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.     

Genetic Selection for High and Low Alcohol Consumption in a Limited-Access Paradigm

BACKGROUND: Several rat lines have been bred for their differences in alcohol consumption based on a continuous-access paradigm in which alcohol solution is available 24 hr/day. The limited-access paradigm (LAP), in which access to alcohol solution is restricted to a short period per day, however, has been used extensively to investigate the neurochemical mechanisms underlying alcohol consumption. There is evidence of possible differences in genetic determination of alcohol drinking in a continuous- versus limited-access condition. For these reasons, selective breeding for high- and low-alcohol consumption (HARF and LARF, respectively) based on a LAP was conducted. METHODS: N/Nih rats were used as the breeding stock. A within-family breeding procedure was used to develop HARF and LARF lines with 10 families per line. Access to alcohol solution was restricted to 20 min/day. Alcohol was provided as 3%, 6% and 12% w/v solutions. Average intake of alcohol during the 12% phase was used as the selection criterion. Inbreeding began in the seventh generation. RESULTS: After the sixth generation of selection, rats from the HARF line consumed an average of 1.2 g/kg, whereas rats from the LARF line consumed an average of 0.6 g/kg of alcohol during the 20-min access period. Alcohol consumption remained stable over the next eight generations of inbreeding. In the continuous-access-drinking paradigm, the HARF and LARF rats consumed an average of 5.5 to 7.0 g/kg and 1.0 to 2.0 g/kg of alcohol per day respectively. An estimated heritability of 0.25 was obtained. CONCLUSIONS: These findings indicate that alcohol drinking in the LAP is influenced by genetic factors. Differences in alcohol drinking in the LAP also generalize to continuous access drinking. These rat lines will be very useful for investigations into the genetic and neurochemical mechanisms underlying alcohol drinking.     

Thyrotropin-Releasing Hormone Analog TA-0910 Reduces Voluntary Alcohol Intake of P Rats Subchronically in a Limited Scheduled Access Paradigm

We previously reported that single intraperitoneal injections of the thyrotropin-releasing hormone analog TA-0910 dose-dependently reduce alcohol intake in alcohol-preferring (P) rats in a free-choice continuous access protocol. We later showed, using the same protocol, that a transient tolerance develops to this effect after several consecutive, once-daily injections. In the present study, P rats that had been accustomed to continuous access to alcohol were acclimated to a limited scheduled access protocol in which alcohol was available only between 10 and 11 AM. This resulted in an elevated rate of alcohol intake. Rats were then injected once daily with TA-0910 (0.75 mg/kg) or an equal volume of a saline vehicle at 9:45 AM for 12 consecutive days. After 11 days of scheduled access, rats were allowed continuous access to alcohol. Intake of alcohol and water was measured each day at 11:00 AM. Compared with vehicle, TA-0910 reduced alcohol intake on the 11 days of scheduled access and during the first hour of day 12 when continuous access was restored, but did not reduce total (24 hr) alcohol intake on day 12. Data from this experiment show that TA-0910 reduces alcohol intake over a long period of time in a limited scheduled access protocol.     

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.     

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.     

Effects of stress on alcohol consumption in rats selectively bred for high or low alcohol drinking

BACKGROUND: Stress has long been thought to influence the initiation and maintenance of alcohol drinking in humans. However, results of studies in animals suggest that the relationship between stress and alcohol drinking is not well understood. The purpose of this study was to examine the effect of unpredictable and uncontrollable restraint stress on alcohol consumption in two sets of rat lines selectively bred for alcohol preference (P) and high alcohol drinking (HAD1) and for alcohol nonpreference (NP) and low alcohol drinking (LAD1). METHODS: Male P (n = 26) and NP (n = 26) and HAD1 (n = 17) and LAD1 (n = 20) rats were counterbalanced on the basis of alcohol intake and assigned, in matched pairs, to either a stress (Stress) or a no-stress (Control) group. All rats were given a free choice between a 10% v/v alcohol solution and water, with food freely available. Unpredictable, uncontrollable stress, which consisted of immobilization in a nylon restraint sleeve for 30 to 120 min/day, was applied for 10 consecutive days. RESULTS: Stress moderately reduced alcohol intake in both P and HAD1 rats versus controls and had no effect on alcohol intake in either the NP or the LAD1 rats during the 10 days of stress application. Alcohol intake was increased for the first 5 days after stress termination in P rats but not in HAD1 rats. Alcohol intake remained stable for several weeks in both the NP and LAD1 lines after stress termination and then increased during the last 15 days of the 35-day poststress period in NP rats, but not in LAD1 rats. CONCLUSIONS: A reduction in alcohol intake during stress in rats with a genetic predisposition toward high alcohol intake seems to be a moderate but consistent finding, whereas an increase in alcohol intake after stress termination is less consistent and may be influenced by genetic background.     

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.     

Evaluation of Lactational Parameters after Alcohol Administration for Four Days during Early or Midlactation in the Rat

This study was conducted to examine the effects of alcohol administered for 4 days during early lactational (days 5 to 8; experiment I) or midlactational (days 9 to 12; experiment II) stage in the rat on various lactational parameters. Litter size was adjusted to eight on day 2, and dams were implanted with an atrial catheter on day 3 (experiment I) or day 7 (experiment ll). From days 5 to 8 in experiment I and days 9 to 12 in experiment II, dams were infused with saline (control rats) or alcohol in saline solutions (1.0 and 2.0 g/kg body weight; experimental groups). Blood alcohol levels (BALs) achieved after infusion of the initial doses were maintained for 4 hr daily by continuing infusion. To control for the reduced food intake in the high dose alcohol group, one control group and the group given 1.0 g/kg of body weight alcohol were pair-fed to the 2.0 g/kg body weight alcohol group. On day 8 (experiment I) or day 12 (experiment II), pups were separated from the dam at 0800 hr, and an extension was attached to the catheter. Alcohol or saline was infused, and the BALs achieved after infusion of initial doses were maintained for 4 hr. After removal of a baseline blood sample, pups were returned to dams, and additional blood samples were taken for prolactin measurement 10, 30, 60, and 120 min after suckling started. Suckling latency and milk consumed during the 120 min of suckling were measured. Litters were weighed every other day from days 2 to 21. In both studies, suckling-induced prolactin was inhibited by alcohol. Milk consumed by the pups during the 2-hr period was lower for alcohol groups, compared with control. The suckling latencies were comparable among groups. Litter weights showed no alcohol dose effect. In summary, based on the results from our previous and present studies, we conclude the following: alcohol administered for 1, 4, or 8 days inhibited sucklinginduced prolactin release in lactating rats. During a 2-hr test period after alcohol administration, milk consumed by pups was not adversely affected after alcohol administration for 1 day. Whereas, 4 or 8 days of administration had a significant effect. The adverse effect of alcohol on litter growth, however, was evident only after 8 days of alcohol administration. Thus, the detrimental effects of alcohol on different lactational parameters seem to be correlated to the duration of alcohol administration to dams during lactation.     

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.     

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.     

Additive Reduction of Alcohol Drinking by 5-HT1A Antagonist WAY 100635 and Serotonin Uptake Blocker Fluoxetine in Alcohol-Preferring P Rats

We found previously that alcohol-preferring (P) rats have fewer serotonin (5-HT) neurons and fibers in key brain regions than alcoholnonpreferring (NP) rats. Because 5-HT uptake blockers increase synaptic 5-HT content and 5-HT_1A receptor antagonists increase 5-HT release by disinhibiting 5-HT autoinnervation, in the present study, our intent was to determine whether increased synaptic 5-HT content and/or 5-HT release in P rats would effectively reduce alcohol consumption. In experiment 1, the 5-HT antagonist WAY 100635 (WAY) was tested on adult female P rats maintained on 24-hr free-choice access to ethanol (10% v/v) and water. Twice daily doses of WAY (0.05, 0.1, 0.5, and 1.0 mg/kg, subcutaneously) were administered to each rat in a counterbalanced order. Baseline ethanol intake, derived from the mean ethanol intakes of the three previous non-drug days, was approximately 8 g/kg/day. Results indicated that 0.05,0.1, and 0.5 mg/kg doses of WAY reduced 24-hr ethanol drinking by 25-30% ( p < 0.01) without affecting 24-hr water intake or body weight In the second experiment, the effects of WAY (0.5 mg/kg), fluoxetine (1.0 mg/kg), or a combination of both were tested in another group of female P rats. WAY and fluoxetine, each alone, reduced ethanol drinking by around 20% and, when combined, decreased ethanol intake by 50%, whereas the body weight and the total fluid intake were not significantly affected. Taken together, these results indicate that both fluoxetine and WAY preferentially reduce ethanol drinking in the P line of rats and, when administered together, reduce ethanol intake in an additive manner. It is proposed that coadministration of these two compounds with distinct mechanisms of action may be a new strategy for reducing alcohol intake.     

Effects of topiramate on ethanol and saccharin consumption and preferences in C57BL/6J mice

BACKGROUND: Topiramate has recently been found to be more effective than placebo as an adjunct treatment for alcohol dependence, but it has not yet been investigated in animal models of ethanol consumption. The current experiment examined the effects of topiramate on ethanol drinking in mice using a continuous access, two-bottle choice procedure. METHOD: C57BL/6J male mice were offered a 10% v/v ethanol solution versus tap water over 4 consecutive days per week. Mice were assigned to topiramate (1-50 mg/kg) or saline groups and received injections before the beginning of the dark phase of the light cycle. Topiramate dose increased over 5 successive weeks (1, 5, 10, 25, and 50 mg/kg). Fluid intake was measured 2, 4, and 23 hr after injection. Body weight and food intake were measured at the time of injection. In a second phase, mice were offered saccharin solutions (0.2 and 2.5% w/v) versus tap water after topiramate (50 mg/kg) or saline injections. RESULTS: Results revealed that high topiramate doses (25 and 50 mg/kg) increased water intake and decreased ethanol preference. Compared with saline controls, topiramate produced dose-dependent, bidirectional effects on ethanol dose, with 25 mg/kg of topiramate increasing ethanol dose at 4 and 23 hr after injection but 50 mg/kg topiramate decreasing ethanol dose at 2 hr after injection. During saccharin exposure, topiramate decreased saccharin preference (for 2.5% w/v saccharin solution) and marginally increased water intake but did not directly alter intake of the saccharin solutions. Topiramate had no effects on body weight or daily food intakes. CONCLUSIONS: Topiramate reduced ethanol preference in C57BL/6J mice, but this effect was primarily attributable to elevated water intake. Topiramate also reduced saccharin preference, likely through marginally significant increases in water intake. Increases in water intake and bidirectional effects of topiramate on ethanol dose complicate conclusions with regard to the effects of topiramate on ethanol reward.     

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.     

P rats develop physical dependence on alcohol via voluntary drinking: changes in seizure thresholds, anxiety, and patterns of alcohol drinking

BACKGROUND: It has been proposed that the alcohol-preferring P rat meets many of the criteria for an animal model of alcoholism. However, the development of alcohol dependence has not been explored in rats that self-administer ethanol for less than 15-20 weeks. The present study investigated the development of physical dependence upon alcohol after 2-6 weeks of voluntary alcohol intake. Changes in bicuculline-induced seizure thresholds, microstructure of alcohol drinking, and anxiety-related behavior were used as indices of alcohol dependence. In addition, we evaluated the microstructure of alcohol drinking associated with the development of physical dependence upon alcohol. METHODS: Alcohol (10% ethanol solution) was measured in graduated drinking tubes with both alcohol and water available continuously. Microstructure of alcohol intake was monitored by a computerized drinkometer. Physical dependence upon alcohol was determined by measuring bicuculline-induced seizure thresholds after alcohol withdrawal. Anxiety-related behavior of P rats after alcohol withdrawal was determined by the social interaction and elevated plus maze tests. RESULTS: Initial alcohol intake in the alcohol-preferring P rat was relatively modest (3.9 +/- 0.4 g/kg/day). Four days of forced alcohol exposure (initiation) followed by 6 weeks of voluntary drinking resulted in an increase of alcohol intake to 5.5 +/- 0.2 g/kg/day. Ethanol self-administration for 6 weeks, but not for 2 or 4 weeks, produced a significant reduction (30%; p < 0.05) in bicuculline-induced seizure thresholds during alcohol withdrawal. Alterations in the microstructure of alcohol intake (i.e., 90% increase in the size of alcohol drinking bouts compared to the baseline [p < 0.001] with no change in bout frequency) were associated with the development of alcohol dependence. Termination of alcohol intake after 6 weeks of voluntary alcohol consumption resulted in increased anxiety according to both the social interaction and elevated plus maze tests. CONCLUSIONS: The results of this study indicate that 6 weeks of voluntary alcohol intake are sufficient for the development of physical dependence upon alcohol in the alcohol-preferring P rats as measured by susceptibility to bicuculline-induced seizures. This time is much shorter than the 15-20 weeks reported earlier. Development of physical dependence to alcohol was associated with an increase in daily alcohol intake (40% over the baseline), an increase in alcohol intake during each drinking bout (90% over the baseline), and elevated anxiety during alcohol withdrawal.     

Pattern and Duration of the Inhibitory Effect of Alcohol Administered Acutely on Suckling-Induced Prolactin in Lactating Rats

We have characterized the pattern and duration of the inhibitory effect of acute alcohol administration on suckling-induced prolactin (PRL) release in the lactating rat. On day 2 of lactation, litters were adjusted to eight pups. On day 6, dams were implanted with an atrial catheter and experiments were conducted on day 10 of lactation. Pups were removed from the dams at 0800 hr. An extension tube filled with heparinized saline was attached to the catheter at 1300 hr. At 1400 hr, a preinfusion (PRE 0) blood sample was removed and was followed by infusion of saline (control) or alcohol in saline (0.5, 1.0, 2.0, 2.5 g/kg body weight doses) solutions. Following the removal of a postinfusion (POST 0) blood sample, pups were returned to the mother. Subsequent blood samples were obtained 10, 30, 60, 120, and 180 min after initiation of suckling. In separate groups, the effects of alcohol on basal PRL were studied by collecting blood samples PRE 0, POST 0 and 20, 40, 60, 80, 100, and 120 min following infusion of saline or alcohol in saline to lactating rats also separated from their pups for 6 hr. Alcohol infusion did not alter basal PRL. However, suckling-induced PRL was inhibited at 10, 30, 60, and 120 min of suckling by alcohol administered at doses greater than or equal to 1.0 g/kg body weight. After 180 min of suckling, plasma PRL levels were comparable among groups. The suckling latency for the 2.5 g/kg body weight alcohol group was greater than for other groups, but the quantities of milk consumed during the 3-hr suckling period were comparable.(ABSTRACT TRUNCATED AT 250 WORDS)     

A Small Dose of Morphine Leads Rats to Drink More Alcohol and Achieve Higher Blood Alcohol Concentrations

Male Sprague-Dawley rats were maintained on a daily regimen of 22 hr of fluid deprivation followed by a 2-hr opportunity to take a sweetened alcoholic beverage and water for over 6 months. Durinc the week before the formal procedures of the experiment describee herein, access to the alcoholic beverage was limited to 1.5 hr, but access to water was still for 2 hr. Intakes of ethanol, in terms of g/kg, were tabulated at 30 min for half of the rats and at 90 min for the rest. On the day of formal procedures, half of the rats of the 30- and 90-min measures were given 1 mg/kg of morphine sulfate just before the drinking session, whereas the rest received physiological saline Morphine increased mean g/kg intakes of ethanol, as compared with controls, at 30 and 90 min. Blood alcohol levels were also increased These data suggest that the well-documented ability of small doses of morphine to increase rats' intake of ethanol is probably not related to its ability to produce gastrointestinal effects, but rather due to its ability to modulate central motivational mechanisms associated with ingestion.     

Selective Inhibition of Alcohol Intake in Diverse Alcohol-Preferring Rat Strains by the 5-HT2A Antagonists Amperozide and FG 5974

The present studies sought to elucidate the role of 5-HT_2A receptor antagonists in suppressing alcohol intake by comparing the effects of amperozide and FG 5974 on alcohol, food, and water intake in strains of alcohol-preferring rats: P, Alko Alcohol (AA), and Fawn-Hooded (FH). Both amperozide and FG 5974 have 5-HT_2A receptor antagonist properties, but FG 5974 also shows presynaptic 5-HT_1A receptor agonist activity. After establishment of stable baselines for intake measures in a two-bottle continuous access paradigm, rats ( n = 10) were injected with 1 of 5 doses (0, 1.0, 2.5, 5.0, and 10.0 mg/kg, sc) of amperozide or FG 5974 at weekly intervals. Amperozide dose-dependently reduced alcohol intake, total fluid intake, and alcohol preference in all three strains under continuous access conditions, whereas FG 5974 was less effective. Food intake was also suppressed by amperozide at higher doses, whereas it was increased by FG 5974. Amperozide also dose-dependently reduced alcohol intake when it was available for only 1 hr/day, but FG 5974 tended to increase it. After oral administration, amperozide was also more effective than FG 5974 in reducing alcohol intake. Despite these differences in efficacy in suppressing alcohol intake, both compounds produced taste aversion to a novel saccharin solution. These complex findings suggest that biochemical properties other than 5-HT_2A receptor antagonism (e.g., 5-HT_1A receptor agonism) may be involved in the effects of amperozide and FG 5974 on alcohol intake and other consummatory behaviors.     

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.     

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.     

The α1-Adrenergic Receptor Antagonist, Prazosin, Reduces Alcohol Drinking in Alcohol-Preferring (P) Rats

Background:  Preliminary evidence suggest that noradrenergic signaling may play a role in mediating alcohol drinking behavior in both humans and rats. Accordingly, we tested the hypothesis that blockade of α₁-adrenergic receptors will suppress alcohol drinking in rats selectively bred for alcohol preference (P line).
Methods:  Adult male P rats were given 24-hour access to food and water and scheduled access to a 15% (v/v) alcohol solution for 2 hours daily. Rats were injected IP with the α₁-adrenergic receptor antagonist, prazosin (0, 0.5, 1.0, 1.5, or 2.0 mg/kg body weight), once a day at 15 minutes prior to onset of the daily 2-hour 2-bottle choice, alcohol versus water, access period for 2 consecutive days and then 3 weeks later for 5 consecutive days.
Results:  Prazosin significantly reduced ( p  < 0.01) alcohol intake during the initial 2 daily administrations, and this reduction of alcohol intake was maintained for 5 consecutive days by daily prazosin treatment in the subsequent more prolonged trial ( p  < 0.05). The prazosin-induced reduction of alcohol intake was not dependent upon drug-induced motor impairment since increases in water drinking ( p  < 0.05) were exhibited during the 2-hour access periods during both 2- and 5-day prazosin treatment.
Conclusions:  The results indicate that the noradrenergic system plays a role in mediating alcohol drinking in rats of the P line and suggest that prazosin—a safe, well-characterized, and well-tolerated drug—may be an effective pharmacotherapeutic agent for the treatment of alcohol use disorders.