EFFECTS OF ETHANOL SIPPER AND SOCIAL OPPORTUNITY ON ETHANOL DRINKING IN RATS

Arthur Tomie*, Jillian M. Uveges, Kelly M. Burger, Patricia Patterson-Buckendahl and Larissa A. Pohorecky

Department of Psychology and Center of Alcohol Studies, Rutgers University, New Brunswick, NJ 08903, USA

* Author to whom correspondence should be addressed at: Center of Alcohol Studies, Rutgers University, 607 Allison Road, Piscataway, NJ 08854 8001, USA. Tel.: 732 445 3595; Fax: 732 445 3500; E-mail: tomie{at}rci.rutgers.edu

(Received 25 September 2003; in revised form 5 January 2004; accepted 4 February 2004)


    ABSTRACT
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Aims: The present study evaluates the effects of pairing ethanol sipper conditioned stimulus (CS) with social opportunity unconditioned stimulus (US) on CS-directed ethanol drinking in rats. Subjects were Long–Evans male rats (n = 32) deprived of neither food nor water, and the concentration of unsweetened ethanol (3 to 16%) in the sipper CS was increased across sessions. Methods: Group Paired/Ethanol (n = 12) received the ethanol sipper CS for 10 s immediately prior to 15 s of social opportunity US. Control groups received water rather than ethanol in the sipper CS (Paired/Water), or ethanol sipper CS and US presentations randomly (Random/Ethanol), or ethanol sipper CS but no social opportunity US (Sipper Only). Results: Mean ethanol intake in the Paired/Ethanol and Random/Ethanol groups exceeded 1.0 g/kg when the sipper CS contained 12%, 14% and 16% ethanol, and higher fluid intakes were observed in the Paired/Ethanol and Random/Ethanol groups than in the Paired/Water and Sipper Only groups. Conclusions: Social opportunity increased ethanol drinking, and more so than water drinking; however, autoshaping did not induce additional ethanol drinking beyond that observed in random controls.


    INTRODUCTION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Human beings drink ethanol from containers or ‘glassware’ that may serve as conditioned stimuli (CS) when paired repeatedly with unconditioned stimuli (US), such as the eating of palatable foods or the opportunity to engage in social interactions. If ethanol glassware can serve as CS for food or social opportunity US, then human beings may develop reflexive and involuntary drinking from the ethanol glassware CS through a process similar to Pavlovian autoshaping (Tomie, 1995Go, 1996Go, 2001Go). Recently, Tomie and his associates have provided evidence that autoshaping may contribute to the initiation and escalation of ethanol drinking in rats (Tomie et al., 2002aGo,bGo). Their autoshaping procedures closely resemble those employed by Pavlovian autoshaping investigators, who provide for the brief presentation of a localized visual stimulus, conditioned stimulus (CS, e.g. lever), followed closely by the response-independent presentation of a rewarding substance, unconditioned stimulus (US, e.g. food). Repeated CS–US pairings induce acquisition of the Pavlovian autoshaping conditioned response (CR), which is a complex sequence of directed motor responses targeted at the CS (Brown and Jenkins, 1968Go; Tomie et al., 1989Go). Important to the understanding of autoshaping, the performance of the autoshaping CR is not required in order to procure the US; rather, the rewarding US is delivered regardless of whether or not the rat contacts the CS.

Tomie and his associates (Tomie et al., 2002aGo,bGo) modified the autoshaping apparatus by replacing the retractable lever with a retractable sipper tube CS. Insertion of the sipper tube CS into the chamber immediately before the response-independent delivery of the food US induced sipper CS-directed approach and contact responses, culminating in mouthing, chewing, licking and swallowing responses, resulting in drinking of the 6% ethanol (v/v) solution in the sipper CS. Several effects suggest that autoshaping contributes to ethanol drinking. For example, autoshaping of sipper CS-directed ethanol drinking increases as a function of experience with sipper CS–food US pairings (Tomie et al., 2002aGo,bGo, 2003aGo,bGo). Ethanol drinking induced by sipper CS–food US pairings is greater than in controls provided with randomly related presentations of sipper CS and food US (Tomie et al., 2002aGo, 2003aGo,bGo). Thus, autoshaping procedures induce more ethanol drinking than is due to factors related to pseudoconditioning.

The present study explores the effects of autoshaping procedures employing social opportunity US, rather than food US, on ethanol drinking in rats. The autoshaping apparatus was modified by replacing the pellet dispenser with a guillotine door that separated the autoshaping chamber from a stainless steel wire mesh cage housing a conspecific male rat. Effects of repeated sipper tube CS–social opportunity US pairings (Group Paired/Ethanol) on sipper tube CS-directed drinking were evaluated, relative to control groups that either received the CS and US randomly (Random/Ethanol), or received the CS but no US (Sipper Only), or water rather than ethanol in the sipper CS (Paired/Water).


    MATERIALS AND METHODS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Animals and treatment
Adult male Long–Evans hooded rats (n = 47) obtained from Harlan–Sprague–Dawley (Almont, NY) weighing approximately 275 g at the beginning of the study, were used. Rats were individually housed in suspended stainless steel cages with free access to food and water, in a colony room with a 12-h light:12-h dark cycle (lights on at 0400 hrs). All experimental procedures were performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals (publication no. 85–23, revised 1985) and approved by the local Animal Care Committee at Rutgers University.

Apparatus
Experimental chambers for autoshaping were four locally constructed Plexiglas cubicles (24 cm x 24 cm x 26 cm; L x W x H) with a floor consisting of stainless steel rods. The right wall of each chamber was an intelligence panel equipped with a retractable stainless steel sipper tube and a stainless steel guillotine door. The sipper tube contained a stainless steel ball-bearing with an inserted rubber stopper used for holding the fluid in a 50 ml Plexiglas graduated tube (Model 58320, Kimble-Kontes, Vineland, NJ). The graduated tube was mounted on a mechanical bottle insertion mechanism (BCS Machine, Plainfield, NJ), which inserted the stainless steel sipper tube through an aperture located 4 cm above the floor and 6 cm to the left of the front wall. The sipper insertion mechanism moved the sipper tube a total of 2.75 cm from fully retracted to fully inserted. In the fully inserted position, the tip of the sipper tube was 0.5 cm into the chamber. The guillotine door (11 cm x 13 cm; H x W) separated the autoshaping chamber from a stainless steel wire mesh cage (20 cm x 10 cm x 12 cm; L x W x H) that during some of the procedures housed a conspecific male of the same age and weight as the subject. The left edge of the guillotine door was located 0.5 cm to the right of the back wall. The guillotine door was operated by a pulley system connected to a mechanical door opening mechanism (BCS Machine, Plainfield, NJ). Each chamber was powered by a 28 V DC power supply, and session events were controlled by IBM-compatible PCs equipped with I/O relay cards (Model PCL-725, JDR Microdevices, San Jose, CA).

Drugs
Bulk ethanol (95%) was obtained from Rutgers University Chemical Stores. Ethanol was diluted in tap water to produce all ethanol concentrations (volume to volume, v/v) employed in the study.

Autoshaping procedure
Rats were run 5 days per week and received 35 autoshaping trials per session. Prior to each autoshaping session, rats were individually weighed and then immediately placed in the experimental chambers. Rats were randomly assigned to one of four groups. For rats in the Ethanol/Paired group (n = 12), the ethanol sipper CS was inserted into the autoshaping chamber for 10 s immediately prior to the social opportunity US, which consisted of the raising of the guillotine door separating the subject from the conspecific male rat in the wire mesh cage for 15 s. Control groups received water rather than ethanol in the sipper CS (Paired/Water, n = 6), or ethanol sipper CS and social opportunity US randomly with respect to one another (Random/Ethanol, n = 11), or ethanol sipper CS but no social opportunity US (Sipper Only, n = 18). For all groups, the mean intertrial interval (ITI) was 60 s (15 s), and the session duration was ~50 min. Volume of fluid consumed (ml) during each autoshaping session was determined by recording the volume in the tube immediately before and after each session. Unsystematic observations revealed that the raising of the guillotine door was often followed by social interactions between the subject rat and the conspecific male rat housed in the wire mesh cage. Behaviors commonly observed in subject rats were rearing, sniffing, nose poking, and pawing, which were directed at the wire mesh surface of the holding cage that separated the test chamber from the holding cage.

During the first 22 sessions of autoshaping, for the three groups receiving ethanol in the sipper CS (Ethanol/Paired, Ethanol/Random, and Sipper Only), the ethanol sipper CS contained 3% ethanol (v/v), followed by nine sessions (23–31) of autoshaping with 4% ethanol (v/v), three sessions (32–34) of autoshaping with 8% ethanol (v/v), seven sessions (35–41) of autoshaping with 10% ethanol (v/v), four sessions (42–45) of autoshaping with 12% ethanol (v/v), four sessions (46–49) of autoshaping with 14% ethanol (v/v), and four sessions (50–53) of autoshaping with 16% ethanol (v/v). Training was conducted with each ethanol concentration until variability in g/kg ethanol intake and g/kg fluid intake did not vary by more by 10% between three consecutive sessions. For the Paired/Water group, for the entire duration of the study, the sipper CS contained tap water (0% ethanol).

Blood-ethanol assays
Immediately following the 53rd autoshaping session, all rats were sacrificed by rapid decapitation and trunk blood samples taken from each rat were collected in heparinized tubes. Samples were centrifuged, frozen, and then assayed for blood-ethanol levels using Alcohol Ethyl Enzymatic Alcohol Assay Kit (Product number 33C-1KT, Sigma Diagnostics, St. Louis, MO).

Statistics
For each subject in each autoshaping session, mililiters of fluid consumed and body weight (kg) were measured, then grams of ethanol consumed per kg of body weight (g/kg ethanol intake), and grams of fluid consumed per kg of body weight (g/kg fluid intake) were derived. Effects of autoshaping sessions and ethanol concentrations on mean g/kg ethanol intake and mean g/kg fluid intake were assessed by separate mixed design two-way repeated-measures multivariate analysis of variance using MANOVA (Systat Statistical Software, Richmond, CA). Statistical adjustments were made to maintain family-wise P-values at an alpha level of 0.05 by dividing 0.05 by the number of effects reported in the family-wise analysis. Fisher's Least Significant Difference (LSD) test provided pair-wise comparisons at individual points (alpha = 0.05). All analyses of the effects of ethanol concentration were conducted on the mean of the last three sessions of training with each concentration. Effects of Groups on mean blood-ethanol levels were assessed by one-way analysis of variance using ANOVA (Systat).


    RESULTS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Initiation of ethanol drinking from the sipper CS
Analysis of mean g/kg ethanol intake during the first 22 days of training (see Fig. 1), for the Paired/Ethanol, Random/Ethanol and Sipper Only groups, wherein the sipper CS contained 3% ethanol (v/v), revealed that the Paired/Ethanol group initiated ethanol intake more rapidly than the Sipper Only group, but the Paired/Ethanol and Random/Ethanol groups did not differ. The overall three group analysis revealed a significant main effect of Groups [F(2,38) = 6.07, P < 0.01], a significant main effect of Sessions [F(21,798) = 17.87, P < 0.01], and a significant interaction effect between Groups and Sessions [F(42,798) = 3.27, P < 0.01]. Fisher's LSD revealed significantly higher ethanol intake (P < 0.05) in the Paired/Ethanol group than in the Sipper Only group on sessions 12 and 14–22, and significantly higher ethanol intake in the Random/Ethanol group than in the Sipper Only group on sessions 2, 9–12, and 14–22, and significantly higher ethanol intake in the Random/Ethanol group than in the Paired/Ethanol group on sessions 4–5, 9–10, and 20, and significantly higher ethanol intake in the Paired/Ethanol group than in the Random/Ethanol group on session 18. Mean fluid intake from the sipper CS on session 1 was 0.34 g/kg and 0.27 g/kg for the Paired/Ethanol and Paired/Water groups, respectively. Mean fluid intake for both groups increased across sessions, and on session 22, mean fluid intake was 6.51 g/kg and 3.30 g/kg for the Paired/Ethanol and Paired/Water groups, respectively.



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Fig. 1. Mean grams of ethanol intake per kg body weight (g/kg) per autoshaping session by rats in the Paired/Ethanol (n = 12), Random/Ethanol (n = 11), and Sipper Only (n = 18) Groups during the first 22 daily sessions of training with autoshaping procedures. The sipper tube CS contained 3% ethanol (v/v).

 
Escalation of drinking of higher concentrations of ethanol
Analysis of effects of ethanol concentration (3 to 16% v/v) on mean g/kg ethanol intake (see Fig. 2), for the Paired/Ethanol, Random/Ethanol and Sipper Only groups revealed that the Paired/Ethanol group showed more ethanol intake than the Sipper Only group, but the Paired/Ethanol and Random/Ethanol groups did not differ. The overall three group analysis yielded a significant main effect of Groups [F(2,38) = 14.04, P < 0.01], a significant main effect of Concentrations [F(6,228) = 88.55, P < 0.01], and a significant interaction effect between Groups and Concentrations [F(12,228) = 3.93, P < 0.01]. Fisher's LSD revealed significantly higher ethanol intake (P < 0.05) in the Paired/Ethanol and the Random/Ethanol groups than in the Sipper Only group when the ethanol concentration in the sipper CS was 4%, 8%, 10%, 12%, 14%, and 16%, and ethanol intake in the Paired/Ethanol and Random/Ethanol groups did not differ at any of the ethanol concentrations. When the Paired/Ethanol group received 3% ethanol in the sipper CS, mean daily fluid intakes for the Paired/Ethanol and Paired/Water groups were 5.78 g/kg and 3.36 g/kg, respectively. When the Paired/Ethanol group received 16% ethanol in the sipper CS, mean daily fluid intakes for the Paired/Ethanol and Paired/Water groups were 7.37 g/kg and 4.94 g/kg, respectively. Analysis of mean g/kg fluid intake for the Paired/Ethanol and Paired/Water groups revealed a significant main effect of Groups [F(1,16) = 12.57, P < 0.01], and no significant interaction effect between Groups and Concentrations [F(6,96) = 1.55, P > 0.05].



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Fig. 2. Mean grams of ethanol intake per kg body weight (g/kg) per autoshaping session by rats in the Paired/Ethanol (n = 12), Random/Ethanol (n = 11), and Sipper Only (n = 18) Groups as a function of increasing ethanol concentrations [(3%, 4%, 8%, 10%, 12%, 14%, 16% (v/v)] in the sipper tube CS across autoshaping sessions. Groups means were derived from the last 3 days of training with each concentration.

 
To further evaluate the effects of the combination of social opportunity US and ethanol sipper CS as a significant determinant of drinking from the sipper CS, the two groups that experienced both of these factors (Paired/Ethanol and Random/Ethanol groups) were combined to form the Ethanol Sipper AND Social Opportunity Group, while the two groups that experienced only one of these factors (Paired/Water and Sipper Only groups) were combined to form the Ethanol Sipper OR Social Opportunity Group. Analysis of the effects of ethanol concentration on mean g/kg fluid intake for the Ethanol Sipper AND Social Opportunity Group and the Group Ethanol Sipper OR Social Opportunity Group (see Fig. 3) yielded a significant main effect of Groups [F(1,45) = 34.20, P < 0.01], a significant main effect of Concentrations [F(6,270) = 8.57, P < 0.01], and no significant interaction effect between Groups and Concentrations [F(6,270) = 1.56, P > 0.05].



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Fig. 3. Mean grams of fluid intake per kg body weight (g/kg) per autoshaping session by rats in the Ethanol Sipper AND Social Opportunity Group (n = 23) and by rats in the Ethanol Sipper OR Social Opportunity Group (n = 24) as a function of increasing ethanol concentrations [(3%, 4%, 8%, 10%, 12%, 14%, 16% (v/v)] in the sipper tube CS across autoshaping sessions. The Ethanol Sipper AND Social Opportunity Group was composed of all of the rats in the Paired/Ethanol and Random/Ethanol groups. The Ethanol Sipper OR Social Opportunity Group was composed of all of the rats in the Paired/Water and Sipper Only groups. Group means were derived from the last 3 days of training with each concentration. Vertical bars indicate the standard errors of the means.

 
Blood-ethanol levels
Mean blood-ethanol levels for the Paired/Ethanol, Random/Ethanol, and Sipper Only groups were 113.33 mg/dl, 104.64 mg/dl, and 74.24 mg/dl, respectively. Analysis comparing the Paired/Ethanol and Sipper Only groups revealed a significant effect of Groups [F(1,27) = 12.10, P < 0.01]. Analysis comparing the Paired/Ethanol and Random/Ethanol groups revealed no significant effect of Groups [F(1,21) < 1].


    DISCUSSION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The 23 rats in the Paired/Ethanol and Random/Ethanol groups, all deprived of neither food nor water, initiated the intake of unsweetened ethanol from the sipper CS, and did so without any training other than the experience of ethanol sipper CS and social opportunity US in the test apparatus. In these groups, ethanol intake escalated with increasing ethanol concentrations, reaching group mean levels in excess of 1.0 g/kg during training with 12%, 14% and 16% ethanol concentrations. Across concentrations, the Paired/Ethanol group drank approximately twice as much ethanol as did the Sipper Only control group, and in addition, the Paired/Ethanol group drank at least 50% more fluid than the Paired/Water control group, and in both cases, did so at each of the ethanol concentrations evaluated (3 to 16% v/v).

Ethanol intake in the Paired/Ethanol and Random/Ethanol groups was not entirely due to the intermittent presentations of the ethanol sipper CS per se, as revealed by the much lower levels of ethanol intake observed in the Sipper Only group. This indicates that the intermittent presentations of the social opportunity US contributed to ethanol sipper CS-directed ethanol drinking in the Paired/Ethanol and Random/Ethanol groups. Direct comparisons of ethanol intake in the Paired/Ethanol and Sipper Only groups revealed that social opportunity US contributed to the faster rate of initiation of intake of 3% ethanol and to the more rapid escalation of ethanol intake observed when higher concentrations of ethanol were available in the sipper CS. Thus, social opportunity US serves to exaggerate g/kg ethanol intake from the sipper CS and this effect was evident across a broad range of ethanol concentrations.

The induction of g/kg ethanol intake by social opportunity may be due to several factors. For example, unsystematic observation indicated that rats in the Paired/Ethanol and Random/Ethanol groups were more active than rats in the Sipper Only group, indicating that social opportunity may have induced arousal and motor activation. Another possibility is that social opportunity is rewarding, and intermittent presentations of social opportunity reward induce adjunctive polydipsia or excessive ethanol drinking (Falk et al., 1972Go). Finally, it should be noted that the social opportunity US includes the opening of the door, and the opportunity to see out of the chamber may be rewarding (Reed et al., 1996Go).

Gradually exposing rats to increasingly concentrated ethanol solutions in the home cage, a procedure known as ‘acclimation’, has been reported to maximize ethanol consumption (Veale and Myers, 1969Go; Amit et al., 1970; Wise, 1973Go); thus, acclimation may have contributed to the high levels of ethanol intake observed here. Our procedures differ from those typically employed in studies reporting acclimation effects in several ways. Our study does not include a control that received exposure only to high concentrations of ethanol, and our rats were exposed to increasingly concentrated ethanol solutions in a test chamber, away from the home cage. Most significantly, acclimation procedures did not induce high levels of ethanol intake in the Sipper Only group but did so in the Paired/Ethanol and Random/Ethanol groups. Acclimation procedures have also been employed in autoshaping studies with food US inducing high ethanol intake of unsweetened 16% ethanol in food-deprived rats (Tomie et al., 2003bGo) and high intake of unsweetened 28% ethanol in rats deprived of neither food nor water (Tomie et al., 2003aGo).

The effect of the social opportunity US on sipper CS-directed drinking was far more evident when the sipper CS contained ethanol as compared to when the sipper CS contained water. Higher mean daily g/kg fluid intake was observed in the Paired/Ethanol group than in the Paired/Water control, and this difference was evident across a broad range of ethanol concentrations (3 to 16% v/v). Studies reporting autoshaping of ethanol drinking employing food US have also noted that daily fluid intake in the Paired/Ethanol groups was higher than in the Paired/Water groups (Tomie et al., 2002bGo, 2003bGo); however, it should be noted that water drinking induced by food US was far higher than the water drinking induced by social opportunity US reported here. As noted by Tomie and his associates, prandial drinking effects (Kisileff, 1969Go) and schedule-induced polydipsia effects (Falk, 1966Go; Roehrs et al., 1976Go; DeCarolis et al., 2003Go) may serve to increase water drinking in situations employing food US. Intermittent presentations of food may induce more prandial drinking and schedule-induced drinking than is induced by social opportunity, and this may account for the lower levels of water drinking in autoshaping studies using social opportunity as compared to food.

The high levels of ethanol intakes observed in the Paired/Ethanol and Random/Ethanol groups were comparable and this indicates that additional ethanol drinking was not induced by temporally contiguous pairings of the CS and US. This is in contrast to the results obtained in previous food studies reporting autoshaping of ethanol drinking, which typically report ~20 to 30% more ethanol drinking in the Paired condition relative to the Random condition (Tomie et al., 2002aGo,bGo, 2003aGo,bGo). This difference is consistently observed even though there are factors related to food US that might be expected to increase ethanol drinking in the Random condition, including prandial drinking (Neill et al., 1994Go) and schedule-induced polydipsia (Falk et al., 1972Go). On the other hand, there are several aspects of social opportunity US that may also contribute to elevations of drinking in the Random/Ethanol group. For example, sounds and odors from the rat behind the door that are observed by the subject rat during the interval of time between US presentations would serve to make the social opportunity US less punctate and discrete, increasing the likelihood of pairings of sounds and odor stimuli with the ethanol sipper CS. Perhaps social opportunity is an appetitive Pavlovian US that does not require close temporal contiguity with the sipper CS to induce Pavlovian autoshaping CR performance. There is abundant evidence in the Pavlovian conditioning literature, for example, that gastrointestinal distress US experienced hours after a novel flavor CS induces Pavlovian taste-aversion CRs (Logue, 1979Go).

Low levels of ethanol intake were observed in the Sipper Only group, even though they received gradually increasing concentrations of ethanol solutions (i.e. acclimation procedures) in the sipper CS. This may be due to a number of factors. Rats in the Sipper Only group were deprived of neither food nor water, thus drinking for the caloric value of ethanol (Samson, 1986Go) was unlikely to contribute substantially to ethanol intake. In addition, rats in the Sipper Only group, had access to only unsweetened ethanol solutions in the sipper CS, therefore, initiation and escalation of ethanol intake were not confounded by the effects of sweeteners, which have been widely used in studies with rats, to facilitate the initiation of ethanol drinking in self-administration procedures (Samson, 1986Go, 1999Go; Weiss et al., 1990Go), as well as in schedule-induction procedures (Samson and Falk, 1974Go). Despite the fact that all rats in this study were deprived of neither food nor water and had access only to unsweetened ethanol solutions, at the higher ethanol concentrations, mean daily ethanol intake for rats in the Paired/Ethanol and Random/Ethanol groups was over 1.0 g/kg.

While the facilitation of ethanol drinking by social interaction opportunities is well established in human beings (Koposov et al., 2002Go; for review see Pohorecky, 1981Go), a similar effect is far less evident in studies employing rats (Pohorecky, 1990Go; van Erp and Miczek, 2001Go). In fact, the opposite effect has often been reported. For example, animal researchers (for review see Pohorecky et al., 1995Go) have noted that social interaction opportunity afforded by group housing conditions may reduce ethanol drinking relative to isolation housed controls (Parker and Radow, 1974Go; Kulkosky et al., 1980Go; c.f., Heminway and Furumoto, 1972Go; Wolffgramm, 1990Go), and bouts of aggression between conspecific males typically results in the lowering of ethanol intake (van Erp and Miczek, 2001Go; van Erp et al., 2001Go). Procedures employed to study effects of social interaction opportunities on ethanol intake in animals differ in many ways, including housing conditions, duration and nature of social interaction, timing of ethanol availability relative to social opportunity, ethanol intake procedures, and measures of ethanol intake (for reviews, see Pohorecky, 1990Go, 1995Go). While the present procedures clearly provide evidence of augmentation of ethanol intake by social opportunity, further experimental analysis of the precise features of the social opportunity US complex employed in the present procedures that contributed to the initiation and escalation of ethanol intake is required.


    ACKNOWLEDGEMENTS
 
This research was supported in part by NIAAA grant R21 AAA-12023-02 awarded to A.T., NIAAA grant R21 AA12705-01 awarded to P.P.-B. and NIAAA grant R01 AAA-10124-03 awarded to L.A.P.


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