced and estradiol-induced conditioned taste avoidance (Cannon et al., 1977; De Beun et al., 1993; Riley et al., 1976; Rabin et al., 1989; Suarez and Barker, 1976). Fourth, extinction is accelerated when a 10-mm estradiol-filled capsule is implanted subcutaneously during the postacquisition/preextinction period, that is, when implanted 2 days after acquisition and removed 8 days later, which was one day before the first extinction test (Yuan and Chambers, 1999b). Similar results have been obtained when LiCl is used as the postacquisition/preextinction exposure agent. Taste avoidance is attenuated when one injection of LiCl is given on a day that is 2 days after acquisition of a LiCl-induced avoidance and 2 days before the postacquisition test (Mikulka, Leard, and Klein, 1977). Fifth, extinction is prolonged when a 10 mm estradiol-filled capsule is implanted subcutaneously during extinction, that is, during reexposures to the conditioned taste stimulus, which are not followed by LiCl illness (Yuan and Chambers, 1999b). These results are what one would expect if estradiol acted as an illness-inducing agent. The presence of estradiol during reexposures to the
conditioned taste stimulus would be equivalent to repeated acquisition trials and therefore should prolong extinction. The only finding that is not consistent with the illness-associated hypothesis is the failure to find a significant proximal preexposure effect in Experiment 2. As mentioned above, this may only reflect an inappropriate choice of the parameters used in the experiment. On the other hand, this may indicate that the stimulus properties of estradiol that allow it to serve as a conditioning and preexposure agent in conditioned taste avoidance paradigms are different than those of LiCl. Illness stimuli, such as those produced by administration of LiCl, are not the only stimuli that can induce conditioned taste avoidance and preexposure effects. Reinforcing agents such as morphine and amphetamine and satiety agents such as cholecystokinin can induce conditioned taste avoidance and serve as preexposure agents (Booth, 1985; Cappell and Le Blanc, 1977; Cappell, Le Blanc, and Herling, 1975; CrossMellor, Kent, Ossenkopp, and Kavaliers, 1999; Eckel and Ossenkopp, 1995; Hunt and Amit, 1987; Katz and Gormezano, 1979; Parker, 1995; Reicher and Homan, 1977; van Ree, 1979; Wise, Yokel, and Dewitt, 1976). Because these agents do not increase aversive taste reactivity responses, it is thought that the avoidance inducing stimuli they evoke are qualitatively different than those produced by administration of LiCl (CrossMellor, et al., 1999; Eckel and Ossenkopp, 1995; Hunt and Amit, 1987; Parker, 1995). Although some investigators have reported an increase in aversive taste reactions after pairing estradiol with a taste solution (Ossenkopp et al., 1996), others and we have failed to observe these changes (Flanagan-Cato, Grigson, and King, 2001; Kunz, 2001; unpublished data). This raises the possibility that the stimulus properties of estradiol are qualitatively different than those of LiCl.
ACKNOWLEDGMENT This work was supported by BNRF.
REFERENCES Barker, L. M., and Smith, J. C. (1974). A comparison of taste aversions induced by radiation and lithium chloride in CS-US and US-CS paradigms. J. Comp. Physiol. Psychol. 87, 644 – 654. Berman, R. F., and Cannon, D. S. (1974). The effect of prior ethanol experience on ethanol-induced saccharin aversions. Physiol. Behav. 38, 1041–1044.
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Bernstein, I. L., Courtney, L., and Braget, D. J. (1986). Estrogens and the Leydig LTW(m) tumor syndrome: Anorexia and diet aversion attenuated by area postrema lesions. Physiol. Behav. 38, 159 –163. Bluthe, R.-M., Dantzer, R., Mormede, P., and Le Moal, M. (1985). Specificity of aversive stimulus properties of vasopressin. Psychopharmacol. 87, 238 –241. Booth, D. A. (1985). Food-conditioned eating preferences and aversion with interoceptive elements: Conditioned appetites and satieties. Ann. N.Y. Acad. Sci. 443, 22– 41. Braveman, N. S. (1975). Formation of taste aversions in rats following prior exposure to sickness. Learn. Mot. 6, 512–534. Breslin, P. A. S., Spector, A. C., and Grill, H. J. (1992). A quantitative comparison of taste reactivity behaviors to sucrose before and after lithium chloride pairings: A unidimensional account of palatability. Behav. Neurosci. 106, 820 – 836. Brosnihan, K. B., Moriguchi, A., Nakamoto, H., Dean, R. H., Ganten, D., and Ferrario, C. M. (1994). Estrogen augments the contribution of nitric oxide to blood pressure regulation in transgenic hypertensive rats expressing the mouse Ren-2 gene. Am. J. Hypertens. 7, 576 –582. Brownson, E. A., Sengstake, C. B., and Chambers, K. C. (1994). The role of serum testosterone in the accelerated extinction of a conditioned taste aversion in fluid deprived male rats. Physiol. Behav. 55, 273–278. Cannon, D. S., Baker, T. B., and Berman, R. F. (1977). Taste aversion disruption by drug pretreatment: Dissociative and drug-specific effects. Pharm. Biochem. Behav. 6, 93–100. Cannon, D. S., Berman, R. F., Baker, T. B., and Atkinson, C. A. (1975). Effect of preconditioning unconditioned stimulus experience on learned taste aversions. J. Exp. Psychol.: Anim. Behav. Proc. 104, 270 –284. Cappell, H., and Le Blanc, A. E. (1977). Parametric investigations of the effects of prior exposure to amphetamine and morphine on conditioned gustatory aversion. Psychopharm. 51, 265–271. Cappell, H., Le Blanc, A. E., and Herling, S. (1975). Modification of the punishing effects of psychoactive drugs in rats by previous drug experience. J. Comp. Physiol. Psychol. 89, 347–356. Chambers, K. C., Sengstake, C. B., Brownson, E. A., and Westfahl, P. K. (1993). Decreased testosterone levels and accelerated extinction of a conditioned taste aversion in fluid-deprived male rats. Behav. Neurosci. 107, 299 –305. Chambers, K. C., and Yuan, D. L. (1990). Blockage of the effects of testosterone on extinction of a conditioned taste aversion by estradiol: Time of action. Physiol. Behav. 48, 277–281. Cross-Mellor, S. K., Kent, W. D., Ossenkopp, K.-P., and Kavaliers, M. (1999). Differential effects of lipopolysaccharide and cholecystokinin on sucrose intake and palatability. Amer. Physiol. Soc. 277, R705–R715. De Beun, R., Jansen, E., Smeets, M. A. M., Niesing, J., Slangen, J. L., and Van De Poll, E. (1991). Estradiol-induced conditioned taste aversion and place aversion in rats: Sex- and dose-dependent effects. Physiol. Behav. 50, 995–1000. De Beun, R., Peeters, B. W. M. M., and Broekkamp, C. L. E, (1993). Stimulus characterization of estradiol applying a crossfamiliarization taste aversion procedure in female mice. Physiol. Behav. 53, 715–719. Domjan, M. (1978). Effects of proximal unconditioned stimulus preexposure on ingestional aversions learned as a result of taste presentation following drug treatment. Anim. Lrn. Behav. 6, 133– 142. Domjan, M., and Best, M. R. (1977). Paradoxical effects of proximal unconditioned stimulus preexposure: Interference with and con-
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ditioning of a taste aversion. J. Exp. Psychol: Anim. Behav. Proc. 3, 310 –321. Domjan, M., and Gemberling, G. A. (1980). Effects of expected vs. unexpected proximal US preexposure on taste-aversion learning. Anim. Lrn. Behav. 8, 204 –210. Eckel, L. A., and Ossenkopp, K-P. (1995). Cholecystokinin reduces ingestive taste reactivity responses to water in fluid-replete but not fluid-deprived rats. Physiol. Behav. 57, 599 – 603. Eckel, L. A., and Ossenkopp, K-P. (1996). Area postrema mediates the formation of rapid, conditioned palatability shifts in lithiumtreated rats. Behav. Neurosci. 110, 202–212. Ettenberg, A., van der Kooy, D., Le Moal, M., Koob, G. F., and Bloom, F. E. (1983). Can aversive properties of (peripherallyinjected) vasopressin account for its putative role in memory? Behav. Brain Res. 7, 331–350. Flanagan-Cato, L. M., Grigson, P. S., and King, J. L. (2001). Estrogeninduced suppression of intake is not mediated by taste aversion in female rats. Physiol. Behav. 72, 549 –558. Gamzu, E. (1977). The multifaceted nature of taste-aversion-inducing agents: Is there a single common factor? In L. Barker, M. Barker, and M. Domjan (Eds.), Learning Mechanisms in Food Selection (pp. 477–509). Baylor University Press, Waco, TX. Ganesan, R., and Simpkins, J. W. (1990). The role of conditioned taste aversion in the suppression of food intake by estradiol. Physiol. Behav. 48, 647– 652. Ganesan, R., and Simpkins, J. W. (1991). Conditioned taste aversion induced by estradiol pellets. Physiol. Behav. 50, 849 – 852. Goodman, L. S., and Gilman, A. (Eds.). (1975). The pharmacological basis of therapeutics. Macmillan, New York. Gustavson, C. R., and Gustavson, J. C. (1986). Estrogen based conditioned taste aversion: A neuroethological model of anorexia nervosa. Soc. Neurosci. Abstr. 12, 1451. Gustavson, C. R., and Gustavson, J. C. (1987). Estrogen induced anorexia in the rat: An LiCl comparison suggests it is estrogen induced nausea. Soc. Neurosci. Abstr. 13, 555. Gustavson, C. R., Gustavson, J. C., Young, J. K., Pumariega, A. J., and Nicolaus, L. K. (1989). Estrogen induced malaise. In J. M. Lakoski, J. R. Perez-Polo, and D. K. Rassin (Eds.), Neural Control of Reproductive Function (pp. 501–523). Alan R. Liss, New York. Gustavson, C. R., Reinarz, D. E., Gustavson, C. R., and Pumariega, A. J. (1988). Estrogen based conditioned taste aversion in a single human subject. West Psychol. Assoc. Metg., San Francisco, CA. Holman, E. (1976). The effect of drug habituation before and after taste aversion learning in rats. Anim. Lrn. Behav. 4, 329 –332. Hulman, S. Brodsky, N., Miller, J., Donnelly, C., Helms, J., and Falkner, B. (1996). Effect of estrogen withdrawal on blood pressure and insulin resistance in sucrose-fed juvenile rats. Am. J. Hypertens. 9, 1200 –1205. Hunt, T., and Amit, Z. (1987). Conditioned taste aversion induced by self-administered drugs: Paradox revisited. Neurosci. Biobehav. Rev. 1, 107–130. Karsch, F. J., Dierschke, D. J., Weick, R. F., Yamaji, T., Hotchkiss, J., and Knobil, E. (1973). Positive and negative feedback control by estrogen of luteinizing hormone secretion in the rhesus monkey. Endocrinol. 92, 799 – 804. Katz, R. J., and Gormazano, G. (1979). A rapid and inexpensive technique for assessing the reinforcing effects of opiate drugs. Pharm. Biochem. Behav. 11, 231–233. Kunz, R. D. (2001). Hedonic aspects of conditioned taste aversion in rats and humans. Unpublished masters thesis, University of Southern California. Legan, S. J., Coon, G. A., and Karsch, F. J. (1975). Role of estrogen as
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initiator of daily LH surges in the ovariectomized rat. Endocrinol. 96, 50 –56. Manwaring, P., Morfis, L., Diamond, T., and Howes, L. G. (2000). Effects of hormone replacement therapy on ambulatory blood pressure and vascular responses in normotensive women. Blood Pressure, 9, 22–27. Merwin, A. A., and Doty, R. L. (1994). Early exposure to low levels of estradiol (E 2) mitigates E 2-induced conditioned taste aversions in prepubertally ovariectomized female rats. Physiol. Behav. 55, 185–187. Miele, J., Rosellini, R. A., and Svare, B. (1988). Estradiol benzoate can function as an unconditioned stimulus in a conditioned taste aversion paradigm. Horm. Behav. 22, 116 –130. Mikulka, P. J., Leard, B., and Klein, S. B. (1977). Illness-alone exposure as a source of interference with the acquisition and retention of a taste aversion. J. Exp. Psychol: Anim. Behav. Proc. 3, 189 –201. Morrison, J. M., Pritchard, H. D., Brande, M. L., and Aguanns, W. D. (1971). Plasma and brain lithium levels after lithium carbonate and lithium chloride administration by different routes in rats. Proc. Soc. Exp. Biol., 137, 795–797. Nachman, M. (1963). Learned aversion to the taste of lithium chloride and generalization to other salts. J. Comp. Physiol. Psychol. 56, 343–349. Nachman, M., and Ashe, J. H. (1973). Learned taste aversions in rats as a function of dosage, concentration, and route of administration of LiCl. Physiol. Behav. 10, 73–78. Nicolaus, L. K., Farmer, P. V., Gustavson, C. R., and Gustavson, J. C. (1989). The potential of estrogen-based conditioned aversion in controlling depredation: A step closer toward the “magic bullet.” App. Anim. Behav. Sci. 23, 1–14. Nicolaus, L. K., Herrera, J., Nicolaus, J. C., and Gustavson, C. R. (1989). Ethinyl estradiol and generalized aversions to eggs among free-ranging predators. App. Anim. Behav. Sci. 24, 313–324. O’Connor, E. F., Cheng, S. W. T., and North, W. G. (1987). Effects of intraperitoneal injection of lithium chloride on neurohypophyseal activity: Implication for behavioral studies. Physiol. Behav. 40, 91–95. Ossenkopp, K-P., Rabi, Y. J., Eckel, L. A. (1996). Oestradiol-induced taste avoidance is the result of a conditioned palatability shift. Neuroreport. 7: 2777–2780. Parker, L. A. (1995). Rewarding drugs produce taste avoidance, but not taste aversion. Neurosci. Biobehav. Rev. 19, 143–151. Peeters, B. W. M. M., Smets, R. J. M., and Broekkamp, C. L. E. (1992). Sex steroids possess distinct stimulus properties in female and male mice. Brain Res. Bull. 28, 319 –321.
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Rabin, B. M., Hunt, WA., and Lee, J. (1987). Taste aversion learning produced by combined treatment with subthreshold radiation and lithium chloride. Pharmacol. Biochem. Behav. 27, 671– 675. Rabin, B. M., Hunt, W. A., and Lee, J. (1989). Attenuation and cross-attenuation in taste aversion learning in the rat: Studies with ionizing radiation, lithium chloride and ethanol. Pharm. Biochem. Behav. 31, 909 –918. Reicher, M. A., and Holman, E. W. (1977). Location preference and flavor aversion reinforced by amphetamine in rats. Anim. Lrn. Behav. 5, 343–346. Rice, A. G., Lopez, A., and Garcia, J. (1987). Estrogen produces conditioned taste aversions in rats which are blocked by antihistamine. Soc. Neurosci. Abstr. 13, 556. Riley, A. L., Jacobs, W. J., and LoLordo, V. M. (1976). Drug exposure and the acquisition and retention of a conditioned taste aversion. J. Comp. Physiol. Psychol. 90, 799 – 807. Schou, M. (1968). Lithium in psychiatry—A review. In Pharmacology: A Review of Progress 1957–1967, E. H. Efron (Ed). Public Health Service Publication No 1836, pp. 701–718. Sengstake, C. B., and Chambers, K. C. (1979). Differential effects of fluid deprivation on the acquisition and extinction phases of a conditioned taste aversion. Bull. Psychon. Soc. 14, 85– 87. Sengstake, C. B., Chambers, K. C., and Thrower, J. H. (1978). Interactive effects of fluid deprivation and testosterone on the expression of a sexually dimorphic conditioned taste aversion. J. Comp. Physiol. Psychol. 92, 1150 –1155. Suarez, E. M., and Barker, L. M. (1976). Effects of water deprivation and prior LiCl exposure in conditioning taste aversions. Physiol. Behav. 17, 555–559. Trautner, E. M., Morris, R., Noach, C. H., and Gershon, S. (1955). The excretion and retention of ingested lithium and its effects on the ionic balance in man. Med. J. Australia, 42, 280 –291. van Ree, J. M. (1979). Reinforcing stimulus properties of drugs. Neuropharmacol. 18, 963–969. Wise, R., Yokel, P., and Dewitt, H. (1976). Both positive reinforcement and conditioned aversion from amphetamine and from apomorphine in rats. Sci. 191, 1273–1274. Yuan, D. L., and Chambers, K. C. (1999a). Estradiol accelerates extinction of a conditioned taste aversion in female and male rats. Horm. Behav. 36, 1–16. Yuan, D. L., and Chambers, K. C. (1999b). Estradiol accelerates extinction of lithium chloride-induced conditioned taste aversions through its illness-associated properties. Horm. Behav. 36, 287–298.
Exposure to Estradiol before but Not during Acquisition of LiCl-Induced Conditioned Taste Avoidance Accelerates Extinction Kathleen C. Chambers 1 and Unja L. Hayes Department of Psychology, University of Southern California, Los Angeles, California 90089 Received February 13, 2001; revised May 24, 2001; accepted October 15, 2001
Estradiol accelerates extinction of LiCl-induced conditioned taste avoidance when it is present continuously before and during acquisition. We have suggested that the effect of estradiol on extinction is due to its illnessassociated, rather than learning-associated, properties. If this were the case, then one would expect estradiol to act before but not during acquisition. This expectation is based on previous work showing attenuation of learned taste avoidance when rats are given distal preexposure (greater than 24 h before conditioning) or proximal preexposure (less than 24 h before conditioning) to the illness-inducing agent LiCl before acquisition of a LiClinduced conditioned taste avoidance. In three separate experiments, estradiol was administered during three different time periods via subcutaneous implantation of a 10-mm estradiol-filled capsule. In each experiment, the extinction of estradiol-treated females was compared to that of females implanted with empty capsules. In the first experiment, female rats were given distal exposure to estradiol before acquisition. Capsules were implanted 11 days before acquisition and were removed 2 days before acquisition. In the second experiment, female rats were given proximal exposure to estradiol before acquisition. Capsules were implanted 2.5 h before LiCl was paired with a sucrose solution and were removed 16.5 h later. In the third experiment, female rats were given exposure to estradiol during acquisition. Capsules were implanted at the same time as LiCl administration and were removed 18 h later. The only estradiol-treated females to show accelerated extinction were those given distal preexposure to estradiol in Experiment 1. These data do not support a learning-associated hypothesis and only partially support an illnessassociated hypothesis. The failure to find accelerated extinction following proximal preexposure may reflect an inappropriate choice of the parameters used in the
1 To whom correspondence and reprint requests should be addressed. E-mail: [email protected].
0018-506X/02 $35.00 © 2002 Elsevier Science (USA) All rights reserved.
experiment or a difference in the stimulus properties of LiCl and estradiol that allow each to serve as conditioning and preexposure agents in conditioned taste avoidance paradigms. Extinction of a LiCl-induced conditioned taste avoidance is accelerated when estradiol is present before and during acquisition. In the study that demonstrated this effect, exposure to estradiol was given continuously via a subcutaneously implanted capsule during a period that started 8 days before acquisition and continued until 3 days after acquisition. © 2002 Elsevier Science (USA)
Daily extinction tests were initiated a week later and were conducted in the absence of estradiol (Yuan and Chambers, 1999a). Two hypotheses have been suggested to account for this effect of estradiol, an illnessassociated and a learning-associated hypothesis. We raised the possibility that the illness-inducing properties of estradiol could account for the accelerated extinction (Chambers and Yuan, 1990; Yuan and Chambers, 1999a, 1999b). LiCl is a putative illness-inducing agent and it has been suggested that supraphysiological levels of estradiol induce an illness that parallels that of LiCl (DeBeun, Jansen, Smeets, Niesing, Slangen, and Van de Poll, 1991; Gustavson and Gustavson, 1987; Gustavson, Gustavson, Young, Pumariega, and Nicolaus, 1989). Both estradiol and LiCl are known to produce nausea and vomiting in humans (Goodman and Gilman, 1975; Schou, 1968). In addition, both can be used as an illness-inducing agent to produce conditioned taste aversion, defined as a decrease in consumption of the taste stimulus and a shift in the hedonic evaluation of the taste stimulus, as measured by decreases in ingestive and increases in aversive orofacial and somatic responses when the taste stimulus is place directly on the tongue. Different dosages and concentrations of LiCl and different administration routes induce conditioned
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taste avoidance as well as decreases in ingestive and increases in aversive taste reactivity behaviors (Breslin, Spector, and Grill, 1992; Eckel and Ossenkopp, 1996; Nachman and Ashe, 1973). Estradiol in different forms, doses, and routes of administration can induce conditioned taste avoidance when paired with a novel flavor in rats, mice, and humans (Bernstein, Courtney, and Braget, 1986; De Beun et al., 1991; De Beun, Peeters, and Broekkamp, 1993; Ganesan and Simpkins, 1990, 1991; Gustavson and Gustavson, 1986, 1987; Gustavson et al., 1989; Gustavson, Reinarz, Gustavson, and Pumariega, 1988; Merwin and Doty, 1994; Miele, Rosellini, and Svare, 1988; Nicolaus, Farmer, Gustavson and Gustavson, 1989; Nicolaus, Herrera, Nicolaus, and Gustavson, 1989; Peeters, Smets, and Broekkamp, 1992; Rice, Lopez, and Garcia, 1987; Yuan and Chambers, 1999b). It also can produce conditioned negative shifts in palatability after it has been paired with a novel sweet taste solution (Ossenkopp, Rabi, and Eckel, 1996). Illness inducing agents have not only been used as conditioning agents in conditioned taste avoidance paradigms but as preexposure agents (Berman and Cannon, 1974; Braveman, 1975; Cannon, Baker, and Berman, 1977; Gamzu, 1977). It is well known that exposure to an illness-inducing agent before pairing a novel taste stimulus with either the same illness-inducing agent (termed an intraagent) or a different illness-inducing agent (termed an interagent) will attenuate expression of taste avoidance. For example, when LiCl is injected 8, 5, and 2 days before acquisition of conditioned taste avoidance induced by LiCl, radiation, or ethanol, the taste avoidance is attenuated (Rabin, Hunt, and Lee, 1989). Two different kinds of preacquisition exposure regimens in which LiCl is both the preexposure agent and the conditioning agent have been described. Remote or distal preexposure is characterized as taking place 24 h or more before conditioning and proximal preexposure is given less than 24 h before conditioning (Domjan, 1978). The distal preexposure regimen that successfully attenuates taste avoidance is varied, e.g., 1 preexposure given 1 day before acquisition, 8 daily preexposures starting 9 days before acquisition, or 6 preexposures every 4th day starting 25 days before acquisition (Cannon, Berman, Baker, and Atkinson, 1975; Holman, 1976; Riley, Jacobs, and LoLordo, 1976). For proximal preexposure, animals are exposed to LiCl minutes to hours before acquisition. Taste avoidance has been shown to be attenuated when LiCl is given 30, 110, 180, 270, and 360 minutes before access to a taste solution and the subsequent conditioning administration of LiCl (Domjan, 1978; Domjan and
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Best, 1977; Domjan and Gemberling, 1980). An important defining characteristic of preexposure disruption is that the preexposure agent must be present before acquisition or extinction, not during. In the experiment mentioned above, estradiol was present both before and during acquisition (Yuan and Chambers, 1999a). The presence of estradiol before acquisition may have served as an interagent disrupter and consequently led to an accelerated extinction. We also raised the possibility that estradiol disrupts a learning-associated process by reducing the effectiveness of LiCl during acquisition (Yuan and Chambers, 1999a). There is some evidence to suggest that increases in blood pressure can serve as an aversive stimulus to induce conditioned taste avoidance. Vasopressin produces increases in blood pressure and it induces conditioned taste avoidance (Ettenberg, van der Kooy, Le Moal, Koob, and Bloom, 1983). However, vasopressin-induced learned avoidance can be prevented by pretreatment with an antagonist that completely blocks the increase in blood pressure induced by the subcutaneous injection of vasopressin. In addition, conditioned taste avoidance cannot be induced by the vasopressin analogue, dDAVP, which has no vasopressor effects (Bluthe, Dantzer, Mormede, and Le Moal, 1985). LiCl also raises arterial blood pressure, but estradiol lowers it (Brosnihan, Moriguchi, Nakamoto, Dean, Ganten, and Ferrario, 1994; Hulman, Brodsky, Miller, Donnelly, Helms, and Falkner, 1996; Manwaring, Morfis, Diamond, and Howes, 2000; O’Connor, Cheng, and North, 1987). Thus the net effect of combining estradiol and LiCl may be a reduction in the illness efficacy of LiCl and consequently accelerated extinction of conditioned taste avoidance. The following experiments were designed to determine whether extinction is accelerated when estradiol is present before acquisition of a LiCl-induced conditioned taste avoidance, which would be consistent with an illness-associated hypothesis, or whether extinction is accelerated when estradiol is present at the time of LiCl administration, which would be consistent with a learning-associated hypothesis.
METHODS Subjects The subjects were adult female Fischer 344 rats (Simonsen Laboratories, Gilroy, CA). The vivarium in which the rats were quartered was temperature (21– 22°C), humidity (51%), and light controlled (a 12:12
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hour light/dark cycle with lights on at 1000 and lights off at 2200). The rats were housed in pairs in solid bottom cages (58 ⫻ 38 cm) that had wood chips as bedding material. Testing was done in the home cage but a stainless steel divider was placed in the middle of each cage to separate each pair of rats during behavioral testing. During avoidance testing, water was available 23 h a day and a sucrose solution was available for 1 h. In previous studies, we found that rats given similar drinking schedules are essentially nondeprived (Brownson, Sengstake, and Chambers, 1994; Chambers, Sengstake, Brownson, and Westfahl, 1993; Sengstake and Chambers, 1979; Sengstake, Chambers, and Thrower, 1978). When water as well as sucrose was available during the 1- or 2-h test period, most rats drank 2– 4 ml of water both before and after conditioning. Preparation of Estradiol-Filled Capsules Estradiol-treated groups were implanted with capsules that contained crystalline estradiol (Steraloids, Wilton, NH) and untreated groups received capsules that were empty. The Silastic capsules had inside diameters of 0.157 cm and outside diameters of 0.318 cm and both ends of each capsule were sealed with silicone type A Silastic adhesive. The length of the filled or empty portion of the capsule was 10 mm and the length of each sealed end was 1 mm.
postacquisition recovery period, and extinction tests. All solutions used during testing were stored under refrigeration and they were given to the rats at the beginning of the dark portion of the light/dark cycle. Each day during preconditioning, the water bottle of each rat was replaced with one cylinder containing chilled tap water. After 1 h, the cylinder was replaced with the regular water bottle. Preconditioning rats with cold water just after the lights switch off increases the likelihood that nondeprived rats will drink the novel sucrose solution during acquisition. On acquisition day, the water bottle of each rat was replaced with one cylinder containing a 10% sucrose solution, (w/v, 0.29 M). One hour later, the amount of sucrose consumption was recorded and the cylinder was removed. Each rat was removed from its cage, injected with a LiCl solution (0.15 M, 10 ml/kg of body weight), returned to its cage, and then its regular water bottle was returned. Daily extinction tests were initiated 2 (Experiment 1) or 3 (Experiments 2 and 3) days after acquisition. Extinction tests were conducted in the same manner as the acquisition test except no LiCl injections were given. For Experiment 3A, each rat was given one extinction test daily for 8 days. For all of the other experiments, each rat was given one extinction test daily for 14 days. Those rats that had not regained their acquisition day consumption by the 14th test were given additional daily extinction tests until they did or until 5 more extinction tests had been given.
Surgical Procedures Ovariectomies and implantation of Silastic capsules were performed while the rats were under halothane anesthesia (Halocarbon Laboratories, River Edge, NJ). The halothane was vaporized (Fluotec 3) and mixed with oxygen by a Fraser Harlake VMC small animal inhalation anesthesia machine (Datex-Ohmeda, Madison, WI). This gas mixture was delivered to each rat through a nose cone. The percent of halothane in the gas mixture was maintained between 1.5 and 2.0 and the oxygen flow rate was maintained between 3.5 and 4.0 l/min. Ovariectomies included bilateral incisions of the skin and muscles (1 to 2 cm from midline and anterior to the hip) and removal of the ovaries. The Silastic capsules were implanted subcutaneously at the nape of the neck. Conditioned Taste Avoidance Procedure The conditioned taste avoidance procedure included preconditioning tests, an acquisition test, a
Experimental Design Experiment 1: Distal Preexposure. Twenty females were randomly assigned to one of two groups: empty capsule (n ⫽ 10) or estradiol-filled capsule (n ⫽ 10). The experimental procedure was divided into the following six periods: ovariectomy and capsule implantation (day 1), preconditioning (days 2–9), capsule removal and recovery (days 10 –11), acquisition (day 12), postacquisition recovery (day 13), and extinction tests (days 14 –27). The capsules were implanted at the same time the females were ovariectomized and they were removed the day following the last preconditioning test. Experiment 2: Proximal Preexposure. Nineteen females were randomly assigned to one of two groups: empty capsule (n ⫽ 9) or estradiol-filled capsule (n ⫽ 10). The experimental procedure was divided into the following six periods: ovariectomy (day 1), preconditioning (days 2–11), capsule implantation and acquisition (day 12), capsule removal (day 13), postacquisi-
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tion recovery (day 14), and extinction tests (days 15– 28). Capsules were implanted approximately 1.5 h before access to sucrose, which was 2.5 h before LiCl injection, and they were removed 18 h later. Experiment 3: During Acquisition. Females were randomly assigned to one of two groups: empty capsule (n ⫽ 10 in Part A and n ⫽ 6 in Part B) or estradiol-filled capsule (n ⫽ 8 in Part A and n ⫽ 6 in Part B). The experimental procedure was divided into the following six periods: ovariectomy (day 1), preconditioning (days 2–9), acquisition and capsule implantation (day 10), capsule removal (day 11), postacquisition recovery (day 12), and extinction tests (days 13–20). Capsules were implanted immediately after access to a sucrose solution and at the same time that LiCl was injected. They were removed 18 h later. Statistical Analyses Acquisition was assessed by using a two-factor (groups ⫻ tests) analysis of variance (ANOVA) with repeated measures on tests to analyze the amount of sucrose consumed across the acquisition and first extinction test. Extinction was assessed in two ways. A two-factor (groups ⫻ tests) ANOVA with repeated measures on tests was used to analyze the amount of sucrose consumed across all of the extinction tests. The number of daily tests to reach 100% of acquisition day consumption levels (extinction criterion) was determined and these values were analyzed with independent t tests.
RESULTS Experiment 1: Distal Preexposure The results showed that extinction was accelerated in females given distal exposure to estradiol before acquisition (see Fig. 1). The estradiol-treated females extinguished in 13.5 days and the untreated females extinguished in 18.2 days. Sucrose consumption for all animals in both groups decreased across the acquisition and first extinction test and the extent of the decrease was similar for both groups (F(1, 18) ⫽ 96.91, P ⬍ 0.001 for test main effect). All animals increased their consumption of sucrose during extinction but the estradiol-treated females consumed more sucrose and showed a greater rate of increase in consumption across the 14 extinction tests than the untreated females (F(13, 234) ⫽ 10.80, P ⬍ 0.001 for tests main effect; F(1, 18) ⫽ 5.29, P ⫽ 0.033 for group
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FIG. 1. Mean (⫾SE) sucrose consumption (ml) during acquisition (ACQ) and extinction tests (E1–E14) for gonadectomized female rats implanted with an estradiol-filled Silastic capsule (E, n ⫽ 10) or an empty capsule (O, n ⫽ 10) before acquisition of a LiCl-induced conditioned taste avoidance. Capsules were implanted 11 days before acquisition and were removed 2 days before acquisition (distal preexposure). *Mean sucrose consumption and rate of increase in consumption across extinction tests was significantly greater and mean number of days to regain acquisition day consumption levels was significantly less than for the O group, P ⱕ 0.05.
main effect, F(13, 234) ⫽ 2.13, P ⫽ 0.013 for interaction effect, T(18) ⫽ 2.11, P ⫽ 0.049 for extinction criterion). Experiment 2: Proximal Preexposure The results showed that extinction was not significantly accelerated in females given proximal exposure to estradiol before acquisition (see Fig. 2). The estradiol-treated females extinguished in 12.3 days and the untreated females extinguished in 15.2 days. Sucrose consumption for all animals in both groups decreased across the acquisition and first extinction test and the extent of the decrease was similar for both groups (F(1, 17) ⫽ 58.95, P ⬍ 0.001 for test main effect). All animals increased their consumption of sucrose during extinction and the amount of sucrose consumed and rate of increase in consumption across the 14 extinction tests was similar for both groups (F(13, 221) ⫽ 19.84, P ⬍ 0.001 for test main effect). Experiment 3: During Acquisition For both experiments, the results showed that extinction was not accelerated in females exposed to estradiol during acquisition (see Fig. 3). The estradioltreated females extinguished in 6.3 days in Part A and 17.3 days in Part B and the untreated females extin-
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FIG. 2. Mean (⫾SE) sucrose consumption (ml) during acquisition (ACQ) and extinction tests (E1–E14) for gonadectomized female rats implanted with an estradiol-filled Silastic capsule (E, n ⫽ 10) or an empty capsule (O, n ⫽ 9) before acquisition of a LiCl-induced conditioned taste avoidance. Capsules were implanted 2.5 hours before pairing LiCl with a sucrose solution and were removed 15.5 h later (proximal preexposure). No significant overall differences were found.
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After 1 h, the levels are 759.6 pg/ml and after 6 h, they are 464.2 pg/ml (Yuan and Chambers, 1999b). These data suggest that both estradiol and LiCl reached peak blood levels at about the same time. The extinction rates of the untreated females in experiment 3A were faster than those of the untreated females in Experiments 1 and 2 (means for extinction criterion ⫽ 4.8, 18.2, and 15.2 days, respectively. The same was true of the estradiol treated females in Experiment 3A (means for extinction criterion ⫽ 6.3, 13.5, and 12.3). Because the animal supplier, age and sex of the rats, housing conditions, batch of sucrose and LiCl, and experimenter were the same for all of the experiments, variations in these factors cannot account for the differences in extinction rates. We occasionally have found that an entire batch of ani-
guished in 4.8 days in Part A and 14.3 days in Part B. Sucrose consumption for all animals in both groups decreased across the acquisition and first extinction test and the extent of the decrease was similar for both groups (F(1, 16) ⫽ 139.22, P ⬍ 0.001 in Part A and F(1, 10) ⫽ 78.77, P ⬍ 0.001 in Part B for test main effect). All animals increased their consumption of sucrose during extinction and the amount of sucrose consumed and rate of increase in consumption across the 14 extinction tests was similar for both groups (F(7, 112) ⫽ 13.72, P ⬍ 0.001 in Part A and F(13, 130) ⫽ 8.62, P ⬍ 0.001 in Part B for test main effect).
DISCUSSION Learning-Associated Hypothesis The presence of estradiol during LiCl illness did not accelerate extinction of a conditioned taste avoidance. It is unlikely that the failure to find accelerated extinction in the estradiol treated females of both experiments was due to inappropriate timing of the administration of estradiol and LiCl. Plasma lithium levels reach their peak 30 min after administration (Morrison, Pritchard, Brande, and Aguanns, 1971). In a pilot study, we found that serum blood levels of estradiol increase to a mean of 748 pg/ml (n ⫽ 4, range ⫽ 394 –1049 pg/ml) 30 min after implantation of a 10 mm estradiol-filled capsule in Fischer 344 female rats.
FIG. 3. Mean (⫾SE) sucrose consumption (ml) during acquisition (ACQ) and extinction tests (E1–E8 in A and E1–E14 in B) for gonadectomized female rats implanted with an estradiol-filled Silastic capsule (E, n ⫽ 8 for A and n ⫽ 6 for B) or an empty capsule (O, n ⫽ 10 for A and n ⫽ 6 for B) during acquisition of a LiCl-induced conditioned taste avoidance. Capsules were implanted at the same time as LiCl administration and were removed 18 h later. No significant overall differences were found.
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mals in a study extinguish either more quickly or more slowly than is typical. However, in subsequent replications of these studies, we have found that this variability does not alter the results, that is, the relative differences between groups remains the same. This also was the case for experiment 3. The extinction rates in experiment 3B were more typical of what is observed under our testing conditions, and as was true for experiment 3A, the presence of estradiol during LiCl illness did not accelerate extinction of a conditioned taste avoidance. If estradiol acted on some learning process, then one would have expected it to accelerate extinction when it was present at the time of association between the sucrose solution and the stimulus effects of LiCl. However, in Experiment 3, there was a tendency for the estradiol treated females in both experiments to consume less, rather than more, sucrose during most of the extinction tests and to increase sucrose consumption at a slower rate. Estradiol treated females consumed significantly less sucrose on the first extinction test in Experiment 3A and there was a tendency for them to consume less on extinction test 3 in both Experiments 3A and 3B (T(16) ⫽ 2.23, P ⫽ 0.04, T(16) ⫽ 1.86, P ⫽ 0.08 and T(10) ⫽ 3.87, P ⫽ 0.003, respectively). The tendency for estradiol to strengthen a conditioned taste avoidance when combined with LiCl is consistent with studies of the effect of combining LiCl with other illness-inducing agents. For example, subthreshold doses of LiCl and radiation, that alone do not produce conditioned taste avoidance, can induce avoidance when both are given (Rabin, Hunt, and Lee, 1987). Illness-Associated Hypothesis Distal preexposure. Extinction of a LiCl-induced conditioned taste avoidance was accelerated when rats were given distal preexposure to estradiol in Experiment 1. This result is consistent with an illnessassociated hypothesis. Elevated blood levels of estradiol cannot account for the accelerated extinction at the time of acquisition. The results of Experiment 3 show that elevated estradiol levels during acquisition do not produce accelerated extinction. Further, blood levels of estradiol fall rapidly after removal of a 10 mm capsule; they are at baseline within 2 hours after removal (Karsch, Dierschke, Weick, Yamaji, Hotchkiss, and Knobil, 1973; Legan, Coon, and Karsch, 1975). Since the acquisition trial was given 2 days after capsule removal, this suggests that estradiol levels were not elevated at the time of acquisition.
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Proximal preexposure. When rats were given proximal preexposure to estradiol in Experiment 2, extinction of a LiCl-induced conditioned taste avoidance was not accelerated. This result is not consistent with an illness-associated hypothesis. It is worth noting, however, that there was a tendency for estradioltreated females to consume more sucrose during extinction than untreated females; this difference was significant on extinction day 8 (T(17) ⫽ 2.29, P ⫽ 0.03). It is unlikely that the failure to find a significant proximal effect is tied to the prolonged presence of estradiol (18 h) after LiCl administration. The biological effects of lithium are determined by its bioavailable concentration since it is neither protein bound or metabolized by any means (Schou, 1968). Investigators who have consumed lithium, report that lithium illness lasts about 2 h and that within 10 –20 minutes of the peak illness sensations, which are correlated with the peak lithium concentration in the blood, the symptoms subside (Trautner, Morris, Noack, and Gershon, 1955). In rats that have been injected intraperitoneally with four different concentrations of LiCl, plasma lithium levels reach their peak 30 min after administration, regardless of dose, and decrease to half of the peak level in 1–2 h (Morrison et al., 1971). Quantified descriptions using reduced activity and reduced water intake as indices of LiCl-induced illness, indicate that the greatest effects occur 15 to 60 min after administration (Barker and Smith, 1974; Nachman, 1963). This suggests that in at least some of the proximal preexposure studies, LiCl from the preexposure administration was still in the circulatory system and still having its greatest illness effect at the time of the conditioning administration. Yet, rather than having an additive effect, the preexposure administration had an attenuating effect on learned taste avoidance. There are two other explanations that might account for the failure to find a proximal preexposure effect. First, the dose of estradiol may not have been high enough. When LiCl is used as both the preexposure and conditioning agent, the higher the preexposure dose of LiCl, the greater the attenuation of learned taste avoidance in both distal and proximal preexposure situations (Cannon et al., 1975; Domjan, 1978). If the dose of estradiol in the present study was not high enough, then this would further suggest that proximal preexposure requires a higher dose to produce an effect than distal preexposure. In addition, it would suggest that proximal preexposure did not contribute to the acceleration of extinction found when estradiol was present both before and during acquisition (Yuan
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and Chambers, 1999a). A second possibility is that for the dose of estradiol used, the amount of time exposed to estradiol before acquisition was not long enough to produce a proximal preexposure effect. In the proximal preexposure study, the rats were exposed to estradiol for only 2.5 h before conditioning with LiCl. Perhaps a longer period of exposure to estradiol before conditioning would have produced accelerated extinction. All of the evidence. There is a considerable amount of evidence supporting the hypothesis that the acceleration of extinction of a LiCl-induced conditioned taste avoidance when estradiol is present before and during extinction can be accounted for by its illness-inducing properties. First, subcutaneous implantation of a 10 mm estradiol-filled capsule can induce conditioned taste avoidance after pairing it with a novel sucrose solution (Yuan and Chambers, 1999b). Second, the results of Experiment 1 show that distal preexposure to estradiol, administered subcutaneously via a 10 mm capsule, accelerates extinction of a LiCl-induced conditioned taste avoidance. Third, comparisons of the temporal characteristics of estradiol and LiCl indicate that these agents can serve as mutual distal interagents before acquisition. Distal preexposure to estradiol weakens acquisition and accelerates extinction of conditioned taste avoidance induced by estradiol as well as LiCl (De Beun et al., 1993; Merwin and Doty, 1994). Distal preexposure to LiCl attenuates acquisition of both a LiCl-induced and estradiol-induced conditioned taste avoidance (Cannon et al., 1977; De Beun et al., 1993; Riley et al., 1976; Rabin et al., 1989; Suarez and Barker, 1976). Fourth, extinction is accelerated when a 10-mm estradiol-filled capsule is implanted subcutaneously during the postacquisition/preextinction period, that is, when implanted 2 days after acquisition and removed 8 days later, which was one day before the first extinction test (Yuan and Chambers, 1999b). Similar results have been obtained when LiCl is used as the postacquisition/preextinction exposure agent. Taste avoidance is attenuated when one injection of LiCl is given on a day that is 2 days after acquisition of a LiCl-induced avoidance and 2 days before the postacquisition test (Mikulka, Leard, and Klein, 1977). Fifth, extinction is prolonged when a 10 mm estradiol-filled capsule is implanted subcutaneously during extinction, that is, during reexposures to the conditioned taste stimulus, which are not followed by LiCl illness (Yuan and Chambers, 1999b). These results are what one would expect if estradiol acted as an illness-inducing agent. The presence of estradiol during reexposures to the
conditioned taste stimulus would be equivalent to repeated acquisition trials and therefore should prolong extinction. The only finding that is not consistent with the illness-associated hypothesis is the failure to find a significant proximal preexposure effect in Experiment 2. As mentioned above, this may only reflect an inappropriate choice of the parameters used in the experiment. On the other hand, this may indicate that the stimulus properties of estradiol that allow it to serve as a conditioning and preexposure agent in conditioned taste avoidance paradigms are different than those of LiCl. Illness stimuli, such as those produced by administration of LiCl, are not the only stimuli that can induce conditioned taste avoidance and preexposure effects. Reinforcing agents such as morphine and amphetamine and satiety agents such as cholecystokinin can induce conditioned taste avoidance and serve as preexposure agents (Booth, 1985; Cappell and Le Blanc, 1977; Cappell, Le Blanc, and Herling, 1975; CrossMellor, Kent, Ossenkopp, and Kavaliers, 1999; Eckel and Ossenkopp, 1995; Hunt and Amit, 1987; Katz and Gormezano, 1979; Parker, 1995; Reicher and Homan, 1977; van Ree, 1979; Wise, Yokel, and Dewitt, 1976). Because these agents do not increase aversive taste reactivity responses, it is thought that the avoidance inducing stimuli they evoke are qualitatively different than those produced by administration of LiCl (CrossMellor, et al., 1999; Eckel and Ossenkopp, 1995; Hunt and Amit, 1987; Parker, 1995). Although some investigators have reported an increase in aversive taste reactions after pairing estradiol with a taste solution (Ossenkopp et al., 1996), others and we have failed to observe these changes (Flanagan-Cato, Grigson, and King, 2001; Kunz, 2001; unpublished data). This raises the possibility that the stimulus properties of estradiol are qualitatively different than those of LiCl.
ACKNOWLEDGMENT This work was supported by BNRF.
REFERENCES Barker, L. M., and Smith, J. C. (1974). A comparison of taste aversions induced by radiation and lithium chloride in CS-US and US-CS paradigms. J. Comp. Physiol. Psychol. 87, 644 – 654. Berman, R. F., and Cannon, D. S. (1974). The effect of prior ethanol experience on ethanol-induced saccharin aversions. Physiol. Behav. 38, 1041–1044.
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Bernstein, I. L., Courtney, L., and Braget, D. J. (1986). Estrogens and the Leydig LTW(m) tumor syndrome: Anorexia and diet aversion attenuated by area postrema lesions. Physiol. Behav. 38, 159 –163. Bluthe, R.-M., Dantzer, R., Mormede, P., and Le Moal, M. (1985). Specificity of aversive stimulus properties of vasopressin. Psychopharmacol. 87, 238 –241. Booth, D. A. (1985). Food-conditioned eating preferences and aversion with interoceptive elements: Conditioned appetites and satieties. Ann. N.Y. Acad. Sci. 443, 22– 41. Braveman, N. S. (1975). Formation of taste aversions in rats following prior exposure to sickness. Learn. Mot. 6, 512–534. Breslin, P. A. S., Spector, A. C., and Grill, H. J. (1992). A quantitative comparison of taste reactivity behaviors to sucrose before and after lithium chloride pairings: A unidimensional account of palatability. Behav. Neurosci. 106, 820 – 836. Brosnihan, K. B., Moriguchi, A., Nakamoto, H., Dean, R. H., Ganten, D., and Ferrario, C. M. (1994). Estrogen augments the contribution of nitric oxide to blood pressure regulation in transgenic hypertensive rats expressing the mouse Ren-2 gene. Am. J. Hypertens. 7, 576 –582. Brownson, E. A., Sengstake, C. B., and Chambers, K. C. (1994). The role of serum testosterone in the accelerated extinction of a conditioned taste aversion in fluid deprived male rats. Physiol. Behav. 55, 273–278. Cannon, D. S., Baker, T. B., and Berman, R. F. (1977). Taste aversion disruption by drug pretreatment: Dissociative and drug-specific effects. Pharm. Biochem. Behav. 6, 93–100. Cannon, D. S., Berman, R. F., Baker, T. B., and Atkinson, C. A. (1975). Effect of preconditioning unconditioned stimulus experience on learned taste aversions. J. Exp. Psychol.: Anim. Behav. Proc. 104, 270 –284. Cappell, H., and Le Blanc, A. E. (1977). Parametric investigations of the effects of prior exposure to amphetamine and morphine on conditioned gustatory aversion. Psychopharm. 51, 265–271. Cappell, H., Le Blanc, A. E., and Herling, S. (1975). Modification of the punishing effects of psychoactive drugs in rats by previous drug experience. J. Comp. Physiol. Psychol. 89, 347–356. Chambers, K. C., Sengstake, C. B., Brownson, E. A., and Westfahl, P. K. (1993). Decreased testosterone levels and accelerated extinction of a conditioned taste aversion in fluid-deprived male rats. Behav. Neurosci. 107, 299 –305. Chambers, K. C., and Yuan, D. L. (1990). Blockage of the effects of testosterone on extinction of a conditioned taste aversion by estradiol: Time of action. Physiol. Behav. 48, 277–281. Cross-Mellor, S. K., Kent, W. D., Ossenkopp, K.-P., and Kavaliers, M. (1999). Differential effects of lipopolysaccharide and cholecystokinin on sucrose intake and palatability. Amer. Physiol. Soc. 277, R705–R715. De Beun, R., Jansen, E., Smeets, M. A. M., Niesing, J., Slangen, J. L., and Van De Poll, E. (1991). Estradiol-induced conditioned taste aversion and place aversion in rats: Sex- and dose-dependent effects. Physiol. Behav. 50, 995–1000. De Beun, R., Peeters, B. W. M. M., and Broekkamp, C. L. E, (1993). Stimulus characterization of estradiol applying a crossfamiliarization taste aversion procedure in female mice. Physiol. Behav. 53, 715–719. Domjan, M. (1978). Effects of proximal unconditioned stimulus preexposure on ingestional aversions learned as a result of taste presentation following drug treatment. Anim. Lrn. Behav. 6, 133– 142. Domjan, M., and Best, M. R. (1977). Paradoxical effects of proximal unconditioned stimulus preexposure: Interference with and con-
Chambers and Hayes
ditioning of a taste aversion. J. Exp. Psychol: Anim. Behav. Proc. 3, 310 –321. Domjan, M., and Gemberling, G. A. (1980). Effects of expected vs. unexpected proximal US preexposure on taste-aversion learning. Anim. Lrn. Behav. 8, 204 –210. Eckel, L. A., and Ossenkopp, K-P. (1995). Cholecystokinin reduces ingestive taste reactivity responses to water in fluid-replete but not fluid-deprived rats. Physiol. Behav. 57, 599 – 603. Eckel, L. A., and Ossenkopp, K-P. (1996). Area postrema mediates the formation of rapid, conditioned palatability shifts in lithiumtreated rats. Behav. Neurosci. 110, 202–212. Ettenberg, A., van der Kooy, D., Le Moal, M., Koob, G. F., and Bloom, F. E. (1983). Can aversive properties of (peripherallyinjected) vasopressin account for its putative role in memory? Behav. Brain Res. 7, 331–350. Flanagan-Cato, L. M., Grigson, P. S., and King, J. L. (2001). Estrogeninduced suppression of intake is not mediated by taste aversion in female rats. Physiol. Behav. 72, 549 –558. Gamzu, E. (1977). The multifaceted nature of taste-aversion-inducing agents: Is there a single common factor? In L. Barker, M. Barker, and M. Domjan (Eds.), Learning Mechanisms in Food Selection (pp. 477–509). Baylor University Press, Waco, TX. Ganesan, R., and Simpkins, J. W. (1990). The role of conditioned taste aversion in the suppression of food intake by estradiol. Physiol. Behav. 48, 647– 652. Ganesan, R., and Simpkins, J. W. (1991). Conditioned taste aversion induced by estradiol pellets. Physiol. Behav. 50, 849 – 852. Goodman, L. S., and Gilman, A. (Eds.). (1975). The pharmacological basis of therapeutics. Macmillan, New York. Gustavson, C. R., and Gustavson, J. C. (1986). Estrogen based conditioned taste aversion: A neuroethological model of anorexia nervosa. Soc. Neurosci. Abstr. 12, 1451. Gustavson, C. R., and Gustavson, J. C. (1987). Estrogen induced anorexia in the rat: An LiCl comparison suggests it is estrogen induced nausea. Soc. Neurosci. Abstr. 13, 555. Gustavson, C. R., Gustavson, J. C., Young, J. K., Pumariega, A. J., and Nicolaus, L. K. (1989). Estrogen induced malaise. In J. M. Lakoski, J. R. Perez-Polo, and D. K. Rassin (Eds.), Neural Control of Reproductive Function (pp. 501–523). Alan R. Liss, New York. Gustavson, C. R., Reinarz, D. E., Gustavson, C. R., and Pumariega, A. J. (1988). Estrogen based conditioned taste aversion in a single human subject. West Psychol. Assoc. Metg., San Francisco, CA. Holman, E. (1976). The effect of drug habituation before and after taste aversion learning in rats. Anim. Lrn. Behav. 4, 329 –332. Hulman, S. Brodsky, N., Miller, J., Donnelly, C., Helms, J., and Falkner, B. (1996). Effect of estrogen withdrawal on blood pressure and insulin resistance in sucrose-fed juvenile rats. Am. J. Hypertens. 9, 1200 –1205. Hunt, T., and Amit, Z. (1987). Conditioned taste aversion induced by self-administered drugs: Paradox revisited. Neurosci. Biobehav. Rev. 1, 107–130. Karsch, F. J., Dierschke, D. J., Weick, R. F., Yamaji, T., Hotchkiss, J., and Knobil, E. (1973). Positive and negative feedback control by estrogen of luteinizing hormone secretion in the rhesus monkey. Endocrinol. 92, 799 – 804. Katz, R. J., and Gormazano, G. (1979). A rapid and inexpensive technique for assessing the reinforcing effects of opiate drugs. Pharm. Biochem. Behav. 11, 231–233. Kunz, R. D. (2001). Hedonic aspects of conditioned taste aversion in rats and humans. Unpublished masters thesis, University of Southern California. Legan, S. J., Coon, G. A., and Karsch, F. J. (1975). Role of estrogen as
Estradiol before Acquisition
initiator of daily LH surges in the ovariectomized rat. Endocrinol. 96, 50 –56. Manwaring, P., Morfis, L., Diamond, T., and Howes, L. G. (2000). Effects of hormone replacement therapy on ambulatory blood pressure and vascular responses in normotensive women. Blood Pressure, 9, 22–27. Merwin, A. A., and Doty, R. L. (1994). Early exposure to low levels of estradiol (E 2) mitigates E 2-induced conditioned taste aversions in prepubertally ovariectomized female rats. Physiol. Behav. 55, 185–187. Miele, J., Rosellini, R. A., and Svare, B. (1988). Estradiol benzoate can function as an unconditioned stimulus in a conditioned taste aversion paradigm. Horm. Behav. 22, 116 –130. Mikulka, P. J., Leard, B., and Klein, S. B. (1977). Illness-alone exposure as a source of interference with the acquisition and retention of a taste aversion. J. Exp. Psychol: Anim. Behav. Proc. 3, 189 –201. Morrison, J. M., Pritchard, H. D., Brande, M. L., and Aguanns, W. D. (1971). Plasma and brain lithium levels after lithium carbonate and lithium chloride administration by different routes in rats. Proc. Soc. Exp. Biol., 137, 795–797. Nachman, M. (1963). Learned aversion to the taste of lithium chloride and generalization to other salts. J. Comp. Physiol. Psychol. 56, 343–349. Nachman, M., and Ashe, J. H. (1973). Learned taste aversions in rats as a function of dosage, concentration, and route of administration of LiCl. Physiol. Behav. 10, 73–78. Nicolaus, L. K., Farmer, P. V., Gustavson, C. R., and Gustavson, J. C. (1989). The potential of estrogen-based conditioned aversion in controlling depredation: A step closer toward the “magic bullet.” App. Anim. Behav. Sci. 23, 1–14. Nicolaus, L. K., Herrera, J., Nicolaus, J. C., and Gustavson, C. R. (1989). Ethinyl estradiol and generalized aversions to eggs among free-ranging predators. App. Anim. Behav. Sci. 24, 313–324. O’Connor, E. F., Cheng, S. W. T., and North, W. G. (1987). Effects of intraperitoneal injection of lithium chloride on neurohypophyseal activity: Implication for behavioral studies. Physiol. Behav. 40, 91–95. Ossenkopp, K-P., Rabi, Y. J., Eckel, L. A. (1996). Oestradiol-induced taste avoidance is the result of a conditioned palatability shift. Neuroreport. 7: 2777–2780. Parker, L. A. (1995). Rewarding drugs produce taste avoidance, but not taste aversion. Neurosci. Biobehav. Rev. 19, 143–151. Peeters, B. W. M. M., Smets, R. J. M., and Broekkamp, C. L. E. (1992). Sex steroids possess distinct stimulus properties in female and male mice. Brain Res. Bull. 28, 319 –321.
305
Rabin, B. M., Hunt, WA., and Lee, J. (1987). Taste aversion learning produced by combined treatment with subthreshold radiation and lithium chloride. Pharmacol. Biochem. Behav. 27, 671– 675. Rabin, B. M., Hunt, W. A., and Lee, J. (1989). Attenuation and cross-attenuation in taste aversion learning in the rat: Studies with ionizing radiation, lithium chloride and ethanol. Pharm. Biochem. Behav. 31, 909 –918. Reicher, M. A., and Holman, E. W. (1977). Location preference and flavor aversion reinforced by amphetamine in rats. Anim. Lrn. Behav. 5, 343–346. Rice, A. G., Lopez, A., and Garcia, J. (1987). Estrogen produces conditioned taste aversions in rats which are blocked by antihistamine. Soc. Neurosci. Abstr. 13, 556. Riley, A. L., Jacobs, W. J., and LoLordo, V. M. (1976). Drug exposure and the acquisition and retention of a conditioned taste aversion. J. Comp. Physiol. Psychol. 90, 799 – 807. Schou, M. (1968). Lithium in psychiatry—A review. In Pharmacology: A Review of Progress 1957–1967, E. H. Efron (Ed). Public Health Service Publication No 1836, pp. 701–718. Sengstake, C. B., and Chambers, K. C. (1979). Differential effects of fluid deprivation on the acquisition and extinction phases of a conditioned taste aversion. Bull. Psychon. Soc. 14, 85– 87. Sengstake, C. B., Chambers, K. C., and Thrower, J. H. (1978). Interactive effects of fluid deprivation and testosterone on the expression of a sexually dimorphic conditioned taste aversion. J. Comp. Physiol. Psychol. 92, 1150 –1155. Suarez, E. M., and Barker, L. M. (1976). Effects of water deprivation and prior LiCl exposure in conditioning taste aversions. Physiol. Behav. 17, 555–559. Trautner, E. M., Morris, R., Noach, C. H., and Gershon, S. (1955). The excretion and retention of ingested lithium and its effects on the ionic balance in man. Med. J. Australia, 42, 280 –291. van Ree, J. M. (1979). Reinforcing stimulus properties of drugs. Neuropharmacol. 18, 963–969. Wise, R., Yokel, P., and Dewitt, H. (1976). Both positive reinforcement and conditioned aversion from amphetamine and from apomorphine in rats. Sci. 191, 1273–1274. Yuan, D. L., and Chambers, K. C. (1999a). Estradiol accelerates extinction of a conditioned taste aversion in female and male rats. Horm. Behav. 36, 1–16. Yuan, D. L., and Chambers, K. C. (1999b). Estradiol accelerates extinction of lithium chloride-induced conditioned taste aversions through its illness-associated properties. Horm. Behav. 36, 287–298.