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Establishment and maintenance of oral ethanol self-administration in the baboon
Drug and Alcohol Dependence, 7 (1981) 113 - 124 0 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands
ESTABLISHMENT ADMINISTRATION
AND MAINTENANCE IN THE BABOON
113
OF ORAL ETHANOL
SELF-
JACK E. HENNINGFIELD National Institute on Drug Abuse/Addiction Research Center, Baltimore, 21224 (U.S.A.) and The Johns Hopkins University School of Medicine.
Maryland,
NANCY A. ATOR and ROLAND R. GRIFFITHS* The Johns Baltimore,
Hopkins Maryland
University School 21205 (U.S.A.)
of Medicine,
Division
of Behavioral
Biology,
(Received November 2, 1980)
Summary A simple and reliable method was developed to study the self-administration of orally available ethanol by baboons. Two baboons were individually housed in a minimally controlled laboratory environment with visual and auditory access to other baboons and to laboratory technicians. The cages were equipped with standard drinking bottles and spouts. Each baboon was fed his entire daily ration of dry food at the same time each morning, at which time a fresh’solution was added to the liquid reservoir. Three hours later, the amount of liquid consumed was measured. This procedure generated high rates of water drinking during the 3-h sessions (“food-induced drinking”). Next, the water available during the sessions was replaced by gradually increasing concentrations of aqueous ethanol (0.5 - 8%, w/v). When 8% ethanol was reached, the concentration was held constant across daily sessions as session feedings were gradually reduced and shifted to 30 min postsession. Eventually, daily test sessions consisted of simply 3 h access to ethanol, and water was continuously available during the 21-h intersession period. Over a range of ethanol concentrations of 8 - 3276, ethanol intake (g/kg) and blood ethanol levels remained fairly constant, while volumes (ml) of solution consumed were inversely related to the concentration. Finally, an additional liquid spout was added to each cage and the baboons were provided concurrent access to both ethanol (8%) and water during the sessions. The results indicated clearly that ethanol had come to serve as a positive reinforcer for both of these baboons. This simple preparation should be particularly useful in laboratories that are not equipped with the elaborate technology required in earlier described preparations, and might lend itself to the study of orally effective drugs other than ethanol. *Send reprint requests to Dr. Roland R. Griffiths, The Johns Hopkins University School of Medicine, Department of Psychiatry and Behavioral Sciences, Division of Behavioral Biology, 720 Rutland Avenue, Baltimore, Maryland 21205, U.S.A.
114
Key words: ethanol, stration.
baboon,
food-induced
drinking,
oral self-admini-
Although the study of ethanol self-administration has been possible using the intravenous (see, for example, refs. 1 and 2) and intragastric [3] routes, both practical and theoretical considerations have made it desirable to develop a method for studying self-administration of orally delivered ethanol [ 4 - 61. In oral preparations, the significance of using appropriate training procedures is illustrated by the wide range of procedures which have been tested and which failed to overcome the apparently innate aversion to the taste of ethanol by animals (cf. reviews [ 5 - 71). For instance, even when animals were required to consume ethanol for long periods (for example, as their sole source of fluid or as a shock-avoidance response) [ 81, drinking typically did not continue when an alternative fluid was available or when the contingencies on drinking were removed (see above reviews). Neither was the establishment of physical dependence (as defined by evidence of a withdrawal syndrome) sufficient to establish ethanol as a reinforcer [ 91. More recently, however, it has been demonstrated that by following certain training procedures, ethanol can come to serve as an orally effective reinforcer in rats [lo, 111 and rhesus monkeys [12 - 141. The general method involves feeding food-deprived animals once a day. Although water is continuously available, this procedure induces consumption of a large quantity of water following eating. This phenomenon has been termed foodinduced drinking [ 141. Under these conditions, ethanol solutions in gradually increasing concentrations are substituted for water at feeding time and are made available for a period of several hours. When substantial quantities of ethanol are being regularly consumed, the daily feeding is shifted postsession. Thereafter, the animals are simply provided access to ethanol at the same time every day. Despite the fact that the animals are never deprived of water, they generally continue to consume intoxicating quantities of ethanol. The present paper describes the results using this oral method to establish and maintain ethanol drinking by another primate species - the baboon. Additionally, the current study demonstrates that the oral preparation can be successfully developed in a minimally controlled open laboratory environment using a simple and nonautomated technology. After ethanol drinking was established, behavior was studied over a range of ethanol concentrations and in the presence of concurrent water availability.
Materials and methods Subjects The subjects were two male baboons (Papio anubis) weighing 28 (AP) and 18 (KU) kg at the start of the experiment. Both baboons had served in
115
studies of intravenous self-administration with a variety of drugs (AP for 18 months and KU for 6 months). Apparatus The baboons were individually housed in standard primate squeeze cages (0.81 X 0.94 X 1.22 m high). The cages were located in an active selfadministration laboratory in which the baboon subjects had visual and auditory access to other baboons and to laboratory personnel. The room lights were turned on at approximately 8:00 a.m. and turned off at the end of the work day (between the hours of 4:00 and 6:00 p.m. on weekdays and at 1:00 p.m. on weekends). A calibrated Nalgene reservoir was mounted on a wooden platform on the top of each cage and liquid was gravity-fed through Tygon tubing to a standard brass poultry drinking spout (H. W. Hart Manufacturing Co., Glendale, California) which protruded through the platform into the top of the cage. Partway through the experiment (as described below), each baboon was moved into a large, sound-attenuated wooden enclosure which was continuously illuminated with a 15-W frosted bulb. During some of the sessions, a drinkometer was connected to the drinking spout and drinking-spout contacts were recorded on a Gerbrands cumulative recorder. Procedure Establishment of ethanol drinking The baboons were provided continuous access to water (except as described below). Daily feedings were one or two fresh fruits and an individually determined quantity of l-g Noyes banana pellets. Each day, at 9:00 a.m., the liquid reservoirs were emptied and their contents measured to determine the volume of water consumed since the end of the previous day’s session. Fresh tap water (1000 ml) was added to the reservoir, and the baboons were fed their entire daily ration of banana pellets. Three hours later, the volume of liquid consumed was measured, and the reservoir filled with 2000 ml of water. The daily ration of fruit was provided 30 min following the session. After drinking was stable for four consecutive sessions (i.e. no trends in volume consumed across sessions), aqueous ethanol solutions were substituted for water. The solutions were prepared using 95% ethanol and tap water. When volume consumed was stable at 8% (w/v), a procedure of gradually fading out the presession feeding was begun. The number of pellets presented at the beginning of the session was systematically decreased by 50% until one and then none, were presented. The balance of the daily food ration was provided along with the fruit 30 min after the session. The sequence of manipulations and the number of sessions at each stage are presented in Table 1. The primary criterion for increasing the number of food pellets was that at least four sessions at a given value had occurred and that the volume of ethanol consumed was generally stable. Due to space considerations in the laboratory, baboon KU was moved into the wooden enclosure halfway through the phase in which the number of pre-
116
session food pellets was decreased. The door to the enclosure during sessions but open much of the day.
was closed
Manipulation of ethanol concentration When all feeding was occurring 30 min postsession, sessions consisted simply of 3-h access to an ethanol solution. For both baboons ethanol concentrations were presented in the following ascending series: 8, 11.3, 16, 22.6, and 32% (w/v). For baboon KU, a return to 8% then followed 32%. For baboon AP, the concentrations were repeated in descending order ending with the return to 8%. Each concentration was present for at least five sessions and concentrations were changed when no trends were occurring in volume consumed. Numbers of sessions at each concentration are given in Table 1. Blood e than01 determinations Approximately 30 min after the final session at each concentration in the ascending series for baboon KU and in the descending series for baboon AP, the baboons were anesthetized with ketamine hydrochloride (i.m.) and an approximately l-ml sample of blood was collected into a Vacutainer@ . These samples were analyzed for their ethanol content by a medical hematology laboratory using gas chromatography. Concurrent access to ethanol and water Upon completing the ethanol concentration manipulations, an additional liquid reservoir was mounted on each cage such that the spouts were positioned about 30 cm apart. Procedures for measuring and changing solutions and for feeding the baboons were the same as in previous conditions, except that during the 21-h intersession period water was available via both drinking spouts. During sessions an 8% ethanol solution and water were concurrently available; their relative side positions were switched each day. The number of sessions under this condition was 20 for baboon KU and 54 for baboon AP. Substitution of water for e than01 solutions Finally, after completing the concurrent water-ethanol phase, the newer drinking system was removed and only 8% ethanol was available during sessions. During this period, baboon AP also was moved to a wooden enclosure; conditions were as for KU above. After 2 and 19 sessions at 8% for KU and AP, respectively, the ethanol was replaced with tap water. During the next 3 days, the baboons were closely observed during the day for specific signs of ethanol withdrawal (cf. ref. 15). Results Establishment of ethanol drinking Both baboons drank substantial volumes of ethanol solution under the food-induced drinking procedure (Table 1). Baboon AP drank the greatest
550(500-700) 675 (500 - 800) 350(200-500) 775 (400 - 900) 688 (450 - 800) 538 (450 - 600) 505 (420 - 600) 425(300-500) 439 (400 - 510) 408 (400 - 430) 379(325-425) 305 (240 -425) 316 (275 - 350) 328 (300 - 363) 329 (290 - 375)
150/o 150/o 150/o 150/o 150/o 150/o 150/o 75175 38/112 19/131 10/140 51145 21148 l/149 o/150
22 13 8 9 14 11 10 6 8 4 9 6 8 6 5
(ml)
Pellets session/ postsession
Mean volume consumed*
0.123 0.128 0.574 1.026 1.155 1.536 1.308 1.367 1.283 1.208 0.984 0.991 1.050 1.053
28.0 27.5 27.3 27.0 26.8 26.5 26.3 26.0 25.7 25.4 25.1 24.8 25.5 25.0 25.0
(kg)
0 0.5 1 2 4 5.7 8 8 8 8 8 8 8 8 8 8
(% w/v)
Ethanol
Baboon
procedures
Weight
drinking
(g/kg per 3 h)
Ethanol dose
and results of the food-induced
Sessions
of conditions
AP
1
*Last four sessions.
0 0.5 1 2 4 5.7 8 8 8 8 8 8 8 8 8
(% w/v)
Ethanol
Baboon
Sequence
TABLE
50/O 50/O 75/o 75/o 100/o 100/o 100/o 125/O 62163 31194 16/109 8/117 41121 21123 l/l24 O/125
Pellets session/ postsession
KU
9 13 8 5 9 7 8 7 18 7 6 5 4 7 6 10
Sessions
425(300-500) 600 (500 - 700) 450 (100 - 800) 775 (400 - 900) 713 (400 - 900) 863 (850 - 900) 650 (600 - 700) 666 (590 - 700) 679 (600 - 750) 543 (500 - 575) 594 (550 - 650) 629 (620 - 650) 581(550-620) 601(525 - 680) 495 (425 - 565) 555 (525 - 590)
(ml)
Mean volume consumed*
0.170 0.257 0.891 1.649 2.860 .3.023 3.098 3.158 2.526 2.763 2.926 2.702 2.828 2.329 2.612
(g/kg per 3 h)
Ethanol dose
18.0 17.5 17.5 17.4 17.3 17.2 17.2 17.2 16.0 15.5 16.3 16.5 16.5 17.0 17.3 17.0
(kg)
Weight
118
volume at a concentration of 4%, and baboon KU drank the greatest volume at 8%. For both baboons, the greatest quantity (g/kg) of ethanol was obtained at 8%. At concentrations of 4% and greater, both baboons became somewhat sedated and occasionally ataxic during sessions. Throughout this experimental phase, each baboon displayed a distinct drinking pattern. Baboon AP distributed eating and drinking bouts across the first hour of the session; the food was usually eaten by the second hour of the session, but sporadic drinking bouts continued until the end of the session. Baboon KU quickly consumed all available food at the start of the session and then drank in one protracted drinking bout. Later in the session, a few short drinking bouts occurred; baboon KU regularly drank rapidly at the end of the session when the experimenter began to remove the ethanol solution. When food was gradually shifted from the session to the postsession period, volume consumed decreased slightly, and there was little change in ethanol intake in g/kg per session, since the weights of the baboons also decreased slightly (Table 1). When the cage of baboon KU was enclosed in the wooden chamber, the volume consumed decreased slightly on the first day, but recovered to the preceding level (over 600 ml) by the second day. Ethanol drinking as a function of concentration When ethanol concentration was increased, the volume (ml) of solution consumed decreased while intake of ethanol (g/kg) was relatively unchanged (Fig. 1). Blood ethanol levels were fairly stable for both baboons, with KU drawing consistently higher levels than AP (Table 2). This latter finding is consistent with the larger volumes consumed and the more pronounced ataxia that was observed with baboon KU. Periodic observation of drinking behavior suggested that both baboons continued to do most of their drinking during the first hour of each session, then to drink intermittently during the rest of the session. When the 8% concentration was repeated for baboon KU, the volumes consumed and quantities of ethanol obtained were similar to those obtained during the first exposure to that concentration. During the descending series for baboon AP, however, average volumes consumed at each concentration were higher than those obtained during the ascending series. Specifically, mean volumes consumed by AP during the descending series were: 165 ml at 22.6%, 210 ml at 16%, and 443 ml at 8% (n = 5). (At 11.3%, too few sessions were conducted on the descending series to provide comparable data.) Concurrent access to ethanol and water Providing access to water concurrently with the 8% ethanol solution had no effect on volumes of ethanol consumed for either baboon (Fig. 1). For baboon KU, the volume of water consumed during those sessions never exceeded that of ethanol. For baboon AP, the volume of ethanol consumed remained extremely stable for over 50 sessions (generally 400 - 500 ml per session), yet the volume of water consumed in those sessions was highly variable, often exceeding that of ethanol.
119
8
11.3
ETHANOL
16
CONCENTRATION
(%W/V)
Fig. 1. Mean volume of solution consumed (a) and mean quantity of ethanol obtained (0) as a function of concentration over the last five sessions for each baboon. Vertical bars indicate the range of volumes at each concentration, and R indicates the return to 8%. The 8% and 0% points on the right side of the figure indicate volumes consumed during the condition of concurrent access to water and ethanol. TABLE
2
Blood ethanol levels (BEL) as a function of ethanol concentration Baboon KU
Baboon AP Ethanol (% w/v)
Sessionsa
BEL (mg %)
Volumeb (ml)
8 11.3 16 22.6 32
5(7) 6(2) 8(7) 6(5) 10
122 128 157 123 86
380 275 250 140 50
Weight (kg)
23.3 23.3 23.5
Sessionsa
BEL (mg %)
Volumeb (ml)
Weight (kg)
lO(12) 15 9 19 16
235 182 182 273 204
550 365 260 225 150
17.3 17.0 17.5 17.0c 18.0’
aNumbers are for ascending series; numbers in parentheses are for descending series. bVolume consumed in the session which immediately preceded the blood sample. ‘A supplemental ration of 25 g of Purina monkey biscuits was added to the postsession fruit and pellets to maintain good health in this baboon.
120
The patterns of drinking-spout contact shown in the event records (Fig. 2) revealed that contact with the spout delivering ethanol predominated in the first 30 - 45 min of each session, regardless of side position, for both baboons. Although both spouts typically were sampled at the beginning of the sessions, the number and duration of contacts with the ethanol spout always exceeded those of the spout delivering water in the first part of the session. For baboon KU, the number of contacts with the water spout were always very low, as reflected in the low volume of water consumed. For baboon AP, however, contacts with the spout delivering water occurred frequently, but duration and relative number of bouts were lower than for the ethanoldelivering spout early in the session. By the end of the first hour of the sessions, drinking from both spouts had decreased (Fig. 2). In the re-
Fig. 2. Event records from final sessions of the condition of concurrent access to ethanol (8%, w/v) and water (0%) for both baboons. Each record shows the first 60 min of a 3-h session. The pen(s) on a cumulative recorder deflected with drinking spout contact and remained deflected for the duration of contact. The records for 8% and 0% for baboon KU were recorded during alternate sessions and represent the last six sessions of the concurrent access condition. Each pair of records for baboon AP shows contact with both drinking spouts within the same session and are for the last five sessions in which records were available.
121
maining 2 h of the session, few spout contacts occurred for baboon KU, but baboon AP continued to make frequent brief contacts with both spouts. Both baboons showed slight position preferences in volumes consumed from the two bottles during the 21-h intersession period (left side for KU and right side for AP), yet during sessions neither patterns of spout contact nor volumes of solutions consumed reflected a position preference.
Substitution
of water for ethanol solutions
When water was substituted monkeys were carefully observed ethanol withdrawal (as described
for ethanol during the 3-h sessions, the during the day for 3 days: no signs of an by Ellis and Pick [15] ) were observed.
Discussion A procedure was used to establish ethanol drinking by two baboons in which food-induced drinking of water was initially established and subsequently the water was replaced by aqueous ethanol solutions in gradually increasing concentrations. Both baboons continued to drink ethanol after the food-induced drinking procedure had been terminated and daily sessions consisted simply of 3 h access to ethanol. As ethanol concentration was increased from 8% to 32% (w/v), the volume (ml) of solution consumed decreased but the quantity (g/kg) of ethanol obtained remained relatively stable. Behavioral observations and blood ethanol levels confirmed that the baboons were ingesting intoxicating quantities of ethanol in each session. Across the 3-h sessions, ethanol drinking was a negatively accelerated pattern of discrete intermittent bouts with the largest number of bouts during the first 30 - 45 min of access. The continued high ethanol intake exhibited during the concurrent ethanol-water phase confirmed that ethanol maintained drinking in its own right, apart from its nonspecific properties as a liquid, and without the presence of physiological dependence, as indicated by the absence of any signs of a withdrawal syndrome when water was substituted for the ethanol. This study shows that the strategies used to establish orally delivered ethanol as a reinforcer for rats and rhesus monkeys are similarly effective when applied to baboons. Further, it shows that the establishment and maintenance of ethanol drinking can be achieved without the elaborate and expensive technology used in earlier studies (cf. ref. 14). The power of these procedures is illustrated by the fact that ethanol consumption was generated under relatively uncontrolled laboratory conditions in which baboons were housed in open cages with visual and auditory access to other baboons and to laboratory personnel. This finding mitigates the possible criticism of earlier ethanol self-administration studies that the selfadministration behavior was due to the physcial isolation and sound attenuation procedures used in those studies. Taken together, these findings indicate that a wide range of laboratories may be able to employ this relatively simple methodology to study the phenomena of ethanol dependence.
122
The results of the present study are consistent with those obtained when the establishment and maintenance of ethanol drinking was studied in rhesus monkeys using analogous procedures. Also, where comparisons are possible, the functional relationships obtained (for example, concentrationresponse function) are similar to those obtained in studies of ethanol drinking by rats [ 71, intravenous ethanol self-administration by monkeys and rats [16,17], and intragastric ethanol self-administration by rats [17]. In general, findings from these studies are also consistent with those obtained in experimental studies of ethanol drinking by humans [ 18,191. Jointly considered, these studies show that when ethanol serves as a reinforcer, it controls behavior in an orderly fashion under a wide range of conditions. The procedures employed in the present experiment for inducing alcohol consumption may also provide an effective means of studying selfadministration of drugs other than ethanol (cf. refs. 20 - 22). The potential usefulness of the oral method for studies of drug dependence is especially clear when compared to the more expensive and elaborate intravenous and intragastric procedures (cf. refs. 23 and 24). An additional practical consideration is that once the drinking performance is established, it is reliable and could be maintained for many years*. As a model for studying alcoholism (and perhaps dependence on CNS depressants), the oral self-administration procedure may provide important data not obtainable using intravenous or intragastric preparations. Recent oral ethanol and drug self-administration studies have shown that there are some important differences in the performances generated by orally delivered drugs. For example, the taste and odor of ethanol and other drugs may acquire conditioned stimulus properties (I$. refs. 25 and 26) and these properties may serve to generate stronger and more persistent performance than that which is maintained by intravenous drug delivery (for example, ref. 22). A particular advantage of the food-induced drinking procedures used in the present study is that, since reliable oral consumption is induced prior to physiological dependence and maintained in the absence of concurrent behavioral contingencies on drinking, there is the potential for manipulating a range of variables which may be important in controlling the behavior of ethanol drinking. Finally, the present study demonstrated the application of a relatively simple procedure and technology to establish and maintain the self-administration of orally delivered ethanol. The baboons were housed in open cages and were exposed to the uncontrolled activity of the normal laboratory milieu. The robust ethanol consumption generated under these conditions attests to the power and generality of the method. This primate preparation may be useful in a wide variety of laboratories where it is of interest to study ethanol drinking when the ethanol is functioning as a reinforcer and the drinking behavior is voluntary.
*R. A. Meisch,
personal
communication.
123
Acknowledgements This study was supported by Drug Enforcement Administration Contract No. DEA-78-9, and National Institute on Drug Abuse Grant No. DA01147. We thank Scott Deamond, William Kearns, Sharyn Olson, and Richard Wurster for their technical assistance in conducting this study.
References 1 G. Deneau, T. Yanagita and M. H. Seevers, Self-administration of psychoactive substances by the monkey. Psychopharmacologia, 16 (1969) 30 - 48. 2 G. D. Winger and J. H. Woods, The reinforcing property of ethanol in the rhesus monkey: Initiation, maintenance and termination of intravenous ethanol-reinforced responding. Ann. N.Y. Acad. Sci., 215 (1973) 162 - 175. 3 H. L. Altshuler and L. Talley, Intragastric self-administration of ethanol by the rhesus monkey: An animal model of alcoholism. In F. A. Seixas (ed.), Currents in Alcoholism, Vol. 1, Grune and Stratton, New York, 1977, pp. 243 - 253. 4 H. J. Friedman and D. Lester, A critical review of progress towards an animal model of alcoholism. In D. L. Bard and M. G. Hamilton (eds.), Alcohol and Opiates: Neurochemical and Behavioral Mechanisms, Academic Press, New York, 1977, pp. 1 - 19. 5 N. K. Mello, A review of methods to induce alcohol addiction in animals. Pharmacol. Biochem. Behau., 1 (1973) 89 - 101. 6 R. D. Meyers and W. L. Veale, The determinants of alcohol preference in animals. In B. Kissin and H. Begleiter (eds.), The Biology of Alcoholism, Vol. 11, Plenum Press, New York, 1971, pp. 131 - 168. 7 R. A. Meisch, Ethanol self-administration: Infrahuman studies. In T. Thompson and P. B. Dews (eda.), Advances in Behavioral Pharmacology, Vol. 1, Academic Press, New York, 1977, pp. 35 - 84. 8 N. K. Mello and J. H. Mendelson, The effects of drinking to avoid shock on alcohol intake in primates. In M. K. Roach, W. M. Isaac and P. J. Craven (eds.), Biological Aspects of Alcohol, University of Texas Press, Austin, 1971, pp. 313 - 340. 9 R. D. Meyers, W. P. Stoltman and G. E. Martin, Effects of ethanol dependence induced artificially in the rhesus monkey on the subsequent preference for ethyl alcohol. Physiol. Behau., 9 (1972) 43 - 48. 10 R. A. Meisch, The function of schedule-induced polydipsia in establishing ethanol as a positive reinforcer. Pharmacol. Rev., 27 (1978) 19 - 25. 11 R. A. Meisch and T. Thompson, Rapid establishment of ethanol as a reinforcer for rats. Psychopharmacologia, 37 (1974) 311 - 321. 12 J. E. Henningfield and R. A. Meisch, Ethanol drinking by rhesus monkeys as a function of concentration. Psychopharmacology, 57 (1978) 133 - 136. 13 J. E. Henningfield and R. A. Meisch, Ethanol drinking by rhesus monkeys with concurrent access to water. Pharmacol. Biochem. Behau., 10 (1979) 777 - 782. 14 R. A. Meisch and J. E. Henningfield, Drinking of ethanol by rhesus monkeys: Experimental strategies for establishing ethanol as a reinforcer. In M. M. Gross (ed.), Alcohol Intoxication and Withdrawal: Experimental Studies, Vol. IIIb, Plenum Press, New York, 1977, pp. 443 - 463. 15 F. W. Ellis, and J. R. Pick, Experimentally induced ethanol dependence in rhesus monkeys. J. Pharmacol. Exp. Ther., 175 (1970) 88 - 93. 16 A. J. Karoly, G. D. Winger, F. Ikomi and J. H. Woods, The reinforcing property of ethanol in the rhesus monkey. Psychopharmacology, 58 (1978) 19 - 25. 17 S. G. Smith, T. E. Werner and W. M. Davis, Comparisions between intravenous and intragastric alcohol self-administration. Physiol. Psychol., 4 (1976) 91 - 93.
124 18 G. E. Bigelow, R. R. Griffiths and I. A. Liebson, Effects of response requirement upon human sedative self-administration and drug-seeking behavior. Pharmacol. Biochem. Behau., 5 (1976) 681 - 685. 19 N. K. Mello and J. H. Mendelson, A quantitative analysis of drinking patterns in alcoholics. Arch. Gen. Psychiatry, 25 (1971) 527 - 539. 20 M. E. Carroll and R. A. Meisch, Oral phencyclidine (PCP) self-administration in rhesus monkeys: Effects of feeding conditions. J. Pharmocol. Exp. Z’her., 214 (1980) 339 - 346. 21 M. E. Carroll and R. A. Meisch, Etonitazene as a reinforcer: Oral intake by rhesus monkeys. Psychopharmacology, 59 (1978) 225 - 229. 22 J. E. Henningfield, D. J. Kliner and R. A. Meisch, Oral Pentobarbital Self-administration by Rhesus Monkeys, Committee on Problems of Drug Dependence, Baltimore, 1978. 23 R. R. Griffiths, J. V. Brady and L. D. Bradford, Predicting the abuse liability of drugs with animal drug self-administration procedures: Psychomotor stimulants and hallucinogens. Adv. Behav. Pharmacol. 2, (1979) 163 - 208. 24 C. E. Johanson, Drugs as reinforcers. In D. E. Blackman and D. J. Sanger (eds.), Contemporary Research in Behavioral Pharmacology, Plenum Press, 1978, pp. 325 - 390. 25 M. E. Carroll and R. A. Meisch, Concurrent etonitazene and water intake in rats: Role of taste, olefaction, and auditory stimuli. Psychopharmacology, 64 (1979) 1 - 7. 26 J. E. Triebergs and R. A. Meisch, Ethanol-reinforced performance of rats: Effects of brief stimuli and food deprivation and satiation. Reports from the Research Laboratories of the Department ofPsychiatry, University of Minnesota, 1979, PR-79-2.
ESTABLISHMENT ADMINISTRATION
AND MAINTENANCE IN THE BABOON
113
OF ORAL ETHANOL
SELF-
JACK E. HENNINGFIELD National Institute on Drug Abuse/Addiction Research Center, Baltimore, 21224 (U.S.A.) and The Johns Hopkins University School of Medicine.
Maryland,
NANCY A. ATOR and ROLAND R. GRIFFITHS* The Johns Baltimore,
Hopkins Maryland
University School 21205 (U.S.A.)
of Medicine,
Division
of Behavioral
Biology,
(Received November 2, 1980)
Summary A simple and reliable method was developed to study the self-administration of orally available ethanol by baboons. Two baboons were individually housed in a minimally controlled laboratory environment with visual and auditory access to other baboons and to laboratory technicians. The cages were equipped with standard drinking bottles and spouts. Each baboon was fed his entire daily ration of dry food at the same time each morning, at which time a fresh’solution was added to the liquid reservoir. Three hours later, the amount of liquid consumed was measured. This procedure generated high rates of water drinking during the 3-h sessions (“food-induced drinking”). Next, the water available during the sessions was replaced by gradually increasing concentrations of aqueous ethanol (0.5 - 8%, w/v). When 8% ethanol was reached, the concentration was held constant across daily sessions as session feedings were gradually reduced and shifted to 30 min postsession. Eventually, daily test sessions consisted of simply 3 h access to ethanol, and water was continuously available during the 21-h intersession period. Over a range of ethanol concentrations of 8 - 3276, ethanol intake (g/kg) and blood ethanol levels remained fairly constant, while volumes (ml) of solution consumed were inversely related to the concentration. Finally, an additional liquid spout was added to each cage and the baboons were provided concurrent access to both ethanol (8%) and water during the sessions. The results indicated clearly that ethanol had come to serve as a positive reinforcer for both of these baboons. This simple preparation should be particularly useful in laboratories that are not equipped with the elaborate technology required in earlier described preparations, and might lend itself to the study of orally effective drugs other than ethanol. *Send reprint requests to Dr. Roland R. Griffiths, The Johns Hopkins University School of Medicine, Department of Psychiatry and Behavioral Sciences, Division of Behavioral Biology, 720 Rutland Avenue, Baltimore, Maryland 21205, U.S.A.
114
Key words: ethanol, stration.
baboon,
food-induced
drinking,
oral self-admini-
Although the study of ethanol self-administration has been possible using the intravenous (see, for example, refs. 1 and 2) and intragastric [3] routes, both practical and theoretical considerations have made it desirable to develop a method for studying self-administration of orally delivered ethanol [ 4 - 61. In oral preparations, the significance of using appropriate training procedures is illustrated by the wide range of procedures which have been tested and which failed to overcome the apparently innate aversion to the taste of ethanol by animals (cf. reviews [ 5 - 71). For instance, even when animals were required to consume ethanol for long periods (for example, as their sole source of fluid or as a shock-avoidance response) [ 81, drinking typically did not continue when an alternative fluid was available or when the contingencies on drinking were removed (see above reviews). Neither was the establishment of physical dependence (as defined by evidence of a withdrawal syndrome) sufficient to establish ethanol as a reinforcer [ 91. More recently, however, it has been demonstrated that by following certain training procedures, ethanol can come to serve as an orally effective reinforcer in rats [lo, 111 and rhesus monkeys [12 - 141. The general method involves feeding food-deprived animals once a day. Although water is continuously available, this procedure induces consumption of a large quantity of water following eating. This phenomenon has been termed foodinduced drinking [ 141. Under these conditions, ethanol solutions in gradually increasing concentrations are substituted for water at feeding time and are made available for a period of several hours. When substantial quantities of ethanol are being regularly consumed, the daily feeding is shifted postsession. Thereafter, the animals are simply provided access to ethanol at the same time every day. Despite the fact that the animals are never deprived of water, they generally continue to consume intoxicating quantities of ethanol. The present paper describes the results using this oral method to establish and maintain ethanol drinking by another primate species - the baboon. Additionally, the current study demonstrates that the oral preparation can be successfully developed in a minimally controlled open laboratory environment using a simple and nonautomated technology. After ethanol drinking was established, behavior was studied over a range of ethanol concentrations and in the presence of concurrent water availability.
Materials and methods Subjects The subjects were two male baboons (Papio anubis) weighing 28 (AP) and 18 (KU) kg at the start of the experiment. Both baboons had served in
115
studies of intravenous self-administration with a variety of drugs (AP for 18 months and KU for 6 months). Apparatus The baboons were individually housed in standard primate squeeze cages (0.81 X 0.94 X 1.22 m high). The cages were located in an active selfadministration laboratory in which the baboon subjects had visual and auditory access to other baboons and to laboratory personnel. The room lights were turned on at approximately 8:00 a.m. and turned off at the end of the work day (between the hours of 4:00 and 6:00 p.m. on weekdays and at 1:00 p.m. on weekends). A calibrated Nalgene reservoir was mounted on a wooden platform on the top of each cage and liquid was gravity-fed through Tygon tubing to a standard brass poultry drinking spout (H. W. Hart Manufacturing Co., Glendale, California) which protruded through the platform into the top of the cage. Partway through the experiment (as described below), each baboon was moved into a large, sound-attenuated wooden enclosure which was continuously illuminated with a 15-W frosted bulb. During some of the sessions, a drinkometer was connected to the drinking spout and drinking-spout contacts were recorded on a Gerbrands cumulative recorder. Procedure Establishment of ethanol drinking The baboons were provided continuous access to water (except as described below). Daily feedings were one or two fresh fruits and an individually determined quantity of l-g Noyes banana pellets. Each day, at 9:00 a.m., the liquid reservoirs were emptied and their contents measured to determine the volume of water consumed since the end of the previous day’s session. Fresh tap water (1000 ml) was added to the reservoir, and the baboons were fed their entire daily ration of banana pellets. Three hours later, the volume of liquid consumed was measured, and the reservoir filled with 2000 ml of water. The daily ration of fruit was provided 30 min following the session. After drinking was stable for four consecutive sessions (i.e. no trends in volume consumed across sessions), aqueous ethanol solutions were substituted for water. The solutions were prepared using 95% ethanol and tap water. When volume consumed was stable at 8% (w/v), a procedure of gradually fading out the presession feeding was begun. The number of pellets presented at the beginning of the session was systematically decreased by 50% until one and then none, were presented. The balance of the daily food ration was provided along with the fruit 30 min after the session. The sequence of manipulations and the number of sessions at each stage are presented in Table 1. The primary criterion for increasing the number of food pellets was that at least four sessions at a given value had occurred and that the volume of ethanol consumed was generally stable. Due to space considerations in the laboratory, baboon KU was moved into the wooden enclosure halfway through the phase in which the number of pre-
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session food pellets was decreased. The door to the enclosure during sessions but open much of the day.
was closed
Manipulation of ethanol concentration When all feeding was occurring 30 min postsession, sessions consisted simply of 3-h access to an ethanol solution. For both baboons ethanol concentrations were presented in the following ascending series: 8, 11.3, 16, 22.6, and 32% (w/v). For baboon KU, a return to 8% then followed 32%. For baboon AP, the concentrations were repeated in descending order ending with the return to 8%. Each concentration was present for at least five sessions and concentrations were changed when no trends were occurring in volume consumed. Numbers of sessions at each concentration are given in Table 1. Blood e than01 determinations Approximately 30 min after the final session at each concentration in the ascending series for baboon KU and in the descending series for baboon AP, the baboons were anesthetized with ketamine hydrochloride (i.m.) and an approximately l-ml sample of blood was collected into a Vacutainer@ . These samples were analyzed for their ethanol content by a medical hematology laboratory using gas chromatography. Concurrent access to ethanol and water Upon completing the ethanol concentration manipulations, an additional liquid reservoir was mounted on each cage such that the spouts were positioned about 30 cm apart. Procedures for measuring and changing solutions and for feeding the baboons were the same as in previous conditions, except that during the 21-h intersession period water was available via both drinking spouts. During sessions an 8% ethanol solution and water were concurrently available; their relative side positions were switched each day. The number of sessions under this condition was 20 for baboon KU and 54 for baboon AP. Substitution of water for e than01 solutions Finally, after completing the concurrent water-ethanol phase, the newer drinking system was removed and only 8% ethanol was available during sessions. During this period, baboon AP also was moved to a wooden enclosure; conditions were as for KU above. After 2 and 19 sessions at 8% for KU and AP, respectively, the ethanol was replaced with tap water. During the next 3 days, the baboons were closely observed during the day for specific signs of ethanol withdrawal (cf. ref. 15). Results Establishment of ethanol drinking Both baboons drank substantial volumes of ethanol solution under the food-induced drinking procedure (Table 1). Baboon AP drank the greatest
550(500-700) 675 (500 - 800) 350(200-500) 775 (400 - 900) 688 (450 - 800) 538 (450 - 600) 505 (420 - 600) 425(300-500) 439 (400 - 510) 408 (400 - 430) 379(325-425) 305 (240 -425) 316 (275 - 350) 328 (300 - 363) 329 (290 - 375)
150/o 150/o 150/o 150/o 150/o 150/o 150/o 75175 38/112 19/131 10/140 51145 21148 l/149 o/150
22 13 8 9 14 11 10 6 8 4 9 6 8 6 5
(ml)
Pellets session/ postsession
Mean volume consumed*
0.123 0.128 0.574 1.026 1.155 1.536 1.308 1.367 1.283 1.208 0.984 0.991 1.050 1.053
28.0 27.5 27.3 27.0 26.8 26.5 26.3 26.0 25.7 25.4 25.1 24.8 25.5 25.0 25.0
(kg)
0 0.5 1 2 4 5.7 8 8 8 8 8 8 8 8 8 8
(% w/v)
Ethanol
Baboon
procedures
Weight
drinking
(g/kg per 3 h)
Ethanol dose
and results of the food-induced
Sessions
of conditions
AP
1
*Last four sessions.
0 0.5 1 2 4 5.7 8 8 8 8 8 8 8 8 8
(% w/v)
Ethanol
Baboon
Sequence
TABLE
50/O 50/O 75/o 75/o 100/o 100/o 100/o 125/O 62163 31194 16/109 8/117 41121 21123 l/l24 O/125
Pellets session/ postsession
KU
9 13 8 5 9 7 8 7 18 7 6 5 4 7 6 10
Sessions
425(300-500) 600 (500 - 700) 450 (100 - 800) 775 (400 - 900) 713 (400 - 900) 863 (850 - 900) 650 (600 - 700) 666 (590 - 700) 679 (600 - 750) 543 (500 - 575) 594 (550 - 650) 629 (620 - 650) 581(550-620) 601(525 - 680) 495 (425 - 565) 555 (525 - 590)
(ml)
Mean volume consumed*
0.170 0.257 0.891 1.649 2.860 .3.023 3.098 3.158 2.526 2.763 2.926 2.702 2.828 2.329 2.612
(g/kg per 3 h)
Ethanol dose
18.0 17.5 17.5 17.4 17.3 17.2 17.2 17.2 16.0 15.5 16.3 16.5 16.5 17.0 17.3 17.0
(kg)
Weight
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volume at a concentration of 4%, and baboon KU drank the greatest volume at 8%. For both baboons, the greatest quantity (g/kg) of ethanol was obtained at 8%. At concentrations of 4% and greater, both baboons became somewhat sedated and occasionally ataxic during sessions. Throughout this experimental phase, each baboon displayed a distinct drinking pattern. Baboon AP distributed eating and drinking bouts across the first hour of the session; the food was usually eaten by the second hour of the session, but sporadic drinking bouts continued until the end of the session. Baboon KU quickly consumed all available food at the start of the session and then drank in one protracted drinking bout. Later in the session, a few short drinking bouts occurred; baboon KU regularly drank rapidly at the end of the session when the experimenter began to remove the ethanol solution. When food was gradually shifted from the session to the postsession period, volume consumed decreased slightly, and there was little change in ethanol intake in g/kg per session, since the weights of the baboons also decreased slightly (Table 1). When the cage of baboon KU was enclosed in the wooden chamber, the volume consumed decreased slightly on the first day, but recovered to the preceding level (over 600 ml) by the second day. Ethanol drinking as a function of concentration When ethanol concentration was increased, the volume (ml) of solution consumed decreased while intake of ethanol (g/kg) was relatively unchanged (Fig. 1). Blood ethanol levels were fairly stable for both baboons, with KU drawing consistently higher levels than AP (Table 2). This latter finding is consistent with the larger volumes consumed and the more pronounced ataxia that was observed with baboon KU. Periodic observation of drinking behavior suggested that both baboons continued to do most of their drinking during the first hour of each session, then to drink intermittently during the rest of the session. When the 8% concentration was repeated for baboon KU, the volumes consumed and quantities of ethanol obtained were similar to those obtained during the first exposure to that concentration. During the descending series for baboon AP, however, average volumes consumed at each concentration were higher than those obtained during the ascending series. Specifically, mean volumes consumed by AP during the descending series were: 165 ml at 22.6%, 210 ml at 16%, and 443 ml at 8% (n = 5). (At 11.3%, too few sessions were conducted on the descending series to provide comparable data.) Concurrent access to ethanol and water Providing access to water concurrently with the 8% ethanol solution had no effect on volumes of ethanol consumed for either baboon (Fig. 1). For baboon KU, the volume of water consumed during those sessions never exceeded that of ethanol. For baboon AP, the volume of ethanol consumed remained extremely stable for over 50 sessions (generally 400 - 500 ml per session), yet the volume of water consumed in those sessions was highly variable, often exceeding that of ethanol.
119
8
11.3
ETHANOL
16
CONCENTRATION
(%W/V)
Fig. 1. Mean volume of solution consumed (a) and mean quantity of ethanol obtained (0) as a function of concentration over the last five sessions for each baboon. Vertical bars indicate the range of volumes at each concentration, and R indicates the return to 8%. The 8% and 0% points on the right side of the figure indicate volumes consumed during the condition of concurrent access to water and ethanol. TABLE
2
Blood ethanol levels (BEL) as a function of ethanol concentration Baboon KU
Baboon AP Ethanol (% w/v)
Sessionsa
BEL (mg %)
Volumeb (ml)
8 11.3 16 22.6 32
5(7) 6(2) 8(7) 6(5) 10
122 128 157 123 86
380 275 250 140 50
Weight (kg)
23.3 23.3 23.5
Sessionsa
BEL (mg %)
Volumeb (ml)
Weight (kg)
lO(12) 15 9 19 16
235 182 182 273 204
550 365 260 225 150
17.3 17.0 17.5 17.0c 18.0’
aNumbers are for ascending series; numbers in parentheses are for descending series. bVolume consumed in the session which immediately preceded the blood sample. ‘A supplemental ration of 25 g of Purina monkey biscuits was added to the postsession fruit and pellets to maintain good health in this baboon.
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The patterns of drinking-spout contact shown in the event records (Fig. 2) revealed that contact with the spout delivering ethanol predominated in the first 30 - 45 min of each session, regardless of side position, for both baboons. Although both spouts typically were sampled at the beginning of the sessions, the number and duration of contacts with the ethanol spout always exceeded those of the spout delivering water in the first part of the session. For baboon KU, the number of contacts with the water spout were always very low, as reflected in the low volume of water consumed. For baboon AP, however, contacts with the spout delivering water occurred frequently, but duration and relative number of bouts were lower than for the ethanoldelivering spout early in the session. By the end of the first hour of the sessions, drinking from both spouts had decreased (Fig. 2). In the re-
Fig. 2. Event records from final sessions of the condition of concurrent access to ethanol (8%, w/v) and water (0%) for both baboons. Each record shows the first 60 min of a 3-h session. The pen(s) on a cumulative recorder deflected with drinking spout contact and remained deflected for the duration of contact. The records for 8% and 0% for baboon KU were recorded during alternate sessions and represent the last six sessions of the concurrent access condition. Each pair of records for baboon AP shows contact with both drinking spouts within the same session and are for the last five sessions in which records were available.
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maining 2 h of the session, few spout contacts occurred for baboon KU, but baboon AP continued to make frequent brief contacts with both spouts. Both baboons showed slight position preferences in volumes consumed from the two bottles during the 21-h intersession period (left side for KU and right side for AP), yet during sessions neither patterns of spout contact nor volumes of solutions consumed reflected a position preference.
Substitution
of water for ethanol solutions
When water was substituted monkeys were carefully observed ethanol withdrawal (as described
for ethanol during the 3-h sessions, the during the day for 3 days: no signs of an by Ellis and Pick [15] ) were observed.
Discussion A procedure was used to establish ethanol drinking by two baboons in which food-induced drinking of water was initially established and subsequently the water was replaced by aqueous ethanol solutions in gradually increasing concentrations. Both baboons continued to drink ethanol after the food-induced drinking procedure had been terminated and daily sessions consisted simply of 3 h access to ethanol. As ethanol concentration was increased from 8% to 32% (w/v), the volume (ml) of solution consumed decreased but the quantity (g/kg) of ethanol obtained remained relatively stable. Behavioral observations and blood ethanol levels confirmed that the baboons were ingesting intoxicating quantities of ethanol in each session. Across the 3-h sessions, ethanol drinking was a negatively accelerated pattern of discrete intermittent bouts with the largest number of bouts during the first 30 - 45 min of access. The continued high ethanol intake exhibited during the concurrent ethanol-water phase confirmed that ethanol maintained drinking in its own right, apart from its nonspecific properties as a liquid, and without the presence of physiological dependence, as indicated by the absence of any signs of a withdrawal syndrome when water was substituted for the ethanol. This study shows that the strategies used to establish orally delivered ethanol as a reinforcer for rats and rhesus monkeys are similarly effective when applied to baboons. Further, it shows that the establishment and maintenance of ethanol drinking can be achieved without the elaborate and expensive technology used in earlier studies (cf. ref. 14). The power of these procedures is illustrated by the fact that ethanol consumption was generated under relatively uncontrolled laboratory conditions in which baboons were housed in open cages with visual and auditory access to other baboons and to laboratory personnel. This finding mitigates the possible criticism of earlier ethanol self-administration studies that the selfadministration behavior was due to the physcial isolation and sound attenuation procedures used in those studies. Taken together, these findings indicate that a wide range of laboratories may be able to employ this relatively simple methodology to study the phenomena of ethanol dependence.
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The results of the present study are consistent with those obtained when the establishment and maintenance of ethanol drinking was studied in rhesus monkeys using analogous procedures. Also, where comparisons are possible, the functional relationships obtained (for example, concentrationresponse function) are similar to those obtained in studies of ethanol drinking by rats [ 71, intravenous ethanol self-administration by monkeys and rats [16,17], and intragastric ethanol self-administration by rats [17]. In general, findings from these studies are also consistent with those obtained in experimental studies of ethanol drinking by humans [ 18,191. Jointly considered, these studies show that when ethanol serves as a reinforcer, it controls behavior in an orderly fashion under a wide range of conditions. The procedures employed in the present experiment for inducing alcohol consumption may also provide an effective means of studying selfadministration of drugs other than ethanol (cf. refs. 20 - 22). The potential usefulness of the oral method for studies of drug dependence is especially clear when compared to the more expensive and elaborate intravenous and intragastric procedures (cf. refs. 23 and 24). An additional practical consideration is that once the drinking performance is established, it is reliable and could be maintained for many years*. As a model for studying alcoholism (and perhaps dependence on CNS depressants), the oral self-administration procedure may provide important data not obtainable using intravenous or intragastric preparations. Recent oral ethanol and drug self-administration studies have shown that there are some important differences in the performances generated by orally delivered drugs. For example, the taste and odor of ethanol and other drugs may acquire conditioned stimulus properties (I$. refs. 25 and 26) and these properties may serve to generate stronger and more persistent performance than that which is maintained by intravenous drug delivery (for example, ref. 22). A particular advantage of the food-induced drinking procedures used in the present study is that, since reliable oral consumption is induced prior to physiological dependence and maintained in the absence of concurrent behavioral contingencies on drinking, there is the potential for manipulating a range of variables which may be important in controlling the behavior of ethanol drinking. Finally, the present study demonstrated the application of a relatively simple procedure and technology to establish and maintain the self-administration of orally delivered ethanol. The baboons were housed in open cages and were exposed to the uncontrolled activity of the normal laboratory milieu. The robust ethanol consumption generated under these conditions attests to the power and generality of the method. This primate preparation may be useful in a wide variety of laboratories where it is of interest to study ethanol drinking when the ethanol is functioning as a reinforcer and the drinking behavior is voluntary.
*R. A. Meisch,
personal
communication.
123
Acknowledgements This study was supported by Drug Enforcement Administration Contract No. DEA-78-9, and National Institute on Drug Abuse Grant No. DA01147. We thank Scott Deamond, William Kearns, Sharyn Olson, and Richard Wurster for their technical assistance in conducting this study.
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