Physiology and Behavior, Vol. 8, pp. 471-475. Brain Research Publications Inc., 1972. Printed in Great Britain
Ethanol Intake During Schedule-Induced Polydipsia R I C H A R D A. M E I S C H ~ A N D T R A V I S T H O M P S O N
Departments of Pharmacology and Psychiatry, University of Minnesota, Minneapolis, Minnesota, 55455, U.S.A. AND
Psychiatry Research Unit, Mayo Box 392, Medical School, University of Minnesota (Received 21 June 1971) R. A. AND T. THOMPSON. Ethanolintake during schedule-inducedpolych'psia. PHYSIOL.BEHAV. 8 (3) 471-475, 1972.--Schedule-induced polydipsia was established by maintaining 4 male Sprague-Dawley rats on concurrent variable interval 1 rain food reinforcement and continuous water reinforcement. Five ethanol concentrations (2, 4, 8, 16, and 32 % W/V) were substituted for water. The number of liquid reinforcements and volume of liquid consumed varied inversely with ethanol concentration while the quantity of ethanol intake varied directly with the concentration. Ethanol reinforcements were above water control levels during the first l0 rain ethanol was present. For the same interval increases occurred in the number of ethanol, but not water reinforcements when each concentration was presented a second time. Decreases occurred in the food baseline as a function of concentration with intermediate concentrations having the greatest effect. These decreases were greater the second time the ethanol concentrations were presented. MEISCH,
Ethanol self-administration Schedule-induced polydipsia Ethanol concentration Rats
FALK  reported that when rats were placed on an intermittent schedule of food reinforcement and concurrently given access to water, they drank up to one-half of their body weight in water over a 3.17 hr period. He termed this phenomenon schedule-induced polydipsia (SIP) and demonstrated that animals would respond (lever press) for water presentation . Subsequently, Lester  used Falk's polydipsia procedure to induce rats to self-administer 5.6% (W/V) ethanol; intoxication was produced in 3-hr test sessions with blood alcohol levels reaching 0.2%. His results have since been replicated . However, following polydipsia training, Senter and Sinclair found no increase in the ratio of ethanol solution consumed to total liquid intake. Using the SIP procedure, Holman and Myers  varied ethanol concentration and observed a decrease in the volume consumed with increases in drug concentration. Relative to intake levels measured in the absence of polydipsia, ethanol drinking increased during polydipsia only at concentrations below 8 % (V/V). Meisch and Pickens (unpublished data) and Meisch  used SIP to study self-administration of ethanol and sodium pentobarbital. Unlike previous drug SIP studies, liquid presentation was contingent on another operant response (lever pressing) and the time course changes in food and liquid responding were recorded. Presence of the drug solutions was found to produce significant changes in the
food and liquid baselines which had not been reported in previous studies. The purpose of the present study was to confirm the initial observations concerning ethanol induced changes in the food and liquid baselines and to replicate the results within as well as across subjects. In addition, time course changes in the food and liquid baselines were studied as a function of ethanol experience. METHOD
Animals Four male albino Sprague-Dawley rats were maintained at 80 % of their free-feeding weights. They were approximately 300 days old at the beginning of the experiment and were individually housed in a temperature controlled (23.9°C), constantly illuminated room. Water was always available in the animals' home cages.
Apparatus The apparatus was a standard Foringer operant conditioning chamber. The chamber was equipped with two levers, a food magazine, and a dipper for presenting liquid. The levers were separated by the reinforcement mechanisms, with the food magazine directly above the dipper. Each operation of the food magazine produced a single 45 mg Noyes food pellet, and operation of the dipper made available 0.25 ml of liquid for 4 sec. The operant conditioning chamber
1U.S.P.H.S. Postdoctoral Research Fellow 1 FO2 MH 46770-01. 2This research was supported in part by Research Grants MH-15349 and MH-14112 from the United States Public Health Service to the University of Minnesota. We thank Dr. Glenn E. Bartsch for his advice concerning the statistical analysis of the data. 471
MEISCH AND THOMPSON
was housed in a ventilated sound-shielding enclosure. White masking noise was constantly present. Programming and data recording were automatic, by standard electromechanical equipment located in an adjacent room.
The results of this procedure and a similar manipulation performed after the present experiment are reported in detail elsewhere .
The control values for the dependent variables at each time period were analyzed separately using a split-plot design . The one exception was the analysis of liquid reinforcements over ten min intervals; in this case a split-split plot design was used. The variability of the ethanol values was assumed to be the same as that of the control values. Two comparisons were made, one was the difference between experimental and control values, and the other was the difference between the first value and its replicate.
The animals were placed in the operant conditioning chamber at a regular starting time for six hr each day. Responding on the left lever delivered food on a variableinterval (VI) 1 min schedule. On such a schedule a rat receives a food pellet on the average of once per rain, ranging from a few sec to two min. No stimulus indicated which lever press would be followed by a food pellet. Each response on the other lever produced liquid. At the end of the session the rats were given supplementary feedings in their home cage with Purina laboratory rat chow to maintain their weights at 8 0 ~ of the free-feeding value. Responses and reinforcements for both food and liquid were recorded every 10rnin by a print-out counter. The temporal pattern of responding and reinforcement presentation was continuously recorded separately for food and liquid by cumulative recorders. Volume of liquid consumed was measured at the end of the first and sixth hr by calculating the difference between the volume added to the reservoir and the volume remaining. All volumes were corrected for evaporation by subtracting the volume lost when naive rats which did not press the lever were substituted for the experimental rats. All the ethanol concentrations were prepared using absolute ethanol and tap water. The solutions were always prepared at least five hr prior to their use and kept in stoppered containers. The concentrations are in terms of grams percent, The rats were shaped by hand to respond on the right lever for food . After receiving approximately 75 food reinforcements on continuous reinforcement (i.e., each lever press produced food), the rats were switched to the VI 1 minute schedule. Acquisition of responding for water on the left lever was acquired by all rats within three sessions after having been switched to the VI 1 min food reinforcement schedule. Each rat received at least 30 SIP sessions with water before being presented with an ethanol solution for the first time.
Experimental Design Each ethanol concentration was presented on the second day of a three day sequence. A water control day immediately preceded and followed each ethanol day. When an ethanol concentration was presented, it was substituted for water at the end of the first hour of the session. To maintain parallel procedures on control days, water present during the first hour was replaced with fresh water. Food reinforcement was always concurrently available. Five ethanol concentrations, 2, 4, 8, 16, and 3 2 ~ (W/V), were presented twice to each rat. Each concentration was presented once during Series I and once during Series II. The order of presentation of the concentrations was randomized and different for each rat. However, for a particular rat the sequence used in Series I was repeated in Series II. Immediately prior to the present experiment each rat was given one five hr exposure to each of the concentrations. During exposure to these concentrations concurrent food reinforecment was absent, in order to determine the rats' ethanol intake in the absence of schedule-induced polydipsia.
Changes in the food and liquid baselines. Liquid reinforcements and ethanol volume decreased as a function of ethanol concentration (Fig. 1). Food responses and reinforcements also decreased below water control values (Fig. 1). However, the relation between ethanol concentration and food responses and reinforcements varied with the series of ethanol presentations. When each concentration was presented the first (I) time, the decreases in the food baseline did not vary with the concentration, but when each concentration was presented a second (II) time, there was an increase in the range of experimental values, and the concentration effect became evident (Fig. 1). Food responses and reinforcements were decreased the most at 4 and 8 ~ , respectively. Progressively smaller decreases occurred at concentrations above and below these values. Most decreases in the food and liquid baselines were to levels significantly below water control values. Time course. Ethanol reinforcements were above water control levels during the first 10 rain of ethanol availability (Fig. 2). The increase was greatest at 8 ~ and progressively less at concentrations above and below 8 ~ (Fig. 2). For the first ten minutes the average value for the five ethanol concentrations was significantly above the water control value during the second (II) (p < 0.001) but not the first series (1). During the subsequent two 10 rain periods ethanol reinforcements were below water control levels (Fig. 2) and remained below for the entire session (Fig. 3). Over successive hours ethanol reinforcements decreased as a function of concentration; the greater the concentration, the earlier and more profound was the decrease (Fig. 3). The time course of the food baseline at any particular concentration often consisted of decreases followed by increases and then decreases again (Fig. 3). Many of the decreases were to levels significantly below water control values. Records of food responding from individual animals also showed cyclical variations in response rate. Only during the first hour that ethanol was available did changes in the food baseline relate in an orderly way to the ethanol concentration. Then the greatest decrease occurred at 8 ~o with progressively smaller decreases occurring at concentrations above and below this value (Fig. 3). During subsequent hours the cyclical patterns differed at each concentration resulting in no relation between concentration and food baseline values. Comparison between the first (1) and second (H) series of ethanol presentations. Presenting each ethanol concentration a second time resulted in an increased rate of ethanol intake and a decreased rate of food intake. These rate changes were reflected in more pronounced changes in the time course
SCHEDULE-INDUCED POLYDIPSIA AND ETHANOL
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FIG. 2. Time course by min of liquid reinforcements as a function of ethanol concentration. Values in the upper half of the figure are for the first (I) presentation of each ethanol concentration while the values in the lower half are for the second (I1) presentation. The striped bar represents the mean value for the 30 min water control period immediately preceding the exchange of liquid reservoirs. The bars numbered one, two and three represent mean values for the first, second, and third ten min periods respectively following the exchange of liquid reservoirs with the introduction of ethanol. For zero percent, N = 40 (4 rats × 10 sessions); for the other concentrations, N = 4 (4 rats × l session).
6000 3000 0 400 300 200 100 0
8 z n
16 j. rr
(GRAMS PER CENT) FIG. 1. Effect of ethanol concentration during SIP on four dependent variables: liquid reinforcements, volume consumed, food responses, and food reinforcements. Results for the first (1) and second (I1) presentation of each concentration are compared. Each bar represents a mean. For zero percent, N = 40 (4 rats x 10 sessions); for other concentrations, N = 4 (4 rats × 1 session). The vertical lines at the top of the bars represent the mean (N = 4) standard error of the mean. The striped portion at the bottom of the bars indicates the value of the dependent variables during Hour I when only water was available.
values than in the session total values. During the first 10 minutes of ethanol availability the average number of ethanol reinforcements was significantly greater (p < 0.05) during the second (II) series relative to the first (I). However, there was no increase in ethanol reinforcements for the first and subsequent hours ethanol was present. A similar comparison of the time course values of food responses and reinforcements showed decreases (p < 0.01 and p < 0.001 respectively) during the first hour ethanol was present. F o o d responses were also decreased during the second hour ethanol was present (p < 0.05). N o differences in food responses and reinforcements were found for subsequent hours of the experiment.
Comparison of session total values revealed increased ethanol reinforcements and ethanol volume consumed. These increases were significant for the volumes consumed at concentrations of 2 ~ and 16~o (p < 0.01 and p < 0.05, respectively). The average experimental values for food responses and reinforcements decreased (p < 0.05 and p < 0.05). There were no significant differences in control values between the first (I) and second (II) series. Consequently, changes in the experimental values were not secondary to baseline shifts. Quantity of ethanol intake. Table 1 presents the quantity of ethanol consumed at each concentration in terms of milligrams per hundred grams of body weight per hour. In general, the quantity of ethanol consumed increased directly with the concentration.
DISCUSSION Changes in the food baseline demonstrate that the ethanol consumed was affecting the animal's behavior. Furthermore, these changes provide a quantitative measure continuous over time of behavioral effects due to drug ingestion . Previous studies using SIP to induce ethanol drinking have either not reported effects on the food baseline , found no effects , or have not reported both drug and control food baseline values .
ME1SCH A N D THOMPSO ETHANOL H L f Q U t O $N
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( &WATER ONLY)
FIG. 3. Time course by hours of the dependent variables as a function of ethanol concentration. Values are for the second (11) presentation of each ethanol concentration. Each bar represents a mean. For zero percent, N -- 40 (4 rats × 10 sessions; for other concentrations, N = 4 (4 rats × 1 session). The vertical lines at the top of the bars are the mean (N = 4) standard error of the mean.
The second time each concentration was presented, the greatest decreases were at 4 % for food responses and at 8 % for food reinforcements. Below or above these concentrations the effect was progressively smaller, a result in accord with findings of a prior study where the greatest depression in both food responses and reinforcements was at 8 % [unpublished data]. The above control response rates for ethanol during the first ten minutes of its availability suggest ethanol was serving as a reinforcer. The findings are consistent with results obtained with these animals in the absence of concurrent food reinforcement . A n increase in the rate of ethanol intake with experience was indicated by changes in the values of the dependent variables from the first (1) to the second (II) series of ethanol presentations. During the first ten minutes of ethanol availability, ethanol reinforcements increased, and during the first h o u r of ethanol availability, food responses and reinforcements decreased. Similar changes occurred in session total values. These data illustrate the importance of recording values of the dependent variables over time in the analysis of drug self-administration [5, 6, 8]. Decreases in the food baseline as a function of concentration (Fig. 1) are directly related to thel initial ~ate of ethanol responding (Fig. 2) and not to the total quantity of ethanol consumed (Table I). With successive opportunities to drink, changes occur not so much in session total values as in the time course. In this study increases in intake with experience occurred for values for the first ten but not sixty minutes of ethanol availability. The quantity of ethanol consumed increased directly with the concentration. The same relation between quantity of intake arid concentration was observed in these animals in the abserlCe of concurrent food reinforcement . The present results confirm Lester's observation  of high ethanol intake during SIP and extend his findings to include a wide range of ethanol concentrations.
TABLE 1 QUANTITYOF ETHANOLINTAKEAS A FUNCTIONOF CONCENTRATION(IN rag/100 g oF BODY WEIGHT/HR) Ethanol Concentration
*Values listed under 1 are from the first presentation of each ethanol concentration while the values listed under 11 are from the second presentation. tValues are from single sessions.
S C H E D U L E - I N D U C E D POLYDIPSIA A N D ETHANOL
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6. Meisch, R. A. and T. Thompson. Ethanol intake in the absence of concurrent food reinforcement. Psychopharmacologia 22: 72-79, 1971. 7. Michael, J. Laboratory Studies in Operant Behavior. New York, New York: McGraw-Hill, 1963. 8. Schuster, C. R. and T. Thompson. Self-administration of and behavioral dependence on drugs. A. Rev. Pharmac. 9: 483502, 1969. 9. Senter, R. J. and J. D. Sinclair. Self-maintenance of intoxication in the rat: A modified replication. Psychonom. ScL 9: 291-292, 1967. 10. Steel, R. G. D. and J. H. Torrie. Principles and Procedures of Statistics. New York, New York: McGraw-Hill, 1960.