Behavioral Consequences of Repeated Nicotine During Adolescence in Alcohol-Preferring AA and Alcohol-Avoiding ANA Rats

Background: Epidemiological studies suggest that exposure to nicotine at adolescent age is associated with increased potential to use alcohol and that genetic predisposition may further increase the risk. The present study addressed adolescent vulnerability to repeated nicotine exposure and its influence on subsequent ethanol self‐administration by investigating interactions between nicotine‐induced behavioral sensitization and voluntary ethanol consumption in alcohol preferring AA (Alko Alcohol) and alcohol nonpreferring ANA (Alko Non‐Alcohol) rat lines selected for differential ethanol intake. Methods: Adolescent and adult rats received 10 injections of nicotine (0.5 mg/kg s.c.), given every second day from postnatal day (Pnd) 27 and 75, respectively. Nicotine‐induced (0.5 mg/kg) locomotor activity was measured acutely after the first injection, and after the repeated treatment with nicotine on Pnds 52 and 86 in the adolescent groups and on Pnd 99 in the adult groups. After this, acquisition of voluntary ethanol (10% v/v) consumption as well as nicotine‐induced (0.5 mg/kg) ethanol intake was measured in the AA rats. Results: Adolescent AA rats were more sensitive than adolescent ANA rats to the locomotor effects of nicotine. They were also stimulated more than adult AA rats, but such a difference was not found among ANA rats. Adolescent and adult rats did not differ in their susceptibility to nicotine‐induced behavioral sensitization. Genetic predisposition to ethanol self‐administration did not interact with development of behavioral sensitization in either adolescents or adults. Acquisition of ethanol intake was enhanced in the adolescent groups relative to the adult groups in a manner that was independent of the nicotine treatment. An increase in ethanol intake was found after challenging animals with nicotine, and this effect was enhanced in the nicotine‐treated adolescent group. Conclusions: These findings provide no or little support for the views that adolescent animals are more sensitive to the neurobehavioral effects of repeated exposure to nicotine and that exposure to nicotine in adolescence may contribute to enhanced vulnerability to ethanol abuse. Furthermore, genetic predisposition to high or low ethanol self‐administration does not seem to be a factor that influences individual vulnerability to the neurobehavioral effects of repeated administration of nicotine.     

Naltrexone Blocks Acquisition of Voluntary Ethanol Intake in Rats

The effects of naltrexone (NTX) on the acquisition of ethanol drinking was assessed in rats. NTX (0, 2.5, 5.0, or 10.0 mg/kg) was administered to rats presented with an ascending series of ethanol concentrations (2%, 4%, 6%, and 8% v/v) and water. The 2.5 and 10 mg/kg doses of NTX attenuated the acquisition of voluntary drinking of 8% ethanol, but the 5.0 mg/kg dose of NTX had no effect on ethanol intake. The acquisition paradigm was repeated in experiment 2 with naïve animals that received 0, 5.0, or 7.5 mg/kg of NTX. Neither dose of NTX affected ethanol intake, preference for alcohol, or water intake. Total fluid intake was suppressed in the NTX groups, but only on the second presentations of the 2% and 6% concentrations of ethanol. We suggest that the 2.5 and 10 mg/kg doses of NTX may have attenuated the acquisition of ethanol drinking by at least two different behavioral mechanisms.     

Strain differences in alcohol-induced neurochemical plasticity: a role for accumbens glutamate in alcohol intake

Background: Repeated alcohol administration alters nucleus accumbens (NAC) basal glutamate content and sensitizes the capacity of alcohol to increase NAC extracellular glutamate levels. However, the relevance of alcohol‐induced changes in NAC glutamate for alcohol drinking behavior is under‐investigated. Methods: To examine the relationship between genetic variance in alcohol consumption and alcohol‐induced neuroadaptations within the NAC, in vivo microdialysis was conducted in the alcohol‐preferring C57BL/6J (B6) and alcohol‐avoiding DBA2/J (D2) mouse strains on injections 1 and 8 of repeated alcohol treatment (8 × 2 g/kg, IP). To confirm an active role for NAC glutamate in regulating alcohol drinking behavior, the glutamate reuptake inhibitor dl ‐threo‐β‐benzyloxyaspartic acid (TBOA) (300 μM) and the Group 2 metabotropic glutamate autoreceptor agonist (2R,4R)‐4‐aminopyrrolidine‐2,4‐dicarboxylate (APDC) (50 μM) were infused into the NAC of B6 and D2 mice prior to alcohol consumption in a 4 bottle‐choice test. Results: While strain differences were not apparent for NAC basal levels of dopamine, serotonin or γ‐amino butyric acid (GABA), repeated alcohol treatment elevated NAC basal glutamate content only in B6 mice. Strain differences in both the acute and the sensitized neurochemical responses to 2 g/kg alcohol were observed for all neurotransmitters examined. While the alcohol‐induced rise in NAC dopamine and glutamate levels sensitized in B6 mice, a sensitization was not observed in D2 animals. Moreover, B6 mice exhibited a sensitized serotonin and GABA response to alcohol followed repeated treatment, whereas neither tolerance nor sensitization was observed in D2 animals. An intra‐NAC APDC infusion reduced alcohol intake in both B6 and D2 mice by approximately 50%. In contrast, TBOA infusion elevated alcohol intake selectively in B6 mice. Conclusions: These data indicate an active role for NAC glutamate in regulating alcohol consumption in mice and support the hypothesis that predisposition to high alcohol intake involves genetic factors that facilitate alcohol‐induced adaptations in glutamate release within the NAC.     

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.     

Tolerance to ethanol's ataxic effects and alterations in ethanol-induced locomotion following repeated binge-like ethanol intake using the DID model

Background: Tolerance to the behavioral and subjective effects of alcohol (ethanol) is thought to be a major predictive factor for the development of alcoholism. Evidence from rodent models has supported this view with those animals most likely to develop tolerance generally drinking and preferring ethanol more so than those resistant to it. Despite this evidence, very little is known about the behavioral relationships between ethanol‐induced tolerance and consumption. The goal of this study was to evaluate the development of tolerance to the ataxic effects of ethanol using a mouse model of binge‐like intake dubbed “Drinking in the Dark” (DID; Physiol Behav 2005, 84:53–63). We hypothesized that mice would become tolerant to the ataxic effects of ethanol as this behavior is known to be altered at the blood ethanol concentrations reached using this model (≥80 mg/dl). Methods: To evaluate this, we gave daily DID ethanol or water access sessions to male C57BL/6J (B6) mice and monitored ataxia (and in some cases locomotion) at various time points. Results: In general, mice given 14 consecutive days of ethanol access displayed tolerance to the ataxic effects of ethanol compared to water‐drinking controls. These effects were coupled with alterations in locomotor behavior and in some cases differences in ethanol pharmacokinetics. Conclusions: Thus, we can conclude that tolerance to the behavioral effects of binge‐like ethanol intake might play a key role in the daily maintenance of this behavior and that these effects may be evidence of important neuroadaptations involved in the development of alcoholism.     

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.     

Ethanol and sucrose seeking and consumption following repeated administration of the GABA(B) agonist baclofen in rats

BACKGROUND: Baclofen, a GABA(B) agonist, has been found to decrease alcohol craving in humans and to nonselectively decrease ethanol intake in some rodent models. This experiment assessed the effects of repeated administration of baclofen on reinforcer seeking and consumption using the sipper tube appetitive/consummatory model of ethanol access. METHODS: Subjects were divided into 2 groups and trained to make 30 lever press responses that resulted in access to either 10% ethanol or 2% sucrose in a sipper tube-drinking spout for 20 minutes. Three doses of baclofen were tested (0.3, 1.0, and 3.0 mg/kg) and each drug treatment was assessed using the following schedule: Monday, saline; Tuesday to Thursday, baclofen; and Friday, saline. RESULTS: The low dose of baclofen had no effect on the seeking or intake of either sucrose or ethanol, and the 1.0 mg/kg dose also had no effect on the appetitive, seeking response. However, the 1.0 mg/kg dose significantly decreased sucrose intake (from an average of 0.56 to 0.41 g/kg) and significantly increased ethanol intake (from an average of 0.77 to 1.00 g/kg). Similarly, the high dose (3.0 mg/kg) decreased sucrose intake and had a tendency to increase ethanol intake while decreasing both sucrose seeking and ethanol seeking. CONCLUSIONS: Overall, baclofen treatment affected reinforcer intake at doses that had no effect on reinforcer seeking, and effective doses decreased both sucrose seeking and ethanol seeking. Moreover, the effects on reinforcer intake were disparate, in that baclofen increased ethanol drinking and decreased sucrose drinking. The nonspecific effects of baclofen suggest that the GABA(B) system may be involved in general consummatory or drinking behaviors and does not appear to specifically regulate ethanol-motivated responding.     

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.     

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.     

Drug challenges reveal differences in mediation of stress facilitation of voluntary alcohol drinking and withdrawal-induced anxiety in alcohol-preferring P rats

BACKGROUND: There is controversy over whether exposure to stress precipitates relapse and/or increases alcohol (ethanol) intake. Our laboratory has demonstrated that repeated stress prior to withdrawal from a brief forced exposure to alcohol results in withdrawal-induced anxiety-like behavior. Because anxiety is often regarded as a precipitating factor in relapsing alcoholics, we decided to examine the consequences of stressing alcohol-preferring P rats on both voluntary alcohol drinking and withdrawal-induced anxiety. METHODS: P rats were subjected to 3 cycles of 5 days of voluntary alcohol drinking and 2 days of deprivation. Restraint stress (60 min) was applied to some animals during the first and second deprivations/withdrawals (at 4 h). Drugs (flumazenil, buspirone, SB242,084, CP154,526, CRA1000, naloxone, haloperidol, olanzapine, naloxone, and haloperidol) were given to some rats 30 min prior to restraint stress. RESULTS: Stressed, deprived P rats exhibited both a longer duration of elevated alcohol drinking and anxiety-like behavior in the social interaction test upon withdrawal after the third cycle of voluntary alcohol drinking. When given prior to each of the restraint stresses, the benzodiazepine receptor antagonist flumazenil (5 mg/kg), the corticotrophin releasing factor receptor antagonists CRA1000 (3 mg/kg) and CP154,526 (10 mg/kg), the serotonin 5-HT(1A) receptor partial agonist buspirone (0.6 mg/kg), and the mixed 5-HT(2C)/D2 receptor antagonist olanzapine were effective in reducing the increased duration of elevated alcohol drinking and the withdrawal-induced anxiety-like behavior. In contrast, while the opiate receptor antagonist naloxone (20 mg/kg), the 5-HT(2C) receptor antagonist SB242084 (3 mg/kg), and the dopamine receptor antagonist haloperidol (0.1 mg/kg) also reduced drinking, they did not significantly alter anxiety like behavior. CONCLUSION: These results suggest that stress-induced facilitation of alcohol drinking and withdrawal-induced anxiety-like behavior in P rats may be closely but imperfectly linked.     

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.     

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.     

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.     

Effects of Pregnanolone and Dehydroepiandrosterone on Ethanol Intake in Rats Administered Ethanol or Saline during Adolescence

Background: Adolescent alcohol use may contribute to long‐term changes in the receptors and neuroactive steroids that may mediate its effects and to subsequent alcohol abuse and dependence as an adult. Therefore, in this study, ethanol preference and intake as an adult were examined after adolescent ethanol or saline administration. In addition, ethanol intake in the same groups was examined after administration of 2 neuroactive steroids with modulatory effects at GABA_A receptors. Methods: Two groups of male Long‐Evans rats were administered 15 intraperitoneal (i.p.) injections of either ethanol (2 g/kg, 20% v/v) or saline between postnatal days 35 and 63. Starting on postnatal day 75, both groups were trained to consume 10% ethanol using a saccharin‐fading procedure, and ethanol intake and preference were measured after a series of manipulations involving food deprivation, changes in the duration of access to ethanol, and changes in the concentrations of ethanol presented. Following these manipulations, pregnanolone (1 to 10 mg/kg) and dehydroepiandrosterone (DHEA, 1 to 100 mg/kg) were administered prior to preference sessions with an 18% ethanol solution. Results: Adult ethanol preference and intake did not differ significantly in subjects treated with either saline or ethanol as adolescents during training, the substitution of other ethanol concentrations (3.2 to 32%), ad‐lib feeding, or moderate food deprivation. Pregnanolone administration altered the intake of both adolescent‐treated groups after the first injection of 3.2 mg/kg and after repeated injections with 10 mg/kg, a dose that produced sedation. In contrast, multiple doses of DHEA consistently decreased intake of an 18% ethanol concentration in both groups after repeated injections and 3 doses of DHEA (10, 32, and 56 mg/kg) administered with various ethanol concentrations dose‐dependently shifted the ethanol‐concentration curves for the volume and dosage of ethanol consumed downward. Conclusions: These results indicate that chronic intermittent ethanol (CIE) administration of 2 g/kg during adolescence did not alter preference or overall consumption of ethanol in outbred rats trained to drink ethanol as an adult under the conditions tested, and that DHEA may be more effective than pregnanolone at significantly decreasing ethanol consumption.     

Suppression of Alcohol Intake after Administration of the Chinese Herbal Medicine, NPI-028, and Its Derivatives

The Chinese herbal medicine, NPI-028, has been used for centuries in China to counteract alcohol intoxication. The present study used a number of different experimental conditions to determine whether NPI-028 and its derivatives might selectively influence alcohol intake in rodents that naturally exhibit high alcohol intakes. It was determined that intraperitoneal (IP) injections of NPI-028 (0.5, 0.75, and 1.0 g/kg) suppressed alcohol intake by up to 30% in both alcohol-preferring P and Fawn-Hooded (FH) rats during a continuous access schedule. These injections did not significantly affect food or water intakes, nor did the highest dose of NPI-028 (1 g/kg) alter blood ethanol levels after an IP injection of 2.5 g/kg of ethanol. In P rats, it was found that NPI-028 was orally active with the dose of 1.5 g/kg having a greater effect on ethanol intake than the 1.0 g/kg dose; once again, food and water intakes were not significantly altered. In FH rats maintained on a limited access schedule (1 hr/day), alcohol intake was completely abolished by 1.5 g/kg of NPI-028. Chronic IP administration of NPI-028 (0.75 g/kg) for four consecutive days in FH rats maintained on a continuous access schedule did not lead to any diminution of its alcohol-suppressant effects. Thus, NPI-028 has significant effects on alcohol intake without much effect on water and food intake, and tolerance does not readily develop to these effects. The IP administration of a partially purified extract (NPI-031) of NPI-028, obtained by countercurrent chromatography, also dose-dependently suppressed ethanol intake in FH rats, but the highest dose (200 mg/kg) also significantly decreased food intake. Finally, the IP administration of puerarin (NPI-31G), an isoflavone isolated from NPI-031 by countercurrent chromatography, significantly reduced ethanol intake in FH rats without affecting food or water intake. Therefore, NPI-028 and one of its pure components, NPI-031G, selectively reduced ethanol intake in alcohol-preferring rats.     

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.     

Consistent, high-level ethanol consumption in pig-tailed macaques via a multiple-session, limited-intake, oral self-dosing procedure

Background:  Alcohol abuse is a major public health burden that can lead to many adverse health effects such as impaired hepatic, gastrointestinal, central nervous system and immune system function. Preclinical animal models of alcohol abuse allow for experimental control over variables often difficult to control in human clinical studies (e.g., ethanol exposure before or during the study, history of other drug use, access to medical care, nutritional status, etc). Nonhuman primate models in particular provide increased genetic, anatomic and physiologic similarity to humans, relative to rodent models. A small percentage of macaques will spontaneously consume large quantities of ethanol; however, most nonhuman primate models of "voluntary" ethanol intake produce relatively low daily ethanol intake in the majority of monkeys.
Methods:  To facilitate study of chronic exposure to high levels of ethanol intake, a macaque model has been developed that induces consistent, daily high-level ethanol consumption. This multiple-session procedure employed 4 drinking sessions per day, with sessions occurring once every 6 hours.
Results:  The group average alcohol consumption was 4.6 g/kg/d (SEM 0.4), roughly twice the group average consumption of previous reports. Ethanol drinking sessions produced group mean blood ethanol levels of 95 mg/dl after 60 minutes, and fine motor control was impaired up to 90 minutes after a drinking session.
Conclusion:  This model of multiple-session, limited access, oral ethanol self-dosing produced consistent, high-level ethanol consumption with each session qualifying as a "binge" drinking session using the definition of "binge" provided by the NIAAA (>80 mg/dl/session). This model of ethanol drinking in macaques will be of great utility in the study of immunological, physiological and behavioral effects of ethanol in nonhuman primates.     

Effect of Pentylenetetrazole on Ethanol Intake, Ethanol Kinetics, and Social Behavior in Male Wistar Rats

Stress and anxiety are often implicated in excessive alcohol use. The nature of this interaction, however, is not understood. The aim of this study was to examine the effect of the anxiogenic agent, pentylenetetrazole (PTZ), on the acquisition and maintenance of ethanol drinking behavior in male Wistar rats. In rats maintained on a limited access procedure, with a choice between a 12% w/v ethanol (ETOH) solution and water available for 30 min each day, acute PTZ administration (1.5 to 15.0 mg/kg) did not modify ETOH intake. Chronic PTZ administration elicited a significant suppression in ETOH intake; however, this effect developed gradually over time. During the acquisition phase, chronic PTZ treatment also suppressed ETOH consumption. Chronic, but not acute, treatment with PTZ seemed to enhance water consumption. To assess whether the effect of PTZ on ETOH intake was due to either alterations in ETOH kinetics or behavior, blood ETOH levels and social interaction behaviour were examined. PTZ (15.0 mg/kg) produced a significant suppression in social interaction behavior, although tolerance developed to this effect on chronic PTZ administration. Both acute and chronic PTZ treatment (15 mg/kg) resulted in lower blood ETOH levels achieved after administration of 1.0 g/kg po of ETOH. Because the anxiogenic effect of PTZ was not maintained on repeated administration, yet the suppression of ETOH intake was only observed after chronic treatment, this suggests a dissociation between the processes regulating these behaviors.     

Drinking typography established by scheduled induction predicts chronic heavy drinking in a monkey model of ethanol self-administration

Background: We have developed an animal model of alcohol self‐administration that initially employs schedule‐induced polydipsia (SIP) to establish reliable ethanol consumption under open access (22 h/d) conditions with food and water concurrently available. SIP is an adjunctive behavior that is generated by constraining access to an important commodity (e.g., flavored food). The induction schedule and ethanol polydipsia generated under these conditions affords the opportunity to investigate the development of drinking typologies that lead to chronic, excessive alcohol consumption. Methods: Adult male cynomolgus monkeys (Macaca fascicularis) were induced to drink water and 4% (w/v in water) ethanol by a Fixed‐Time 300 seconds (FT‐300 seconds) schedule of banana‐flavored pellet delivery. The FT‐300 seconds schedule was in effect for 120 consecutive sessions, with daily induction doses increasing from 0.0 to 0.5 g/kg to 1.0 g/kg to 1.5 g/kg every 30 days. Following induction, the monkeys were allowed concurrent access to 4% (w/v) ethanol and water for 22 h/day for 12 months. Results: Drinking typographies during the induction of drinking 1.5 g/kg ethanol emerged that were highly predictive of the daily ethanol intake over the next 12 months. Specifically, the frequency in which monkeys ingested 1.5 g/kg ethanol without a 5‐minute lapse in drinking (defined as a bout of drinking) during induction strongly predicted (correlation 0.91) subsequent ethanol intake over the next 12 months of open access to ethanol. Blood ethanol during induction were highly correlated with intake and with drinking typography and ranged from 100 to 160 mg% when the monkeys drank their 1.5 g/kg dose in a single bout. Forty percent of the population became heavy drinkers (mean daily intakes >3.0 g/kg for 12 months) characterized by frequent “spree” drinking (intakes >4.0 g/kg/d). Conclusion: This model of ethanol self‐administration identifies early alcohol drinking typographies (gulping the equivalent of 6 drinks) that evolve into chronic heavy alcohol consumption in primates (drinking the equivalent of 16 to 20 drinks per day). The model may aid in identifying biological risks for establishing harmful alcohol drinking.     

Long-term sensitization to the activation of cerebral delta-opioid receptors by the deltorphin Tyr-D-Ala-Phe-Glu-Val-Val-Gly-NH2 in rats exposed to morphine.

In experiments to evaluate responses to the activation of cerebral delta-opioid receptors, repeated daily injection of the selective delta-opioid agonist Tyr-D-Ala-Phe-Glu-Val-Val-Gly-NH2 ([D-Ala2]deltorphin II) into rat brain resulted in the development of tolerance, whereas repeated daily injection or continuous infusion of morphine resulted in sensitization to the behavioral activating effects of the delta-opioid agonist. Although the rats did not modify their spontaneous locomotor activity after morphine withdrawal, they became markedly hyperresponsive to the locomotor and stereotypy-producing effects of a challenge dose of the delta-opioid agonist. Sensitization to activation of delta-opioid receptors persisted for at least 60 days after discontinuing morphine treatment. These results show that the development of tolerance and long-term sensitization to opioids involves delta-opioid as well as mu-opioid receptors.