Alcohol, Vol. 9, pp. 167-170,1992
0741-8329/92$5.00 + .00 Copyright©1992PergamonPress Ltd.
Printed in the U.S.A. All rightsreserved.
RAPID COMMUNICATION
Ethanol Tolerance Developed During Intoxicated Operant Performance in Rats Prevents Subsequent Ethanol-Induced Conditioned Taste Aversion D A V I D V. G A U V I N I A N D F R A N K A. H O L L O W A Y
Department o f Psychiatry and Behavioral Sciences, University o f Oklahoma Health Sciences Center, Oklahoma City, O K 73190-3000 Received 10 July 1991; Accepted 12 September 1991 GAUVIN, D. V. AND F. A. HOLLOWAY. Ethanol tolerance developed during intoxicated operant performance in rats prevents subsequent ethanol-induced conditioned taste aversion. ALCOHOL 9(2) 167-170, 1992.- Four groups of SpragueDawley rats (n = 10 per group) were trained in a two-phase conditioning experiment. All rats were initially trained in an FR30 operant task (phase 1), and subsequently trained in a conditioned taste aversion (CTA) task. The groups of rats differed in their ETOH exposure. All rats received 2-week chronic exposure in phase 1. Two groups receivedchronic presession ETOH and, therefore, the opportunity for intoxicated practice; another group, yoked to this latter group, received postsession ETOH; the final group received presession saline injections. The presession ETOH groups were conditioned in the CTA task with either ETOH or saline; both increased their intakes of the conditioned tastant. The presession saline and the postsession ETOH groups received ETOH CTA; both developed a robust CTA. Thus, prior history of intoxicated practice under the operant task prevented the development of ETOH-induced CTA. We argue that ETOH exposure may be a necessary but not sufficient condition for tolerance to develop to the aversive attributes of ETOH. Ethanol
Behavioraltolerance
Conditioned taste aversion
ONE consequence of repeated drug administration, tolerance, is an alteration in responsiveness to the drug's actions with a concomitant increase in the dose required to reproduce the initial effect (9). In some studies, tolerance may be mediated by behavioral adjustments which allow rewarding stimuli to be acquired (6). Tabakoff and Hoffman (11) suggested that repeated administration of ETOH may produce tolerance to certain aversive properties which would, in turn, allow an individual to be more able to consume larger quantities of ETOH. Over repeated administration, it is possible that tolerance sufficiently develops to internal aversive events to allow the individual to cue into (or come under the control of) the rewarding or reinforcing properties of ETOH. The majority of psychoactive drugs induce conditioned taste aversions (4). Reductions in intake of a drug-paired substance have almost universally been accepted to be the result
of the development of an association between some aversive stimulus property of the drug and the taste of the novel fluid. Conditioned taste aversion (CTA) seems to be a simple form of Pavlovian conditioning of an association between a tastant and some "aversive" treatment. ETOH CTA was described by Lester and colleagues (10) and has been replicated in a number of laboratories (1,3,7). CTAs induced by drugs have demonstrated that the magnitudes of these aversions are less than those produced by lithium chloride, and usually maintain some level of drinking after successful CS-UCS pairings. This may allow for a graded (quantitative) behavioral measure of the aversive properties of drugs. The purpose of the present study was to examine and compare the degree of CTA induced by ETOH between groups of rats differing in the amount of intoxicated practice and, therefore, the amount of prior behavioral tolerance developed
J Requests for reprints should he addressed to David V. Gauvin, PhD, University of Oklahoma Health Sciences Center, Research Building, 306-R, P.O. Box 26901, Oklahoma City, OK 73190-3000.
i 6"/
168
GAUVIN AND HOLLOWAY
under an operant schedule of lever-press responding. We hypothesized that the magnitude or degree of CTA induced by ETOH would be directly related to the amount of behavioral tolerance developed under the operant schedule. METHOD
Subjects Forty-eight male Sprague-Dawley rats weighing 275-325 g were obtained from Amitech Inc. (now Dominion Inc., Omaha, NE) and individually housed in standard stainlesssteel suspended cages. The home cages were located in a temperature- and humidity-controlled colony room maintained on a 12:12 h light/dark cycle. The animals and colony room were maintained by technicians and veterinarians from the AAALAC-accredited Department of Animal Resources at the University of Oklahoma Health Science Center. Animals were initially maintained on ad lib food and water and allowed 2 weeks to accommodate to the new environment. Subsequently, rats were food-deprived and maintained at 85070 of their free-feeding weights by supplemental feeding to the food acquired during daily operant sessions. Target weights were allowed to increase gradually over the course of phase 1 of the experiment (5070 per month) to allow for normal growth. During phase 2 of the experiment (taste-aversion conditioning), rats were allowed ad lib access to food. The behavioral sessions for each animal were run at the same time each day, 2-6 h after light onset, 5-7 days per week.
Apparatus Six rodent operant chambers were each equipped with a single operant lever, stimulus lamp, and pellet dispenser; furthermore, each chamber was housed within a soundattenuating enclosure cabinet (Lafayette Instruments, Lafayette, IN). All behavioral/experimental contingencies and data collection was accomplished by a PROMAL-based Commodore 64C microcomputer system (American Neuroscience Research Foundation, Yukon, OK) interfaced with the six operant chambers (Rayfield Instruments, Waitsfield, NH).
Operant Procedure Rats were shaped by successive approximation to press the lever for food pellets (45 mg; Bioserv Inc., Frenchtown, N J) during a three-cycle training session. The multicycle sessions were adapted after Wenger (14). All sessions began with a 15-min time-out period (no food reinforcement and stimulus and house lights off); each time-out period was followed by a 10-min time-in period (schedule-controlled food reinforcement and stimulus and house lights on). Over successive training sessions, the number of lever-press responses required to produce food was raised from the initial FRI to FR30. Training continued until rates of responding across all three cycles for 5 consecutive days varied less than _+ 10070. Rats were assigned to one of four experimental/treatment groups (see Table 1). Twenty rats were assigned to one treatment group which would receive an initial ETOH dose-effect curve, 2 weeks chronic presession ETOH injections, and a postchronic ETOH dose-effect curve. Once the chronic ETOH regimen was completed, this group was further subdivided into two subgroups differing in the taste aversion protocol they received (see following). Ten rats were assigned to a group in
which each rat was yoked to a rat cohort in the presession ETOH group. Each rat in this group received an equal dose of ETOH as its yoked cohort approximately 10 min after the experimental session; subsequently, this group received taste conditioning with ETOH. This group of postsession ETOH remained in their home cage the day following a postoperant session ETOH injection, because of previous data from this laboratory (6) which suggested that practice in an operant task 24 h after a high dose of ETOH resulted in a measurable degree of tolerance to ETOH's immediate intoxicating effects. Thus, the chronic exposure period for this group lasted 1 month, which corresponded to 15 days of chronic ETOH exposure in its yoked presession ETOH cohorts. The final 10 rats were assigned to a group which received a 2-week chronic period of presession saline injections, and subsequently this group received taste conditioning with ETOH. No initial or final ETOH dose-effect curves were generated in the two groups of rats administered either chronic presession saline or yoked postsession ETOH because we did not want these groups to have any ETOH-associated intoxicated practice. Wenger and colleagues (14,15) suggested that a degree of tolerance may develop over the course of simply generating dose-effect curves (even in saline control animals). Because the postsession ETOH group was yoked to a rat cohort in the presession ETOH Group, these subjects received an equivalent dose of ETOH in their home cages on dose-effect test days. This laboratory demonstrated that the repeated testing of dose-effect functions in a similarly trained presession saline treatment group did not shift the initial ethanol dose-effect curves (5). However, repeated testing of the dose-effect functions in a postsession ETOH group did result in a significant (p < 0.001) increase in response rates at high ETOH test doses (1.25 g/kg), suggesting some degree of tolerance development due to exposure to intoxicated practice during repeated dose-effect test sessions (5).
Ethanol Dose-Effect Curve Procedures Once stable performance was achieved, a 15-day chronic ETOH period was imposed. Chronic ETOH or saline injections were given to all rats, as depicted in Table 1. The presession ETOH group's baseline performance was determined by intraperitoneal (i.p.) injections of saline alone in a volume equivalent to that of the corresponding ETOH dose that would be administered in subsequent ETOH cumulative dosing test sessions. These initial saline tests and dose-effect tests were conducted in a five-cycle test session (125 min). The rates of response during these saline test sessions were used as control response rates for the equivalent cycle of ETOH doseeffect tests. An initial dose-effect curve was determined in each subject of the presession ETOH group using a cumulative dosing regimen. Saline was injected at the beginning of each session and a dose of ETOH was administered at each of the four time-out periods. Four sequential ETOH doses (10°70 w/v solution with 0.9070 saline vehicle) were administered by i.p. injections. The ETOH doses were: 0.25, 0.25, 0.5, and 0.5 g/kg, respectively, which provided cumulative doses of 0.25, 0.5, 1.0, and 1.5 g/kg. Note that the interval between injections and the next time-in period was always 15 min and the interinjection interval was always 25 rain. Once these initial dose-effect tests were conducted, a period of chronic ETOH exposure commenced. Each rat initially received its individual EDs0 dose (defined as the dose of ETOH required to suppress responding to 50070 of its associated saline control rates of responding). If a rat exhibited stable response rates
ETOH CONDITIONED TASTE AVERSION
169 TABLE 1
Group
Phase II Taste-Aversion Treatment
Phase 1 Operant Chronic Treatment
Presession ethanol (n = 20)
Chronic presession ethanol (maximum tolerable dose)
Initial DEC, first week chronic DEC, second week chronic DEC
Postsession ethanol (n = 10)
Chronic postsession ethanol (each rat yoked to a presession ethanol group rat) Chronic presession saline (ml-equivalent to yoked chronic presession ethanol rat)
No DECs
Ethanol taste aversion (n = 10) Saline taste aversion (n = 10) Ethanol taste aversion
No DECs
Ethanol taste aversion
Chronic presession saline (n = 10)
(_+ 10070) over the three cycles of the training session and earned at least four reinforcers per cycle, the dose of ETOH administered on the following day was increased by 0.25 g/ kg. At the end of a 2-week period of this maximally tolerable chronic ETOH dosing regimen, a second dose-effect curve was generated. The second and final dose-effect curve was generated using four cumulative ETOH injections of 0.5 g/kg increments, which provided cumulative doses of 0.5, 1.0, 1,5, and 2.0 g/kg. Following the 2-week chronic dosing regimen and subsequent dose-effect curves, a l-week washout period was imposed prior to taste aversion conditioning. The presession ETOH group (n = 20) was subdivided into two groups (n = 10 per group) prior to taste aversion conditioning. One group was subsequently conditioned with ETOH, and the other group conditioned with saline. Group assignments were counterbalanced for equivalent: (1) body weight; (2) maximally tolerable ETOH dose during the chronic ETOH phase; (3) response rates during the operant tasks; and (4) the ETOH EDs0 calculated from the postchronic phase dose-effect curve.
analysis (least squares procedure) of the response rate data from individual dose-effect curves. The group comparisons for total volume of saccharin consumption (milliliters) during the CTA task was analyzed using a repeated measures analysis of variance (ANOVA) with a posteriori comparisons for dally differences between groups using Duncan's New Multiple Range test. Statistical significance was set at p < 0.05. RESULTS
The mean EDs0 score for response rate suppression in the presesaion ETOH group shifted almost three-fold by chronic ETOH exposure [test 1 EDs0 = .61 (+_ .11) g/kg; test 2 EDs0 = 1.72 (+ .2) g/kg]. The mean chronic dose administered to these animals on day 1 of chronic was .55 ( + .05) g/kg and on day 15 was 1.71 ( + .07) g/kg. The difference between the EDs0 score from the initial dose-effect curve and the mean chronic
PRE-SESSJON SAL - ETOH T/A
[]--[] --
Conditioned Taste A version The CTA task was assessed using the procedure described by Jackson and Sanger (8). After the 1-week washout period, in which all rats were allowed ad lib food and water, rats were placed on a short-term water deprivation schedule. Rats were allowed access to tap water in the home cage for 15 rain (10301045 h) in the morning and for 60 min (1500-1600 h) in the afternoon in calibrated drinking tubes. This procedure was continued for 3 days, until the animals were drinking approximately 10 ml of water during the morning access session. On day 4, rats were presented with a 0.1 070w/v solution of sodium saccharin in place of water in the morning drinking session. Immediately after 15 min access to the solution of ~accharin, each rat was injected with either 1.5 g/kg ETOH or saline, dependent on group assignment (see Table 1) and the total volume of the saccharin consumed was recorded. They were allowed access to tap water for 60 min during the afternoon period. This procedure was repeated daily for 4 days. On day 5, the animals were presented with the 0.1070 saccharin solution for 15 min during the morning session, and the intake of saccharin was recorded and the experiment terminated.
Data Analysis The individual EDs0 scores for response rate suppression in the FR30 operant task was calculated by linear regression
O
POST-SESSION EYOH - ETOH T/A
O~O
PRE-SESSION ETOH - SAL T/A
~--~
PRE-SESSlON ETOH - El'OH T/A
20T
E
v LJ v
0741-8329/92$5.00 + .00 Copyright©1992PergamonPress Ltd.
Printed in the U.S.A. All rightsreserved.
RAPID COMMUNICATION
Ethanol Tolerance Developed During Intoxicated Operant Performance in Rats Prevents Subsequent Ethanol-Induced Conditioned Taste Aversion D A V I D V. G A U V I N I A N D F R A N K A. H O L L O W A Y
Department o f Psychiatry and Behavioral Sciences, University o f Oklahoma Health Sciences Center, Oklahoma City, O K 73190-3000 Received 10 July 1991; Accepted 12 September 1991 GAUVIN, D. V. AND F. A. HOLLOWAY. Ethanol tolerance developed during intoxicated operant performance in rats prevents subsequent ethanol-induced conditioned taste aversion. ALCOHOL 9(2) 167-170, 1992.- Four groups of SpragueDawley rats (n = 10 per group) were trained in a two-phase conditioning experiment. All rats were initially trained in an FR30 operant task (phase 1), and subsequently trained in a conditioned taste aversion (CTA) task. The groups of rats differed in their ETOH exposure. All rats received 2-week chronic exposure in phase 1. Two groups receivedchronic presession ETOH and, therefore, the opportunity for intoxicated practice; another group, yoked to this latter group, received postsession ETOH; the final group received presession saline injections. The presession ETOH groups were conditioned in the CTA task with either ETOH or saline; both increased their intakes of the conditioned tastant. The presession saline and the postsession ETOH groups received ETOH CTA; both developed a robust CTA. Thus, prior history of intoxicated practice under the operant task prevented the development of ETOH-induced CTA. We argue that ETOH exposure may be a necessary but not sufficient condition for tolerance to develop to the aversive attributes of ETOH. Ethanol
Behavioraltolerance
Conditioned taste aversion
ONE consequence of repeated drug administration, tolerance, is an alteration in responsiveness to the drug's actions with a concomitant increase in the dose required to reproduce the initial effect (9). In some studies, tolerance may be mediated by behavioral adjustments which allow rewarding stimuli to be acquired (6). Tabakoff and Hoffman (11) suggested that repeated administration of ETOH may produce tolerance to certain aversive properties which would, in turn, allow an individual to be more able to consume larger quantities of ETOH. Over repeated administration, it is possible that tolerance sufficiently develops to internal aversive events to allow the individual to cue into (or come under the control of) the rewarding or reinforcing properties of ETOH. The majority of psychoactive drugs induce conditioned taste aversions (4). Reductions in intake of a drug-paired substance have almost universally been accepted to be the result
of the development of an association between some aversive stimulus property of the drug and the taste of the novel fluid. Conditioned taste aversion (CTA) seems to be a simple form of Pavlovian conditioning of an association between a tastant and some "aversive" treatment. ETOH CTA was described by Lester and colleagues (10) and has been replicated in a number of laboratories (1,3,7). CTAs induced by drugs have demonstrated that the magnitudes of these aversions are less than those produced by lithium chloride, and usually maintain some level of drinking after successful CS-UCS pairings. This may allow for a graded (quantitative) behavioral measure of the aversive properties of drugs. The purpose of the present study was to examine and compare the degree of CTA induced by ETOH between groups of rats differing in the amount of intoxicated practice and, therefore, the amount of prior behavioral tolerance developed
J Requests for reprints should he addressed to David V. Gauvin, PhD, University of Oklahoma Health Sciences Center, Research Building, 306-R, P.O. Box 26901, Oklahoma City, OK 73190-3000.
i 6"/
168
GAUVIN AND HOLLOWAY
under an operant schedule of lever-press responding. We hypothesized that the magnitude or degree of CTA induced by ETOH would be directly related to the amount of behavioral tolerance developed under the operant schedule. METHOD
Subjects Forty-eight male Sprague-Dawley rats weighing 275-325 g were obtained from Amitech Inc. (now Dominion Inc., Omaha, NE) and individually housed in standard stainlesssteel suspended cages. The home cages were located in a temperature- and humidity-controlled colony room maintained on a 12:12 h light/dark cycle. The animals and colony room were maintained by technicians and veterinarians from the AAALAC-accredited Department of Animal Resources at the University of Oklahoma Health Science Center. Animals were initially maintained on ad lib food and water and allowed 2 weeks to accommodate to the new environment. Subsequently, rats were food-deprived and maintained at 85070 of their free-feeding weights by supplemental feeding to the food acquired during daily operant sessions. Target weights were allowed to increase gradually over the course of phase 1 of the experiment (5070 per month) to allow for normal growth. During phase 2 of the experiment (taste-aversion conditioning), rats were allowed ad lib access to food. The behavioral sessions for each animal were run at the same time each day, 2-6 h after light onset, 5-7 days per week.
Apparatus Six rodent operant chambers were each equipped with a single operant lever, stimulus lamp, and pellet dispenser; furthermore, each chamber was housed within a soundattenuating enclosure cabinet (Lafayette Instruments, Lafayette, IN). All behavioral/experimental contingencies and data collection was accomplished by a PROMAL-based Commodore 64C microcomputer system (American Neuroscience Research Foundation, Yukon, OK) interfaced with the six operant chambers (Rayfield Instruments, Waitsfield, NH).
Operant Procedure Rats were shaped by successive approximation to press the lever for food pellets (45 mg; Bioserv Inc., Frenchtown, N J) during a three-cycle training session. The multicycle sessions were adapted after Wenger (14). All sessions began with a 15-min time-out period (no food reinforcement and stimulus and house lights off); each time-out period was followed by a 10-min time-in period (schedule-controlled food reinforcement and stimulus and house lights on). Over successive training sessions, the number of lever-press responses required to produce food was raised from the initial FRI to FR30. Training continued until rates of responding across all three cycles for 5 consecutive days varied less than _+ 10070. Rats were assigned to one of four experimental/treatment groups (see Table 1). Twenty rats were assigned to one treatment group which would receive an initial ETOH dose-effect curve, 2 weeks chronic presession ETOH injections, and a postchronic ETOH dose-effect curve. Once the chronic ETOH regimen was completed, this group was further subdivided into two subgroups differing in the taste aversion protocol they received (see following). Ten rats were assigned to a group in
which each rat was yoked to a rat cohort in the presession ETOH group. Each rat in this group received an equal dose of ETOH as its yoked cohort approximately 10 min after the experimental session; subsequently, this group received taste conditioning with ETOH. This group of postsession ETOH remained in their home cage the day following a postoperant session ETOH injection, because of previous data from this laboratory (6) which suggested that practice in an operant task 24 h after a high dose of ETOH resulted in a measurable degree of tolerance to ETOH's immediate intoxicating effects. Thus, the chronic exposure period for this group lasted 1 month, which corresponded to 15 days of chronic ETOH exposure in its yoked presession ETOH cohorts. The final 10 rats were assigned to a group which received a 2-week chronic period of presession saline injections, and subsequently this group received taste conditioning with ETOH. No initial or final ETOH dose-effect curves were generated in the two groups of rats administered either chronic presession saline or yoked postsession ETOH because we did not want these groups to have any ETOH-associated intoxicated practice. Wenger and colleagues (14,15) suggested that a degree of tolerance may develop over the course of simply generating dose-effect curves (even in saline control animals). Because the postsession ETOH group was yoked to a rat cohort in the presession ETOH Group, these subjects received an equivalent dose of ETOH in their home cages on dose-effect test days. This laboratory demonstrated that the repeated testing of dose-effect functions in a similarly trained presession saline treatment group did not shift the initial ethanol dose-effect curves (5). However, repeated testing of the dose-effect functions in a postsession ETOH group did result in a significant (p < 0.001) increase in response rates at high ETOH test doses (1.25 g/kg), suggesting some degree of tolerance development due to exposure to intoxicated practice during repeated dose-effect test sessions (5).
Ethanol Dose-Effect Curve Procedures Once stable performance was achieved, a 15-day chronic ETOH period was imposed. Chronic ETOH or saline injections were given to all rats, as depicted in Table 1. The presession ETOH group's baseline performance was determined by intraperitoneal (i.p.) injections of saline alone in a volume equivalent to that of the corresponding ETOH dose that would be administered in subsequent ETOH cumulative dosing test sessions. These initial saline tests and dose-effect tests were conducted in a five-cycle test session (125 min). The rates of response during these saline test sessions were used as control response rates for the equivalent cycle of ETOH doseeffect tests. An initial dose-effect curve was determined in each subject of the presession ETOH group using a cumulative dosing regimen. Saline was injected at the beginning of each session and a dose of ETOH was administered at each of the four time-out periods. Four sequential ETOH doses (10°70 w/v solution with 0.9070 saline vehicle) were administered by i.p. injections. The ETOH doses were: 0.25, 0.25, 0.5, and 0.5 g/kg, respectively, which provided cumulative doses of 0.25, 0.5, 1.0, and 1.5 g/kg. Note that the interval between injections and the next time-in period was always 15 min and the interinjection interval was always 25 rain. Once these initial dose-effect tests were conducted, a period of chronic ETOH exposure commenced. Each rat initially received its individual EDs0 dose (defined as the dose of ETOH required to suppress responding to 50070 of its associated saline control rates of responding). If a rat exhibited stable response rates
ETOH CONDITIONED TASTE AVERSION
169 TABLE 1
Group
Phase II Taste-Aversion Treatment
Phase 1 Operant Chronic Treatment
Presession ethanol (n = 20)
Chronic presession ethanol (maximum tolerable dose)
Initial DEC, first week chronic DEC, second week chronic DEC
Postsession ethanol (n = 10)
Chronic postsession ethanol (each rat yoked to a presession ethanol group rat) Chronic presession saline (ml-equivalent to yoked chronic presession ethanol rat)
No DECs
Ethanol taste aversion (n = 10) Saline taste aversion (n = 10) Ethanol taste aversion
No DECs
Ethanol taste aversion
Chronic presession saline (n = 10)
(_+ 10070) over the three cycles of the training session and earned at least four reinforcers per cycle, the dose of ETOH administered on the following day was increased by 0.25 g/ kg. At the end of a 2-week period of this maximally tolerable chronic ETOH dosing regimen, a second dose-effect curve was generated. The second and final dose-effect curve was generated using four cumulative ETOH injections of 0.5 g/kg increments, which provided cumulative doses of 0.5, 1.0, 1,5, and 2.0 g/kg. Following the 2-week chronic dosing regimen and subsequent dose-effect curves, a l-week washout period was imposed prior to taste aversion conditioning. The presession ETOH group (n = 20) was subdivided into two groups (n = 10 per group) prior to taste aversion conditioning. One group was subsequently conditioned with ETOH, and the other group conditioned with saline. Group assignments were counterbalanced for equivalent: (1) body weight; (2) maximally tolerable ETOH dose during the chronic ETOH phase; (3) response rates during the operant tasks; and (4) the ETOH EDs0 calculated from the postchronic phase dose-effect curve.
analysis (least squares procedure) of the response rate data from individual dose-effect curves. The group comparisons for total volume of saccharin consumption (milliliters) during the CTA task was analyzed using a repeated measures analysis of variance (ANOVA) with a posteriori comparisons for dally differences between groups using Duncan's New Multiple Range test. Statistical significance was set at p < 0.05. RESULTS
The mean EDs0 score for response rate suppression in the presesaion ETOH group shifted almost three-fold by chronic ETOH exposure [test 1 EDs0 = .61 (+_ .11) g/kg; test 2 EDs0 = 1.72 (+ .2) g/kg]. The mean chronic dose administered to these animals on day 1 of chronic was .55 ( + .05) g/kg and on day 15 was 1.71 ( + .07) g/kg. The difference between the EDs0 score from the initial dose-effect curve and the mean chronic
PRE-SESSJON SAL - ETOH T/A
[]--[] --
Conditioned Taste A version The CTA task was assessed using the procedure described by Jackson and Sanger (8). After the 1-week washout period, in which all rats were allowed ad lib food and water, rats were placed on a short-term water deprivation schedule. Rats were allowed access to tap water in the home cage for 15 rain (10301045 h) in the morning and for 60 min (1500-1600 h) in the afternoon in calibrated drinking tubes. This procedure was continued for 3 days, until the animals were drinking approximately 10 ml of water during the morning access session. On day 4, rats were presented with a 0.1 070w/v solution of sodium saccharin in place of water in the morning drinking session. Immediately after 15 min access to the solution of ~accharin, each rat was injected with either 1.5 g/kg ETOH or saline, dependent on group assignment (see Table 1) and the total volume of the saccharin consumed was recorded. They were allowed access to tap water for 60 min during the afternoon period. This procedure was repeated daily for 4 days. On day 5, the animals were presented with the 0.1070 saccharin solution for 15 min during the morning session, and the intake of saccharin was recorded and the experiment terminated.
Data Analysis The individual EDs0 scores for response rate suppression in the FR30 operant task was calculated by linear regression
O
POST-SESSION EYOH - ETOH T/A
O~O
PRE-SESSION ETOH - SAL T/A
~--~
PRE-SESSlON ETOH - El'OH T/A
20T
E
v LJ v
