Thyrotropin Releasing Hormone Analog TA-0910 Suppresses Alcohol Intake in Alcohol Drinking African Green Monkeys

In previous studies, we found that single injections of the thyrotropin-releasing hormone analog TA-0910 dose-dependently reduced alcohol intake and preference in alcohol-preferring (P) and Fawn-Hooded (FH) rats over a 24-hr period of continuous access to alcohol and water. However, several consecutive daily injections of TA-0910 resulted in the development of tolerance to these effects. In the present study, we found that in a 5-hr limited-access schedule in which monkeys could select an aqueous alcohol solution (7.5% v/v) or tap water, single doses of TA-0910 (0.0625, 0.125, 0.25, 0.5, and 0.75 mg/kg), similar to those found effective in P and FH rats, reduced consumption of alcohol. In this protocol, tolerance to the attenuating effects of TA-0910 on alcohol intake was not evident after five consecutive once-daily doses of 0.5 mg/kg. Furthermore, it was shown that a single dose of 0.75 mg/kg TA-0910 did not significantly influence 24-hr water intake when water was the only available fluid, but did reduce the intake of a preferred solution of saccharin. These findings suggest that activation of brain thyrotropin-releasing hormone systems reduces alcohol intake in primates and that tolerance to this effect is not evident within 5 days under a limited access schedule.     

Effects of MDL 72222, a serotonin3 antagonist, on operant responding for ethanol by alcohol-preferring P rats

BACKGROUND: Previous studies indicated that, under continuous access conditions, the 5-HT3 antagonist MDL 72222 (MDL) effectively reduced ethanol drinking of alcohol-preferring P rats. However, MDL was without effect when similar doses were tested under scheduled access conditions, unless the ethanol access period was randomly presented. This study examined the effects of MDL on operant responding for ethanol and water by adult male alcohol-preferring P rats. METHODS: During the dark cycle, subjects in the first experiment were trained to respond concurrently for 15% ethanol and water on a fixed-ratio 5 (FR-5) and FR-1 schedule of reinforcement, respectively. Approximately 30 min before the 4-hr operant session, rats were injected subcutaneously (sc) with saline or MDL (1, 3, or 5 mg/kg). A second experiment tested the effects of 1 mg/kg MDL on operant responding for 15% ethanol in 1-hr sessions when operant access was given at a fixed time each day (fixed scheduled access, FSA group) or at variable time periods throughout the dark cycle (variable scheduled access, VSA group). RESULTS: In the first experiment, only the 5 mg/kg dose of MDL decreased responding for ethanol (approximately 20%) during the first 30 min of the 4-hr session. This dose also reduced total 4-hr responding for ethanol and water. In the second experiment, the 1 mg/kg dose of MDL had no effect on operant responding by the FSA group, but significantly reduced ethanol responding by the VSA group. CONCLUSIONS: These results suggest that 5-HT3 receptors may be involved in mediating the reinforcing effects of ethanol, and that temporal-environmental cues associated with the presentation of ethanol may be one factor involved in reducing the effectiveness of 5-HT3 antagonists to attenuate ethanol intake.     

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.     

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.     

Herbal remedies for alcoholism: promises and possible pitfalls

This review summarizes the findings of the effects on alcohol intake in alcohol-preferring rats of extracts or purified compounds from two of the most promising herbs: kudzu (Pueraria lobata) and St. John's Wort (Hypericum perforatum). It is a summary of a symposium presented at the 2002 RSA meeting in San Francisco. The meeting organizers/co-chairs were David Overstreet and Wing-Ming Keung. The presentations were (1) Introduction to the symposium, by David Y. W. Lee and David H. Overstreet; (2) Effects of daidzin on alcohol intake-search for mechanisms of action, by Wing-Ming Keung; (3) Long-term suppressive effects of puerarin on alcohol drinking in rats, by David Overstreet and David Y. W. Lee; (4) St. John's Wort extract reduces alcohol intake in FH and P rats, by Amir Rezvani and David Overstreet; and (5) extracts reduce alcohol intake in Marchigian Sardinian alcohol-preferring rats, by Maurizio Massi.     

Hypericum perforatum CO2 extract and opioid receptor antagonists act synergistically to reduce ethanol intake in alcohol-preferring rats

BACKGROUND: Hypericum perforatum extracts attenuate ethanol intake in alcohol-preferring rats. The opioid receptor antagonists, naloxone and naltrexone, reduce ethanol intake in rats and humans. The combination of different agents that reduce ethanol intake has been proposed as an approach to the pharmacotherapy of alcoholism. This study evaluated the effect on ethanol intake of the combined administration of a CO2 H. perforatum extract and naloxone or naltrexone in genetically selected Marchigian Sardinian alcohol-preferring rats. METHODS: Ten percent (v/v) ethanol intake was offered 2 hr per day at the beginning of the dark phase of the reverse light-dark cycle. H. perforatum CO2 extract was given intragastrically, 1 hr before access to ethanol. Naloxone or naltrexone was given by intraperitoneal injection 10 min before the extract. RESULTS: H. perforatum CO2 extract reduced ethanol intake at 31 or 125 mg/kg, but not 7 mg/kg. These doses neither modified food or water intake during access to ethanol, nor reduce 0.2% saccharin intake. Naloxone reduced ethanol and food intake at 3 or 5 mg/kg, but not 1 mg/kg. When naloxone 1 mg/kg was combined with the three doses of H. perforatum CO2 extract, the attenuation of ethanol intake was more pronounced than that observed after the administration of the extract alone. Alcohol intake was also significantly reduced by 7 mg/kg of H. perforatum CO2 extract combined with naloxone 1 mg/kg. The combined treatments never modified the rat's locomotor activity nor the simultaneous intake of food, water or 0.2% saccharin. Naltrexone reduced ethanol intake at 1 and 3 mg/kg, but not at 0.5 mg/kg. When naltrexone 0.5 mg/kg was combined with H. perforatum CO2 extract 7 mg/kg, ethanol intake was markedly reduced. CONCLUSIONS: These findings provide evidence that H. perforatum CO2 extract and opiate receptor antagonists act synergistically to induce a pronounced and selective reduction of voluntary ethanol consumption in alcohol-preferring rats.     

Alcohol Self-Administration in a Nonrestricted Access Situation with Alcohol-Preferring (P) Rats

Genetic variables have been implicated as contributing factors in the development of alcoholic behavior. Rats bred selectively for alcohol preference have been used in laboratory studies to investigate the role of such variables. In the present study, rats from the alcohol preferring (P) line were placed in operant chambers in which food pellets, water, and 10% ethanol (v/v) were available continuously for 23 hr/day. Food pellets (45 mg) were presented on an FR 1 schedule of reinforcement, while ethanol was presented in a 0.1 ml dipper on an FR 4 schedule of reinforcement. Water was available in a drinking tube with licks monitored by a drinkometer. Data were analyzed in terms of both total daily intakes and computer defined bouts. The P rats showed greater daily ethanol intakes compared with Long-Evans (LE) animals previously studied under similar access conditions. The major difference in intake was a result of the P rats having a greater number of daily ethanol drinking bouts, while having only a slight increase in individual bout size. These data indicate that genetic selection for ethanol preference may result in the regulation of ethanol intake by means of changes in the frequency of ethanol drinking bouts but not by changes in bout size.     

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.     

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.     

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

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

Attenuation of Alcohol Preference in Alcohol-Preferring Rats by a Novel TRH Analogue, TA-0910

Experiments were performed to characterize the acute effect different doses of a novel thyrotropin-releasing hormone (TRH) analogue (TA-0910) on ethanol intake in rats. Selectively bred alcohol-preferring (P) rats received a single intraperitoneal injection of normal saline or 0.083, 0.25 and 0.75 mg/kg of TA-0910 at 9:30 AM, and their consumption of ethanol, water, and food was measured for hr. TA-0910 dose-dependently attenuated ethanol intake and commensurately increased water consumption. Only the highest dose TA-0910 increased the total caloric intake. TA-0910 did not affect the pharmacokinetics of ethanol. These findings indicate involvement of TRH systems in ethanol preference and suggest that centrally acting TRH analogues may be therapeutic in the treatment of alcoholism.     

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.     

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.     

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

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

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.     

Effects of Manipulating Food Availability on Ethanol Self-Administration by P Rats in a Continuous Access Situation

Male rats from the alcohol-preferring (P) line were housed in operant chambers in which food, water, and ethanol (10% v/v) were available continuously 23 hr per day. Over a period of weeks, the fixed ratio (FR) requirement for food reinforcement was gradually increased from FR 1 to FR 64. The response requirements for water and ethanol remained constant throughout the experiment. As the FR requirement for food reinforcement increased, the total number of food-reinforced responses increased significantly, whereas the total number of food pellets delivered per day and total calories per day decreased significantly. Conversely, ethanol intake (g/kg) and the percentage of total calories from ethanol increased significantly as the response requirement for food reinforcement increased. The increase in ethanol intake was accounted for largely by an increase in the number of ethanol drinking bouts per day rather than an increase in the number of dippers presented per bout. The results support the hypothesis that the manipulation of environmental variables, such as FR requirement for food reinforcement, can influence the ethanol self-administration of P rats; an effect observed previously with nonselected Long-Evans rats.     

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 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.     

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

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

Consumption of Sweet, Salty, Sour, and Bitter Solutions by Selectively Bred Alcohol-Preferring and Alcohol-Nonpreferring Lines of Rats

To determine whether selective breeding for high or low oral ethanol consumption is associated with different preferences for nonpharmacological solutions with various flavors, the oral intake of a range of concentrations of sucrose (0.5–64.0 g/100 ml), NaCl(0.025–3.2 g/100 ml), citric acid (0.008–2.048 g/liter), and sucrose octaacetate (0.002–0.512 g/liter) was studied in alcohol-preferring (P) and alcohol-nonpreferring (NP) rats. Separate groups of 7–8 rats from each line were tested for consumption of each of the four flavors. The flavored solutions were presented continuously with water and food always available, and the concentrations were doubled every 48 hr. Although rats from both lines showed a strong preference for the sucrose solutions, P rats consumed greater amounts than NP rats [F(7,98) = 5.57, p < 0.001], Rats of the P line drank less of the NaCl solutions than NP rats [F(7,98) = 3.88, p < 0.0011], but the effect was not as robust as the line differences seen with sucrose. The P and NP rats did not differ in citric acid or sucrose octaacetate intake at any of the concentrations tested. Selective breeding for high oral ethanol preference appears to be positively associated with consumption of sweet solutions and negatively associated with intake of salty solutions.