Ethanol intakes and preferences in the desalivate rat

Desalivate and control rats were tested for ethanol versus water preference (5%, 10% and 20% (v/v) ethanol solutions). Each concentration of ethanol was presented for six days in an ascending, descending, or mixed presentation schedule. Following preference tests, intakes of first 10% (15 days), then 5% (15 days), and finally 10% (5 days) ethanol as the only available fluid were determined. Blood ethanol concentrations were measured (22:00 hr, 24:00 hr, 02:00 hr) during the final 10% ethanol intake test. Desalivate and control rats showed similar aversions to ethanol at all concentrations with relative ethanol intake being a negative function of concentration. During ethanol and water intake tests, desalivates drank significantly greater amounts (ml/100 g body weight) of all drinking fluids than controls. However, for both groups intake of 10% ethanol was reduced significantly from water baseline levels. Although desalivates consumed as much ethanol as controls, their blood ethanol concentrations at all times tested were slightly lower than controls. During the ethanol intake test desalivate rats lost body weight, while control rats gained body weight.     

Chlordiazepoxide''s interaction with ethanol intake in the rat: Relation to ethanol exposure paradigms

Chlordiazepoxide's interaction with ethanol (5% v/v) intake was assessed in rats on a feeding regimen producing high daily quantities of ethanol intake (schedule-induction procedure with intermittent feeding), more moderate amounts of ethanol intake (a single daily feeding), and small amounts of ethanol intake (free feeding). Six days of twice daily sham injections (IP) were followed by 12 days of 0 (vehicle), 5, 10, or 15 mg/kg (twice daily) chlordiazepoxide, and finally six days of the saline (vehicle) injections. Rats in the intermittent feeding daily consumed 9.9–12.3 g/kg (80–95 ml) of ethanol on baseline which was reduced 15 to 33% by the drug. In the single feed condition most rats were drinking 70 to 85 ml (8.8–10.3 g/kg) of ethanol and this was reduced 15–40% by the drug. During the six days after drug, intake in both of these feeding regimens returned to the baseline level. Ethanol intake of rats under the free feeding condition (48 ml, 3.5 g/kg on average) was not affected by the drug, nor was water intake under any of the three feeding regimens.     

Ethanol elimination rates in normal and ethanol dependent animals.

Ethanol elimination rates were determined in rats using an intravenous route of ethanol administration after several experimental manipulations. Twenty-four hr food deprivation resulted in a 30% reduction to 35 mg/100ml blood/hr in elimination rate from a non-deprived rate of 50 mg/100 ml blood/hr. After 2 months of ethanol drinking (5% v/v), 24 hr starvation resulted in only a 10% reduction in elimination rate (45 mg/100 ml blood/hr), and did not increase the non-food-deprived rate (49.2 mg/100 ml blood/hr) over that obtained in the above animals' drinking water rather than 5% ethanol. Animals which chronically overdrank ethanol or water for 3 months on a schedule-induced polydipsia procedure, known to result in ethanol physical dependence, showed a decreased rate of ethanol elimination (37.9 mg/100 ml blood/hr for water drinkers) in the non-food-deprived condition. By providing 750 mg of liver powder daily as a food supplement in the ethanol overdrinking regimen, the ethanol elimination rate remained at a rate comparable to the normal animal (48.4 mg/100 ml blood/hr).     

Schedule-induced ethanol polydipsia: enhancement by saccharin

The effect of adding sodium saccharin to a 5% ethanol solution on intake was examined. One set of animals were maintained at 80% of their free-feeding weight, in their home-cages with either 5% ethanol, or 5% ethanol-0.25% sodium saccharin as the only fluid available for three months (home-cage condition). A second set of animals were maintained in cages with automatic food dispensers that provided a 24 hr feeding regimen known to produce ethanol overdrinking (schedule-induced condition). These animals had 5% ethanol as their only available fluid for one month, followed by the 5% ethanol-0.25% sodium saccharin mixture for two months. No significant differences in ethanol intake were found between the 2 home-cage conditions (5% ethanol = 11.6 g ethanol/kg/day; 5% ethanol in 0.25% sodium saccharin = 11.7 g ethanol/kg/day. However, the addition of saccharin in the schedule-induced condition produced a marked increase in ethanol intake (5% ethanol = 13.1 g ethanol/kg/day; 5% ethanol in 0.25% sodium saccharin = 15.1 g ethanol/kg/day). The home-cage animals showed no sign of an abstinence syndrome upon substitution of water for ethanol. In the schedule-induced group, severe tonic-clonic seizures occured as a result of ethanol withdrawal.     

Induction of high voluntary ethanol intake in dependent rats

The experimental conditions under which oral high intake may be induced in previously intoxicated rats have been investigated. Seventeen rats were administered intragastrically with 10 g/kg/day of ethanol for 15 days. At cessation of treatment, they were presented a single bottle of alcoholic solution (10% v/v) during 24 hr. For the following 6 days, they received either an ethyl alcohol solution or water in alternation for 8 hours each. Ethanol treated rats exhibited a high oral intake of ethanol equivalent to the previously injected doses. Controls displayed a significantly lower intake of ethanol. It is concluded that the suppression of the withdrawal state by an initial priming oral intake of ethanol in physically dependent rats is a condition for the development of a conditioned taste preference for ethanol as a basis for the behavioral dependence.     

Consumption of intoxicating beverages by rats and mice exhibiting high and low preferences for ethanol

Lines of rats selectively bred for alcohol consumption or avoidance (AA and ANA, ALKO, Finland) as well as inbred strains of mice (C57/BL/6J and DBA/2J) and common female Wistar rats (Charles River) exhibiting high and low preferences for ethanol were tested under free-choice conditions for their consumption of solutions of ethanol (5, 10, or 15 g/100 ml tap water), sodium pentobarbital (0.19, 0.038, 0.076 g/100 ml tap water), and different beverages containing ethanol in the range of 8.1–9.6% (red and white wine, Scotch, ethanol in Hawaiian Punch). The Wistar rats and the mice classified as alcohol-preferring also tended to consume more of the pentobarbital solution than did alcohol-avoiding animals. Alcohol-nonaccepting (ANA) rats, however, consumed considerably more of all three pentobarbital solutions than did the alcohol-accepting (AA) rats. The intake of pentobarbital by the ANA rats and C57/BL/6J mice was in the range of 25–40 mg/kg/day, quantities that might be expected to produce pharmacological effects discriminable by those animals. The intake of ethanol by ANA rats was markedly elevated when the ethanol was contained in white wine or in punch.     

Cross-tolerance to phenobarbital following chronic ethanol polydipsia

Using contingent food pellet delivery, rats were trained on a discriminative motor control task requiring that a force transducer be held steadily within a force band. Motor performance following pre-task doses of phenobarbital (40, 60 or 80 mg/kg) both before and after 4 months of chronic ethanol polydipsia (mean intake = 11.1 g/kg/day) indicated the development of cross-tolerance from ethanol to phenobarbital. Days on which saline control injections were given in place of phenobarbital injections (on injection days ethanol was withdrawn 5 hr pre-injection) revealed the development of a mild physical dependence on ethanol polydipsia. Chronic ethanol polydipsia did not alter the time course of phenobarbital elimination from the serum, indicating that the cross-tolerance probably was due to central nervous system changes.     

The effect of naloxone on intragastric ethanol self-administration

The acute effect of 1.25 and 2.50 mg/kg naloxone was tested in a group of male Wistar rats readily self-administering 10% w/v ethanol intragastically following 12% days of forced ethanol intoxication. Compared to saline pretreatment, naloxone did not alter 24 hr intakes of food, water or ethanol. However, both does strongly and significantly inhibited lever pressing for ethanol during 2 hr following pretreatment. The results indicate that naloxone's inhibition of ethanol intake does havea transient postabsorptive component, although this component is unlikely to be specific to ethanol.     

A procedure to produce high alcohol intake in mice

Rationale While prolonged access to ethanol (EtOH), or deprivations, or their combination have occasionally been shown to yield high levels of voluntary self-administration, in almost all cases, rodents do not self-administer alcohol to the degree that they will develop substantial, intoxicating blood alcohol levels and then continue to self-administer at these levels.Objectives The purpose of the present series of experiments was to modify a fluid restriction procedure to demonstrate consistent, high EtOH consumption.Methods Male and female mice from an alcohol preferring inbred strain (C57BL/6J; B6) as well as from a genetically heterogeneous strain (WSC) were given varying periods of access to fluid, ranging from 90 min to 10 h per day, for 12–21 days. Every 3rd or 4th day, separate groups of mice were offered a 5, 7 or 10% EtOH solution for either 10 min or 30 min, followed by water for the remainder of the time.Results In all studies, stable high EtOH doses were consumed by both B6 and WSC mice across the EtOH sessions, exceeding 2 g/kg in a 30-min session. Mean blood EtOH concentration exceeded 1 mg/ml (i.e. 100 mg%), with values in individual animals ranging from 0.6 mg/ml to 3.4 mg/ml. Notably, mice receiving 10 h of fluid/day continued to consume 2 g/kg doses of EtOH. While this procedure did not produce subsequent preference for EtOH in WSC mice, consumption remained high in some animals.Conclusions These data indicate that scheduling fluid intake produces high, stable EtOH consumption and BEC in male and female B6 and WSC mice.     

Effects of corticosterone on place conditioning to ethanol

Rationale and objective Effects of corticosterone on place conditioning to ethanol were investigated in mice using two conditioning schedules; the conventional method and a rapid conditioning schedule in which exposure to the CS+ followed immediately on exposure to the CS–.Methods Effects of administration of corticosterone, 10 mg/kg, on the acquisition of place conditioning produced by ethanol, 1–2.5 g/kg, were investigated using the conventional method of conditioning, with exposure to the CS+ and the CS– on alternate days, and also using the rapid conditioning method. Total and free blood corticosterone concentrations were measured after administration of ethanol and corticosterone.Results In the conventional, alternate day, conditioning schedule, ethanol produced significant place preference at 2 and at 2.5 g/kg, but when these alcohol doses were given with corticosterone 10 mg/kg, significant place conditioning was not seen. In contrast, in the rapid, same day, conditioning schedule corticosterone significantly decreased the dose at which ethanol produced an apparent place preference, with significant place conditioning being seen with ethanol at 1 and 1.5 g/kg in combination with corticosterone, 10 mg/kg. Total and free corticosterone concentrations were increased after ethanol, 1.5 g/kg, compared with controls, and administration of corticosterone, 10 mg/kg, caused a significantly greater increase. There were no significant differences in spontaneous locomotor activity or brain alcohol concentrations between any of the treatment groups.Conclusions The effects of corticosterone on ethanol-induced place conditioning are substantially affected by the conditioning schedule used.     

Effects of phenobarbital on ethanol intake in fluid deprived rats.

Every third day animals were offered either 3 or 7 percent ethanol in place of water during the 1 hr drinking session. Three doses of sodium phenobarbital were administered subcutaneously to 3 groups of animals - 20, 40, and 60 mg/kg. Results indicate that the drug indreases ethavol consumption following the injection but decreases consumption of ethanol on subsequent postdrug days. There was an attenuation in these effects from the first to the third injection. Although a dose effect was not determined, changes in ethanol consumption were greater with the higher concentrations.     

Intraventricular ethanol and ethanol intake: a behavioral and radiographic study.

Ethanol (10% w/v) was infused intraventricularly at a rate of 11 mul/hr, delivered over 50 sec every 10 min for 10 days into 5 Sprague-Dawley and 5 Wistar rats. Thereafter, preference testing with ascending concentrations of alcohol solutions vs . water vs. food gave no significant differences between treated and sham-operated controls, in contradiction to previously reported increases in alcohol consumption. Ethanol's rate of elimination from the ventricle and its pattern of diffusion into the brain were determined using radioactive ethanol: elimination from the brain is rapid with a half-like of 24 to 35 sec, and the amount diffused throughtout the brain small, with a maximal concentration in any one section of 0.004% (such a concentration is at least 20 times less than would result from a moderately intoxicating parenteral dose of ethanol). The character of the elimination and the lack of effect on alcohol intake found here indicate that intraventricularly administered ethanol is a technique with no usefulness in elucidating the processes affecting alcohol addiction.     

Antidepressants attenuate both the enhanced ethanol intake and ethanol-induced anxiolytic effects in diazepam withdrawn rats.

We have recently shown that the abrupt discontinuation of chronic diazepam (DZM) administration facilitated ethanol consumption and enhanced the anxiolytic properties of ethanol. Tricyclic antidepressants such as desipramine and the selective serotonin reuptake inhibitor fluoxetine have been shown to reduce alcohol intake in rodent models of alcoholism and in alcoholics who are depressed. In the present study, we tested whether desipramine (1.25; 2.5 and 5 mg/kg, i.p.) and fluoxetine (5 mg/kg, i.p.) treatment affect both ethanol intake in a free-choice test and the anxiolytic effect induced by ethanol in DZM withdrawn rats. Adult male Wistar rats were submitted to a chronic DZM treatment (2 mg/kg per day) or vehicle (VEH) for 21 days. Twenty-four hours after the last DZM injection, rats were subjected to a free-choice paradigm between water and increasing ethanol concentrations with or without concurrent desipramine or fluoxetine administration (ethanol concentration (v/v) was increased every 4 days as follows: 2, 4, 6, 8 and 10% for the final 8 days). Chronic treatment with desipramine (24 days, twice a day, 2.5 and 5 mg/kg, i.p.) and fluoxetine (24 days, once a day; 5 mg/kg, i.p.) significantly reduced the amount of ethanol intake in DZM withdrawn rats. Furthermore, subchronic treatments with desipramine (4 days, twice a day, 2.5 and 5 mg/kg) and fluoxetine (4 days, once a day, 5 mg/kg, i.p.) blocked the anxiolytic-like behavior in the elevated plus maze induced by ethanol (1 g/kg; i.p.) in DZM withdrawn rats at day 5 of withdrawal. The present findings suggest that desipramine and fluoxetine could be effective pharmacological tools to prevent the subsequent development of ethanol dependence in rats previously exposed to DZM withdrawal.     

Cyamemazine decreases ethanol intake in rats and convulsions during ethanol withdrawal syndrome in mice

The effect of cyamemazine a dopamine D₂ receptor antagonist on voluntary ethanol consumption in rats and on ethanol withdrawal in mice was examined. Male Sprague-Dawley rats were tested in a free choice (water and 10% ethanol) experiment and consumed 5 g/kg ethanol daily. Rats were treated daily IP with cyamemazine ( 0.5, 1, or 2 mg/kg) or acamprosate (100 mg/kg) during 2 weeks. Both acamprosate and 1 mg/kg cyamemazine significantly decreased ethanol intake by 45% without affecting either fluid or food intake. The lowest dose of cyamemazine had no effect on alcohol intake but increased food intake. The highest dose had no effect on any variables. During the post-treatment period, only 1 mg/kg cyamemazine decreased both ethanol and fluid intakes. Mice were made dependent on alcohol using a chocolate fluid diet containing increasing concentrations of alcohol and withdrawn after 9 days. Mice were treated with cyamemazine (1 or 0.5 mg/kg, respectively) or with the same doses of lorazepam acutely on the day of withdrawal or chronically (during alcohol treatment). Both chronic and acute cyamemazine and lorazepam treatments decreased convulsions during ethanol withdrawal. Both acute treatments decreased locomotor activity in control and alcohol dependent mice. Chronic treatment had no effect on locomotor activity. We suggest that cyamemazine could reduce alcohol consumption by antagonizing the activation of the dopaminergic pathways during the induction of alcohol dependence. The action of cyamemazine on 5-HT₃ receptors could also explain its effect on alcohol convulsions during withdrawal convulsions. Received: 19 October 1997/Final version: 6 April 1998     

Selective suppression of schedule-induced ethanol drinking by antialcoholic drugs in rats

Effects of disulfiram and calcium cyanamide, antialcoholic drugs, on schedule-induced ethanol drinking as well as on schedule-controlled response (lever-pressing) under a fixed interval 1 min schedule of food reinforcement were investigated in Wistar strain rats. When ethanol solution was available, the schedule-induced ethanol drinking decreased depending on the ethanol concentration (2-8%). However, the dose of ethanol intake during the 1 hr experimental session was at maximum (2.8 g/kg) when 4% ethanol solution was available. Thereafter, 4% ethanol solution was used in the experiment for studying the effects of disulfiram and calcium cyanamide on the schedule-induced ethanol drinking. Disulfiram (100-200 mg/kg, p.o.), pretreated at 1 hr before the start of the experiment, tended to suppress schedule-induced water drinking. However, the same treatment of calcium cyanamide (5-10 mg/kg, p.o.) did not produce a marked change in it. In contrast, disulfiram (100 and 200 mg/kg) and calcium cyanamide (5 and 10 mg/kg) markedly suppressed schedule-induced ethanol drinking without eliciting a marked change in schedule-controlled response. The present results suggest that both disulfiram and calcium cyanamide selectively suppress ethanol drinking in rats.     

Ethanol exposure as inducer of stable voluntary ethanol drinking in the male rat

The effects of restricted 'Saturday night drinking' on voluntary ethanol intake was tested in male rats. During a treatment period of 57 weeks the animals (group B) could choose between ethanol and water for 24 h each week. After this period of choice they received ethanol (2.0 g/kg) i.v. Total weekly exposure was around 6-7 g/kg. Of two control groups, one was given i.p. injections of saline once a week (group A) and the other, in addition to saline injections, a continuous choice between ethanol (10%) and water as drinking fluid (group C). Weekly ethanol exposure was approximately 14 g/kg in group C. During a testing period of 46 weeks group A and C had continuous access to a choice between ethanol and water. After week 5 of the testing period concentrations of ethanol varied in 3-week intervals. For each tested concentration (5, 15, 20 and 25%) intake was calculated as g/kg per day based on the total period. For the reference concentration (10%) corresponding intake was calculated on 2 weeks prior to and 2 weeks after the tested concentration. In group B there was always a very strong correlation (r = 0.86-0.99) between intake of the different tested concentration and the corresponding reference concentration. This indicates that a strong individual preference for a defined daily dose of ethanol had developed in these rats. The corresponding relation was less developed in group C especially when higher concentrations of ethanol were tested. At the end of the testing period voluntary ethanol intake was slightly higher in group B and C when compared to group A. Analyses of blood ethanol levels at defined times during the testing period indicated an interrupted ethanol intake with occasionally substantial blood levels. Thus intermittent ethanol exposure can induce a voluntary ethanol drinking pattern in male rats which might be used as an animal model of alcoholism.     

Voluntary ethanol intake in rats following exposure to ethanol on various schedules

Voluntary intake of 20% (v/v) ethanol solutions was assesed in groups of male Wistar rats following various forms of ethanol exposure. Some animals were first exposed to gradually increasing weak solutions of ethanol (acclimation); while others were given 20% solutions from the start. Some were given ethanol every day (continuous schedule); others were given ethanol every other day (intermittent schedule). Some were given ethanol solutions with plain water also available (free-choice); others were given ethanol solutions as the only fluid available (forced-choice). The animals on intermittent schedules for a 30 day period developed a slight preference for 20% ethanol solutions; they came to drink an average of over 9 g/kg/day of absolute ethanol when tested in free choice conditions. Previous acclimation did not add significantly to this effect. The effect held whether the animals received their ethanol in free- or forced-choice conditions. Forced-choice experience inhibited subsequent free-choice intake in the continuous-exposure group, but forced-choice coupled with intermittent exposure led to the highest intake levels in the shortest total ethanol exposure. The intake levels of these animals are encouraging for those interested in developing animal analogues for human ethanol abuse.Supported by grants from the Licensed Beverages Industries and the Medical Research Council of Canada.     

Alcohol withdrawal reactions after chronic intake of chlordiazepoxide and ethanol

Withdrawal reactions were compared in C57BL/6J mice, which had been fed an ethanolic liquid diet containing chloridazepoxide (CDP, 3.2 or 6.4 mg/100 ml, group B or C, respectively) with those which had been administered an ethanol diet alone (group A) for 15 days. Group A showed a significantly more pronounced decrease in rectal temperature (4 to 10 hr) and a higher withdrawal score (4 to 14 hr) than mice in groups B and C. The differences in withdrawal signs still persisted even after mice were fed an ethanol diet without CDP for one extra day before withdrawal. The presence of metabolites of CDP in the blood during withdrawal could only account for a minor contribution to the protective effect. Our data are more suggestive of an increased rate of ethanol metabolism leading to lower blood alcohol levels during diet intake period as being the major factor. However, we cannot rule out the alternative possibility that CDP or its metabolites might interfere with the development of tolerance to and physical dependence on alcohol.     

The discriminative stimulus properties of self-administered ethanol are mediated by GABAA and NMDA receptors in rats

RATIONALE: The neurobiological systems that mediate the discriminative stimulus effects of self-administered drugs are largely unknown. The present study examined the discriminative stimulus effects of self-administered ethanol. METHODS: Rats were trained to discriminate ethanol (1 g/kg, IP) from saline on a two-lever drug discrimination task with sucrose (10% w/v) reinforcement. Test sessions were conducted with ethanol (0 or 10% v/v) added to the sucrose reinforcement to determine if self-administered ethanol would interact with the discriminative stimulus effects of investigator-administered ethanol, or with the ethanol-like discriminative stimulus effects of the GABAA-positive modulator pentobarbital or the non-competitive NMDA antagonist MK-801. RESULTS: During a saline test session, ethanol (10% v/v) was added to the sucrose reinforcement. Responding by all animals began accurately on the saline-appropriate lever and then switched to the ethanol-appropriate lever after rats self-administered a mean dose of 1.2 +/- 0.14 g/kg ethanol. During cumulative self-administration trials, responding initially occurred on the saline lever and then switched to the ethanol-appropriate lever after ethanol (0.68 +/- 0.13 g/kg) was self-administered. Investigator-administered MK-801 (0.01-1.0 mg/kg, cumulative IP) and pentobarbital (0.3-10.0 mg/kg, cumulative IP) dose-dependently substituted for ethanol. When ethanol (10% v/v) was added to the sucrose reinforcer, MK-801 and pentobarbital dose-response curves were shifted significantly to the left. CONCLUSIONS: Self-administered ethanol substituted for and potentiated the stimulus effects of investigator-administered ethanol, suggesting that the discriminative stimulus effects of self-administered ethanol are similar to those produced by investigator-administered ethanol. Self-administered ethanol enhanced the ethanol-like discriminative stimulus effects of MK-801 and pentobarbital, which suggests that the discriminative stimulus effects of self-administered ethanol are mediated by NMDA and GABAA receptors.     

The influence of early postweaning ethanol exposure on oral self-administration behavior in the rat

The effects of three early ethanol home cage consumption procedures on the maintenance of operant lever responding reinforced by ethanol presentation were examined in the rat. Two groups of rats, 25 and 31 days of age, were exposed to 10% (v/v) ethanol as the only fluid in the home cage for 3 or 10 days. A third group, 31 days of age, were exposed to 10% ethanol or tap water for 24 h, with the fluid alternating daily for 18 days. All animals were subsequently trained to lever press using 10% ethanol reinforcement under a decreasing water restriction schedule. All three groups were found to have substantial ethanol consumption levels during the initial exposure in the home cage, ranging from 11.2 to 11.9 g/kg/day. The animals were all successfully trained to lever press in the operant chamber with ethanol as the reinforcer when limited to 15 ml/day of water in the home cage. The average number of reinforcements per day ranged from 29 to 43.5, yielding ethanol intakes from 1.06 to 1.97 g/kg in the 30-minute operant session. However, when 50 ml/day of water was available in the home cage, ethanol reinforcements were substantially reduced, with intakes which ranged from 0.14 to 0.18 g/kg/day. The data suggest that early exposure does not enhance ethanol's reinforcing properties later in the animal's life. These results were discussed in terms the effect of early ethanol exposure on later ethanol consumption and the role of ethanol initiation procedures in oral self-administration.