Genetic selection of alcohol preference can be countered by conditioning processes

Effects of forced alcohol drinking on alcohol-water choice in three pairs of rat lines selectively bred for differences in alcohol preference

Three pairs of Indiana University rat lines (inbred alcohol-preferring and nonpreferring rat lines [P/NPs], high- and low-alcohol-drinking rat lines [HAD/LAD1s and HAD/LAD2s]) were bred in the School of Medicine colony to drink high versus low daily amounts of a 10% vol/vol alcohol test solution (>5.0 g/kg body weight vs. <1.5 g/kg body weight), and a high versus low proportion of alcohol to water (>2:1 vs. <0.5:1) by the end of a 3-week alcohol-water choice condition. This choice phase was always preceded by four days of a forcing procedure with alcohol as the only fluid. The present study examined the contribution of the forcing procedure to the alcohol intake of animals in each pair of lines by comparing daily alcohol intake of rats housed in experimental chambers in a forced group (4 days with only alcohol solution to drink followed by 22 choice days) versus a choice group (both alcohol and water available all 26 days). As expected, under the initial alcohol exposure, high-drinking line rats drank more alcohol than low-drinking line rats, and all forced groups drank more alcohol than choice groups. At the start of the choice phase, all low-drinking line forced groups immediately dropped their alcohol intake to the level of their choice groups. In contrast, all high-drinking line forced groups maintained a high level of alcohol intake under choice, whereas all high-drinking line choice groups slowly increased average alcohol intake across the 22-day choice phase, ending near the average intake of their forced groups. However, a small subset of each high-drinking line choice animals failed to increase alcohol intake until subsequently forced with alcohol for 4 days and tested again in choice. These results indicate that the alcohol-forcing procedure used in deriving these lines resulted in the selection of more than one pathway to a high-drinking phenotype. In addition, high-drinking line animals appeared more sensitive to the differences between laboratory- and colony-testing environments than low-drinking line animals. These data suggest that these high-drinking lines may represent an unexpectedly appropriate complex model of how multiple factors may contribute to the genesis of human alcoholism.

Repeated exposure to alcoholic beer does not induce long-lasting changes in alcohol self-administration and intake in sardinian alcohol-preferring and sardinian non-preferring rats

AIMS

Rats avidly consume non-alcoholic beer, and addition of alcohol to non-alcoholic beer may function as a medium to induce intake of large amounts of alcohol in rats. The present study investigated whether Sardinian alcohol-preferring (sP) and Sardinian non-preferring (sNP) rats, initially exposed to non-alcoholic beer, and subsequently to non-alcoholic beer containing increasing concentrations of alcohol, would develop unusually high alcohol self-administration and drinking behaviours: (i) when alcohol was added to non-alcoholic beer, and (2) once beer was withdrawn and a plain alcohol solution was made available.

METHODS

In Experiment 1, rats were exposed to operant, 30-min/day self-administration sessions of non-alcoholic beer with increasing concentrations of alcohol [0, 2.5, 5, 7.5, and 10% (v/v)] for a total of 45 days. After a brief 'beer-fading' phase, the rats were exposed to self-administration sessions of a plain 10% (v/v) alcohol solution. In Experiment 2, the rats were exposed to non-alcoholic beer with increasing concentrations of alcohol [0, 2.5, 5, 7.5, and 10% (v/v)] and water under the 2-bottle choice regimen with unlimited access (24 h/day) for a total of 35 days. After a brief 'beer-fading' phase, the rats were exposed to the choice between a plain 10% (v/v) alcohol solution and water.

RESULTS

sP and sNP rats did not differ in self-administration (Experiment 1) and intake (Experiment 2) of non-alcoholic beer. In Experiment 1, as alcohol content increased, the amount of self-administered alcohol increased progressively in sP rats (up to 1-1.2 g/kg) and remained stable in sNP rats (approximately 0.65 g/kg). When the plain 10% alcohol solution was available, the amount of self-administered alcohol in sP rats initially dropped, and tended to increase-up to approximately 0.6 g/kg-on continuing exposure. In sNP rats, their lever-pressing behaviour was rapidly extinguished after beer withdrawal. In Experiment 2, as alcohol content was increased, daily alcohol intake increased progressively in sP rats (up to 8-9 g/kg) and averaged approximately 2.4 g/kg in sNP rats. When the plain alcohol solution was available, daily alcohol intake in sP rats was initially low, reaching control values on continuing exposure; conversely, daily alcohol intake was completely suppressed in sNP rats.

CONCLUSIONS

These results suggest that exposure to alcoholic beer resulted in unusually high intakes of alcohol in both sP and sNP rats for as long as non-alcoholic beer was added to alcohol; however, these high levels of alcohol self-administration and intake were not maintained once non-alcoholic beer was withdrawn.

Phenotypic characterization of genetically selected Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats

Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats are one of the pairs of rat lines selectively bred for high and low alcohol preference and consumption, respectively, under the homecage, continuous two-bottle choice regimen. sP rats meet most of the fundamental criteria for an animal model of alcoholism, in that they voluntarily consume sufficient amounts of alcohol to achieve significant blood alcohol levels and produce psychopharmacological effects, including anxiolysis and motor stimulation. sP rats are also willing to 'work' (such as lever-pressing) for alcohol. Chronic alcohol drinking in sP rats results in the development of tolerance to a given effect of alcohol (specifically, motor incoordination) and relapse-like drinking (the alcohol deprivation effect). Conversely, sNP rats avoid alcohol virtually completely; their avoidance for alcohol being resistant even to an environmental manipulation such as long-term exposure to alcohol plus sucrose. sP and sNP rats have been characterized for different phenotypes, possibly associated to their different alcohol preference and consumption. In comparison with sNP rats, alcohol-naive sP rats displayed (1) more anxiety-related behaviors; (2) higher initial sensitivity to the locomotor stimulating and sedative/hypnotic effects of alcohol; and (3) lower sensitivity to the aversive effects of alcohol. The present paper reviews the data collected to date on alcohol drinking behavior and other alcohol-related behaviors in sP and sNP rats. The behavioral profile of sP rats is also compared with that of other lines of selectively bred alcohol-preferring rats and the heterogeneity resulting from this comparison is discussed in terms of different animal models for the different forms of alcoholism.

Saccharin consumption and the effect of a long-term exposure to a sweetened alcoholic solution in high- (UChB) and low- (UChA) alcohol-drinking rats

An association between saccharin consumption and alcohol intake has been observed in rodent lines genetically developed for alcohol preference or alcohol avoidance. It has also been proposed that a sweetened alcohol solution can condition rats to consume high amounts of alcohol. This work had two aims. First, to study the relationship between saccharin and alcohol intake in both high-alcohol-drinking UChB rats and low-alcohol-drinking UChA rats and, second, to determine whether a long-term exposure to a sweetened alcohol solution can increase their voluntary alcohol consumption. For the first purpose, UChB and UChA rats were tested under a free-choice paradigm between two graduated bottles, one containing a saccharin solution (0.1, 0.2, or 0.4% [wt/vol]) and the other water. For the second purpose, UChB and UChA rats that were under free choice between 10% alcohol and water, were offered a 10% alcohol solution containing 0.2% saccharin, instead of 10% alcohol for 1 month and were then returned to free choice between 10% alcohol and water. The first experiment showed that both lines have a high preference for saccharin at any concentration, but UChB rats drank twice as much saccharin solution as UChA rats and consequently they increased significantly their total daily fluid intake. This fact has been suggested to be an animal analogue of the clinical phenomenon known as "loss of control." In the second experiment a long-term exposure to a 10% alcohol solution containing 0.2% saccharin induced a significant increase in alcohol consumption in UChB rats once saccharin was faded out, whereas the alcohol consumption in UChA rats returned to the previous low value. This result indicates that UChA rats have a genetic predisposition to avoid alcohol. In conclusion, the results reported here for UChB and UChA rats show an association between saccharin and alcohol preference, and suggest that their different genotypes are probably involved in alcohol aversion.

The cerebellar GABAA α6 subunit is differentially modulated by chronic ethanol exposure in normal (R100R) and mutated (Q100Q) sNP rats

Sardinian alcohol non-preferring (sNP) rats carry a point mutation (R100Q) in the cerebellar expressed GABAA receptor alpha6 subunit gene, leading to a higher sensitivity to ethanol and diazepam. The role of the alpha6 subunit gene cluster in the ethanol non-preferring phenotype was here investigated by measuring the levels of alpha1, alpha6 and gamma2 peptide in the cerebellum of normal (RR) and mutated (QQ) sNP rats after 2 weeks of chronic ethanol administration. Western blot analysis revealed that the alpha6 subunit is increased in RR sNP rats after chronic ethanol exposure (25.44%+/-8.69 versus control), while it remained unchanged in mutated QQ sNP rats. Interestingly, chronic ethanol administration decreased alpha1 peptide levels in the cerebellum of both rat lines to a similar extent (30.99%+/-6.74 and 27.12%+/-9.83 in RR and QQ rats, respectively), while gamma2 peptide levels remained unchanged. To further correlate the genetic and biochemical difference of the normal and mutated sNP rats with their aversive phenotype, we exposed sNP rats to a protocol of acquisition and maintenance of ethanol drinking. QQ sNP rats drank less ethanol than RR rats during the acquisition phase, but such difference was lost during the maintenance phase. These data may contribute to elucidating the mechanisms of alcohol avoidance in rat lines selected for this behavior when exposed to ethanol solution.

Blood alcohol concentrations after scheduled access in high-alcohol-preferring mice

Development of procedures yielding substantial blood alcohol concentrations during voluntary access to an alcohol solution in mice is necessary to further characterize genetic and neurobiologic mechanisms underlying alcohol self-administration. Although, in experimental situations, some populations of mice readily drink an alcohol solution, results from previous studies have not typically revealed high blood alcohol concentrations after voluntary access, probably because of the high alcohol metabolism rate in mice. Toward development of a murine drinking model, 36 selectively bred high-alcohol-preferring mice of both sexes were subjected to a 30-min scheduled-access procedure by using saccharin fading to gradually introduce an alcohol solution. Mice had ad libitum access to food and water 24 h a day. The alcohol solution was available 1 h after the start of the dark part of the cycle for 30 min per day, 5 days per week. After complete removal of saccharin from the drinking tubes, mice consistently drank 1.4 g/kg of a 10% [volume/volume (vol./vol.)] alcohol solution in 30 min. Analysis of tail blood samples, taken immediately after the end of the 30-min access period, indicated blood alcohol concentrations were tightly correlated with alcohol intakes (range, 6-130 mg/dl; average, nearly 60 mg/dl). A concentration-response function of 10%, 12%, 15%, 18%, and 21% (vol./vol.) alcohol solutions indicated an inverted U-shaped relation between alcohol intake and alcohol concentration, with peak intake of greater than 1.75 g/kg per 30 min when a 15% alcohol solution was available. No sex differences were seen. These findings indicate the utility of this procedure in obtaining pharmacologically relevant blood alcohol concentrations after voluntary oral self-administration of an alcohol solution in mice.

Differential effects of saccharin supplementation on alcohol and water consumption by Wistar rats from different sources

The study was aimed to elucidate whether the dissimilar effects of concurrent presentation of sweet water on alcohol consumption previously reported for Wistar rats from different sources remain unchanged when alcohol is also flavored with 0.1% saccharin. Male Wistar rats from Laboratory of Experimental Biological Models (LEBM) and Krukovo animal farm (K) stocks having had 2 months free access to food, tap water, and 10% alcohol were given four consecutive two-bottle drinking tests: alcohol versus water, alcohol versus sweet water, sweet alcohol versus water, or sweet alcohol versus sweet water. The test order was quasi-random and each test lasted 4 days. In Wistar (K) rats, flavoring of either water or alcohol solution increased consumption of each of the fluids and decreased intake of concurrently available fluids. The elevation in water intake induced by its sweetening was antagonized by flavoring of alcohol solution. In Wistar (LEBM) rats, flavoring of either water or alcohol increased consumption of each of the fluid, but did not change the intake of alternative fluids. The stable alcohol consumption by Wistar (LEBM) rats and its suppression seen in Wistar (K) rats induced by concurrent presentation of flavored water parallel the patterns previously observed among P, sP, and HAD rats suggesting the existence among alcohol-consuming animals of typological diversity of alcohol motivation.

Long-term exposure to a sweetened alcoholic solution does not alter genetic aversion to ethanol in Sardinian alcohol-nonpreferring (sNP) rats

Results of a recent investigation revealed that selectively bred Indiana ethanol-nonpreferring (NP) rats could be "environmentally" conditioned to consume high amounts of ethanol. Specifically, a long-term exposure to a sucrose-plus-ethanol solution resulted, when sucrose was faded out, in an ethanol intake that was equivalent to that recorded in the counterpart ethanol-preferring (P) rats. The current study was designed to extend the above investigation to the selectively bred Sardinian alcohol-nonpreferring (sNP) rats. To this aim, rats of the sNP and Sardinian alcohol-preferring (sP) lines were exposed to a 108-day sucrose-fading procedure, which was virtually identical to that previously used with NP and P rats. Results indicated that intake of the sucrose-plus-ethanol solution in sNP rats was maintained predominantly by sucrose, as negligible intakes of ethanol were observed when sucrose was faded out. In contrast, sP rats maintained high levels of ethanol intake both during and after the induction procedure. These results support the suggestion that an environmental manipulation such as a long-term exposure to a sucrose-fading procedure did not overcome the genetically determined predisposition to avoid ethanol in sNP rats.

A relation between maze performance and increased ethanol intake in Long-Evans rats

In addition to the neurochemical and genetic basis of high ethanol consumption, there has been renewed interest in studying the role of behavioral variables and their relation to ethanol consumption. The present study was designed to assess whether a relation exists between a behavioral variable such as maze learning ability and ethanol consumption. Sixty, male, Long-Evans rats, exposed to food and water ad libitum, were given a daily trial in a complex, 16-arm T-maze for 19 consecutive days. The number of errors and time to complete the maze were monitored. Individual maze variable scores were transformed and then combined to allot each animal with an index of overall maze performance, with a smaller maze index score denoting good performance. After completion of maze testing, animals were given alternate-day, free-choice presentations of water and ascending doses of ethanol solutions (2%-10%), followed by a 10-day maintenance period with 10% ethanol. Animals were subsequently separated into two groups of high and low drinkers to examine any relation between differential ethanol intake and maze performance. A significant negative correlation between maze index and ethanol intake for the high drinkers group indicated that a smaller maze index was related to increased ethanol intake. No significant correlation was obtained for the low drinkers group. These results seem to indicate that individual variation in learning ability seems to be related to increased ethanol intake. Thus, innate learning processes may be a relevant trait when one attempts to understand the behaviors related to ethanol intake and preference.

Genetic selection for high and low alcohol consumption in a limited-access paradigm

BACKGROUND

Several rat lines have been bred for their differences in alcohol consumption based on a continuous-access paradigm in which alcohol solution is available 24 hr/day. The limited-access paradigm (LAP), in which access to alcohol solution is restricted to a short period per day, however, has been used extensively to investigate the neurochemical mechanisms underlying alcohol consumption. There is evidence of possible differences in genetic determination of alcohol drinking in a continuous- versus limited-access condition. For these reasons, selective breeding for high- and low-alcohol consumption (HARF and LARF, respectively) based on a LAP was conducted.

METHODS

N/Nih rats were used as the breeding stock. A within-family breeding procedure was used to develop HARF and LARF lines with 10 families per line. Access to alcohol solution was restricted to 20 min/day. Alcohol was provided as 3%, 6% and 12% w/v solutions. Average intake of alcohol during the 12% phase was used as the selection criterion. Inbreeding began in the seventh generation.

RESULTS

After the sixth generation of selection, rats from the HARF line consumed an average of 1.2 g/kg, whereas rats from the LARF line consumed an average of 0.6 g/kg of alcohol during the 20-min access period. Alcohol consumption remained stable over the next eight generations of inbreeding. In the continuous-access-drinking paradigm, the HARF and LARF rats consumed an average of 5.5 to 7.0 g/kg and 1.0 to 2.0 g/kg of alcohol per day respectively. An estimated heritability of 0.25 was obtained.

CONCLUSIONS

These findings indicate that alcohol drinking in the LAP is influenced by genetic factors. Differences in alcohol drinking in the LAP also generalize to continuous access drinking. These rat lines will be very useful for investigations into the genetic and neurochemical mechanisms underlying alcohol drinking.

Alcohol place preference conditioning in high- and low-alcohol preferring selected lines of mice

High- and low-alcohol preferring (HAP and LAP) selected lines of mice diverge greatly in free-choice alcohol consumption. This study investigated whether the lines differ in a measure of alcohol reward not dependent on drinking, specifically place conditioning. Mice were subjected to a differential conditioning procedure in which four alcohol-paired CS+ trials on one floor cue (0, 1.5, 3, or 4 g/kg; ns=20-24) alternated with four saline-paired CS- trials on a different floor cue. Testing was on a split floor, half CS+ and half CS-. HAP and LAP mice showed no preference at 0 g/kg, and equivalent, moderate preference at 1.5 and 3 g/kg alcohol. At 4 g/kg, LAP, but not HAP mice showed an increase in preference. The present findings imply greater efficacy of alcohol preference conditioning in LAP mice, but do not speak for line differences in sensitivity. Results do not support the hypothesis that selection for high drinking yields greater efficacy of alcohol as a reinforcer when reward is measured using a technique that does not rely on drinking. Low drinking in LAP mice may emerge from innate taste avoidance of alcohol as a result of selective breeding for low preference, which prevents them from encountering alcohol's rewarding, pharmacological effects.

Environmental influences on the failure to drink in inbred rats with an ethanol preference

To investigate the environmental influences on the initiation of voluntary consumption of 10% ethanol (EtOH) in rats with differing genetic susceptibility to excessive EtOH consumption, Maudsley reactive (MR/Har) and nonreactive (MNRA/Har) inbred rats were observed in different types of caging environments. Singly housed male and female rats of both strains living in Observational (O) cages drank markedly less EtOH during 3 weeks of two-bottle choice than did rats living in standard-control (C) individual cages. When male rats had a preexisting moderate or heavy pattern of EtOH intake (manipulated through prior EtOH experience), moving to the O cage did not reduce EtOH intake. To investigate the nature of the above cage effect (the reduced initiation of EtOH consumption), we compared the manner in which food had been distributed (traditional food hopper in C cages versus loose distribution in O cages) independently of cage type. The results showed that MR/Har male rats that obtained food through a hopper in both O or C cages drank significantly more EtOH than rats that had food loosely distributed in the O or C cages. The results suggest that differences in the mode of food procurement and caging can play a large role in whether the phenotype for excessive EtOH intake is expressed in the acquisition of an EtOH preference in genetically vulnerable rats.