Ethanol self-administration in ALKO rats: I. Effects of selection and concentration

The ALKO Alcohol Accepting (AA) rats and Alcohol Non-Accepting (ANA) rats were used to study the relationship between ethanol preference in a two-bottle choice paradigm and oral ethanol self-administration in an operant conditioning paradigm. Ethanol served as a positive reinforcer in the preferring AA line. Under a continuous reinforcement schedule (FR 1), ethanol deliveries were consistently greater than water (vehicle) deliveries and varied as an orderly inverted U-shaped function of ethanol concentration. Conversely, in nonpreferring ANA animals, ethanol did not serve as a reinforcer. Findings obtained with the AA rats were compared with those obtained with Sprague-Dawley rats. Sprague-Dawley rats maintained higher levels of responding and greater ethanol intake, relative to AA rats, at all concentrations of ethanol tested. The data are consistent with evidence that genotype is a critical factor in determining the extent to which ethanol serves as a reinforcer. The results also suggest that ethanol preference and the maintenance of ethanol reinforced behavior under operant conditions appear to have some common mechanisms. However, since the selection for ethanol preference in AA rats apparently did not maximize the maintenance of ethanol-reinforced behavior in an operant paradigm, ethanol drinking behavior in the preference paradigm may not be completely generalizable to that observed in the operant model.     

Ethanol polydipsic choice: effects of alternative fluid polydipsic history

Two groups of rats drinking either 5% ethanol or 0.9% NaCl solution under a fixed-time 1-min schedule of food pellet delivery became polydipsic during daily 3-hr sessions. When both fluids were made available to animals during sessions, strong side preferences typically developed so that neither fluid was preferred in spite of the fact that one group had a mild-to-moderate physical dependence on ethanol. The group that drank 0.9% NaCl solution initially failed to acquire a strong 5% ethanol polydipsia when this became the sole available fluid, and special procedures were required to induce an ethanol polydipsia comparable to that of the other group. Hence, a history of 0.9% NaCl solution polydipsia interfered with the institution of chronic, ethanol overdrinking in this group. Equal ethanol intakes were maintained in the groups when a compound solution consisting of 5% ethanol plus 0.9% NaCl solution was available along with a 5% ethanol choice. Whenever a 0.9% NaCl solution was presented in competition with either 5% ethanol or the compound 5% ethanol plus 0.9% NaCl solution, ethanol intake was reduced. Implications for the prevention and amelioration of human ethanol overdrinking are discussed.     

Ethanol drinking in rodents: is free-choice drinking related to the reinforcing effects of ethanol?

Many studies have used voluntary ethanol consumption by animals to assess the influence of genetic and environmental manipulations on ethanol drinking. However, the relationship between home cage ethanol consumption and more formal assessments of ethanol-reinforced behavior using operant and instrumental conditioning procedures is not always clear. The present review attempted to evaluate whether there are consistent correlations between mouse and rat home cage ethanol drinking on the one hand, and either operant oral self-administration (OSA), conditioned taste aversion (CTA), or conditioned place preference (CPP) with ethanol on the other. We also review literature on intravenous ethanol self-administration (IVSA). To collect data, we evaluated a range of genetic manipulations that can change both genes and ethanol drinking behavior including selective breeding, transgenic and knockout models, and inbred and recombinant inbred strain panels. For a genetic model to be included in the analysis, there had to be published data resulting in differences on home cage drinking and data for at least one of the other behavioral measures. A consistent, positive correlation was observed between ethanol drinking and OSA, suggesting that instrumental behavior is closely genetically related to consummatory and ingestive behavior directed at ethanol. A negative correlation was observed between CTA and drinking, suggesting that ethanol's aversive actions may limit oral consumption of ethanol. A more modest, positive relationship was observed between drinking and CPP, and there were not enough studies available to determine a relationship with IVSA. That some consistent outcomes were observed between widely disparate behavioral procedures and genetic populations may increase confidence in the validity of findings from these assays. These findings may also have important implications when researchers decide which phenotypes to use in measuring alcohol-reward relevant behaviors in novel animal models.     

Ethanol oral self-administration and rewarding brain stimulation

The effects of orally self-administered ethanol (ETOH) on responding for rewarding brain stimulation were studied. Bipolar electrodes were implanted in either the lateral hypothalamic region of the medial forebrain bundle (MFB-LH) or the ventral tegmental area (VTA) of 6 male F-344 rats. After surgery subjects were trained in a continuous reinforcement procedure (CRF) for constant current rewarding brain stimulation. On alternate days subjects were allowed to drink an ethanol and sucrose solution (12% and 5%, respectively) for 30 min and subsequently tested on the brain stimulation procedure. All subjects showed facilitation of responding (increase in rate) after ingesting low to moderate doses of ETOH (0.4-1.7 g/kg). Depression of responding (decrease in rate) or return to baseline levels (control solution rate) was observed only in those subjects which ingested 2 g/kg or greater during the drinking period. These results indicate that low to moderate doses of self-administered ethanol will increase responding for rewarding brain stimulation. Further, the results suggest that this facilitation of responding is, at least in part, a function of the method of administration and/or the contingent nature of the ethanol delivery (self-administration).     

Ethanol self-administration in ALKO rats: II. Effects of selection and fixed-ratio size

The ethanol-reinforced behavior of ALKO Alcohol Accepting (AA) rats was studied as a function of fixed-ratio (FR) size (1, 2, 4, 8 and 16) across several ethanol concentrations (8, 16 and 32% w/v). A comparison was also made with ethanol-reinforced behavior of Sprague-Dawley (SD) rats. Ethanol, previously shown to serve as a reinforcer in AA and SD rats, maintained responding in these animals under conditions of intermittent reinforcement. SD rats exhibited higher response rates than AA rats to obtain 8% ethanol concentrations as fixed-ratio size was varied in these experiments. These results confirm that, for AA rats, the selection for preference in a two-bottle choice situation did not include the selection for those biological factors which maximize ethanol-reinforced behavior under conditions of intermittent reinforcement. These experiments suggest the existence of distinct, biologically influenced components of ethanol drinking behavior, and have demonstrated several similarities as well as differences between two-bottle choice preference tests and operant studies of ethanol-reinforced behavior.     

Ethanol drinking patterns in a continuous-access operant situation: effects of ethanol concentration and response requirements.

Rats, initiated to self-administer ethanol with either a sucrose-substitution procedure or a secondary-conditioning procedure, were maintained in a continuous-access environmental system in which operant lever press responses were required to receive 10% ethanol and food reinforcement. Water available from a drinking tube was electronically monitored to detect licks. Total daily consumption and patterns of food, water, and ethanol responding were analyzed under conditions in which the concentration of ethanol presented as a reinforcer was either 10% or 20%, and the response requirement for ethanol reinforcement was either a fixed ratio 4 schedule or a fixed ratio 1 schedule. Either increasing the ethanol concentration or decreasing the response requirement resulted in an increase in total daily ethanol intake. There was no significant difference between initiation procedures. These results are similar to observations in studies using a limited-access operant situation. This increased ethanol intake resulted from a complex alteration in the daily ethanol drinking pattern. The greatest ethanol intakes were observed when both the ethanol concentration was increased and response requirement was decreased. This was predominantly the result of increasing the number of ethanol drinking bouts per day when the response requirement was decreased, and by decreasing individual bout size by less than half when the ethanol concentration was doubled. These studies indicate that concentration of the ethanol presented as the reinforcer and the response cost required for reinforcement are involved in regulating ethanol consumption in the continuous-access condition. Type of initiation did not appear to interact with these variables.     

Ethanol self-administration in Maudsley reactive and Maudsley nonreactive inbred rats.

This study was performed to investigate ethanol self-administration in inbred Maudsley rats, which were selected for differences in stress susceptibility and which often differ in their home cage ethanol consumption. Adult, male, Maudsley reactive (MR/Har) and Maudsley nonreactive (MNRA/Har) rats were tested in a standard protocol for the sucrose-substitution procedure for the initiation of self-administration of ethanol in an operant setting. Before and after initiation for self-administration in the operant setting, rats were tested for home cage consumption of 10% (vol./vol.) ethanol in a two-bottle test for 14 consecutive days. During the sucrose-substitution procedure, MNRA/Har rats consumed more sucrose and ethanol than did MR/Har rats. In addition, MNRA/Har rats self-administered a greater amount of ethanol during a concentration manipulation with the use of a fixed ratio (FR) 4 response requirement. However, both strains self-administered low amounts of 10% ethanol (MNRA/Har, 0.15 g/kg/day; MR/Har, 0.08 g/kg/day) after concentration manipulation compared with those observed in outbred rats and alcohol-preferring rats tested under identical conditions in other studies. Both MR/Har and MNRA/Har rats markedly increased their ethanol intake in the home cage after the initiation protocol, but there was no difference between MR/Har and MNRA/Har on that measure. The failure of MR/Har rats to self-administer ethanol was inconsistent with their home cage drinking in other studies, and this is distinctly different from the self-administration pattern of high-alcohol-drinking rat lines tested in this paradigm.     

Accumbal dopamine concentration during operant self-administration of a sucrose or a novel sucrose with ethanol solution.

The goal of the current study was to determine the effect of operant self-administration of (1) 10% sucrose and (2) a first-time solution of 10% sucrose with 5% or 10% ethanol, on dopamine concentration in the nucleus accumbens. We used an operant procedure that distinguished lever pressing (an appetitive behavior) from drinking to better assess the effect of fluid consumption on accumbal dopamine activity. Male Long-Evans rats were trained to bar press by using 10% sucrose reinforcement, and they were required to emit an escalating number of bar presses across daily sessions. Completion of the response requirement resulted in 20 min of access to the solution. Microdialysis samples were collected before, during, and after bar pressing and drinking, and content of ethanol and dopamine was determined. Dopamine concentration in the dialysate was slightly, but significantly, increased in both groups during lever pressing. However, after consumption began, dopamine concentration increased in the sucrose, but not in the sucrose with ethanol, group, followed by a return to baseline values. Ethanol consumption was low (0.27 +/- 0.02 g/kg) and corresponded to low dialysate ethanol concentrations, which appeared within 5 min of drinking. These results demonstrate that operant self-administration of sucrose increases accumbal dopamine concentration during consummatory phases of behavior, but that a similar increase is not apparent when a novel, perhaps aversive, solution (sucrose with ethanol) is presented. This difference may be due to the sensory-related stimulus properties of each solution. In addition, oral self-administration of ethanol at 0.27 +/- 0.02 g/kg over 20 min is not sufficient for stimulation of dopamine activity in the nucleus accumbens.     

Comparison of the effects of allopregnanolone with direct GABAergic agonists on ethanol self-administration with and without concurrently available sucrose.

Behavioral effects of ethanol are mediated by actions at multiple neurotransmitter receptors and signaling systems; prominent among these is the type A gamma-aminobutyric acid (GABA(A)) receptor. Previous work has shown that the GABAergic neuroactive steroid allopregnanolone enhances ethanol-reinforced instrumental responding in rat. In the current study, we compared the effects of allopregnanolone with the direct GABA(A) agonist muscimol and the direct type B GABA (GABA(B)) agonist baclofen in male Long-Evans rats lever pressing for a 10% ethanol solution in a limited-access procedure. The effects of concurrently available sucrose were also tested to determine the selectivity of these drugs for altering ethanol self-administration when an alternate reinforcer was available. In Experiment 1, we found that presession systemic administration of both muscimol (0.3 and 1 mg/kg) and baclofen (1 and 3 mg/kg) reduced responding for ethanol. In contrast, allopregnanolone (3 and 5.6 mg/kg) enhanced responding for ethanol. In Experiment 2, we found that a 1-mg/kg dose of baclofen reduced responding for ethanol, but not for sucrose, whereas both baclofen and muscimol, administered at a higher dose of 3 mg/kg, decreased both ethanol- and sucrose-reinforced responding. Allopregnanolone, at a dose of 5.6 mg/kg, but not of 3 mg/kg, selectively increased ethanol-reinforced responding, indicating a less robust effect of allopregnanolone on responding within the concurrent reinforcement procedure than that observed when ethanol alone was available. The results support the suggestion that direct agonist action at either the GABA(A) or the GABA(B) receptor decreases ethanol self-administration. Muscimol produces a nonselective decrease in instrumental responding, whereas baclofen may selectively reduce ethanol intake at lower doses, but not higher ones, possibly limiting its potential use for treatment of alcohol abuse in human beings. In contrast, allopregnanolone can selectively enhance ethanol self-administration in the presence of a concurrently available alternate reinforcer, indicating that the direct GABA(A) agonist muscimol and the allosteric GABA(A) modulator allopregnanolone do not produce similar behavioral effects on instrumental responding for ethanol reinforcement.     

Ethanol self-administration in a nonrestricted access situation: effect of ethanol initiation

Two groups of rats (male, Long-Evans) were studied in a continuous access situation, in which ethanol, food and water intake patterns were monitored, 23 h/day. One group of rats was initiated to lever press for ethanol prior to study in the continuous access situation by use of a secondary-conditioning procedure. The other group had no prior initiation. It was found that the ethanol self-administration pattern of the initiated rats was similar to a previous study using another initiation procedure. After four weeks, the noninitiated group also demonstrated an ethanol intake pattern similar to initiated animals. However, the specific nature of individual ethanol drinking bouts in the noninitiated animals was found to be different, suggesting that initiation resulted in larger and more ethanol-drinking bouts. In addition, the noninitiated animals failed to show any home-cage shift in ethanol preference, which is observed after the use of the initiation procedures. The only major difference found between the sucrose-substitution initiation procedure and the secondary-conditioning procedure occurred when response requirements to obtain food were increased. In this situation, ethanol intake increased only in the sucrose-substitution initiated animals. The relation of this finding to the underlying theoretical basis for each type of initiation procedure is discussed.     

One-year drinking history and mortality

The one-year drinking history of 94 men was recorded by recurrent interviews (mean: 20 per person). The cohort was followed for 18.3 years; during that time, 13 men died. Cox's proportional hazards survival models including age and social class as confounders, indicated that mortality was significantly associated with total annual alcohol consumption, frequency of drinking, and frequency of intoxicating drinking. Estimates of risk of death for various consumption levels are presented: For having 10 drinks (each containing 12 grams of pure ethanol) a week vs one drink a week, the estimated relative risk of death (95% confidence limits in parentheses) was 2.3 (1.6-3.3). For being intoxicated once a week vs no intoxications at all during one year the respective risk was 2.1 (1.3-3.1). The risk estimates for the frequency of intoxication were found to be higher than those in an earlier study using single interview data on drinking. This suggests that more accurate measurement of alcohol consumption may yield higher risk of death estimates than found in studies based on single interview data on alcohol.     

Tea components: antimutagenic and anticarcinogenic effects.

BACKGROUND. Tea from the Camellia sinensis species of the Theaceae family is one of the most ancient and, next to water, the most widely consumed beverage in the world. Since tea contains several polyphenols and since several other naturally occurring dietary polyphenols have shown antimutagenic effects in bacteria and anticarcinogenic effects in animal bioassay systems, we studied whether polyphenols extracted from Chinese green tea (GTP) also possess antimutagenic and anticarcinogenic effects. RESULTS. GTP and its constituent epicatechin derivatives were found to interact with hepatic cytochrome P450 (P450) and inhibited the P450-dependent mixed-function oxidase enzymes in skin and liver. GTP and its epicatechin derivatives exhibited antimutagenic effects in several test systems. GTP showed substantial anti-skin-tumor-initiating and anti-skin-tumor-promoting activities when assessed in murine skin tumorigenesis bioassay systems. In these model systems polyaromatic hydrocarbons, benzo[a]pyrene (BP), 3-methyl-cholanthrene, 7,12-dimethylbenz[a]anthracene, and (+)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (an ultimate carcinogenic metabolite of BP) were used as model skin carcinogens. The feeding of GTP in drinking water to SKH-1 hairless mice also afforded significant protection against ultraviolet-B-radiation-induced skin photocarcinogenesis. CONCLUSIONS. These data suggest that tea components possess antimutagenic and anticarcinogenic effects, and that they could protect humans against the risk of cancer by environmental agents.     

Deconstructing the vanilla milkshake: the dominant effect of sucrose on self-administration of nutrient-flavor mixtures

Rats and humans avidly consume flavored foods that contain sucrose and fat, presumably due to their rewarding qualities. In this study, we hypothesized that the complex mixture of corn oil, sucrose, and flavor is more reinforcing than any of these components alone. We observed a concentration-dependent increase in reinforcers of sucrose solutions received (0%, 3%, 6.25%, and 12.5%) in both fixed ratio and progressive ratio procedures, but with equicaloric corn oil solutions (0%, 1.4%, 2.8%, and 5.6%) this finding was replicated only in the fixed ratio procedure. Likewise, addition of 1.4% oil to 3% or 12.5% sucrose increased fixed ratio, but not progressive ratio, reinforcers received relative to those of sucrose alone. Finally, addition of 3% vanilla flavoring did not change self-administration of 3% sucrose or 3% sucrose+1.4% oil solutions. These data suggest that, calorie-for-calorie, sucrose is the dominant reinforcing component of novel foods that contain a mixture of fat, sucrose, and flavor.     

Ethanol and lactation: effects of milk lipids and serum constituents.

To determine how chronic alcohol administration during lactation affects milk composition and the nutritional status of the dam, EtOH (3 g/kg) as a 20% solution was administered by intubation to Sprague-Dawley rats from days 2 through 15 of lactation. Control dams were pair fed to account for the reduction in food intake observed in the alcohol group, while another control group maintained ad lib food intake. Dams and their litters were weighed daily throughout the study. On day 16, dams were sacrificed and samples taken for further analysis. Blood alcohol levels as well as serum levels of calcium, cholesterol, glucose, iron, lipids, phosphorous, and triglycerides were measured. Liver lipid levels and the total composition and fatty acid profile of the phospholipids in milk were also measured. Results indicate that EtOH administration and pair feeding reduced dam body weight, but not litter growth. Serum iron levels was increased in both EtOH-exposed and pair-fed controls, whereas serum cholesterol was elevated only in EtOH-exposed dams. Finally, of the phospholipids in milk, only one, phosphatidylserine, was slightly but significantly increased by EtOH. If and how these changes impact the development of the offspring remain to be studied.     

Ethanol self-administration is genetically independent of locomotor stimulation in fast and slow mice

One substance abuse hypothesis proposes that rewarding effects of drugs are causally related to their psychostimulant effects. We examined this hypothesis by comparing operant self-administration of ethanol in mice selectively bred for either high (Fast) or low (Slow) locomotor stimulation response to ethanol. Mice were trained to lever press for ethanol using postprandial induction and were then tested over a range of conditions to determine the degree of self-administration. There were no significant differences between Fast and Slow mice in either the amount of work produced to obtain ethanol or the amount of ethanol consumed. In general, none of the groups of mice showed robust ethanol-reinforced behavior. This is in contrast with C57BL/6J mice tested concurrently, which showed substantial ethanol-reinforced behavior. Further analysis revealed individual differences in responding within each of the selected lines. However, there was no systematic pattern within or between groups for these individual differences, suggesting that the genes mediating ethanol-reinforced behavior are segregating in a manner independent from genes mediating the locomotor stimulant response to ethanol, and thus, the mechanistic processes mediating reinforcement from ethanol are distinct from those that influence the psychomotor stimulant response to this drug.     

Ethanol drinking in Withdrawal Seizure-Prone and -Resistant selected mouse lines

Withdrawal Seizure-Prone (WSP) and Withdrawal Seizure-Resistant (WSR) mouse lines were bidirectionally selectively bred, respectively, to have severe or mild ethanol withdrawal handling-induced convulsions (HICs) after cessation of 3 days of ethanol vapor inhalation. Murine genotypes with severe withdrawal have been found to show low ethanol consumption, and high consumers show low withdrawal. An early drinking study with WSP and WSR mice showed modest evidence consistent with this genetic correlation, but there were several limitations to that experiment. We therefore conducted a thorough assessment of two bottle ethanol preference drinking in both replicate pairs of WSP/WSR selected lines in mice of both sexes. Greater preference drinking of WSR-2 than WSP-2 female mice confirmed the earlier report. However, in the parallel set of selected lines, the WSP-1 mice drank more than the WSR-1s. Naive mice tested for preference for sucrose, saccharin and quinine did not differ markedly for any tastant. Finally, in a test of binge-like drinking, Drinking in the Dark (DID), WSP mice drank more than WSR mice and attained significantly higher (but still modest) blood ethanol concentrations. Tests of acute withdrawal after DID showed a mild, but significant elevation in handling-induced convulsions in the WSP line. These results provide further evidence that 2-bottle ethanol preference and DID are genetically distinguishable traits.     

Volume and dose effects of experimenter-administered ethanol preloads on ethanol seeking and self-administration.

The present experiment used a behavioral model developed to separate the initial behavior required to obtain access to ethanol (appetitive responding or lever presses) from the actual self-administration (consummatory responding or intake) to test the hypothesis that these responses are under the control of different behavioral/physiological processes, and therefore differentially affected by an ethanol priming dose. In male, Long Evans rats, "preload" volume (0.5 and 2.0ml) and dose (approximately 10%, 25%, and 50% of the total normally consumed in nontreatment sessions translating to 0.1, 0.25, and 0.5g/kg) of ethanol were varied and administered by the experimenter via oral gavage prior to an operant session. Overall, there were no priming effects, or increases, in ethanol-reinforced responding resulting from the ethanol preloads. The findings showed that the low preload volume produced linear, dose-dependent decreases in both intake and seeking. However, while the high volume also produced a linear dose-dependent decrease in ethanol seeking, there was a decrease in intake at every dose. That is, ethanol seeking was insensitive to preload volume, while intake was affected in a dose-dependent manner except at the lowest dose when preload volume did play a role in intake regulation. These findings indicate that "fullness" and pharmacological cues differentially impact the appetitive and consummatory behaviors reinforced by ethanol solutions, with intake being more sensitive to preload volume and seeking being more sensitive to preload pharmacology.     

Prolonged neurophysiological effects of cumulative wine drinking.

The effects of a single, large dose of alcohol have been studied extensively, but how alcohol affects the brain under more realistic social drinking situations has received scant attention. The neurophysiological effects of a cumulative dose of alcohol were investigated as subjects drank three glasses of alcoholic or placebo red wine, 1 h apart. In a double-blind procedure, electroencephalographic (EEG) activity was recorded for social drinkers during rest and performance of a working memory task at two levels of difficulty. Background EEG power in the theta, slow alpha, and beta bands increased with alcohol consumption. Along with this systemic increase in background cortical resonant activity, event-related potential (ERP) amplitudes decreased between 200 and 350 ms poststimulus and P300 latency increased, effects that occurred while relevant stimulus factors were being evaluated. These neurophysiological effects endured 3 h after drinking, whereas blood/breath alcohol concentration had decreased considerably and cognitive performance returned to normal. These findings seem to indicate that moderate social alcohol consumption has cumulative effects on brain function that persist for hours after chemical and behavioral indicators of intoxication have diminished. The results seem to indicate that neuronal populations needed for stimulus processing were less available after wine consumption (as evidenced by reduced ERP amplitudes) because of increased background oscillatory activity (as evidenced by increased background EEG power).     

Chronic ethanol self-administration in a continuous-access operant situation: the use of a sucrose/ethanol solution to increase daily ethanol intake.

The addition of sucrose to an ethanol solution increases both limited- and continuous-access ethanol consumption. The present study examined if the increased intakes in a continuous-access condition could produce withdrawal signs indicating physical dependence on ethanol. Rats were maintained in a continuous-access operant situation in which one lever press on one lever resulted in the presentation of a food pellet, whereas one lever press on a second lever presented 0.1 ml of fluid in a dipper. Water was available from a drinking spout. Ten rats received a 10% sucrose/20% ethanol mixture in the dipper and six rats 10% sucrose. After 30 days the animals were tested for withdrawal signs after 8 h without ethanol using an activity test and response to key shaking. They were then given an additional 30 days of access to the solutions and retested for withdrawal. This was followed by a final 30 days of access and a third withdrawal test. Over the 90 days, the sucrose/ethanol group consumed 8-10 g of ethanol per kilogram of body weight per day. Over this time both groups gained weight. At the third withdrawal test, a significant reduction in activity occurred in the ethanol-drinking group, compared with the sucrose group. No severe withdrawal effects were observed to the key shake test. The results suggest that the higher ethanol intakes previously observed using this sucrose/ethanol solution can be maintained over long periods of time. Although this intake was not sufficient to produce severe withdrawal signs, the results suggest that longer exposure might result in more severe ethanol dependence.