Behavioral sensitization and voluntary ethanol drinking in alcohol-preferring AA rats exposed to different regimens of morphine treatment

The purpose of the study was to investigate the effects of three different regimens of morphine treatment on subsequent voluntary ethanol drinking in alcohol-preferring AA (Alko Alcohol) rats. The rats were given morphine subcutaneously either intermittently on alternating days (15 x 10 mg/kg or 5 x 5-20 mg/kg in escalating doses) or subchronically on four consecutive days (3-20 mg/kg/d). Horizontal locomotor activity was monitored after challenges with additional morphine injections (3 mg/kg) ten days and six weeks after termination of the pretreatment to test if behavioral sensitization was induced by repeated morphine administration. Both intermittent pretreatments induced sensitized locomotor response after the first challenge, whereas subchronic injections did not. After the challenge the rats were given a free choice between tap water and 10% (v/v) ethanol solution for four weeks. The rats pretreated and challenged with morphine did not differ significantly in the acquisition of ethanol drinking from the saline-treated controls. In contrast, ethanol drinking was impaired during the first week of ethanol access in the saline-treated rats given a single morphine injection. The second morphine challenge given after the ethanol-drinking phase did not reveal sensitization in any of the groups. The results suggest that pattern of morphine administration rather than the dose or number of exposures to the drug is the most important factor in induction of behavioral sensitization, and that exposure to ethanol may interfere with this process. They also support earlier findings showing that acute morphine may suppress voluntary ethanol drinking, but failed to provide clear evidence for behavioral sensitization to morphine contributing to predilection towards ethanol in AA rats.     

Intravenous heroin and ethanol self-administration by alcohol-preferring AA and alcohol-avoiding ANA rats

The alcohol-preferring AA rats have previously been shown to drink more solution containing the opioid etonitazene than the alcohol-avoiding ANA rats. The present experiments were initiated to see whether the line difference in opioid and alcohol intake would persist if an intravenous (IV) route of self-administration is used. Following establishment of stable heroin responding (0.03 mg/kg per infusion), AA and ANA rats were first subjected to three within-session dose-response determinations during which they were allowed to respond for ascending heroin doses (0.0075, 0.015, 0.03, and 0.06 mg/kg per infusion) and then to one progressive-ratio schedule session. AA rats obtained more heroin infusions than ANAs during the first acquisition sessions but there were no significant differences between the lines either in their baseline heroin responding, across the ascending within-session doses, or on the progressive ratio probe. When, after additional heroin baseline sessions, ethanol (1.0 mg/kg per infusion) was substituted for heroin, AA rats initially increased their responding and showed stable rates for responding across ascending ethanol doses (2.0 and 4.0 mg/kg), whereas ANAs declined below their heroin baseline. These findings give evidence for only an initial line difference in IV opiate self-administration but for a sustained difference in IV ethanol self-administration, thus suggesting that the differential alcohol drinking of the AA and ANA rats is dependent at least partly on non-oral factors.     

Chronic alcohol consumption in alcohol-preferring P rats attenuates subsequent conditioned taste aversion produced by ethanol injections

Rats of the P line were tested for the development of tolerance to the aversive effects of ethanol during 33 days of continuous availability of food, water and a 10% (v/v) ethanol solution. Beginning on the day following the removal of ethanol, five daily conditioned taste aversion (CTA) trials were administered to the ethanol-drinking P rats and an ethanol-naive control group. The CTA trials consisted of a 20-min access to a Polycose solution, followed by IP injection of saline, 0.5, 1.0, or 1.5 g ethanol/kg. The ethanol-drinking rats developed a preference for the Polycose solution when it was paired with 0.5 g ethanol injections, but the control rats did not. Both control and ethanol groups had similar CTAs at the 1.5 g dose. However, at the 1.0 g dose, the ethanol group had an attenuated CTA compared with the water control group. The results suggest that P rats develop tolerance to aversive effects of ethanol during chronic drinking. This tolerance could contribute to the high ethanol intake in these selectively-bred rats.     

Attenuation of alcohol consumption by MDMA (ecstasy) in two strains of alcohol-preferring rats.

Alcohol preference and manifestation of alcoholism are thought by many to be associated with serotonin (5-HT) dysfunction in the brain. Thus, experiments were performed to determine the effect of acute and subchronic administration of (+/-) 3,4-methylenedioxymethamphetamine (MDMA), an amphetamine analog that stimulates 5-HT release, on alcohol preference in two strains of alcohol-preferring rats, the Fawn-Hooded (FH) and alcohol-preferring (P) rats. Rats were individually housed and provided free access to a solution of 10% ethanol, food, and water. Ethanol, food, and water intakes were measured daily. After establishing a stable baseline for ethanol and water intake, each rat was injected SC with a dose of 5.0 mg/kg MDMA or an equal volume of saline for 1 or 3 consecutive days. Body temperature was recorded immediately before and 120, 240, and 360 min after MDMA treatment. Ethanol, food, and water intake were measured for the preceding 24 h. Further, to determine the effect of MDMA on alcohol metabolism rats were injected with 5.0 mg/kg MDMA or saline and 15 min later with 2.5 g/kg alcohol. Then, blood alcohol levels were determined at 1, 3, and 5 h after alcohol administration. Our results show that a single administration of 5.0 mg/kg MDMA significantly decreased ethanol intake in both FH and P rats and increased water intake. Subchronic administration of 5.0 mg/kg MDMA for 3 consecutive days significantly attenuated alcohol intake in both strains but only increased water intake in P rats. Administration of MDMA induced hyper- and hypothermia in FH and P rats, respectively. This drug failed to exert any significant effect on the pharmacokinetics of alcohol, indicating a central effect.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characteristics of ethanol tolerance in alcohol drinking (AA) and alcohol avoiding (ANA) rats

The development of tolerance to ethanol was examined in two rat lines selected for high (AA) and low (ANA) ethanol consumption. In the first experiment, the acquisition of tolerance to the motor-impairment, hypothermic and hypnotic effects of ethanol produced by daily treatment with 5 g/kg ethanol for a period of 24 days was examined. Tolerance to these effects of ethanol was observed in the AA rats while marginal or no tolerance was demonstrated in the ANA rats. In the second experiment the development of rapid tolerance to the hypothermic and hypnotic effects of ethanol was examined. The hypothermic and hypnotic responses to IP injection of 3.5 g/kg ethanol were found to be attenuated in the AA but not the ANA rats by a single equivalent ethanol injection given 24 h earlier. These results suggest some relationship between the capacity to develop tolerance and voluntary ethanol intake.     

Effects of repeated alcohol deprivations on operant ethanol self-administration by alcohol-preferring (P) rats.

We reported that repeated alcohol deprivations prolonged the expression of an alcohol-deprivation effect (ADE) under 24-h free-choice alcohol-drinking access and that the duration of the initial deprivation period had a positive effect of prolonging the duration of the ADE. In the present study, operant techniques (including progressive ratio measures) were used to examine the effects of initial deprivation length and number of deprivation cycles on the magnitude and duration of the ADE in alcohol-preferring (P) rats to test the hypothesis that repeated deprivations can increase the reinforcing effects of ethanol (ETOH). Adult male P rats were trained in two-lever operant chambers to self-administer 15% ETOH (v/v) on a fixed-ratio 5 (FR-5) and water on a FR-1 schedule of reinforcement in daily 1-h sessions. Following 6 weeks of daily 1-h sessions, the P rats were randomly assigned to one of four groups (n=10/group): nondeprived or deprived of alcohol for 2, 5, or 8 weeks. Following this initial period, the deprived groups were given 15% ETOH again in the operant chambers for a 2-week period, following which they were deprived again for 2 weeks (all three deprived groups). Following the fourth deprivation, the rats underwent a progressive ratio test to determine the breakpoints (FR values) for the nondeprived and the deprived groups. Repeated deprivations increased both the magnitude and duration of the ADE as indicated by increased responding on the ETOH lever. However, the length of the initial deprivation had little effect on expression of the ADE except following the first deprivation, where an ADE was not observed for the 8-week group. Breakpoint values for responding on the ETOH lever for all three deprived groups were two-fold higher than the value for the nondeprived group. The results suggest that repeated cycles of alcohol deprivation and alcohol access increased the reinforcing effects of ETOH in the P rats.     

Suppression by baclofen of alcohol deprivation effect in Sardinian alcohol-preferring (sP) rats

Alcohol deprivation effect (ADE), i.e. the transient increase in alcohol intake that takes place in laboratory animals after a period of alcohol deprivation, has been proposed to model alcohol relapses in alcoholics. The present study investigated the effect of the GABA(B) receptor agonist, baclofen, on the development of ADE in selectively bred Sardinian alcohol-preferring (sP) rats. Acute administration of non-sedative doses of baclofen (0, 1, 1.7 and 3 mg/kg, i.p.) resulted in the complete suppression of the extra-amount of alcohol consumed during the first hour of re-access to alcohol after 7 days of deprivation. These results implicate the GABA(B) receptor in the neural substrate mediating ADE and suggest that baclofen may possess anti-relapse properties.     

Effects of intravenous ethanol and of 4-methylpyrazole on alcohol drinking in alcohol-preferring rats

Studies were undertaken to determine if elevated blood alcohol concentrations (BAC), produced by intravenous (IV) infusion of ethanol or by intraperitoneal (IP) administration of 4-methylpyrazole (4-MP), could reduce the free-choice oral alcohol consumption of adult male alcohol-preferring rats (P-rats). The IV infusion of ethanol either on a 24 or 12 (dark) hourly dose schedule reduced the amount of ethanol voluntarily ingested. There was a significant (p<0.05) inverse correlation between the amount of ethanol consumed orally and the amount of ethanol infused. Daily fluid and caloric intakes were not compromised. When the amount of ethanol infused was 85% or more of the control oral intake, there was a significant correlation between ethanol intake and tail-blood alcohol levels, taken at 5 min (r=0.98; p<0.05) and 55 min (r=0.93,p<0.05) after the last dark cycle infusion. Below the preinfusion level of 85%, the BAC were variable and did not correlate well with total ethanol intake. After a single IP injection of 4-MP, 90 mg/kg body wt, BAC increased from 10 mg% to 50–65 mg% for 2–3 days. Concomitant with the rise in BAC, these animals decreased their drinking of 10% ethanol and proportionately increased their water intake. The present studies suggest that pharmacological factors, distinct from orosensory cues, are important in regulating voluntary ethanol drinking behavior in the P-rats.     

The calcium channel agonist BAY k 8644 reduces ethanol intake and preference in alcohol-preferring AA rats

Applying a 12-h limited access, two-bottle choice procedure, antialcohol effects of the 1,4-dihydropyridine (DHP) L-type calcium (Ca²⁺) channel agonist BAY k 8644 were investigated in alcohol-preferring AA rats. In this Wistar line, selectively bred for a high 10% v/v ethanol (EtOH) preference in a free choice situation, effects on EtOH preference and intake, as well as on food and total fluid intake were evaluated for racemic BAY k 8644 (0.1–1 mg/kg IP; 0.25–2 mg/kg PO), its agonistic (?)-enantiomer (0.1–1 mg/kg IP and PO) and its antagonistic (+)-enantiomer (10–50 mg/kg IP and PO). Irrespective of route of application, BAY k 8644 was found to be effective in reducing both EtOH intake and preference (minimal effective dose: 0.5 mg/kg; maximum effect: approximately 60% of baseline levels). The (+)-enantiomer, acting as a low-potency Ca²⁺ channel antagonist, also reduced EtOH intake and preference, but the effects were not very selective as food intake was also substantially reduced. Moreover, the effects were only obtained at relatively high doses (50 mg/kg). The essential enantiomer involved in the antialcohol effects of BAY k 8644 seems to be the (?)-enantiomer, acting as a strong Ca²⁺ channel agonist. This latter compound was potent (minimal effective dose: 0.3 mg/kg), very effective in reducing EtOH intake (maximum effect: 29% of baseline level) and preference (26% of baseline) and apparently more selective. Although slightly decreasing over days, effects of (?)-BAY k 8644 on EtOH intake and preference were shown to remain after repeated treatment (10 successive days, 0.3 mg/kg IP). Interestingly, the acute antialcohol effects of (?)-BAY k 8644 (0.3–1 mg/kg IP) could not be antagonized with the DHP L-type Ca²⁺ channel antagonists nimodipine (0.01–1 mg/kg IP) and (?)-nimodipine (1–30 mg/kg IP). The present results suggest that a mechanism of action other than L-type Ca²⁺ channel agonism is involved in the antialcohol effects of (±)-and (?)-BAY k 8644. Alternatively, it is possible that the previously described antialcohol effects of DHP Ca²⁺ channel antagonists are not related to antagonistic activity at Ca²⁺ channels. Finally, it cannot be excluded that a mechanism unrelated to Ca²⁺ channels is responsible for the antialcohol effects of both DHP Ca²⁺ channel agonists and antagonists.     

The calcium channel agonist BAY k 8644 reduces ethanol intake and preference in alcohol-preferring AA rats

Applying a 12-h limited access, two-bottle choice procedure, antialcohol effects of the 1,4-dihydropyridine (DHP) L-type calcium (Ca²⁺) channel agonist BAY?k8644 were investigated in alcohol-preferring AA rats. In this Wistar line, selectively bred for a high 10% v/v ethanol (EtOH) preference in a free choice situation, effects on EtOH preference and intake, as well as on food and total fluid intake were evaluated for racemic BAY?k8644 (0.1–1?mg/kg IP; 0.25–2?mg/kg PO), its agonistic (?)-enantiomer (0.1–1?mg/kg IP and PO) and its antagonistic (+)-enantiomer (10–50?mg/kg IP and PO). Irrespective of route of application, BAY?k8644 was found to be effective in reducing both EtOH intake and preference (minimal effective dose: 0.5?mg/kg; maximum effect: approximately 60% of baseline levels). The (+)-enantiomer, acting as a low-potency Ca²⁺ channel antagonist, also reduced EtOH intake and preference, but the effects were not very selective as food intake was also substantially reduced. Moreover, the effects were only obtained at relatively high doses (50?mg/kg). The essential enantiomer involved in the antialcohol effects of BAY?k8644 seems to be the (?)-enantiomer, acting as a strong Ca²⁺ channel agonist. This latter compound was potent (minimal effective dose: 0.3?mg/kg), very effective in reducing EtOH intake (maximum effect: 29% of baseline level) and preference (26% of baseline) and apparently more selective. Although slightly decreasing over days, effects of (?)-BAY?k8644 on EtOH intake and preference were shown to remain after repeated treatment (10 successive days, 0.3?mg/kg IP). Interestingly, the acute antialcohol effects of (?)-BAY?k8644 (0.3–1?mg/kg IP) could not be antagonized with the DHP L-type Ca²⁺ channel antagonists nimodipine (0.01–1?mg/kg IP) and (?)-nimodipine (1–30?mg/kg IP). The present results suggest thata mechanism of action other than L-type Ca²⁺ channel agonism is involved in the antialcohol effects of (±)- and (?)-BAY?k8644. Alternatively, it is possible that the previously described antialcohol effects of DHP Ca²⁺ channel antagonists are not related to antagonistic activity at Ca²⁺ channels. Finally, it cannot be excluded that a mechanism unrelated to Ca²⁺ channels is responsible for the antialcohol effects of both DHP Ca²⁺ channel agonists and antagonists.     

Daily patterns of ethanol drinking in peri-adolescent and adult alcohol-preferring (P) rats

Alcohol abuse among adolescents continues to be a major health problem for our society. Our laboratory has used the peri-adolescent alcohol-preferring, P, rat as an animal model of adolescent alcohol abuse. Even though peri-adolescent P rats consume more alcohol (g/kg/day) than their adult counterparts, it is uncertain whether their drinking is sufficiently aggregated to result in measurable blood ethanol concentrations (BECs). The objectives of this study were to examine daily alcohol drinking patterns of adolescent and adult, male and female P rats, and to determine whether alcohol drinking episodes were sufficiently aggregated to result in meaningful BECs. Male and female P rats were given 30 days of 24 h free-choice access to alcohol (15%, v/v) and water, with ad lib access to food, starting at the beginning of adolescence (PND 30) or adulthood (PND 90). Water and alcohol drinking patterns were monitored 22 h/day with a "lickometer" set-up. The results indicated that (a) peri-adolescent P rats consumed more water and total fluids than adult P rats, (b) female P rats consumed more water and total fluids than male P rats, (c) there were differences in alcohol, and water, licking patterns between peri-adolescent and adult and female and male P rats, (d) individual licking patterns revealed that alcohol was consumed in bouts often exceeding the amount required to self-administer 1 g/kg of alcohol, and (e) BECs at the end of the dark cycle, on the 30th day of alcohol access, averaged 50 mg%, with alcohol intakes during the last 1 to 2 h averaging 1.2 g/kg. Overall, these findings indicate that alcohol drinking patterns differ across the age and sex of P rats. This suggests that the effectiveness of treatments for reducing excessive alcohol intake may vary depending upon the age and/or sex of the subjects being tested.     

The effects of restraint stress on voluntary ethanol consumption in rats

Sixty Wistar rats (Rattus norvegicus) were assigned to 4 groups of 15 rats each: ethanol stress (ES), ethanol no-stress (EN), isocaloric stress (IS) and isocaloric no-stress (IN). The effect of restraint stress on daily intake of ethanol and a 0.72% solution of glucose was examined in an ABA design (stress-no stress-stress). During the stress phases, 2 groups were subjected to daily 15-min restraint stress, whereas 2 groups were placed in different cages for 15 min as a control. All 4 groups were then given 6-hr access to their assigned liquid alone for 4 days followed by a choice between their assigned liquid and water on the 5th day. The ES group significantly increased their ethanol intake (g/kg) compared to the EN group on choice days but not on forced days. Percentage preference for ethanol was significantly greater and increased at a faster rate over the 75-day testing period compared with the EN group. However, total ethanol consumption (g/kg) and percentage preference did not vary as a function of phase. It is notable that the effects of restraint stress on ethanol self-administration persisted even after the stress schedule was removed.     

Effects of alpha 2-adrenergic drugs on the alcohol consumption of alcohol-preferring rats

The effects of seven-day subcutaneous infusion of an alpha 2-adrenoceptor agonist, medetomidine, and an alpha 2-adrenoceptor antagonist, atipamezole, on the voluntary alcohol consumption of alcohol-preferring rats were studied. The drugs were administered by means of implanted osmotic minipumps. Sham-operated control rats had no pumps implanted. The rats had a free choice between 10% alcohol and plain water for 30 days before pump implantation and again for six days starting 24 hr after the operation. Atipamezole increased the alcohol consumption during the first day of free choice. Medetomidine had no significant effect. During the remaining period of infusion, the alcohol consumption did not differ from that preceding the pump implantation in each treatment group. Animals in the atipamezole group gained more weight during the seven-day trial than did those in the medetomidine and control groups. The amine changes in different regions of the brain were consistent with medetomidine decreasing and atipamezole increasing the noradrenaline turnover. The present results indicate that specific drugs acting on the alpha 2-adrenoceptors produce only minor changes in the voluntary alcohol drinking of alcohol-preferring rats.     

Brain ethanol levels in rats after voluntary ethanol consumption using a sweetened gelatin vehicle

A novel procedure for initiation of voluntary ethanol consumption in the rat was evaluated in terms of ease of initiation, consistency, and resulting brain ethanol levels. The "jello shot" consists of 10% ethanol in gelatin along with a caloric source (Polycose). Initiation of "jello shot" consumption in Sprague-Dawley rats required no food or water restriction and resulted in initial daily (8.4+/-0.6 g/kg body weight) and eventual hourly (1.1+/-0.1 g/kg body weight) intake of ethanol comparable to other procedures using either alcohol-preferring or non-genetically selected rats. Rat intake of ethanol via "jello shots" recovered quickly from environmental alterations and surgical implantation of a guide cannula. During 1-h free access sessions, consumption of the "jello shot" occurred during the initial 10 min and resulted in a dose-related increase in ethanol levels in nucleus accumbens measured using microdialysis. These brain ethanol levels were comparable to those achieved using other self-administration methods. However, when 0.5 g/kg ethanol was gavaged either in "jello shot" or saline, there was about a 20% decrease in brain ethanol concentrations after gavage of the "jello shot" compared to saline. Even so, lack of a need for initial food or water deprivation and the rapidity with which stable self-administration can be achieved both suggest utility of the "jello shot" as a completely voluntary ethanol procedure.     

Enhanced morphine- and cocaine-induced behavioral sensitization in alcohol-preferring AA rats

Locomotor stimulation and behavioral sensitization induced by acute and repeated treatment with alcohol, cocaine or morphine were studied in the alcohol-preferring AA (Alko, Alcohol), alcohol-avoiding ANA (Alko, Non-Alcohol) rats and non-selected Wistar rats. Daily treatment with alcohol (ethanol, 0.4 or 1.0 g/kg, IP) for 6 days had no effect on locomotor activity either in the AA or ANA rats. Acute cocaine (5, 10 or 20 mg/kg, IP) produced a locomotor stimulation in the animals of all lines studied, and there was no difference in this effect between the AA and ANA rats. During a 4-day repeated cocaine treatment, the AA rats became sensitized with the 10 mg/kg dose, while the ANA rats did not show any sensitization with this dose. With the 20 mg/kg cocaine dose, in addition to locomotor stimulation, the rats of all lines studied showed stereotyped behavior, which response was enhanced during repeated treatment. Morphine-induced locomotor stimulation was larger in the AA rats than in the ANA or Wistar rats both with 1.0 and 3.0 mg/kg doses and only the AA rats were sensitized during 4-day treatment with the 1 mg/kg dose. With the 3.0 mg/kg morphine dose, only the AA rats showed a weak sensitization evident only during the initial 30 min after morphine injection. As the drug-induced behavioral sensitization is an important factor in the development of drug addiction, it is possible that mechanisms underlying the enhanced susceptibility of the AA rats to morphine- and cocaine-induced sensitization contribute to the high intake of alcohol and other abused drugs by these animals. Received: 3 April 1998/Final version: 7 September 1998     

The effect of clonidine and related substances on voluntary ethanol consumption in rats

Clonidine, guanfacine and tiamenidine, in equihypotensive doses, significantly reduced alcohol intake in ethanol-preferring rats having free choice between 10% ethanol and drinking water. Water intake was only slightly reduced, especially during the first hours following the administration of clonidine. Simultaneous treatment with yohimbine attenuated the clonidine-induced reduction in ethanol intake. Putative central mechanisms underlying the observed inhibitory actions of clonidine and other alpha-2 adrenoceptor agonists on oral self-administration of alcohol are discussed.     

Effects of nefazodone on voluntary ethanol consumption induced by isolation stress in young and aged rats

Late-onset ethanol (EtOH) consumption is related to life and social stressors of aging. The stress system (hypothalamic-pituitary-adrenal, HPA, axis) coordinates the adaptive response of the organism to stressors, but age-related deficits in HPA function seem to be associated with disorders such as late-onset EtOH consumption, anxiety and depression. In the present study, we examined whether HPA dysfunction is associated with stress-related EtOH consumption in aged rats and whether the treatment with nefazodone hydrochloride, a phenylpiperazine antidepressant, partially reverses the adverse effects of isolation (ISOL) stress. The animals were offered two-bottle choice consumption of 0.2% saccharin and 10% EtOH/0.2% saccharin, and then exposed to 4 days of ISOL stress on an irregular, unpredictable schedule. ISOL stress-induced increases in corticosterone secretion and EtOH consumption both during and following the stress (recovery period) in aged rats. Nevertheless, this effect at the recovery period was not evident in young stressed rats. Nefazodone caused a significant decrease in plasma corticosterone levels and EtOH consumption. The attenuation of stress-induced corticosterone by nefazodone was correlated with reduced EtOH consumption. These findings link the effect of ISOL stress to the induction of voluntary EtOH consumption following the end of the stressor and the limitation of aged HPA to down-regulated corticosterone.