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

Predicting extinction and reinstatement of alcohol and sucrose self-administration in outbred rats

Preventing relapse to drinking or escalation to excessive drinking could be aided by identifying factors that predict these behaviors. Animal models, particularly those that utilize operant self-administration techniques, can be useful. In a prior operant study, we noted a good deal of variability in behaviors during training and test sessions. We utilized data obtained from that study of two groups of rats, trained and tested identically except one responded for alcohol and the other for sucrose, to explore for associations related to relapse (reinstatement) or to excessive drinking (maintenance). Data were obtained from sessions conducted under fixed- and progressive-ratio schedules as well as from extinction and reinstatement sessions. Variables assessed included active and inactive presses, head entries into the dipper trough, and automated recordings of body movements during these sessions as well as alcohol preference before training. First, using multiple regression, we examined whether alcohol preference before training associated with any response variable among alcohol-responding rats. Second, using factor analysis, we identified a training variable, body movements, that associated with responses during tests. Using this measure, rats were divided into low- and high-response groups and compared on active lever presses and head entries across test sessions. Results show that among alcohol-responding rats, alcohol preference predicted head entries during extinction. High-body-movement rats emitted significantly fewer active lever presses and had fewer head entries across test sessions, particularly during reinstatement, compared with low-body-movement rats. Results from this exploratory study provide clues for future experimental studies.

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.

Operant ethanol reward in C57BL/6 mice: influence of gender and procedural variables

Food-deprived C57BL/6 (C57) mice of either sex responded for oral ethanol rewards delivered on ratio schedules of reinforcement, thus extending to female C57 mice effects previously reported only for male members of the strain. Lever responding for ethanol reward was influenced by thirst motivation (post- vs. preprandial tests), time of access to ethanol reward, ethanol concentration, and reinforcement schedule. A particularly high response output for 12% ethanol delivered on a PR2 schedule (e.g., approximately 1400/15 min test session) indicates its efficacy as a reinforcer for C57 mice. Estimated consumption of ethanol differed from lever responding when reward access time was relatively long (10 s) and response demand of the reinforcement schedule was low, but paralleled lever responding when reward access time was restricted (3 s) and response demands were greater. Gender influenced lever responding for ethanol reward and its consumption, the difference depending upon reward access time and reinforcement schedule. When the response demands were low and the reward access time long, females tended to respond more than males for ethanol reward; with greater response demands and shorter reward access time, males tended to respond more. In conjunction with our companion report, the present study helps define the behavioral conditions under which ethanol is rewarding for C57 mice and establish the conditions under which ethanol reward differs for male and female mice.

Ethanol and food pellet self-administration by baboons

During daily 23-h sessions, baboons had concurrent access to food pellets and an oral ethanol/dextrose solution. The effect of increasing the fixed-ratio or "cost" for pellets on pellet and fluid intake was examined when baboons had access to 2%, 4%, or 8% (w/v) ethanol. Increasing the response requirement for a pellet decreased pellet intake. The rate of decrease in pellet intake with increasing pellet cost was unaffected by the availability of ethanol solutions, which were either self-administered or given in investigator-planned doses. Increasing the response cost for pellets significantly increased self-administration of 4% ethanol. The effect of increasing the cost for fluid on fluid and pellet intake was examined when baboons had access to vehicle, 4% or 8% (w/v) ethanol. Although the total daily number of fluid deliveries was significantly greater when 4% ethanol was available, compared to vehicle, increasing the cost for a fluid delivery to 32 responses and above decreased intake of all three fluids similarly. Increasing the cost of ethanol did not affect food intake.

Effects of chronic ethanol exposure on oral self-administration of ethanol or saccharin by Wistar rats

The study of alcohol abuse traditionally has placed great emphasis on the development of tolerance and dependence as key factors. However, animal models of ethanol self-administration in dependent rats have been difficult to establish, caused in part by ethanol's aversive taste cues and subsequent aversive effects (i.e., "hangover" malaise) that prevent substantial ethanol consumption. In this study, this problem was addressed in animals trained to self-administer ethanol (10% w/v) in a sweetened-solution fading procedure before induction of dependence and repeated exposure to withdrawal. Once stable rates of responding for ethanol were achieved, a palatable liquid diet containing 8.7% (v/v) ethanol was introduced as the sole source of calories and fluid for one group of rats [ethanol diet (ED) group]. A second group of rats received a control diet with sucrose isocalorically substituted for ethanol (CD group). After 14-17 days of liquid diet exposure, the rats were withdrawn once a week for 4 weeks and 8 hr into each withdrawal session were allowed to self-administer ethanol or water for 60 min. As compared with CD rats, ED rats showed significantly greater intake of ethanol, but not water. No significant differences were found when separate groups of ED/CD rats were allowed to self-administer an alternate reinforcer (0.0075% saccharin solution). Rats who consistently had blood alcohol levels (BALs) above 100 mg% at the time of withdrawal sustained high levels of ethanol self-administration throughout the four withdrawal sessions. In contrast, rats who had an average BAL at withdrawal below 100 mg% showed progressive decreases in ethanol self-administration during repeated withdrawal episodes. The results demonstrated that chronic exposure to ethanol and repeated periods of abstinence are accompanied by elevated rates of ethanol intake in certain animals, and the persistence of elevated self-administration behavior of individual rats is predicted by their BAL at the time of withdrawal.

Operant ethanol-reinforced behavior in P, NP, HAD, and LAD rats bred for high versus low ethanol preference

These studies examined the reinforcing effects of ethanol in rats selectively bred for high versus low ethanol drinking in a two-bottle choice preference task, namely the Preferring (P), Non-Preferring (NP), High Alcohol Drinking (HAD), and Low Alcohol Drinking (LAD) rats. The results substantiate findings suggesting that genetic factors are significant in determining whether ethanol will come to serve as a reinforcer. P rats exhibited high levels of responding for ethanol compared with the water vehicle, NP and HAD rats exhibited more moderate levels of responding for ethanol, and the behavior of LAD rats suggested that ethanol served only inconsistently as a reinforcer for these rats. Overall, the results suggest the existence of distinct, biologically influenced components of ethanol drinking behavior. Preference appears to measure an inherent facilitative factor allowing animals to initiate ethanol drinking. The operant chamber paradigm appears to measure factors related to whether and to what extent ethanol will serve as a positive reinforcer following conditioned exposure to the drug. Although preferring animals generally find ethanol reinforcing there seems to be little quantitative relationship between degree of preference and whether ethanol will serve as a reinforcer. Lack of preference does not seem to be predictive of lack of reinforcement. Thus, it appears that preference for ethanol and reinforcement from ethanol are somewhat overlapping, but distinct factors that contribute to ethanol drinking. These results suggest the existence of multiple components of behavior mediated by multiple mechanisms that contribute to ethanol drinking.

Genetic models in the study of alcoholism and substance abuse mechanisms

1. Vulnerability to substance abuse is an important emerging issue. Some related factors are the relationship between propensity to self-administer a drug and neurosensitivity to that drug; similarities and differences between various models of drug seeking behavior; and the commonality of drug-seeking behavior across drugs and genotypes, that is, whether reinforcement from and abuse of alcohol and other drugs define variations within a single behavioral phenomenon, or whether reinforcement and abuse must be individually defined for each substance involved. 2. Findings related to these issues are now being obtained from the areas of pharmacogenetics and operant drug self-administration. 3. The results indicate that reinforcement from alcohol and other drugs is only moderately related to preference for alcohol and other drugs. In addition, neurosensitivity to drugs appears to have little influence on whether that drug will come to serve as a positive reinforcer for any given individual or animal. Indeed, the critical factor appears to be the individual organism's innate propensity to find a particular drug reinforcing. 4. Initial findings also show that genotypic patterns of reinforcement from ethanol appear to correlate highly with patterns of reinforcement from cocaine and opiates. 5. From these findings it is concluded that there exist important genetic determinants of drug reinforced behavior; reinforcement is an important and independent effect of several psychoactive drugs; and drug seeking behaviors maintained by ethanol, cocaine and opiates may have at least some common biological determinants.

Do rat strain differences in ethanol consumption reflect differences in ethanol sensitivity or the preparedness to learn?

Three strains of rats (Wistar, Sprague-Dawley, Long-Evans; n = 10/strain) were trained to drink various concentrations of ethanol (ETOH) in the rats' home cage in daily 30-min drinking sessions using a modified "Samson" sucrose-fading procedure. Wistar and Sprague-Dawley rats were similar in their voluntary intake of a wide range of ETOH concentrations and both of these strains drank considerably more ETOH than the Long-Evans strain. For comparison purposes only, pharmacological pretreatment tests were later conducted with the Sprague-Dawley strain of rats using a maintenance concentration of 20% w/v ETOH. Low-dose ETOH pretreatments increased (125% of control), and high-dose ETOH pretreatments decreased the subsequent voluntary consumption of ETOH. Low-dose nicotine pretreatments increased ETOH consumption to 148% of control intake, and high doses of nicotine decreased ETOH consumption. Both opiate antagonists, naloxone and naltrexone, produced dose-dependent decreases in ETOH consumption. The dopamine antagonist, haloperidol, produced dose- and time-dependent increases in voluntary ETOH consumption. The strain differences in voluntary ETOH consumption described in the present study differ from those previously described by other labs. We suggest that this strain-dependent disparity between laboratories, with respect to ETOH consumption/preference tasks, may reflect genetic differences in the preparedness to condition (learn) voluntary ETOH consumption rather than genetic differences in ETOH's reward/reinforcement attributes.

Molecular Mechanisms Associated with Cocaine Effects

Cocaine has been shown to be a highly addictive and toxic drug. It produces these effects and a variety of other physiological and behavioral effects through its interactions with several distinct central nervous system receptor sites. We present the results of a series of studies that utilized multiple site analyses to elucidate which cocaine binding sites influence the reinforcing and toxic effects of cocaine and with what proportion of influence. The nature of cocaine interactions with monoamine transporters is also discussed, especially with the dopamine transporter, which has been shown to be the cocaine binding site that is primarily associated with the reinforcing effects of cocaine. We also provide evidence that vulnerability to both the toxic and addictive effects of cocaine may be significantly influenced by genetic differences in both humans and animals. In view of the fact that cocaine is commonly abused in a polydrug situation, we present the results of both behavioral and biochemical experiments which suggest that common biochemical pathways may mediate the reinforcing or addictive properties of drugs of abuse. Finally, we discuss research on the biochemical mechanisms associated with effects of ethanol, particularly those which may also influence cocaine self-administration and speculate on pharmacotherapeutic strategies for concurrent abuse of cocaine and ethanol.

Stimulus-controlled responding for ethanol in AA and Wistar rats

A method for establishing stimulus control of ethanol responding was developed. After acquisition of lever pressing for oral ethanol, rats of the high-drinking AA (Alko, Alcohol) line and of the moderate-drinking Wistar strain were subjected to alternating 20-min alcohol access periods signaled by a stimulus light, and 40-min nonaccess periods with no light. Ethanol responding during access periods progressively increased and decreased during nonaccess. These changes were faster in the AAs than the Wistars, probably related to differential reinforcement from ethanol. In a second experiment, rats responding under stimulus control were given periods of alcohol deprivation of 3, 6, 12, and 24 h, indicated by a stimulus light. Deprivations shorter than 24 h increased the first-hour intake after renewed access by the AAs, but the Wistars showed no increase until after a 24-h deprivation. The results show stimulus control of ethanol responding and demonstrate the applicability of the procedure for causing ethanol responding to occur at a time chosen by the experimenter.

The effects of ethanol initiation procedures on ethanol reinforced behavior in the alcohol-preferring rat

Rats from the alcohol preferring (P) line developed at Indiana University were initiated to self-administer ethanol orally without food or water restriction using either a sucrose-fading or a secondary-conditioning procedure. Following initiation, they were tested under a variety of operant conditions to examine the ability of ethanol to reinforce lever pressing behavior. Regardless of initiation procedure, the animals maintained lever pressing behavior with ethanol reinforcement, even at ethanol concentrations as high as 40% (v/v). Slightly higher daily session intakes (g/kg) were found at the higher ethanol concentrations following the secondary-conditioning initiation procedure compared with the sucrose-fading technique. When both ethanol and water were concurrently available, the rats showed a high preference for ethanol reinforcement. When varying concentrations of sucrose were substituted for water, the amount of ethanol ingested decreased as the concentration of the alternative sucrose increased. However, if the response requirement for the sucrose was substantially greater than that for ethanol, the rats shifted their responding to the lever associated with ethanol presentation. The results are discussed in relation to prior work using similar procedures with Long-Evans non-selected rats and with the alcohol non-preferring (NP) rat line.

Differential reinforcement and diurnal rhythms of lever pressing for ethanol in AA and Wistar rats

High-drinking AA (Alko, Alcohol) and moderate-drinking Wistar rats, after ethanol drinking experience in their home cages, were housed continually in operant chambers with free access to water and food. Ethanol and water could be obtained by lever pressing on a concurrent FR1:FR1 schedule. The AA rats readily learned the operant response for oral ethanol, responded significantly more for ethanol than water, and increased ethanol responding when the fixed-ratio schedule for it was increased from FR1 to FR2 and FR4. This indicates that ethanol was serving as a reinforcer for the AAs. In contrast, the Wistars showed little evidence for ethanol reinforcement. Both AAs and Wistars had a three-peak pattern of ethanol responding during the dark phase, but peaks for the Wistars preceded those for the AAs by 1 or 2 hr. The patterns were similar when on an FR4 schedule, which greatly reduced the amount of alcohol, suggesting that they are not controlled by blood alcohol levels. The difference between the AA and Wistar patterns may, however, be related to the differential ethanol reinforcement.

Genetic approaches to studying drug abuse: correlates of drug self-administration

Some important issues in substance abuse are the relationship between propensity to self-administer a drug and neurosensitivity to that drug; similarities and differences between various models of drug-seeking behavior; and the commonality of drug-seeking behavior across drugs and genotypes. Findings related to these issues are now emerging from the areas of pharmacogenetics and operant drug self-administration. Ethanol has been readily established as a positive reinforcer in AA (Alcohol Accepting), P (Preferring) and LEWIS rats, as well as C57BL/6J and LS/Ibg mice. In low ethanol preferring F344 and NP (Non-Preferring) rats, ethanol maintains significant but low levels of responding. Ethanol does not maintain lever-pressing behavior in BALB/cJ or SS/Ibg mice, and is avoided in DBA/2J mice. This pattern of reinforcement from ethanol is only moderately correlated with ethanol preference, and is not correlated with neurosensitivity to ethanol, at least as measured by duration of loss of the righting reflex (LORR). However, these genotypic patterns of reinforcement from ethanol do appear to correlate highly with patterns of reinforcement from cocaine and opiates. From these findings it is concluded that: 1) there exist important genetic determinants of drug reinforced behavior; 2) ethanol preference is not a highly accurate measure of reinforcement from ethanol; 3) sensitivity to ethanol as measured by LORR and self-administration of this drug are not highly genetically correlated; and 4) drug-seeking behaviors maintained by ethanol, cocaine and opiates may have at least some common biological determinants.