Motor impairing effects of ethanol and diazepam in rats selectively bred for high and low ethanol consumption in a limited-access paradigm

BACKGROUND: Some clinical studies suggest that an initial low-level response in ethanol sensitivity is a good predictor of risk for developing subsequent high levels of ethanol consumption in humans; however, there are some inconsistencies in the data. In experimental research, this association between low ethanol sensitivity and high ethanol intake has not been consistently reported in studies that have used rat lines that have been genetically selected for differences in ethanol intake under continuous access conditions (e.g., UChA versus UchB, P versus NP, AA versus ANA). The present study investigated ethanol sensitivity in high (HARF) and low (LARF) ethanol-preferring rats selectively bred under limited-access conditions. For comparative purposes, motor impairment induced by diazepam was also examined. METHODS: Motor impairment was assessed using the tilt plane. Ethanol (1.25, 2.0, and 2.5 g/kg, intraperitoneally) was administered to ethanol-naive male and female HARF and LARF rats, and their performance was assessed at t = 0, 30, and 60 min. Blood ethanol levels were measured in a separate group of ethanol-naive rats. Finally, in a separate group of male and female HARF and LARF rats, diazepam-induced (1, 3, and 10 mg/kg, intraperitoneally) motor impairments were evaluated in a similar manner. RESULTS: In the ethanol study, HARF rats showed greater dose-dependent impairments than their LARF counterparts. Male rats exhibited greater sensitivity to ethanol-induced impairment than their female counterparts. These observations were unrelated to sex or line differences in the blood ethanol levels achieved. Similar impairments were observed with diazepam, with HARF rats exhibiting greater motor impairment than LARF rats. CONCLUSIONS: The results suggest that selective breeding for high and low ethanol drinking in a limited-access paradigm has led to inherent differences in sensitivity to ethanol- and diazepam-induced motor impairments. The pattern of diazepam-induced impairments suggests possible variations in GABA(A) receptor activity, although more research is necessary to determine such involvement.     

High- and low-alcohol-preferring mice show differences in conditioned taste aversion to alcohol

Background: Genetic differences in sensitivity to the aversive effects of alcohol may contribute to alcohol drinking behavior. The present study examined the development of conditioned taste aversion (CTA) to various doses of alcohol in two pairs of mouse lines selectively bred for high (HAP) and low (LAP) alcohol preference. Methods: Alcohol‐naïve, male and female HAP and LAP mice from both replicate 1 (HAP n= 29; LAP n= 28) and replicate 2 (HAP n= 34; LAP n= 35) were adapted to a 2‐hr per day water restriction regimen. During five conditioning trials at 48 hr intervals, mice received an intraperitoneal injection of saline or 2 g/kg or 4 g/kg alcohol immediately following 1 hr of access to a 0.20 M NaCl solution. Results: LAP mice of both replicates showed a significantly greater magnitude of CTA to both 2 g/kg and 4 g/kg alcohol compared with HAP mice of both replicates. There were no line differences in consumption of the NaCl solution in the saline control groups. Conclusions: These data suggest that mice selectively bred for low alcohol preference are more sensitive to the development of alcohol CTA than mice selectively bred for high alcohol preference. The present findings indicate that common genes mediate both alcohol preference and the aversive effects of alcohol as measured in the CTA paradigm.     

Effects of long-term episodic access to ethanol on the expression of an alcohol deprivation effect in low alcohol-consuming rats

Background: The alcohol‐preferring (P) and ‐nonpreferring (NP) and high alcohol–drinking (HAD) and low alcohol–drinking (LAD) rats have been selectively bred for divergent preference for ethanol over water. In addition, both P and HAD rats display an alcohol deprivation effect (ADE). This study was undertaken to test whether the NP, LAD‐1, and LAD‐2 lines of rats could display an ADE as well. Method: Adult female NP, LAD‐1, and LAD‐2 rats were given concurrent access to multiple concentrations of ethanol [5, 10, 15% (v/v)] and water in an ADE paradigm involving an initial 6 weeks of 24‐hr access to ethanol, followed by four cycles of 2 weeks of deprivation from and 2 weeks of re‐exposure to ethanol (5, 10, and 15%). A control group had continuous access to the ethanol concentrations (5, 10, and 15%) and water through the end of the fourth re‐exposure period. Results: For NP rats, a preference for the highest ethanol concentration (15%) was evident by the end of the fifth week of access (～60% of total ethanol fluid intake). Contrarily, LAD rats did not display a marked preference for any one concentration of ethanol. All three lines displayed an ADE after repeated cycles of re‐exposure to ethanol, with the general ranking of intake being LAD‐1 > NP > LAD‐2 (e.g., for the first day of reinstatement of the third re‐exposure cycle, intakes were 6.5, 2.9, and 2.4 g/kg/day compared with baseline values of 3.1, 2.0, and 1.3 g/kg/day for each line, respectively). By the 13th week, rats from all three lines, with a ranking of LAD‐1 > NP > LAD‐2, were drinking more ethanol (3.3, 2.2, and 2.0 g/kg/day, respectively) compared with their consumption during the first week of access (～1.1 g/kg/day for all three lines). Conclusion: These data indicate that access to multiple concentrations of ethanol and exposure to multiple deprivation cycles can partially overcome a genetic predisposition of NP, LAD‐1, and LAD‐2 rats for low alcohol consumption. In addition, the findings suggest that genetic control of low alcohol consumption in rats is not associated with the inability to display an ADE.     

Increase of Rat Alcohol Drinking Behavior Depends on the Age of Drinking Onset

Background Although alcohol drinking onset in younger people is associated with an increased risk of alcohol-related injuries, other factors, such as habituation and susceptibility to alcohol, in the process of aging have not been adequately examined in animal models. In the present study, we determined whether age of drinking onset affected alcohol drinking behavior and led to alcohol tolerance in experimental animals, and extrapolated some of the findings to human alcohol drinking patterns.
Methods In the first experiment, 18 rats that were naive to alcohol were tested at the age of 1, 4, and 10 months with 4 hr of access to 10% (v/v) alcohol. After the time access tests, these animals (1, 4, and 10 months of age) were housed individually and given free access to 10% alcohol solution and tap water. At 3 and 6 months later, all rats that had experienced alcohol drinking were studied for the voluntary consumption of the alcohol solution, alcohol preference, under the two-bottle method in a second experiment.
Results In the 4-hr alcohol-access test, alcohol intake (g/kg/hr) was significantly increased at 0.5 and 1 hr in 1- and 4-month-old naive rats compared with 10-month-old naive rats. The daily alcohol intake (g/kg/day) of rats with drinking onset at 1 month of age was significantly increased at 3 and 6 months after the voluntary alcohol consumption. The daily alcohol intake in the rats with drinking onset at 4 months of age was significantly increased at 6 months only. However, the daily alcohol intake did not change in the rats with drinking onset at 10 months of age through the alcohol preference test.
Conclusions Alcohol drinking behavior in experimental animals depends on the age of alcohol drinking onset.     

Voluntary ethanol drinking during the first three postnatal weeks in lines of rats selectively bred for divergent ethanol preference

BACKGROUND: Using a procedure first developed by Hall (1979), we examined ethanol self-administration in preweanling pups from Wistar rats and in lines of rats selectively bred for divergent ethanol preference (alcohol-preferring P, alcohol-nonpreferring NP, high-alcohol-drinking HAD-1 and -2, and low-alcohol-drinking LAD-2) to determine if factors contributing to high and low alcohol intakes are present early in development. METHODS: From postnatal days 5 to 20, nondeprived male and female rat pups received 30 min daily access to either water or a 15% (v/v) ethanol solution. In each daily session, pups were placed in a heated chamber containing Kimwipes soaked with a water or ethanol solution. Pups were weighed before and after each session, and intake levels were calculated as a percentage of body weight change. RESULTS: Similar to previous reports, Wistar pups exhibited over a 2-fold higher level of ethanol ingestion than water on postnatal days 9 through 14, with ethanol intakes approaching 3 g/kg body weight. When the drinking patterns of the selected lines were examined, only the HAD replicate lines showed a comparable preference for ethanol versus water during the preweanling period. The ethanol consumption of P, NP, and LAD lines was not consistently distinguishable from water intake levels. To reveal whether early ethanol exposure would influence later ethanol drinking behavior, a subset of HAD and LAD rat pups received free-choice ethanol access upon weaning. Although the divergent ethanol preference between high- and low-alcohol-drinking lines was evident within the first 4 days of access (>4 g/kg/day for HAD; <2 g/kg/day for LAD), preweanling ethanol exposure did not alter the acquisition or maintenance of ethanol drinking in either line. CONCLUSIONS: Overall, these results suggest that (a) the enhanced ethanol ingestion observed during the middle portion of the preweanling period is a robust phenomenon and generalizes across nonselected strains of rats, (b) selective breeding for divergent alcohol preference has arrested this age-specific effect in all but the HAD lines of rats, and (c) early ethanol exposure does not alter genetic dispositions for later high or low alcohol preference.     

Alcohol drinking in MCH receptor-1-deficient mice

Background: Recently, we demonstrated that exogenous melanin‐concentrating hormone (MCH) increases alcohol drinking in rats when administered into the brain. However, because the physiological relevance of this finding is unclear, we tested the hypothesis that endogenous MCH signaling enhances alcohol consumption. Methods: Alcohol intake was assessed in male and female wildtype (WT), heterozygous (HET), and homozygous MCH receptor‐1‐deficient (KO) mice. Mice were given 24‐hour access to a series of alcohol‐containing solutions. Following this, the mice were given limited (1‐hour) access to 10% alcohol. Finally, mice were allowed 24‐hour access to sucrose/quinine as a caloric control and a means to assess taste preference. A naïve cohort of male WT and KO mice was tested for alcohol clearance following intraperitoneal administration of 3 g/kg alcohol. Another naïve cohort of female mice was utilized to confirm that intracerebroventricular administration of MCH (5 μg) would augment alcohol drinking in mice. Results: Exogenous MCH enhanced 10% alcohol consumption in mice (saline=0.45±0.08 g/kg, 5 μg MCH=0.94±0.20 g/kg). Male KO mice consumed more 10% alcohol (11.50±1.31 g/kg) than WT (6.26±1.23 g/kg) and HET mice (6.49±1.23 g/kg) during ad libitum access. However, alcohol intake was similar among genotypes during 1 hour daily access. Male KO mice tended to consume less 17.75% sucrose+1.3 mM quinine than controls (WT=10.5±3.6, HET=7.5±1.7, KO=4.4±0.9 g/kg). Alcohol metabolism was similar between WT and KO mice. Conclusions: The finding that male KO consume more alcohol than WT and HET mice, are reminiscent of the counterintuitive reports that KO mice are hyperphagic and yet eat more when administered exogenous MCH. Changes in taste preference or alcohol metabolism do not appear to be important for the increased alcohol drinking in KO mice.     

Effect of Calcitonin on the Alcohol Drinking of Rats

Previous work has shown that calcitonin inhibits eating by rats and that it affects several neurotransmitter systems suspected to play a role in alcohol consumption. The present study was an initial test of whether calcitonin does affect voluntary alcohol consumption by male Wistar rats with prolonged alcohol experience. Calcitonin (20 IU/kg) or saline was injected subcutaneously on 10 consecutive days when the rats (n = 20) had continual access to 10% (v/v) ethanol solution, and to food and water. Using a cross-over design, the effects of 40 IU/kg calcitonin vs. saline were then examined in a second 10-day treatment period. Similar patterns of effects were obtained with both calcitonin doses, but the patterns differed with alcohol, food, and water intake. Alcohol drinking showed biphasic changes with both doses, producing highly significant Treatment x Day interactions (p < 1E-10 and p = 6E-7): it was significantly reduced on the first day of calcitonin treatment and significantly increased on the last few days. Food intake was reduced on all calcitonin days although most markedly on the first. Water drinking was not altered on the first calcitonin day, but was greatly increased on the second, then gradually returned toward the baseline. In a second experiment, the animals were switched to 1 hr of alcohol access per day, and calcitonin (20 IU/kg) was administered periodically to one group 4 hr before the alcohol access. Alcohol drinking was significantly reduced in all cases when the calcitonin injection was preceded by at least 1 day without calcitonin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Low-dose stimulatory effects of ethanol during adolescence in rat lines selectively bred for high alcohol intake

Abstract : Background: The low‐dose stimulatory effect of ethanol (EtOH) in rats has been hypothesized to reflect its hedonic effects and to be associated with a genetic predisposition toward high alcohol preference. To test the hypothesis that phenotypes associated with high alcohol preference in adulthood are also present in adolescent rats at the time of onset of alcohol drinking, the current study examined the effects of EtOH on locomotor activity (LMA) during adolescence in lines of rats selectively bred for divergent alcohol intakes. Methods: Subjects were adolescent (31–40 days of age) rats from the alcohol‐preferring (P) and ‐nonpreferring (NP) lines and from the high–alcohol‐drinking (HAD) and low–alcohol‐drinking (LAD) replicate lines. On day 1, all subjects (n= 8–10/line/gender/dose) received intraperitoneal saline injections and were placed in the activity monitor for 30 min. On day 2, subjects received intraperitoneal saline or 0.25, 0.50, 0.75, 1.0, or 1.5 g EtOH/kg. Results: The LMA of male and female P rats was increased with low doses (0.25–0.75 g/kg) and decreased at the highest dose (1.5 g/kg) of EtOH. Similar effects were observed with low doses of EtOH on the LMA of HAD‐1 and HAD‐2 rats. None of the EtOH doses stimulated LMA in the NP, LAD‐1, or LAD‐2 rats, although all of the low–alcohol‐intake lines of rats showed decreased LMA at the highest dose of EtOH. Only the P rats among the high–alcohol‐consuming lines of rats showed decreased LMA at the highest dose of EtOH. Conclusion: Selective breeding for high alcohol consumption seems to be associated with increased sensitivity to the low‐dose stimulating effects of EtOH and reduced sensitivity to the high‐dose motor‐impairing effects of ethanol. The expression of these phenotypes emerges during adolescence by the age of onset of alcohol‐drinking behavior.     

Intermittent access to 20% ethanol induces high ethanol consumption in Long-Evans and Wistar rats

Background: There has been some difficulty getting standard laboratory rats to voluntarily consume large amounts of ethanol without the use of initiation procedures. It has previously been shown that standard laboratory rats will voluntarily consume high levels of ethanol if given intermittent‐access to 20% ethanol in a 2‐bottle‐choice setting [ Wise, Psychopharmacologia 29 (1973), 203 ]. In this study, we have further characterized this drinking model. Methods: Ethanol‐naïve Long–Evans rats were given intermittent‐access to 20% ethanol (three 24‐hour sessions per week). No sucrose fading was needed and water was always available ad libitum. Ethanol consumption, preference, and long‐term drinking behaviors were investigated. Furthermore, to pharmacologically validate the intermittent‐access 20% ethanol drinking paradigm, the efficacy of acamprosate and naltrexone in decreasing ethanol consumption were compared with those of groups given continuous‐access to 10 or 20% ethanol, respectively. Additionally, ethanol consumption was investigated in Wistar and out‐bred alcohol preferring (P) rats following intermittent‐access to 20% ethanol. Results: The intermittent‐access 20% ethanol 2‐bottle‐choice drinking paradigm led standard laboratory rats to escalate their ethanol intake over the first 5 to 6 drinking sessions, reaching stable baseline consumption of high amounts of ethanol (Long–Evans: 5.1 ± 0.6; Wistar: 5.8 ± 0.8 g/kg/24 h, respectively). Furthermore, the cycles of excessive drinking and abstinence led to an increase in ethanol preference and increased efficacy of both acamprosate and naltrexone in Long–Evans rats. P‐rats initiate drinking at a higher level than both Long–Evans and Wistar rats using the intermittent‐access 20% ethanol paradigm and showed a trend toward a further escalation in ethanol intake over time (mean ethanol intake: 6.3 ± 0.8 g/kg/24 h). Conclusion: Standard laboratory rats will voluntarily consume ethanol using the intermittent‐access 20% ethanol drinking paradigm without the use of any initiation procedures. This model promises to be a valuable tool in the alcohol research field.     

Inverse genetic association between alcohol preference and severity of alcohol withdrawal in two sets of rat lines selected for the same phenotype

Background: The purpose of the present study was to determine whether alcohol‐naïve rats selectively bred for alcohol preference or nonpreference differ in alcohol withdrawal severity using two sets of rat lines selectively bred for the same phenotype. Methods: Alcohol‐naïve male rats from the high alcohol drinking (HAD1) and low alcohol drinking (LAD1) rat lines and from the alcohol preferring (P) and nonpreferring (NP) rat lines received an intragastric infusion of alcohol (4.0 g/20.3 ml/kg; 25% v/v) or an equal volume of water once a day for 10 consecutive days. Alcohol withdrawal severity was assessed at using a behavioral rating scale and a radiant heat assay measured analgesia at 10, 12, 14, 16, 18, and 24 hrs following infusion of alcohol or water on days 1, 5, and 10 of treatment. Results: Data were analyzed using body weight as a co‐factor to correct for differences in body weight between the HAD1/LAD1 and P/NP lines. Acute (1 day) but not repeated alcohol treatment (5 or 10 days) produced mild behavioral signs of withdrawal in LAD1 but not in HAD1 rats. HAD1 and LAD1 rats showed alcohol‐induced analgesia after 1 and 5 days of alcohol treatment that disappeared by day 10 in both lines. Repeated alcohol treatment (5 days) produced mild behavioral signs of withdrawal in NP but not in P rats. Neither P nor NP rats showed alcohol‐induced analgesia after 1, 5, or 10 days of alcohol treatment. Conclusions: An inverse genetic association was found between alcohol preference and severity of alcohol withdrawal in two sets of rat lines selected for the same phenotype. The pattern of alcohol withdrawal that emerged over the course of the 10 days of alcohol treatment differed between the two lines selected for low alcohol drinking (LAD1 and NP), suggesting that unique sets of genes may influence alcohol withdrawal severity in the two lines.     

High-Alcohol Preferring Mice Are More Impulsive Than Low-Alcohol Preferring Mice as Measured in the Delay Discounting Task

Background: Repeated studies have shown that high impulsivity, when defined as the tendency to choose small immediate rewards over larger delayed rewards, is more prevalent in drug addicts and alcoholics when compared with nonaddicts. Assessing whether impulsivity precedes and potentially causes addiction disorders is difficult in humans because they all share a history of drug use. In this study, we address this question by testing alcohol‐naïve mice from lines showing heritable differences in alcohol intake. Methods: Replicated selected lines of outbred high‐alcohol preferring (HAP) mice were compared to a low‐alcohol preferring (LAP) line as well as the low‐drinking progenitor line (HS/Ibg) on an adjusting amount delay discounting (DD) task. The DD task employs 2 levers to present subjects with a choice between a small, immediate and a large, delayed saccharin reward. By adjusting the quantity of the immediate reward up and down based on choice behavior, the task allows an estimate of how the subjective value of the delayed reinforcer decreases as delays increase. Latency to respond was also measured for each trial. Results: Both HAP2 and HAP1 lines of mice were more impulsive than the LAP2 and HS/Ibg lines, respectively. Hyperbolic curve‐fitting confirmed steeper discounting in the high‐alcohol drinking lines. In addition, the high‐alcohol drinking lines demonstrated greater within‐session increases in reaction times relative to the low‐alcohol drinking lines. No other differences (consumption of saccharin, total trials completed) consistently mapped onto genetic differences in alcohol drinking. Conclusions: Alcohol‐naïve outbred mice selected for high‐alcohol drinking were more impulsive with saccharin reinforcers than low‐alcohol drinkers. These data are consistent with results seen using inbred strain descendents of high‐alcohol drinking and low‐alcohol drinking rat lines, and suggest that impulsivity is a heritable difference that precedes alcoholism.     

Effects of Taste Aversion Training on the Acquisition of Alcohol Drinking in Adolescent P and HAD Rat Lines

Early alcohol drinking has been hypothesized to cause alcohol-related problems in adulthood. In addition, a potential role for genetic factors exist in the etiology of some types of alcoholism. The objective of the present study was to determine if taste aversion training to ethanol during adolescence in previously ethanol-naive, alcohol-preferring P and high-alcohol drinking HAD-1 lines of rats would retard or prevent the onset of high alcohol drinking. Taste aversion training began at 30 days of age. Male and female rat pups were fluid-deprived for 24 hr before 30 min access to a 10% (v/v) ethanol solution, followed by an intraperitoneal injection of either saline or 0.15 M LiCl (10 ml/kg). A total of five training sessions were administered every other day with unrestricted access to water on intervening training days. Twenty-four hours after the last training trial, rats were given continuous free-choice between water and 10% ethanol for 4 weeks with food available ad libitum. There were no obvious gender or line differences to the effects of taste aversion training. All LiCl-treated subjects avoided the usually preferred ethanol solution for the entire 4-week test period, whereas saline-treated rats steadily increased their alcohol intake to over 6.0 g/kg/day by week 4. Rats in the saline and LiCl-treated groups gained weight at comparable rates, and the groups did not differ in total fluid intake. The findings demonstrate that early environmental intervention can prevent the onset of high alcohol drinking in the selectively bred alcohol-preferring P and high-alcohol drinking HAD-1 lines of rats.     

Development of ethanol withdrawal-related sensitization and relapse drinking in mice selected for high- or low-ethanol preference

Background: Previous studies have shown that high alcohol consumption is associated with low withdrawal susceptibility, while at the same time, other studies have shown that exposure to ethanol vapor increases alcohol drinking in rats and mice. In the present studies, we sought to shed light on this seeming contradiction using mice selectively bred for High‐ (HAP) and Low‐ (LAP) Alcohol Preference, first, assessing these lines for differences in signs of ethanol withdrawal and second, for differences in the efficacy of intermittent alcohol vapor exposure on elevating subsequent ethanol intake. Methods: Experiment 1 examined whether these lines of mice differed in ethanol withdrawal‐induced CNS hyperexcitability and the development of sensitization to this effect following intermittent ethanol vapor exposure. Adult HAP and LAP lines (replicates 1 and 2), and the C3H/HeNcr inbred strain (included as a control genotype for comparison purposes) received intermittent exposure to ethanol vapor and were evaluated for ethanol withdrawal‐induced seizures assessed by scoring handling‐induced convulsions (HIC). Experiment 2 examined the influence of chronic intermittent ethanol exposure on voluntary ethanol drinking. Adult male and female HAP‐2 and LAP‐2 mice, along with male C57BL/6J (included as comparative controls) were trained to drink 10% ethanol using a limited access (2 h/d) 2‐bottle choice paradigm. After stable baseline daily intake was established, mice received chronic intermittent ethanol vapor exposure in inhalation chambers. Ethanol intake sessions resumed 72 hours after final ethanol (or air) exposure for 5 consecutive days. Results: Following chronic ethanol treatment, LAP mice exhibited overall greater withdrawal seizure activity compared with HAP mice. In Experiment 2, chronic ethanol exposure/withdrawal resulted in a significant increase in ethanol intake in male C57BL/6J, and modestly elevated intake in HAP‐2 male mice. Ethanol intake for male control mice did not change from baseline levels of intake. In contrast, HAP‐2 female and LAP‐2 mice of both sexes did not show changes in ethanol intake as a consequence of intermittent ethanol exposure. Conclusions: Overall, these results indicate that the magnitude of ethanol withdrawal‐related seizures is inversely related to inherited ethanol intake preference. Additionally, intermittent ethanol vapor exposure appears more likely to affect high‐drinking mice (C57BL/6J and HAP‐2) than low drinkers, although these animals are less affected by ethanol withdrawal.     

A comparative study on alcohol-preferring rat lines: effects of deprivation and stress phases on voluntary alcohol intake

BACKGROUND: Voluntary alcohol intake in rats can be influenced by alcohol deprivation phases and stress. We investigated the magnitude of the effects of both deprivation and stress (forced swimming in cold water and foot-shock had been chosen as stressors distinct in their physical and psychological features) on alcohol intake and the influence of these experiences on the time course of alcohol drinking behavior. For the alcohol drinking procedure, a long-term model of alcohol self-administration originally developed for heterogeneous Wistar rats was used and was compared with different alcohol-preferring rat lines. METHODS: Adult male Alko alcohol (AA), alcohol-preferring (P), high-alcohol-drinking (HAD), and unselected Wistar rats were given ad libitum access to water, 5%, and 20% alcohol solutions for 6 months. A deprivation phase of 14 days was performed after 8 weeks of access to alcohol. After 16 weeks and 22 weeks of alcohol access, all animals were subjected to forced swimming and foot-shock, respectively, for 3 consecutive days, while alcohol intake was still being measured. RESULTS: Alcohol deprivation led to a significant increase in alcohol intake in Wistar rats and P rats. No alcohol deprivation effect was observed in HAD and AA rats; after deprivation, however, their preference for the 20% alcohol solution increased, immediately in the HAD rats and gradually over time in the AA rats. Repeated swim stress caused an increase in alcohol intake in Wistar rats but no changes in the alcohol-preferring rat lines. Foot-shock stress increased alcohol consumption in all lines of rats, but the most pronounced effects were observed in HAD and P rats. CONCLUSIONS: Wistar, HAD, P, and AA rats differentially respond to alcohol deprivation and stress, showing that the genetic background of these different rat lines profoundly affects relapse-like drinking and stress-induced drinking.     

Enhanced morphine-induced ethanol drinking in alcohol-preferring alko alcohol rats sensitized to morphine

BACKGROUND: Alcohol-preferring alko alcohol (AA) rats are more susceptible to morphine-induced behavioral and neurochemical sensitization than alcohol nonpreferring alko nonalcohol (ANA) rats. Alko alcohol rats sensitized to morphine, however, do not show enhanced acquisition of ethanol drinking. The purpose of the present study was to clarify further interactions between morphine-induced behavioral sensitization and voluntary ethanol drinking in the AA rats. METHODS: Alko alcohol rats drinking ethanol in a limited 6-hour access paradigm were sensitized to morphine with repeated injections of morphine (5-15 mg/kg). Injection days alternated with days of ethanol access. Controls had access only to water and/or were given injections of saline. After a 5-day washout period from ethanol and morphine, the rats were challenged with morphine or saline and subsequent ethanol drinking or locomotor activity was recorded. RESULTS: Ethanol intake was suppressed during the repeated treatment with morphine, and the morphine-treated rats did not differ in ethanol intake from the controls when given access to ethanol after the washout. Intake of ethanol was, however, increased when the rats were challenged with morphine [1 or 10 mg/kg, subcutaneously (s.c.)], while in the controls an increase in ethanol intake was seen only after 1 mg/kg morphine. Sensitization to the locomotor stimulating effects of morphine was revealed in the morphine-treated rats after a challenge with morphine (3 or 10 mg/kg, s.c.). The controls that had been drinking ethanol also showed a sensitized response after morphine (3 mg/kg). CONCLUSIONS: Ethanol did not interfere with the development of sensitization to morphine. Furthermore, the neuroadaptations induced by repeated exposure to ethanol were sufficient to cause behavioral cross-sensitization to morphine. Sensitization to the behavioral effects of morphine alone, however, neither enhances the reinforcing properties of voluntarily consumed ethanol nor contributes to increase in its intake. The increase in ethanol intake found after an acute dose of morphine was augmented in rats withdrawn from repeated treatment with morphine. The data suggest that the neuronal mechanisms underlying behavioral sensitization to morphine probably are distinct from those mediating reinforcement from ethanol and that the morphine-induced neuroadaptations contribute to the enhancement of increase in ethanol intake by morphine.     

Effects of prazosin, an α1-adrenergic receptor antagonist, on the seeking and intake of alcohol and sucrose in alcohol-preferring (P) rats

Background: Previous studies show that prazosin, an α₁‐adrenergic receptor antagonist, decreases alcohol drinking in animal models of alcohol use and dependence [Rasmussen et al. (2009) Alcohol Clin Exp Res 3:264–272; Walker et al. (2008) Alcohol 42:91–97] and in alcohol‐dependent men [Simpson et al. (2009) Alcohol Clin Exp Res 33:255–263]. This study extended these findings by using a paradigm that allows for separate assessment of prazosin on motivation to seek versus consume alcohol or sucrose in selectively bred rats. Methods: Alcohol‐preferring (P) rats were trained to complete an operant response that resulted in access to either 2% sucrose or 10% alcohol. A 4‐week Seeking Test Phase examined responding in single, weekly extinction sessions when no reinforcer could be obtained. A 4‐week Drinking Test Phase consisted of rats lever‐pressing to “pay” a specified amount up front to gain access to unlimited alcohol (or sucrose) for a 20‐minute period. On Seeking and Drinking test days, prazosin (0.0, 0.5, 1.0, and 1.5 mg/kg) was administered intraperitoneally 30 minutes prior to behavioral sessions. Results: Rats were self‐administering an average of 0.9 (±0.09) g/kg alcohol on vehicle test day and had pharmacologically relevant blood ethanol concentrations. Prazosin significantly decreased alcohol seeking at all doses tested. The highest dose of prazosin also increased the latency to first response for alcohol and decreased alcohol intake. While sucrose‐seeking and intake were similarly affected by prazosin, the high dose of prazosin did not increase response latency. Conclusions: These findings are consistent with and extend previous research and suggest that prazosin decreases motivation to initiate and engage in alcohol consumption. The specificity of prazosin in attenuating the initiation of alcohol‐ but not sucrose‐seeking suggests that this effect is not because of prazosin‐induced motor‐impairment or malaise. Together with previous findings, these data suggest that prazosin may be an effective pharmacotherapy, with specific application in people that drink excessively or have a genetic predisposition to alcohol abuse.     

Comparison of Alcohol-Preferring and Nonpreferring Selectively Bred Rat Lines. II. Operant Self-Administration in a Continuous-Access Situation

Several rat lines have been developed using preference/nonpreference and daily ethanol intake in the homecage as criteria for selective breeding. Using these lines, behavioral and neural factors that may underlie the genetic basis for the control of ethanol consumption have been examined. In this paper, we report data from eight of these selected lines: the Alcohol-Preferring (P) and Alcohol-Nonpreferring (NP), the Alcohol-Accepting (AA) and Alcohol-Nonaccepting (ANA), and the High Alcohol Drinking (HAD1 and HAD2) and Low Alcohol Drinking (LAD1 and LAD2) rats. All lines were tested using operant procedures and the same protocols for both the ethanol self-administration initiation and measurement of continuous-access ethanol consumption. During continuous access, the animals were housed in operant chambers with access to 10% (v/v) ethanol after responses on one lever, food pellets (45 mg) after responses on a second lever, and water in a drinking tube that was connected to a drinkometer circuit Under these procedures, both similarities and differences among the selected lines on continuous-access operant ethanol intake were observed. For example, overall total homecage ethanol drinking was similar for the AA and both HAD lines. When examined in the operant continuous-access situation, however, the AA rats displayed a different consumption pattern, compared with the HAD lines. Data suggest that the frequency of drinking bouts was a primary factor in the phenotypic homecage selection of the preferring lines that was revealed by the use of the continuous-access operant procedure. In general, data suggest that genes related to ethanol preference and intake in homecage continuous-access situations may not be identical to those related to ethanol's reinforcing function in operant continuous-access conditions. Because ethanol consumption appears to be controlled by different drinking patterns across lines, the selected lines provide for a variety of models to understand how varying genotypes can impact ethanol consumption.     

Comparison of Alcohol-Preferring and Nonpreferring Selectively Bred Rat Lines. I. Ethanol Initiation and Limited Access Operant Self-Administration

Several lines of alcohol-preferring and alcohol-nonpreferring rats have been developed using selective breeding based on 24-hr homecage ethanol consumption. However, it remains unclear if the selection based on two-bottle choice resulted in similar ethanol self-administration when measured using an operant procedure. In this paper, we compare our previous work using alcohol-accepting (AA) and alcohol-nonaccepting (ANA) rats with data obtained using the identical procedures in the (P) and (NP) rat lines, and both replicate lines of the high alcohol drinking (HAD1 and HAD2) and low alcohol drinking (LAD1 and LAD2) lines. All rats from each line were initiated to self-administer 10% ethanol using the sucrose fading procedure. After initiation, increasing concentrations of ethanol up to 30% ethanol were tested. The results indicated that only in the LAD1 and LAD2 lines was ethanol presentation not able to maintain lever pressing after initiation. Compared with the AA line, the P, HAD1, HAD2, and NP lines all self-administered more ethanol in the operant paradigm after initiation. The ANA line self-administered less ethanol than the AA line, but more than the LAD lines. Correlational analysis of homecage consumption with operant ethanol self-administration suggested that -62% of the genetic variance in operant self-administration resulted from genes selected for the homecage drinking. At the same time, it was clear that there were genetic influences on operant self-administration that were not selected for by homecage ethanol drinking.     

Development of Alcohol Drinking Behavior in Rat Lines Selectively Bred for Divergent Alcohol Preference

A characteristic of heritable alcoholism is an early onset of alcohol abuse, which may begin at or before the age of adolescence. The objective of the present study was to determine the ontogeny of alcohol drinking behavior before and during puberty in the selectively bred alcohol-preferring (P), alcohol-nonpreferring (NP), high alcohol drinking (HAD), and low alcohol drinking (LAD) lines of rats. In addition, the effects of postweaning housing conditions (single- or pair-housed) and initiation procedure (4 days forced ethanol or free-choice) were evaluated in male and female P rats. Results indicate that high alcohol drinking in P and HAD (replicate line 2) rats, as well as low alcohol drinking behavior in NP and LAD (replicate line 2) rats, is present as early as 3 to 4 weeks of age. Ethanol intakes in juvenile P and HAD rats reached levels of ∼4 to 5 g/kg/day by 38 to 41 days of age and were comparable with levels observed in adults. Neither housing conditions nor ethanol initiation procedure significantly altered the acquisition or magnitude of alcohol intake levels in juvenile male and female P rats. These results suggest that the neural substrates underlying divergent ethanol drinking behavior in P/NP and HAD/LAD lines of rats are present early in life.