Blood Ethanol Concentrations in Rats Drinking Sucrose/Ethanol Solutions

BACKGROUND: The addition of sucrose to ethanol solutions results in a substantial increase in ethanol self-administration by rats that are deprived of neither food nor water. However, if sucrose alters ethanol absorption or metabolism, resulting in blood ethanol concentrations (BECs) not different from those resulting from lower intakes of ethanol/water solutions, then the usefulness of sucrose/ethanol mixtures in increasing ethanol consumption is questionable. The present study was conducted to determine whether the addition of sucrose to ethanol solutions altered BECs in an operant self-administration paradigm. METHODS: Tail blood (from male Long-Evans rats) was collected 30 min after the intake of four different solutions, i.e., 5% sucrose/20% ethanol, 5% sucrose/10% ethanol, 2% sucrose/10% ethanol, and 10% ethanol. RESULTS: Ethanol intakes (mean, 1.57+/-0.21 g/kg) and BECs (mean, 78.4+/-9.3 mg/100 ml) were highest when 5% sucrose was added to the ethanol solution. Moreover, the ratios between ethanol intakes and resulting BECs were approximately the same for all solutions. CONCLUSIONS: These findings indicate that, under the conditions of this procedure, the BEC reached is dependent on the amount of ethanol consumed and is not influenced by the addition of sucrose to the solution.     

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.     

Induction and maintenance of ethanol self-administration in cynomolgus monkeys (Macaca fascicularis): long-term characterization of sex and individual differences

BACKGROUND: Investigations of oral ethanol self-administration in nonhuman primates have revealed important parallels with human alcohol use and abuse, yet many fundamental questions concerning the individual risk to, and the biological basis of, excessive ethanol consumption remain unanswered. Moreover, many conditions of access to ethanol in nonhuman primate research are largely unexplored. This set of experiments extends within- and across-session exposure to ethanol to more fully characterize individual differences in oral ethanol self-administration. METHODS: Eight male and eight female adult cynomolgus monkeys (Macaca fascicularis) were exposed to daily oral ethanol self-administration sessions for approximately 9 months. During the first 3 months, a fixed-time (FT) schedule of food delivery was used to induce the consumption of an allotted dose of ethanol in 16-hr sessions. Subsequently, the FT schedule was suspended, and ethanol was available ad libitum for 6 months in 16- or 22-hr sessions. RESULTS: Cynomolgus monkeys varied greatly in their propensity to self-administer ethanol, with sex and individual differences apparent within 10 days of ethanol exposure. Over the last 3 months of ethanol access, individual average ethanol intakes ranged from 0.6 to 4.0 g/kg/day, resulting in blood ethanol concentrations from 5 to 235 mg/dl. Males drank approximately 1.5-fold more than females. In addition, heavy-, moderate-, and light-drinking phenotypes were identified by using daily ethanol intake and the percentage of daily calories obtained from ethanol as criteria. CONCLUSIONS: Cynomolgus monkeys displayed a wide intersubject range of oral ethanol self-administration with a procedure that used a uniform and prolonged induction that restricted early exposure to ethanol and subsequently allowed unlimited access to ethanol. There were sex and stable individual differences in the propensity of monkeys to consume ethanol, indicating that this species will be important in characterizing risk factors associated with heavy-drinking phenotypes.     

Oral Ethanol Self-Administration in Free-Feeding Rhesus Monkeys

The ability of a conditioning procedure to establish oral ethanol self-administration in free-feeding rhesus monkeys was assessed. The conditioning procedure required the monkey to drink an ethanol solution in order to have access to a sweet orange-flavored solution. Following an average of 14 sessions under these conditions, the orange solution was no longer delivered and ethanol solution alone was made available in the sessions. During both the conditioning and the ethanol self-administration portions of the experiment each monkey was required to drink an average of 0.5 g/kg ethanol per session in order to continue in the experiment. Of the nine monkeys exposed to these contingencies, five monkeys continued to self-administer ethanol after the presentation of the orange drink was discontinued. However, two of these five monkeys decreased their ethanol solution intake below 0.5 g/kg within 3 weeks after the conditioning sessions had terminated. The three monkeys that sustained high ethanol intake were male and had histories of drug self-administration, suggesting that gender and drug history may influence the initiation of ethanol self-administration. Once ethanol self-administration was established, concentrations of ethanol from 4 to 15% (v/v) were made available. The monkeys consumed intoxicating amounts of ethanol, as indicated by average intakes ranging from 0.5 to 0.9 g/kg and blood ethanol levels over 100 mg/dl. These results demonstrate that ethanol self-administration can be established and maintained through the initial reinforcement of ethanol consumption by the contingent presentation of another reinforcing stimulus. However, the results of this study also indicate that individual differences may be an important determinant of animals initiating ethanol self-administration.     

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.     

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.     

Schedule-induced ethanol self-administration in DBA/2J and C57BL/6J mice

BACKGROUND: The purpose of these experiments was to provide an initial investigation into ethanol self-administration elicited in the schedule-induced polydipsia (SIP) paradigm. METHODS: Mature male mice were food deprived to between 80 and 85% of their baseline weight and received 20 daily 1 hr SIP test sessions in which a food pellet (20 mg) was delivered on a fixed-time 60 sec schedule. In different groups, the acquisition of drinking 5% (v/v) ethanol solution (experiment 1) or water (experiment 2) was recorded along with other behaviors that occurred in the test chambers. RESULTS: Results indicated that C57BL/6J mice drank significantly more ethanol than DBA/2J mice and that C57 mice achieved blood alcohol concentrations as high as 300 mg/dl. Blood alcohol concentrations were consistently correlated with g/kg ethanol intake. The groups did not differ in consumption of water. SIP test sessions using higher concentrations of ethanol (10-20% v/v, experiment 1) or sucrose solutions (0.1-2% w/v, experiment 2) then were performed. Group differences in ethanol consumption were maintained at all ethanol concentrations. Although DBAs drank more of a low concentration of sucrose (0.1%), when expressed as g/kg, sucrose intake was equivalent in the two strains at all concentrations. Analysis of the time course of drinking clearly showed that this behavior was adjunctive in nature. CONCLUSION: These results demonstrate the effectiveness of this procedure in inducing ethanol self-administration and its utility for investigating the genetic bases of vulnerability toward excessive ethanol consumption.     

Reestablishing an intragastric ethanol self-infusion model in rats

BACKGROUND: There is a scarcity of behavioral models that will reliably produce ethanol intakes in rodents at levels that induce or maintain dependence. The present experiments were designed to reestablish a model that uses passive intragastric (IG) infusion of ethanol to induce tolerance/dependence/withdrawal before allowing rats to self-infuse ethanol intragastrically. METHODS: Sprague-Dawley rats were surgically implanted with IG catheters and allowed to recover. During the passive infusion phase (3-6 days), rats in the experimental group were passively infused with 10% (v/v) ethanol (3.3-12.2 g/kg/d). Rats in the control group were not infused. During the self-infusion phase (5-6 days), all rats had access to 2 flavored solutions. Licks on 1 solution were paired with ethanol infusions (20%, v/v) whereas licks on the other solution were unpaired. Experiments differed in the specific passive infusion parameters and in the ethanol intake limit during self-infusion. RESULTS: Rats in the experimental groups self-infused more ethanol per day (means of 4-7 g/kg/d) than did rats in the control group (means of 0-2.6 g/kg/d). Across all 3 studies, individual total daily intakes exceeded 5 g/kg on 35% of the self-infusion days in ethanol-preexposed rats compared with <1% of the self-infusion days in the control rats. Ethanol-exposed rats also infused a substantially higher percentage (42%) of their total ethanol intake in relatively large bouts (>1.5 g/kg) compared with control rats (<10%). The addition of a daily 6-hour ethanol-free period during the passive infusion phase (in Experiments 2 and 3) led to higher ethanol intakes than in Experiment 1. Results of a control experiment showed that differences between experimental and control groups in Experiments 1 to 3 were a result of ethanol experience and not a general effect of differential infusion experience. CONCLUSIONS: Relatively short periods of passive IG infusion of ethanol induced levels of ethanol self-infusion in genetically heterogeneous rats that were comparable with drinking intakes previously reported in rats selectively bred for ethanol intake/preference. Although the induction of dependence/withdrawal may have played a role in this outcome, an alternative interpretation is that experimental rats self-infused more ethanol because passive exposure produced tolerance to aversive pharmacological effects that would otherwise limit intake of the paired flavor because of development of conditioned taste aversion. The current findings provide a strong basis for future work designed to identify parametric determinants of this form of self-administration, its sensitivity to genetic influences, and its neurobiological substrates.     

Neurokinin type-3 receptor stimulation impairs ethanol-associated appetitive behavior in Wistar rats

OBJECTIVES: Stimulating central neurokinin type-3 (NK-3) receptors decreases ethanol intake in rats. Although paraventricular nucleus of the hypothalamus (PVN) has a high density of NK-3 receptors, their influence on ethanol reinforcement has not been examined. This study's purpose was to assess the effects of intra-PVN infusion of senktide, a NK-3 receptor agonist, on ethanol self-administration. In a follow-up study, senktide's effects on ethanol self-administration after intracerebroventricular (ICV) infusion were examined. METHODS: Male Wistar rats were trained to self-administer 10% ethanol (10E) in the "Sipper Tube" model described by Samson and colleagues, Guide cannula were then aimed bilaterally at the PVN or unilaterally at the lateral cerebral ventricle. Intra-PVN (5-100 ng/side) or ICV (30-500 ng/rat) effects of senktide on 10E self-administration were also examined as a preliminary test of senktide's selectivity. RESULTS: Intra-PVN and ICV infusion of senktide reduced the average number of consecutive lever presses and increased the time taken to complete the lever press requirement when 10E served as the reinforcer. Increased duration of the lever-pressing component was observed when senktide was administered prior to 2S self-administration sessions. Neither PVN nor ICV senktide administration significantly altered 10E or 2S consumption. CONCLUSIONS: These data suggest that stimulation of central neurokinin typ-3 receptors in the Wistar rat reduces appetitive behavior while having little or no impact on consummatory behavior. Ethanol "seeking" appeared more sensitive to disruption by senktide than sucrose "seeking." However, further studies assessing the senktide's effects on sucrose-maintained behavior are needed to verify this hypothesis. Lastly, it is hypothesized that lack of effect of senktide on intake is in part related to the use of outbred Wistar rats in these studies instead of selectively bred rats.     

Sensitivity of Liver Mitochondrial Functions to Various Levels of Ethanol Intake in the Rat

Mitochondrial function appears to be an early target for ethanol toxicity, however it is not clear to what extent the effects of ethanol, which occur at levels of intake lower than those already reported in the literature, can induce an alteration of it. To produce different levels of ethanol intake, the spontaneous consumption of ethanol by genetically low (UChA) and genetically high (UChB) rats, as well as the forced intake obtained by offering 10% v/v ethanol solution as the only source of drinking fluid, were employed. The O2 uptake by liver mitochondria of rats submitted to these conditions in the presence of glutamate + malate, succinate or ascorbate + TMPD, was measured polarographically with a Clark electrode at 25 degrees C. Results indicate that alterations of the hepatic mitochondrial function can be detected at levels of ethanol intake much lower than those previously reported. Whereas, a level of a daily ethanol intake of 2-3 g/kg body weight in UChA rats under free choice was insufficient to produce detectable changes in the mitochondrial function, the latter was decreased in the high ethanol consumers (UChB), which drank 4-5 g/kg per day under free choice conditions, and in both strains forced to drink 10% ethanol as only source of fluid, which produced intakes of about 7 g/kg per day. Therefore, mitochondrial dysfunction may contribute to effects observed even at low levels of ethanol intake.     

Testosterone enhances estradiol's cardioprotection in ovariectomized rats

After menopause, the development of cardiovascular disease (CVD) is due not only to estrogen decline but also to androgen decline. This study examined the effects of either estradiol (E(2)) or testosterone replacement alone or E(2)-testosterone combination on isolated myocytes in ovariectomized (Ovx) rats subjected to ischemia/reperfusion (I/R). Furthermore, we determined whether the effects are associated with β(2)-adrenoceptor (β(2)-AR). Five groups of adult female Sprague-Dawley rats were used: Sham operation (Sham) rats, bilateral Ovx rats, Ovx rats with E(2) 40?μg/kg per day (Ovx+E), Ovx rats with testosterone 150?μg/kg per day (Ovx+T), and Ovx rats with E(2) 40?μg/kg per day+testosterone 150?μg/kg per day (Ovx+E/T). We determined the lactate dehydrogenase (LDH) release, percentage of rod-shaped cells and apoptosis of ventricular myocytes from rats of all groups subjected to I/R. Then, we determined the above indices and contractile function with or without a selective β(2)-AR antagonist ICI 118?551. We also determined the expression of β(2)-AR. Our data show that either E(2) or testosterone replacement alone or E(2) and testosterone in combination decreased the LDH release, increased the percentage of rod-shaped cells, reduced apoptotic cells (%), and combination treatment appeared to be more effective than either E(2) or testosterone replacement alone. ICI 118?551 abolished the effects of the three. Combination supplementation also enhanced the expression of β(2)-AR. We concluded that in Ovx rats, testosterone enhances E(2)'s cardioprotection, while E(2) and testosterone in combination was more effective and the protective effects may be associated with β(2)-AR. The study highlights the potential therapeutic application for CVD in postmenopausal women.     

Effects of Acute and Chronic Doses of Naltrexone on Ethanol Self-Administration in Rhesus Monkeys

The effects of acute and chronic administration of intramuscular naltrexone (0.1, 0.3, 1.0, and 3.0 mg/kg) on oral ethanol (8%) self-administration were examined. Naltrexone (1.0 mg/kg) effects on the self-administration of ethanol concentrations ranging from 0.5 to 8% (w/v) were also investigated. Rhesus monkeys with substantial histories of drug and ethanol drinking served as subjects. During daily 3-hr sessions, monkeys were presented with ethanol solutions, concurrently available with water, under fixed-ratio reinforcement schedules. Naltrexone decreased the consumption of ethanol (g/kg). Biphasic temporal effects were observed within sessions. Naltrexone dose-dependently decreased the number of ethanol deliveries by a maximum of 56% ( n = 18; 3 monkeys × 6 sessions) during the first hour of the session. During the second and third hours, however, ethanol intake recovered such that maximum decreases over the 3-hr session were ∼27% ( n = 18), and the mean decrease was 16% ( n = 18). Often marked tolerance was observed, such that the effects of acute naltrexone administration were greater than effects after chronic administration. The self-administration of low ethanol concentrations (≤2% w/v) was increased in several monkeys, by up to 340%, after naltrexone pretreatment. In summary, the effects of naltrexone on ethanol self-administration, in drug- and alcohol-experienced rhesus monkeys, are not characterized by unitary decreases in measures of ethanol self-administration. Rather, differential naltrexone effects were a function of experimental parameters, including the dose and number of naltrexone injections, the ethanol concentration, and the time point of measurement.     

Effects of Morphine and Naloxone on Ethanol- and Sucrose-Reinforced Responding in Nondeprived Rats

In the following series of experiments, effects of morphine (0.1, 0.3, 1.0, 3.0, and 10.0 mg/kg) and naloxone (0.1, 0.3, and 1.0 mg/kg) were assessed in nondeprived rats trained to leverpress with 10% ethanol, sweetened ethanol, or 5% sucrose and water as the reinforcers. Morphine, at doses of 0.1, 0.3, and 1.0 mg/kg had little effect on responding with ethanol or sweetened ethanol available on a fixed ratio 4 (FR4) schedule of reinforcement, but at the 3.0 mg/kg dose, morphine suppressed responding to near zero. Similar results were obtained when 10% ethanol and water were available on a concurrent FR4 FR4 schedule of reinforcement. When 5% sucrose and water were available concurrently, morphine suppressed responding at 3.0 and 10 mg/kg. Naloxone (0.1, 0.3, and 1.0 mg/kg) decreased responding for ethanol, sweetened ethanol, and sucrose solutions in a dose-dependent manner. Naloxone decreased total number of responses/session by shortening the duration of responding without affecting momentary rate. Overall, the data suggest that the endogenous opioid system plays a role in the ability of ethanol to reinforce operant behavior. However, this role does not appear to be specific to ethanol because similar results were observed with sucrose reinforcement. Failure to find enhanced ethanol intakes following morphine injections in the operant situation suggests that the method used to measure ethanol self-administration makes a difference in assessing the effects of drugs on ethanol 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.     

Involvement of nicotinic receptors in alcohol self-administration

BACKGROUND: Alcohol and nicotine, in the form of tobacco, are commonly co-abused. Nicotinic receptors also have been implicated in alcohol action. We designed the present study to examine the possible involvement of nicotinic receptors in alcohol self-administration. METHODS AND RESULTS: Pretreatment with lower doses (0.1-0.4 mg/kg) of nicotine, administered acutely or chronically, did not affect alcohol consumption, whereas a higher dose (0.8 mg/kg) initially suppressed alcohol consumption but stimulated alcohol consumption on repeated treatment. We observed the same pattern of nicotine effects on alcohol self-administration using an operant procedure. A dose of 0.8 mg/kg of nicotine initially suppressed operant responding for alcohol. Such suppression of alcohol self-administration was more pronounced during the first 20 min of the 60 min operant session. Responding for alcohol in the nicotine treated group, however, was significantly increased above the saline treated group by the 5th day of treatment. Mecamylamine, a noncompetitive nicotinic receptor antagonist, reduced alcohol consumption, whereas dihydro-beta-erythroidine (DHbetaE), a competitive nicotinic receptor antagonist, did not modify alcohol consumption. CONCLUSIONS: The stimulation of alcohol intake induced by nicotine treatment and the suppression of alcohol intake induced by mecamylamine provide evidence for the involvement of nicotinic receptors in alcohol consumption and/or self-administration. The failure of DHbetaE to reduce alcohol consumption, however, suggests that ethanol-nicotine interaction is mediated by other nicotinic receptor subtypes rather than alpha4beta2 receptor subtype, or that mecamylamine acts through a nonnicotinic mechanism.     

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.     

Oral Ethanol Self-Administration in Rhesus Monkeys: Behavioral and Neurochemical Correlates

BACKGROUND: Previous research has revealed that orally administered ethanol serves as a reinforcer in nonhuman primates. The purposes of the present study were to examine the relationship between ethanol preferences and intakes in two distinct self-administration contexts and to reveal some of the behavioral and neurochemical correlates of oral ethanol self-administration in monkeys. METHODS: Three cohorts of 13 to 29 rhesus monkeys (Macaca mulatta) were socially housed and given daily, 1-hr, one-spout access to an ethanol solution (8.4%, w/v) sweetened with aspartame. Twelve of these monkeys were subsequently selected, individually housed, and given daily, 2-hr, two-spout access to a range of ethanol concentrations (0.25-16%, w/v) concurrently with water. RESULTS: These monkeys (National Institute on Alcohol Abuse and Alcoholism group) showed a marked preference for ethanol (0.5-4%, w/v) over water, and ethanol preferences were 3-fold greater than those of a second group of 12 monkeys (University of Michigan group) purchased from a commercial vendor. Ethanol consumption was consistent across the self-administration paradigms. Monkeys that consumed large quantities of ethanol under the one-spout, social-housing conditions continued to drink large quantities of ethanol under the two-spout, individual-housing conditions (r = 0.86). An association between ethanol preferences and intakes was also demonstrated. Monkeys with the greatest preferences for ethanol over water under the two-spout choice conditions consumed the largest quantities of ethanol (r = 0.82). Finally, cerebrospinal fluid 5-hydroxyindoleacetic acid concentrations were inversely related to ethanol preference but not to ethanol intake. CONCLUSIONS: These results indicate that ethanol consumption is stable across contexts and is positively correlated with the preference for ethanol over water.     

Effects of Naltrexone and Ro 15-4513 on a Multiple Schedule of Ethanol and Tang Self-Administration

BACKGROUND: Both the opioid antagonist, naltrexone, and GABAA/benzodiazepine-site negative modulator, Ro 15-4513, decrease ethanol self-administration in rodents and nonhuman primates. However, the selectivity of these drugs for decreasing ethanol self-administration relative to reducing responding maintained by other reinforcers in primates is not clear. The present study used a multiple schedule self-administration procedure in cynomolgus monkeys to examine the selectivity of naltrexone and Ro 15-4513 for reducing ethanol self-administration relative to an orange flavored sugar-free sweetened solution (Sugar-free Tang). METHODS: Six adult cynomolgus monkeys were trained to self-administer 4% (w/v) ethanol and 4% or 6% (w/v) Tang under a multiple schedule of liquid access. The effect of acute administration of naltrexone (0.1, 0.3, 1, 3 mg/kg) was examined. The effect of 15 days of chronic, 1 mg/kg naltrexone on ethanol and Tang self-administration was then examined in four monkeys. Acute administration of Ro 15-4513 (0.01, 0.03, 0.1, 0.3 mg/kg) as well as 15 days of chronic administration of 0.1 mg/kg Ro 15-4513 was also examined in four monkeys. RESULTS: Ethanol and Tang were self-administered at similar volumes and patterns under baseline conditions. Acute naltrexone administration significantly decreased total session ethanol and Tang intake as well as the number and volume of ethanol and Tang drinks. Chronic naltrexone also significantly decreased ethanol and Tang intake. Ethanol, but not Tang, drink volume was significantly decreased by chronic 1 mg/kg naltrexone pretreatment. The number of ethanol and Tang drinks and drink duration were not significantly decreased by chronic naltrexone. Acute Ro 15-4513 pretreatment significantly decreased ethanol and Tang intake, mean drinks and median drink duration. Chronic 0.1 mg/kg Ro 15-4513 pretreatment significantly decreased total ethanol intake only during the first week of pretreatment, but it significantly decreased Tang intake for all 3 pretreatment weeks. CONCLUSIONS: Similar to rodent studies, acute and chronic naltrexone and Ro 15-4513 reduced ethanol and Tang intake in cynomolgus monkeys. However, unlike rodent studies, neither drug showed selectivity for reducing ethanol intake compared with a comparison reinforcer. These differences highlight the need for testing putative ethanol abuse treatment drugs under diverse conditions and multiple species before undertaking human clinical trials.     

Naltrexone Suppresses Ethanol Intake in 6-Hydroxydopamine–Treated Rats

BACKGROUND: The suppressive effect of opioid antagonists, such as naltrexone, on ethanol intake has been suggested to be based on the interference with ethanol-induced stimulation of dopamine release in the nucleus accumbens. The aim of this study was to determine whether reduction of dopamine innervation to the nucleus accumbens with the neurotoxin 6-hydroxydopamine (6-OHDA) alters naltrexone-induced suppression of ethanol consumption. Because the mesolimbic dopaminergic neurons have also been implicated in ethanol reinforcement, the effects of 6-OHDA on the maintenance and acquisition of ethanol intake were also studied. METHODS: To damage accumbal terminals of the mesolimbic dopamine neurons, alcohol-preferring Alko Alcohol (AA) rats were given bilateral injections of 6-OHDA or vehicle into the nucleus accumbens after pretreatment with desipramine and pargyline. The effect of the lesion on the acquisition or maintenance of ethanol self-administration was studied in animals having continual access to ethanol solution (10% v/v) and water. Subsequently the effect of naltrexone on ethanol consumption was determined. RESULTS: Naltrexone (0.03-3.0 mg/kg subcutaneously) suppressed ethanol consumption in a dose-dependent manner both in 6-OHDA-treated and control animals given a daily 90-min access to ethanol solution. When the rats had continual access to ethanol, there was a clear day-to-day decline in ethanol intake during the first 5 days of the 7-day naltrexone treatment (10 mg/kg subcutaneously). 6-OHDA treatment had no effect on either the acquisition or maintenance of ethanol self-administration. Postmortem analysis of the brain dopamine content revealed approximately 92% depletion of dopamine in the nucleus accumbens of the 6-OHDA-treated rats. CONCLUSIONS: The suppressive effect of naltrexone does not depend on naltrexone's interaction with dopaminergic terminals in the nucleus accumbens. Furthermore, the role of the mesolimbic dopamine pathway is probably not central either in the acquisition or maintenance of ethanol self-administration in alcohol-preferring AA rats.     

Increased drinking during withdrawal from intermittent ethanol exposure is blocked by the CRF receptor antagonist D-Phe-CRF(12-41)

BACKGROUND: Studies in rodents have determined that intermittent exposure to alcohol vapor can increase subsequent ethanol self-administration, measured with operant and 2-bottle choice procedures. Two key procedural factors in demonstrating increased alcohol intake are the establishment of stable alcohol self-administration before alcohol vapor exposure and the number of bouts of intermittent vapor exposure. The present studies provide additional behavioral validation and initial pharmacological validation of this withdrawal-associated drinking procedure. METHODS: Studies at 2 different sites (Portland and Scripps) examined the effect of intermittent ethanol vapor exposure (3 cycles of 16 hours of ethanol vapor+8 hours air) on 2-hour limited access ethanol preference drinking in male C57BL/6 mice. Separate studies tested 10 or 15% (v/v) ethanol concentrations, and measured intake during the circadian dark. In one study, before measuring ethanol intake after the second bout of intermittent vapor exposure, mice were tested for handling-induced convulsions (HICs) indicative of physical dependence on ethanol. In a second study, the effect of bilateral infusions of the corticotropin-releasing factor (CRF) receptor antagonist D-Phe-CRF(12-41) (0.25 microg/0.5 microL) into the central nucleus of the amygdala (CeA) on ethanol intake was compared in vapor-exposed animals and air controls. RESULTS: Intermittent ethanol vapor exposure significantly increased ethanol intake by 30 to 40%, and the mice had higher blood ethanol concentrations than controls. Intra-amygdala infusions of D-Phe-CRF(12-41) significantly decreased the withdrawal-associated increase in ethanol intake without altering ethanol consumption in controls. Following the second bout of intermittent vapor exposure, mice exhibited an increase in HICs, when compared with their own baseline scores or the air controls. CONCLUSIONS: Intermittent alcohol vapor exposure significantly increased alcohol intake and produced signs of physical dependence. Initial pharmacological studies suggest that manipulation of the CRF system in the CeA can block this increased alcohol intake.