Effects of naltrexone on alcohol self-administration in heavy drinkers

The mechanisms underlying the suppressant effects of naltrexone (NTX) on ad libitum alcohol drinking in a bar/restaurant setting were investigated in heavy beer drinkers. Fifty-one male and female heavy drinkers (mean age = 22) received 50 mg of NTX or placebo (PBO), p.o., on two separate occasions in a randomized, double-blind crossover protocol. After 7 days of taking medication, subjects were provided with the opportunity to consume beer ad libitum during two, 90-min test sessions that were held 1 to 2 weeks apart. Blood samples were collected on test days to ensure medication compliance and to measure blood levels of NTX and the active beta-naltrexol. Less beer was consumed during NTX treatment. NTX decreased urges to consume alcohol. NTX-treated subjects also took significantly longer to finish each glass of beer and were more likely to terminate beer drinking early. Self-report stimulation and ratings of positive mood states were lower during NTX treatment. Negative side effects of NTX, such as nausea and headache, were reported more frequently with NTX. Not all of the subjects decreased their beer intake on NTX, and some subjects drank more beer. Nonresponders to NTX were not related to blood levels of the active metabolite beta-naltrexol or to a family history of alcoholism. Overall, the results of this study suggest that NTX affects a number of the components of alcohol drinking sequence, including lowering cravings, decreasing the positive reinforcing effects of alcohol, and increasing headache and nausea, each of which may contribute to reducing alcohol intake.     

Sex Differences in Alcohol Preference and Drinking Patterns Emerge during the Early Postpubertal Period in Sprague-Dawley Rats

Young male and female Sprague-Dawley rats (30 days old) were assigned randomly to three treatment groups: (1) alcohol treatment—received beer with 5% ethanol added, food, and water ad libitum; (2) pair-fed treatment—received nonalcoholic beer plus sucrose and food to match intake by the alcohol-treated animals; and (3) control treatment—received food and water ad libitum. Animals were tested for alcohol preference for 24 hr and then received their assigned treatments for a period of 30 days, followed by a period of abstinence before alcohol preference testing again at 74 days of age. Males given free access to beer and water did not drink large quantities of beer. Females given free access to beer and water drank a lot of beer on the first day, but decreased intake until ˜52 days of age. A developmental change in young female rats at ˜52 days of age resulted in increased voluntary ethanol intake, possibly caused by hormonal changes associated with the establishment of estrous cycles. When the animals were tested for alcohol preference at 74 days of age after a period of abstinence, males and females in the pair-fed group had greater alcohol preference than animals in the other groups. Females in the pair-fed group had greater alcohol intake based on body weight than males in the pair-fed group and males and females in all other groups. These results provide insight into sex differences in the development of voluntary drinking behavior and responses of drinking behavior to the early stress of pair-feeding.     

Captopril and Hydrochlorothiazide (Capozide®) Combine to Enhance the Reduction in Voluntary Alcohol Intake in Rats

The effect of Capozide®, the combination of captopril with a hydrochlorothiazide diuretic, on voluntary alcohol intake was assessed in two experiments. In experiment 1 naive rats who were maintained on ad libitum food and water were given daily 40-min access to a 6% (w/v) alcohol solution and water. Daily intraperitoneal injections of captopril (10 mg/kg) reduced alcohol intake, but the combination of captopril (5 and 10 mg/kg) and hydrochlorothiazide (2.5, 5, and 10 mg/kg) enhanced the reduction in intake. In experiment 2, captopril alone, hydrochlorothiazide alone, and the combination of captopril and hydrochlorothiazide were again administered daily in the limited access procedure. Captopril (10 mg/kg) again reduced alcohol intake as did all three doses of hydrochlorothiazide (2.5, 5, and 10 mg/kg). Compared with the individual effects of captopril and hydrochlorothiazide, Capozide® exerted a supra-additive reduction in alcohol intake. These effects were not due to drug-induced changes in the pharmacokinetics of alcohol. Taken together these results demonstrate an enhanced potency of Capozide® in suppressing alcohol intake and invite their testing in a population of hypertensive alcoholics and alcohol abusers.     

Ethanol-Induced Social Facilitation in Adolescent Rats: Role of Endogenous Activity at Mu Opioid Receptors

Background: Ethanol consumption is considerably elevated during adolescence. Attractiveness of alcohol for humans during the adolescent developmental period is based, in part, on its ability to induce social facilitation—a facilitation of social interactions not only evident in human adolescents but also in adolescent rats. Endogenous opioid systems are among the multiple neural systems implicated in the behavioral and reinforcing effects of ethanol and may play a substantial role in modulating stimulatory effects of low doses of ethanol on social behavior during adolescence. This possibility was explored in the present study through the use of an animal model of peer‐directed social behavior. Methods: Sprague–Dawley rats were challenged early in adolescence with saline or ethanol intraperitoneally (i.p.), placed into an individual holding cage for 30 minutes, and then tested in a familiar situation with a nonmanipulated partner of the same age and sex. In Experiment 1 , each test subject was injected subcutaneously with one of the three doses of a nonselective opioid antagonist naloxone (0, 0.05, and 0.1 mg/kg), 5 minutes prior to the social interaction test and 25 minutes following challenge with saline or ethanol (0.5 g/kg), whereas in Experiment 2 animals were challenged with one of the six doses of ethanol (0, 0.25, 0.5, 0.75, 1.0, and 1.25 g/kg) prior to injection of either saline or naloxone (0.05 mg/kg). In Experiment 3 , animals were pretreated i.p. with the selective μ‐opioid antagonist CTOP (0, 0.01, 0.025, 0.05, and 0.1 mg/kg) 30 minutes prior to challenge with saline or ethanol (0.5 g/kg). Results: Low doses of ethanol (0.5 and 0.75 g/kg) produced social facilitation, as indexed by significant increases in play fighting and social investigation. Both doses of naloxone and the three highest doses of CTOP blocked the stimulatory effects of ethanol on play fighting but not on social investigation. These effects were not associated with alterations in ethanol pharmacokinetic properties or with shifts in the biphasic ethanol dose–response curve. Conclusions: Ethanol‐induced facilitation of social play behavior seen in adolescent animals is mediated in part through ethanol‐induced release of endogenous ligands for the μ‐opioid receptor or an ethanol‐associated enhancement of sensitivity of these receptors for their endogenous ligands.     

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.     

Suppression of alcohol intake by chronic naloxone treatment in P rats: tolerance development and elevation of opiate receptor binding

BACKGROUND: This study was planned to determine the feasibility of using a slow release naloxone preparation to treat alcoholism, because compliance with medication is a significant problem in alcoholics. METHODS: Experiments were performed in alcohol-preferring P rats maintained either on continuous access or on limited access (1 hr/day) to alcohol with water and food provided ad libitum. Naloxone (Nx) was administered either by twice daily subcutaneous injections or by slow release (1.1 mg/kg/hr) osmotic minipump. In limited access experiments, Nx was injected immediately before access to alcohol. RESULTS: An initial experiment estimated the dose-effect curve for Nx subcutaneous suppression on alcohol intake. Nx (2.5-20 mg/kg) had a stronger effect during the first 2 hr after injection (ED50 = 2.1 mg/kg); however, the effect was more modest on 24-hr consumption. Similar results were found with chronic Nx treatment. Low doses of Nx (0.5 and 2.0 mg/kg) injected immediately before limited access to alcohol produced almost complete suppression of alcohol intake for at least 14 consecutive days. However, 14 days of treatment with 26 mg/kg/day by minipump or injection produced an initial 50% suppression of 24-hr alcohol intake with the gradual development of tolerance. An acute challenge with Nx immediately after the pumps were scheduled to be empty provided additional evidence of tolerance development in chronically Nx-treated rats. Brain micro-opiate receptors, estimated autoradiographically by using the ligand [3H][D-Ala2,N-Me-Phe4, Gly-ol5][tyrosyl-3,5-3H]-enkephalin, showed that rats chronically exposed to Nx and showing tolerance to Nx suppression of drinking exhibited 17% to 250% increases in [3H][D-Ala2,N-Me-Phe4, Gly-ol5][tyrosyl-3,5-3H]-enkephalin binding. CONCLUSIONS: High doses of Nx are required to suppress continuous access alcohol consumption in P rats, and tolerance develops to the ethanol consumption-suppressing effect of Nx that may be related to increases in micro-opiate receptors.     

Responding for Oral Ethanol after Naloxone Treatment by Alcohol-Preferring AA Rats

The present study examined the effect of a relatively nonselective opioid antagonist, naloxone, on lever pressing for oral ethanol by the alcohol-preferring AA rats. The AAs, housed continually in operant chambers with free access to food and water, learned to respond for 10% oral ethanol during daily 60-min alcohol access periods indicated by a stimulus light. The rats developed stable ethanol responding, resulting in mean ethanol intakes of 1.2 g/kg/60 min and measurable blood alcohol levels. In the first experiment, single systemic injections of naloxone (0.05–2.5 mg/kg) had no effect on the initial rate of responding; dose-dependent decreases were observed later during the alcohol access. The second experiment examined the effects of repeated injections of 0.5 and 2.5 mg/kg naloxone on 5 consecutive days. Naloxone suppressed responding dose-relatedly over the treatment days. In contrast to the effects of single injections, repeated injections with 2.5 mg/kg naloxone produced progressive decreases within the first minutes of access. The results suggest that naloxone may attenuate the reinforcing actions of ethanol.     

The effect of wine or beer versus a carbonated soft drink, served at a meal, on ad libitum energy intake

BACKGROUND: Alcoholic beverage drinking may increase total energy intake at a meal by various mechanisms and this effect may depend on the sort of beverage. OBJECTIVE: To test the effect of wine, beer and a soft drink served with a normal meal on food and total energy intake in non-obese men. DESIGN: A supper meal consisting of three consecutive dishes was presented to 22 young men. Ad libitum energy intakes (EI) of the meal were measured at three different occasions in a cross-over design with red wine, lager beer or a carbonated soft drink. This was done in two studies with different design. In the first study the beverages were supplied ad libitum and in a second study the intake of the beverages was fixed: beer and soft drink at 9 ml/kg body weight and wine isoalcoholic to beer, 3.185 ml/kg body weight. RESULTS: In the ad libitum beverage study total EI was higher with wine than with the soft drink and beer (P<0.05). In the fixed beverage study differences in total EI did not reach statistical significance (P=0.14), although the intake of goulash was higher with wine and beer than with the soft drink (P<0.005). CONCLUSION: These data indicate that alcoholic beverages, and wine in particular, may enhance total EI at a meal relative to a soft drink, when served with no restriction.     

Nicotine modulates alcohol-seeking and relapse by alcohol-preferring (P) rats in a time-dependent manner

Background: Alcohol is frequently co‐abused with smoking. In humans, nicotine use can increase alcohol craving and consumption. The objectives of the current study were to assess the acute effects of nicotine on alcohol seeking and relapse at 2 different time points. Methods: Adult female alcohol‐preferring (P) rats were trained in 2‐lever operant chambers to self‐administer 15% ethanol (EtOH) (v/v) and water on a concurrent fixed‐ratio 5–fixed‐ratio 1 (FR5‐FR1) schedule of reinforcement in daily 1‐hour sessions. Following 10 weeks of daily 1‐hour sessions, rats underwent 7 extinction sessions, followed by 2 weeks in their home cages. Rats were then returned to the operant chambers without EtOH or water being present for 4 sessions (Pavlovian Spontaneous Recovery [PSR]). Rats were then given a week in their home cage before being returned to the operant chambers with access to EtOH and water (relapse). Nicotine (0, 0.1, 0.3, or 1.0 mg/kg) was injected subcutaneously immediately or 4 hours prior to PSR or relapse testing. Results: Injections of nicotine immediately prior to testing reduced (5 to 10 responses PSR; 50 to 60 responses relapse), whereas injections of nicotine 4 hours prior to testing increased (up to 150 responses for PSR; up to 400 responses for relapse with 1.0 mg/kg dose) responses on the EtOH lever during PSR and relapse tests. Conclusions: The results of this study demonstrate that acute effects of nicotine on EtOH‐seeking and relapse behaviors may be time dependent, with the immediate effects being a result of nicotine possibly acting as a substitute for EtOH, whereas with a delay of 4 hours, priming effects of nicotine alterations in nicotinic receptors, and/or the effects of nicotine’s metabolites (i.e., cotinine and nornicotine) may enhance the expression of EtOH‐seeking and relapse behaviors.     

Effects of ethanol exposure on subsequent acquisition and extinction of ethanol self-administration and expression of alcohol-seeking behavior in adult alcohol-preferring (P) rats: II. Adult exposure

Background In a preceding study, we reported that ethanol (EtOH) consumption during periadolescence in alcohol‐preferring (P) rats produced significant effects on the acquisition, extinction, Pavlovian spontaneous recovery (PSR), and reacquisition of operant self‐administration of EtOH. The objective of the present study was to determine if EtOH consumption during adulthood produced similar effects on subsequent operant behaviors. Methods Adult female P rats (>135 days of age) were given 24 hr free‐choice access to 15% EtOH for 30 days or were similarly housed and received water only. After a 15 day period of no EtOH access and without any prior training, adult alcohol drinking and adult alcohol‐naïve rats were placed in standard two‐lever (15% EtOH and water) chambers to examine acquisition of EtOH self‐administration. After stable responding was established on a concurrent fixed ratio (FR) 5 FR1 schedule for EtOH versus water, the P rats underwent extinction training for nine sessions. After extinction and a 2 week home cage period (with no operant sessions or access to EtOH), rats were returned to the operant chambers in the absence of reward for seven consecutive sessions to test for PSR. After PSR testing, animals were maintained in their home cage for a week, before being reintroduced to the operant chambers and allowed to respond for EtOH and water. Results Both the adult alcohol‐drinking and adult alcohol‐naïve groups rapidly acquired EtOH self‐administration, expressed a pronounced PSR, which was augmented by EtOH priming and the presence of a discriminative stimulus (odor cue), and increased responding when EtOH was reinstated. Adult pre‐exposure to EtOH did not alter any of the operant measures. Conclusions The results of this study suggest that, unlike the results with EtOH pre‐exposure during periadolescence, chronic alcohol drinking by P rats in adulthood did not produce sufficient long‐lasting changes in neuronal function to alter subsequent operant acquisition of alcohol self‐administration, alcohol relapse, or alcohol‐seeking behavior.     

Limited Access Alcohol Drinking in High- and Low-Alcohol Preferring Selected Lines of Mice

BACKGROUND: Selection studies and genetic analyses of drinking behavior in rodents often involved unlimited access to alcohol over a period of weeks, with water and food freely available. Most studies investigating the pharmacology of alcohol drinking, on the other hand, use procedures in which access to alcohol is limited to a particular time each day. Reconciliation of findings between these two conditions likely depends on their sharing common genetic mechanisms as indicated, for example, by covariation in response to selection. To this end, high- and low-alcohol preferring (HAP and LAP, respectively) mice, selected for differences in 24-hr access alcohol drinking over a 4-week period, were subjected to a limited access alcohol drinking protocol. METHODS: During 2-hr sessions, mice had access to various concentrations of alcohol (7-15%, v/v) in the home cage for 2 hr a day, with ad libitum access to food and water. Additional sessions were conducted with no food present. RESULTS: Although both strains consumed alcohol and water during these sessions, HAP mice drank far more alcohol than did LAP mice. HAP but not LAP mice drank alcohol at a high rate early in the session compared with later in the session. Additionally, HAP mice responded to changes in alcohol concentration, whereas LAP mice did not. Removal of food did not influence alcohol drinking, although water drinking decreased following food removal. HAP mice reached appreciable blood alcohol concentrations after limited access. CONCLUSIONS: These findings indicate that in these selectively bred mice, alcohol drinking during limited and unlimited access may be genetically related, and that drinking during limited access sessions in HAP mice is likely for the pharmacological properties of alcohol.     

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.     

Moderate Alcohol Consumption Does Not Augment Bone Density in Ovariectomized Rats

Moderate levels of alcohol consumption have been reported to have a beneficial effect on bone mineral density in postmenopausal women. The objective of this study was to examine the effect of a moderate level of alcohol consumption on bone density in a rigorously controlled animal model of osteoporosis. Ovariectomized and nonovariectomized rats were placed on standard lab pellets with free access to deionized water ad libitum. Alcohol-treated animals were given 0.38 g/kg of alcohol daily by intubation in the mid-afternoon and free access to standard lab pellets for 6 weeks. The amount of the alcohol solution was calculated daily to give the human equivalent of 2 glasses of wine/day. Pair-fed control animals were given, on the following day, an equal volume of the diet consumed by individual ethanol-fed rats. They received daily intubation solutions, with the ethanol replaced by isocaloric and isovolumetric amounts of maltose-dextrin. Chow-fed control animals received no intubations and were given access to standard lab pellets ad libitum. Ovariectomized animals had increased weight and decreased femur density and bone volume per total volume. They also had decreased total trabecular area, trabecular area, and number, as well as increased trabecular separation. Significant differences were found between the ovariectomized and nonovariectomized animals in the parameters under discussion, but there were no differences between diet groups. No beneficial effects were found after daily alcohol treatments.     

Naltrexone Treatment Increases the Aversiveness of Alcohol for Outbred Rats

Acute naltrexone treatments (0.0, 0.5, 1.0, or 3.0 mg/kg body weight) were administered to separate groups of rats and alcohol taste reactivity and consumption were measured. Rats were given daily naltrexone injections and then tested for taste reactivity to 10% alcohol 30 and 60 min after injection. Each reactivity trial (total of 4) was 60 sec during which 1 ml of fluid was infused. The rats' orofacial and body movements were videotaped and scored later. In the final measure, rats were placed on a restricted fluid access schedule and given naltrexone treatments 10 min before being presented with the 10% alcohol solution in the home cage (60–min drinking period). After 4 days of consumption tests under the drug condition, the rats were given 4 more daily tests without the drug. Results indicated that the two highest naltrexone doses significantly decreased ingestive responding and increased aversive responding, particularly at the 30–min test. Both the 1.0 and 3.0 mg/kg body weight doses also significantly decreased alcohol consumption as measured during the free access tests. Alcohol consumption returned to control levels immediately after the drug treatments were stopped. The data show that dosages of naltrexone 1.0 mg or higher significantly alter both alcohol taste reactivity (increased aversiveness and decreased palatabil-ity) and alcohol consumption (decreased intake) in outbred rats. These results are discussed in relation to naltrexone treatment as a means for decreasing alcohol use and abuse.     

Influence of age at drinking onset on long-term ethanol self-administration with deprivation and stress phases

BACKGROUND: Onset of alcohol use during adolescence has potentially long-lasting consequences, e.g., prospective alcohol dependence. To obtain new insight into the effects of early chronic ethanol consumption, we compared the drinking behavior of two adult male Wistar rat groups: one that initiated alcohol consumption during adolescence (adolescent group) and the other that initiated their drinking during adulthood (adult group) in a model of long-term alcohol self-administration. We investigated the magnitude of the effects of deprivation and stress on alcohol intake and the influence of these events on the alcohol drinking behavior across time. METHODS: Heterogeneous Wistar rats aged 31 days (adolescents) and 71 days (adults) were given ad libitum access to water, as well as 5% and 20% ethanol solutions during an observation period of 30 wk. A deprivation phase of 14 days was instituted after eight wk of access to alcohol. After 16 and 26 wk of alcohol access, all animals were subjected for three consecutive days to forced swimming and electric foot shocks, respectively. RESULTS: At the onset of drinking, adolescent animals consumed less alcohol and showed lower preference than adults. The deprivation phase was followed by increased intake of highly concentrated ethanol solution without appreciable differences between age groups. Repeated swim stress produced a slight increase in ethanol consumption in both animal groups; however, alcohol intake was not significantly different between groups, whereas the foot shock stress-induced increase in alcohol intake was significantly higher in the animal group that initiated alcohol consumption during adolescence. After swim stress, the drinking behavior of the adolescent group resembled that of the adult group. In particular, the adolescent group increased their preference for 20% ethanol solution for the remainder of the experiment. CONCLUSIONS: Age of voluntary alcohol drinking onset does not appear to be a strong predictor for prospective alcohol intake and relapse-like drinking behavior under the present experimental conditions. However, male Wistar rats that initiated alcohol consumption during adolescence seem to be more susceptible to acute stressor-specific effects in terms of alcohol consumption.     

Persistent escalation of alcohol drinking in C57BL/6J mice with intermittent access to 20% ethanol

Background: Intermittent access (IA) to drugs of abuse, as opposed to continuous access, is hypothesized to induce a kindling‐type transition from moderate to escalated use, leading to dependence. Intermittent 24‐hour cycles of ethanol access and deprivation can generate high levels of voluntary ethanol drinking in rats. Methods: The current study uses C57BL/6J mice (B6) in an IA to 20% ethanol protocol to escalate ethanol drinking levels. Adult male and female B6 mice were given IA to 20% ethanol on alternating days of the week with water available ad libitum. Ethanol consumption during the initial 2 hours of access was compared with a short‐term, limited access “binge” drinking procedure, similar to drinking‐in‐the‐dark (DID). B6 mice were also assessed for ethanol dependence with handling‐induced convulsion, a reliable measure of withdrawal severity. Results: After 3 weeks, male mice given IA to ethanol achieved high stable levels of ethanol drinking in excess of 20 g/kg/24 h, reaching above 100 mg/dl blood ethanol concentrations, and showed a significantly higher ethanol preference than mice given continuous access to ethanol. Also, mice given IA drank about twice as much as DID mice in the initial 2‐hour access period. B6 mice that underwent the IA protocol for longer periods of time displayed more severe signs of alcohol withdrawal. Additionally, female B6 mice were given IA to ethanol and drank significantly more than males (ca. 30 g/kg/24 h). Discussion: The IA method in B6 mice is advantageous because it induces escalated, voluntary, and preferential per os ethanol intake, behavior that may mimic a cardinal feature of human alcohol dependence, though the exact nature and site of ethanol acting in the brain and blood as a result of IA has yet to be determined.     

Increase in Alcohol Intake,Reduced Flexibility of Alcohol Drinking,and Evidence of Signs of Alcohol Intoxication in Sardinian Alcohol‐Preferring Rats Exposed to Intermittent Access to 20% Alcohol

Background: This study assessed in Sardinian alcohol‐preferring (sP) rats a procedure known to promote alcohol drinking and based on the intermittent (once every other day) access to 2 bottles containing alcohol (20%, v/v) and water, respectively (Wise, 1973). Methods: To this end, sP rats were exposed – under the 2‐bottle choice regimen – to: (i) 10% (v/v) alcohol with continuous access (CA10%; i.e., the procedure under which sP rats had been selectively bred); (ii) 10% (v/v) alcohol with intermittent access (IA10%); (iii) 20% (v/v) alcohol with continuous access (CA20%); (iv) 20% (v/v) alcohol with intermittent access (IA20%; the “Wise” condition) (Experiment 1). Additional experiments assessed the influence of (i) adulteration with quinine of the alcohol solution (Experiment 2) and (ii) concurrent presentation of a saccharin solution (Experiment 3) on alcohol drinking under the CA10% and IA20% conditions. Finally, it was assessed whether alcohol drinking under the CA10% and IA20% conditions resulted in motor incoordination at the Rota‐Rod task, as a possible sign of alcohol intoxication (Experiment 4). Results: Daily alcohol intake markedly escalated in rats exposed to the IA20% condition, averaging 9.0 g/kg (in comparison with the average intake of 6.5 g/kg in the CA10% rat group). CA20% and IA10% rats displayed intermediate values of daily alcohol intake between those of CA10% and IA20% rats. Alcohol intake was virtually abolished by addition of quinine or by concurrent presentation of the saccharin solution in CA10% rats; conversely, alcohol intake in IA20% rats was only partially affected by gustatory aversion or concurrent presentation of an alternative reinforcer. Finally, alcohol intake in IA20%, but not in CA10%, rats resulted in clear motor‐incoordinating effects. Conclusions: These data suggest that the “Wise” procedure is effective in inducing marked increases in alcohol intake in sP rats. These increases are associated with a reduced flexibility of alcohol drinking (suggesting the development of “behavioral” dependence) and produce signs of alcohol intoxication that are not detected when sP rats are exposed to the more conventional CA10% condition.     

Motivation for Alcohol Becomes Resistant to Quinine Adulteration After 3 to 4 Months of Intermittent Alcohol Self‐Administration

Background: Continued consumption of alcohol despite deleterious consequences is a hallmark of alcoholism and represents a critical challenge to therapeutic intervention. Previous rat studies showed that enduring alcohol self‐administration despite pairing alcohol with normally aversive stimuli was only observed after very long‐term intake (>8 months). Aversion‐resistant alcohol intake has been previously interpreted to indicate pathological or compulsive motivation to consume alcohol. However, given the time required to model compulsive alcohol seeking in previous studies, there is considerable interest in developing more efficient and quantitative rodent models of aversion‐resistant alcohol self‐administration. Methods: Outbred Wistar rats underwent 3 to 4 months or approximately 1.5 months of intermittent, home‐cage, two‐bottle access (IAA) to 20% alcohol (v/v) or water. Then, after brief operant training, the effect of the bitter‐tasting quinine (0.1 g/l) on the motivation to seek alcohol was quantified via progressive ratio (PR). Motivation for quinine‐adulterated 2% sucrose under PR was assayed in a separate cohort of 3 to 4 months IAA rats. The effects of quinine on home‐cage alcohol consumption in IAA rats and rats with continuous access to alcohol were also examined. Finally, a dose–response for quinine taste preference in IAA and continuous‐access animals was determined. Results: Motivation for alcohol after 3 to 4 months IAA, measured using an operant PR procedure, was not altered by adulteration of alcohol with 0.1 g/l quinine. In contrast, after 3 to 4 months of IAA, motivation for sucrose under PR was significantly reduced by adulteration of sucrose with 0.1 g/l quinine. In addition, motivation for alcohol after only approximately 1.5 months IAA was significantly reduced by adulteration of alcohol with 0.1 g/l quinine. Furthermore, home‐cage alcohol intake by IAA rats was insensitive to quinine at concentrations (0.01, 0.03 g/l) that significantly reduced alcohol drinking in animals with continuous access to alcohol. Finally, no changes in quinine taste preference after 3 to 4 months IAA or continuous access to alcohol were observed. Conclusions: We have developed a novel and technically simple hybrid operant/IAA model in which quinine‐resistant motivation for alcohol is evident after an experimentally tractable period of time (3 to 4 months vs. 8 months). Quinine dramatically reduced sucrose and water intake by IAA rats, indicating that continued responding for alcohol in IAA rats despite adulteration with the normally aversive quinine might reflect maladaptive or compulsive motivation for alcohol. This model could facilitate identification of novel therapeutic interventions for pathological alcohol seeking in humans.     

Effects of the triple monoamine uptake inhibitor DOV 102,677 on alcohol-motivated responding and antidepressant activity in alcohol-preferring (P) rats

Background: Concurrent inhibitors of dopamine, norepinephrine, and serotonin uptake have been proposed as novel antidepressants. Given the high comorbidity between alcoholism and depression, we evaluated the activity of DOV 102,677 (DOV) on alcohol‐maintained responding and performance in the forced swim test (FST), a model of antidepressant (AD) activity, using alcohol‐preferring (P) rats. Methods: Following training to lever press for either alcohol (10% v/v) or sucrose (3, 2%, w/v) on a fixed‐ratio 4 (FR4) schedule, DOV (1.56 to 50 mg/kg; PO) was given 25 minutes or 24 hours prior to evaluation. The effects of DOV (12.5 to 50 mg/kg; PO) in the FST were evaluated 25 minutes posttreatment. Results: DOV (6.25 to 50 mg/kg) dose‐dependently reduced alcohol‐maintained responding by 59 to 88% at 25 minutes posttreatment, without significantly altering sucrose responding. The reduction in alcohol responding (44% at 50 mg/kg) was sustained for up to 120 hours after a single dose. Administration of a single dose of DOV (25, 50 mg/kg) 24 hours before testing suppressed alcohol responding for 48 hours by 59 to 62%. DOV (12.5 to 50 mg/kg) also dose‐dependently reduced immobility of P rats in the FST. Conclusions: DOV produces both prolonged and selective reductions of alcohol‐motivated behaviors in P rats. The elimination kinetics of DOV suggests that its long duration of action may be due to an active metabolite. DOV also produced robust AD‐like effects in P rats. We propose that DOV may be useful in treating comorbid alcoholism and depression in humans.     

Effects of ethanol exposure on subsequent acquisition and extinction of ethanol self-administration and expression of alcohol-seeking behavior in adult alcohol-preferring (P) rats: I. Periadolescent exposure

Background The current study examined the effects of ethanol (EtOH) drinking during periadolescence on the subsequent acquisition and extinction of operant self‐administration of EtOH and expression of alcohol‐seeking behavior in adult alcohol‐preferring (P) rats to test the hypothesis that alcohol drinking during periadolescence produces enduring alterations that enhance the reinforcing properties of EtOH. Methods Periadolescent female P rats were given 24 hr free‐choice access to 15% (v/v) EtOH starting at postnatal day (PND) 30 and ending on PND 60 or were similarly housed and received water only. On PND 75, without any prior training, periadolescent alcohol‐drinking and periadolescent alcohol‐naïve rats were placed in standard two‐lever (15% EtOH and water) chambers to examine acquisition of EtOH self‐administration with a fixed ratio (FR) 1 schedule of reinforcement. After the acquisition phase and after stable responding was established on an FR5 for EtOH and FR1 for water, P rats underwent extinction training for both EtOH and water rewards. After extinction training and a 2 week home cage period, rats were returned to the operant chambers in the absence of reward for seven consecutive sessions (Pavlovian spontaneous recovery). After this testing period, animals were maintained in their home cage for a week before being returned to the operant chambers and allowed to respond for EtOH and water (reacquisition). Results Compared with periadolescent alcohol‐naïve rats, periadolescent alcohol‐drinking rats acquired EtOH responding sooner (i.e., in the first acquisition session), displayed a greater resistance to extinguish EtOH responding (i.e., higher levels of responding in sessions 4–6), had higher responding for more sessions on the EtOH lever in the absence of reward after a prolonged home cage rest period, and had a more prolonged elevated level of EtOH responding during reacquisition (four sessions versus one session). Conclusions Overall, the results suggest that periadolescent EtOH drinking by P rats produced long‐lasting alterations in the reinforcing effects of alcohol, which increased the likelihood that alcohol drinking would be initiated in adulthood, decreased the likelihood that once adult alcohol drinking began it could be extinguished easily, and increased the potential for relapse.