Ethanol reinforcement in the alcohol nonpreferring rat: initiation using behavioral techniques without food restriction

Altered reward sensitivity to sucrose outcomes prior to drug exposure in alcohol preferring rats

Addiction involves key impairments in reward sensitivity (RS). The current study explored impaired RS to natural reward as a predisposing factor to addictive-like behavior. Alcohol preferring (P) rats are selectively bred based on significantly greater ethanol consumption and preference and offer the ability to inspect differences in subjects with a positive family history of addictive-like behavior. P rat's RS was compared to RS in the well-used Sprague-Dawley (SD) strain. To assess RS in a novel manner, instrumental incentive contrast, discrimination and consumption of sucrose solution were examined. Animals performed in a free operant situation for different sucrose concentration solutions using a block of 'mixed' trials with alternating outcome concentrations (e.g., 5 and 10 % sucrose) to change outcome value in a predictable manner. Animals also performed for reward in blocks of single outcome trials (5 or 10 or 20 or 40 % sucrose daily exposure) surrounding the mixed block. RS (e.g., reward discrimination and contrast effects between and within-sessions) was measured by changes in trials completed, instrumental response latency and consumption. P rats expressed an altered profile of RS with a greater tendency toward equivalent responding to different outcomes within the same session and an absence of incentive contrast from diverse reward comparisons. In contrast, SD animals expressed within-session reward discrimination and a subset of incentive contrast effects. These effects were moderated by food deprivation more consistently in SD compared to P rats. P rat alterations in processing natural rewards could predispose them to addictive-like behaviors including greater alcohol consumption and preference.

Making organisms model human behavior: situated models in North-American alcohol research, since 1950

We examine the criteria used to validate the use of nonhuman organisms in North-American alcohol addiction research from the 1950s to the present day. We argue that this field, where the similarities between behaviors in humans and non-humans are particularly difficult to assess, has addressed questions of model validity by transforming the situatedness of non-human organisms into an experimental tool. We demonstrate that model validity does not hinge on the standardization of one type of organism in isolation, as often the case with genetic model organisms. Rather, organisms are viewed as necessarily situated: they cannot be understood as a model for human behavior in isolation from their environmental conditions. Hence the environment itself is standardized as part of the modeling process; and model validity is assessed with reference to the environmental conditions under which organisms are studied.

Acute and chronic administration of a low-dose combination of topiramate and ondansetron reduces ethanol's reinforcing effects in male alcohol preferring (P) rats

Topiramate (a GABA/glutamate modulator) and ondansetron (a serotonin-3 antagonist) have shown promise as treatments for alcohol use disorders (AUDs), although efficacy is modest/variable for both medications. We recently showed in animal models of consumption and relapse that acute treatment with a combination of these medications was more efficacious than either alone. To determine whether the mechanism for its beneficial effects is through modulation of ethanol's reinforcing effects, we measured the effect of this combination in male alcohol preferring (P) rats (N = 22) responding for ethanol under a progressive-ratio (PR) schedule. Low doses, which either do not affect (ondansetron; 0.001 mg/kg) or only modestly affect (topiramate; 10 mg/kg) alcohol-related behaviors on their own, were selected in an attempt to maximize their combined efficacy while minimizing potential side effects. In addition to acute treatment (1 day), the effects of chronic administration (10 days) were examined in an attempt to model human treatment approaches. The effects of the combination were compared with the low dose of topiramate alone hypothesizing that the combination would be more efficacious than topiramate alone. Although both topiramate and the combination similarly reduced PR responding for ethanol following acute treatment and during the initial phase of chronic treatment (Days 1-5), after repeated administration (Days 6-10), only the combination produced a sustained reduction in ethanol-maintained responding. These results suggest an advantage of the combination over topiramate alone at producing a sustained reduction in ethanol's reinforcing effects following prolonged treatment, and lend further support for its use as a potential treatment for AUDs.

Effects of oral loperamide on efficacy of naltrexone, baclofen and AM-251 in blocking ethanol self-administration in rats

Naltrexone is a μ-opioid receptor antagonist that has been extensively studied for its ability to block the rewarding effects of ethanol. Opioid receptors are widely distributed within the gastrointestinal tract (GIT). Typically, naltrexone is administered by parenteral routes in nonclinical studies. We initially tested if opioid receptors within the GIT would influence the ability of oral naltrexone to inhibit ethanol oral self-administration in rats using the co-administration of oral loperamide, a peripherally restricted opioid agonist. As expected, oral naltrexone only had modest effects on ethanol intake, and the response was not dose-dependent. However in rats, treatment with loperamide prior to the administration of naltrexone resulted in a suppression of ethanol intake which approached that observed with naltrexone given by the subcutaneous (SC) route. Importantly, administration of loperamide prior to administration of naltrexone did not alter blood concentrations of naltrexone. We then evaluated if oral loperamide would enhance effects of baclofen (a GABA(B) receptor agonist) and AM-251 (a CB-1 receptor antagonist) and found that pre-treatment with loperamide did potentiate the action of both drugs to reduce ethanol self-administration. Finally, the specific opioid receptor type involved was investigated using selective μ- and κ-receptor antagonists to determine if these would affect the ability of the AM-251 and loperamide combination to block ethanol drinking behavior. The effect of loperamide was blocked by ALKS 37, a peripherally restricted μ-receptor antagonist. These data suggest an important role for opioid receptors within the GIT in modulating central reward pathways and may provide new insights into strategies for treating reward disorders, including drug dependency.

A 3-day exposure to 10% ethanol with 10% sucrose successfully initiates ethanol self-administration

The initiation phase of ethanol self-administration is difficult to study using the well-established, sucrose-fading procedure due to the changing concentrations of ethanol in the first few days. The purpose of this experiment was to test whether a modified sucrose-substitution procedure in which rats are initially exposed to high concentrations of ethanol and sucrose for three days would successfully initiate ethanol self-administration. Male Long-Evans rats were trained to lever-press with a 10% sucrose solution in which four or 20 responses allowed 20-min access to the solution. Subsequently, rats were exposed to a 3-day period of operant self-administration of 10% sucrose+10% ethanol. This constant-concentration exposure was followed by the standard procedure in which sucrose is completely faded out. The establishment of ethanol self-administration was determined by ethanol intake, pre- and postprocedure two-bottle choice preference tests, and extinction trials. The mean ethanol intake was 2.2 times higher on day 2 compared with day 1 on the 10% sucrose+10% ethanol solution. After fading out the sucrose, the daily intake of 10% ethanol solution over 5 days was stable at approximately 0.57 g/kg. Ethanol preference was approximately threefold higher after the modified sucrose-fading procedure. Responding during a single session extinction test was dramatically increased from 4 to 61+/-13 or 20 to 112+/-22 responses in 20 min. Similar to the standard sucrose-fading method, we did not observe a significant relationship between extinction responding and ethanol intake. Blood alcohol concentrations were 4.5 mM 20 min after consumption began. We conclude that initiation and establishment of ethanol self-administration will occur using this modified sucrose-fading procedure.

Warsaw high-preferring (WHP) and Warsaw low-preferring (WLP) lines of rats selectively bred for high and low voluntary ethanol intake: preliminary phenotypic characterization

The Warsaw High Preferring (WHP) and Warsaw Low Preferring (WLP) lines were bred from Wistar foundation stock to obtain lines of rats that differ in their preference for ethanol solutions. The WHP line has met several major criteria for an animal model of alcoholism. The WHP rats voluntarily drink excessive amounts of ethanol while the WLP rats consume negligible amounts of ethanol. The WHP rats attain physiologically active blood ethanol concentrations with chronic free-choice drinking. They also develop subtle but visible signs of physical dependence (the withdrawal signs). The patterns of ethanol consumption in WHP and WLP lines are stable in time and independent of the manner of access to ethanol solutions. Notably, when exposed to the increasing ethanol concentrations WHP rats gradually increased total ethanol intake whereas the WLP rats consumed invariably very low amounts of ethanol. Furthermore, the WHP rats show an increased responsiveness to the stimulatory effects of low dose of ethanol.

Restraint stress and ethanol consumption in two mouse strains

BACKGROUND

This study examined the interaction between restraint stress and ethanol drinking in mice that consume low and high amounts of ethanol.

METHODS

Two strains of mice (129SVEV and C57BL/6J) underwent 1 hour of restraint stress twice per day for 4 days in the presence of a CRF-1 receptor antagonist, a glucocorticoid receptor antagonist or vehicle. Ethanol preference and consumption were assessed using a two bottle choice design. In another study, mice were implanted with pellets containing corticosterone; ethanol preference and consumption were assessed using a two bottle choice design.

RESULTS

Restraint stress significantly increased ethanol preference and consumption in 129SVEV mice but not in C57BL/6J mice. Then 129SVEV mice underwent the identical stress procedure; however, mice received either the CRF-1 receptor antagonist, R121919 (15 or 20 mg/kg, ip) or vehicle 30 minutes prior to stress. R121919 did not block the stress-induced change in ethanol preference despite causing a significant blunting in the HPA axis. Negative results were also obtained using the CRF-1 receptor antagonist, Antalarmin (20 mg/kg, ip). In another study, 129SVEV mice were administered either the glucocorticoid receptor antagonist Mifepristone (25, 50 or 100 mug/kg, ip) or vehicle under the same procedure. Mifepristone did not alter ethanol preference. Moreover, the three receptor antagonist did not alter nonstress ethanol consumption either. In the last study, both mouse strains underwent active or sham adrenalectomy, then pellets containing corticosterone or placebo were implanted and preference for ethanol versus water was tested. Corticosterone administration decreased ethanol consumption in a strain-dependent manner.

CONCLUSION

These data show the restraint model for stress can modestly increase ethanol consumption in 129SVEV mice but not in C57BL/6J mice. Pharmacologic manipulation of CRF and corticosterone did not blunt baseline or stress-induced change in ethanol preference nor did administration of corticosterone mimic the effects of restraint stress on ethanol consumption. These findings suggest the mechanism responsible for increasing ethanol consumption in this model is independent of the HPA axis and extra-hypothalamic CRF.

Goal- and signal-directed incentive: conditioned approach, seeking, and consumption established with unsweetened alcohol in rats

RATIONALE

Many theories of addictive behavior propose that cues signaling drug administration influence the likelihood of drug-taking and drug-seeking behavior.

OBJECTIVES

We investigated the behavioral impact of cues associated with unsweetened ethanol and their interaction with responding maintained by ethanol self-administration. Our goal was to establish the influence of such cues on ethanol seeking.

MATERIALS AND METHODS

The experiment used a matching contingency and saccharin-fading procedure to establish equal levels of responding to two spatially distinct levers using unsweetened 10% ethanol solution. After ethanol self-administration was established, a brief cue light located alternately over each lever location was either paired or unpaired (control) with the opportunity to consume the same ethanol solution. Finally, self-administration was re-established, and the effect of the cue was measured in a transfer design.

RESULTS

The reaction to lights paired with the opportunity to ingest unsweetened ethanol had three main effects: (1) induction of operant behavior reinforced by ethanol, (2) stimulation of ethanol-seeking behavior (drinker entries), and (3) cue-directed approach and contact behavior (i.e. autoshaping or sign-tracking). Cue-directed behavior to the light interacted with choice behavior in a manner predicted by the location of the cue light, enhancing responding only when the approach response did not interfere with the operant response.

CONCLUSIONS

These findings replicate and extend the effects of Pavlovian conditioning on ethanol-seeking and support-conditioned incentive theories of addictive behavior. Signals for ethanol influence spatial choice behavior and may be relevant to attentional bias shown to alcohol-associated stimuli in humans.

Dopamine and benzodiazepine-dependent mechanisms regulate the EtOH-enhanced locomotor stimulation in the GABAA alpha1 subunit null mutant mice

The present study investigated the role of the alpha1-containing GABA(A) receptors in the neurobehavioral actions of alcohol. In Experiment 1, mice lacking the alpha1 subunit (alpha1 (-/-)) were tested for their capacity to initiate operant-lever press responding for alcohol or sucrose. Alcohol intake in the home cage was also measured. In Experiment 2, the alpha1 (-/-) mice were injected with a range of alcohol doses (0.875-4.0 g/kg; i.p.) to evaluate the significance of the alpha1 subunit in alcohol's stimulant actions. In Experiment 3, we determined if the alcohol-induced stimulant effects were regulated via dopaminergic (DA) or benzodiazepine (BDZ)-dependent mechanisms. To accomplish this, we investigated the capacity of DA (eticlopride, SCH 23390) and BDZ (flumazenil, betaCCt) receptor antagonists to attenuate the alcohol-induced stimulant actions. Compared with wild-type mice (alpha1 (+/+)), the null mutants showed marked reductions in both EtOH and sucrose-maintained responding, and home-cage alcohol drinking. The null mutants also showed significant increases in locomotor behaviors after injections of low-moderate alcohol doses (1.75-3.0 g/kg). betaCCt, flumazenil, eticlopride, and SCH 23390 were able to attenuate the alcohol-induced stimulation in mutant mice, in the absence of intrinsic effects. These data suggest the alpha1 receptor plays an important role in alcohol-motivated behaviors; however, it also appears crucial in regulating the reinforcing properties associated with normal ingestive behaviors. Deleting the alpha1 subunit of the GABA(A) receptor appears to unmask alcohol's stimulatory effects; these effects appear to be regulated via an interaction of both DA- and GABA(A) BDZ-dependent mechanisms.

Limited-access consumption of ascending ethanol concentrations in alcohol-preferring, nonpreferring, and Sprague-Dawley rats

BACKGROUND

Ethanol intake and preference differences between the selectively bred alcohol-preferring (P) and nonpreferring (NP) rats have generally been studied in a continuous-access paradigm using 10% ethanol. Little is known about the consumption of lower concentrations of ethanol in these lines or consumption of a wide range of ethanol concentrations in limited-access paradigms. Recently, limited-access paradigms have been used to study the biological and pharmacological mechanisms of ethanol consumption in animal models. Such research would be informed by studies investigating ethanol oral self-administration within a limited-access context. Therefore, the current study addressed P, NP, and Sprague-Dawley (SD) rats' consumption of a wide range of ethanol concentrations in a 2-bottle-choice, limited-access procedure.

METHODS

Male P, NP, and SD rats were given concurrent access to water and ethanol solutions for 1 h/d, 7 d/wk. Ethanol solutions were presented in an ascending series ranging from 0.01 to 20% (v/v) over 55 days. Ethanol intakes (g/kg), volumes of solutions consumed (mL/kg), and preference ratios were assessed for each rat line at each concentration.

RESULTS

Clear differences among the 3 types of rats emerged at an ethanol concentration of 4%, although differences between P and NP rats emerged at concentrations as low as 1.8%. Alcohol-preferring rats almost exclusively preferred ethanol solutions over water at ethanol concentrations of 4% and above, whereas SD and NP rats' preference ratios were more variable.

CONCLUSIONS

The results suggest that differences between P and NP rats exist at ethanol concentrations lower than those previously studied in continuous-access paradigms. They also provide a current description of the ranges of ethanol concentrations preferred by P, NP, and SD rats.

Progress in Using Mouse Inbred Strains, Consomics, and Mutants to Identify Genes Related to Stress, Anxiety, and Alcohol Phenotypes

This article summarizes the proceedings of a symposium that took place at the 2005 meeting of the Research Society on Alcoholism. The organizers/chairs were Daniel Goldowitz and Katheen A. Grant. The presentations were as follows: (1) High-Throughput Screening for Ethanol Phenotypes, by Douglas B. Matthews and Kristin M. Hamre; (2) Genetic Basis of Schedule-Induced Polydipsia in Mice, by Guy Mittleman and Elissa J. Chesler; (3) Effects of Stress and Ethanol Dependence on Ethanol Self-administration in Inbred and Mutant Mice, by Howard C. Becker and Marcelo F. Lopez; (4) Changes in Dopaminergic Mechanisms Associated With Ethanol Dependence, by Sara R. Jones and Tiffany A. Mathews; and (5) Defining Brain Region-Specific Gene Networks Relevant to Ethanol Behaviors, by Michael F. Miles and Robnet Kerns.

Assessment of sustained attention in ad libitum fed Wistar rats: effects of MK-801

RATIONALE

Rodent models designed to assess cognitive function, such as sustained attention tasks, use food and/or fluid restriction in order to motivate responding. However, evidence indicates that dietary restriction can have profound effects on brain function and on the neurobehavioral effects of drugs.

OBJECTIVE

The primary objective of this study was to demonstrate the feasibility of using ad libitum fed rats to assess sustained attention in an operant 2-choice reaction time (2-CRT) task. Because N-methyl-D-aspartate (NMDA) receptor function is critical for sustaining attention in animal models, the effects of the NMDA antagonist MK-801 on 2-CRT performance were also assessed.

METHODS

Male Wistar rats (n = 20) rats were trained to perform an operant 2-CRT task. A 10% sucrose solution was used as the reinforcer. After performance levels stabilized, the effects of MK-801 (0.01-0.12 mg/kg, IP) were assessed.

RESULTS

Stable levels of performance on the final version of the 2-CRT task was established after 2-3 months of training. Consistent with prior reports, correct trials varied as a function of stimulus light duration (1000 ms: 67 +/- 3%, 500 ms: 59 +/- 3%, 100 ms: 51 +/- 3%, 50 ms: 43 +/- 2%). Administration of 0.06 mg/kg MK-801 significantly increased choice accuracy. Administration of 0.12 mg/kg MK-801 significantly slowed reaction times and resulted in pronounced motor incoordination.

CONCLUSIONS

This study demonstrates that ad libitum fed rats can be trained to perform a 2-CRT task. However, the levels of choice accuracy are lower than typically observed under conditions of dietary restriction. The increase in choice accuracy following MK-801 is consistent with the effects of psychomotor stimulants and may suggest sustained attention was slightly enhanced by MK-801.

Brain stimulation reward performance and sucrose maintained behaviors in alcohol-preferring and -nonpreferring rats

BACKGROUND

The relation between ethanol (EtOH) preference and sensitivity to brain stimulation reward (BSR) was examined under multiples schedules of reinforcement in the current study. For comparison, the study also examined the relation between EtOH preference and motivation for a sweet, palatable sucrose solution under similar schedules of reinforcement.

METHODS

To investigate sensitivity to BSR performance, alcohol-preferring and -nonpreferring rats were tested using the curve-shift (rate-frequency) paradigm under several intensity levels during a 20-min session. Animals were first trained under an optimal current intensity, which produced maximal responding (i.e., 100%) across a series of descending frequencies (i.e., 300-20 Hz). BSR was then evaluated at 100%, 75%, and 50% of the optimal current. The sensitivity of the curve-shift method was further evaluated under the animal's optimal current using the FR1, FR6, and FR12 schedules. To examine responding for the sucrose solution, a separate group of alcohol-preferring and -nonpreferring rats was initially stabilized on an FR1 schedule and then subsequently on FR6 and FR12 schedules.

RESULTS

The results demonstrated that reducing the reinforcing efficacy of BSR via reduction in current intensity/reinforcement schedule produced marked orderly rightward shifts in the rate-frequency curves relating responding to stimulation frequency in both rat lines. However, no differences were found between the lines with either manipulation. Specifically, both lines demonstrated orderly reductions in response rate and increases in BSR threshold parameters (i.e., half maximal frequency/responding, minimum and maximum frequencies). In contrast to BSR, genetic selection for EtOH preference was highly associated with responding for the sweet, palatable sucrose solution. The association was even more salient as the reinforcement schedule increased (i.e., reward cost).

CONCLUSION

The results demonstrate that responding for BSR is not associated with EtOH preference, insofar as alcohol-preferring and -nonpreferring rats respond similarly under an array of reinforcement schedules and current intensities. In contrast, genetic selection for EtOH preference is highly associated with responding for a palatable sucrose reward, and the relation increases as the reward cost for the sucrose increases. These findings suggest that similar/overlapping mechanisms of action regulate the reinforcing properties of EtOH and sucrose but that overlapping yet distinct neuronal mechanism may modulate the reward characteristics of BSR and EtOH preference.

Effects of Long-Term Episodic Access to Ethanol on the Expression of an Alcohol Deprivation Effect in Low Alcohol???Consuming Rats

BACKGROUND

The alcohol-preferring (P) and -nonpreferring (NP) and high alcohol-drinking (HAD) and low alcohol-drinking (LAD) rats have been selectively bred for divergent preference for ethanol over water. In addition, both P and HAD rats display an alcohol deprivation effect (ADE). This study was undertaken to test whether the NP, LAD-1, and LAD-2 lines of rats could display an ADE as well.

METHOD

Adult female NP, LAD-1, and LAD-2 rats were given concurrent access to multiple concentrations of ethanol [5, 10, 15% (v/v)] and water in an ADE paradigm involving an initial 6 weeks of 24-hr access to ethanol, followed by four cycles of 2 weeks of deprivation from and 2 weeks of re-exposure to ethanol (5, 10, and 15%). A control group had continuous access to the ethanol concentrations (5, 10, and 15%) and water through the end of the fourth re-exposure period.

RESULTS

For NP rats, a preference for the highest ethanol concentration (15%) was evident by the end of the fifth week of access (approximately 60% of total ethanol fluid intake). Contrarily, LAD rats did not display a marked preference for any one concentration of ethanol. All three lines displayed an ADE after repeated cycles of re-exposure to ethanol, with the general ranking of intake being LAD-1 > NP > LAD-2 (e.g., for the first day of reinstatement of the third re-exposure cycle, intakes were 6.5, 2.9, and 2.4 g/kg/day compared with baseline values of 3.1, 2.0, and 1.3 g/kg/day for each line, respectively). By the 13th week, rats from all three lines, with a ranking of LAD-1 > NP > LAD-2, were drinking more ethanol (3.3, 2.2, and 2.0 g/kg/day, respectively) compared with their consumption during the first week of access (approximately 1.1 g/kg/day for all three lines).

CONCLUSION

These data indicate that access to multiple concentrations of ethanol and exposure to multiple deprivation cycles can partially overcome a genetic predisposition of NP, LAD-1, and LAD-2 rats for low alcohol consumption. In addition, the findings suggest that genetic control of low alcohol consumption in rats is not associated with the inability to display an ADE.

Controlled and behaviorally relevant levels of oral ethanol intake in rhesus macaques using a flavorant-fade procedure

BACKGROUND

Flavorant-fading procedures can initiate and maintain oral ethanol intake in rodents. The present study developed a similar procedure to achieve controlled and behaviorally relevant levels of ethanol intake in monkeys.

METHODS

Male rhesus macaques (N = 13) were initially given the opportunity to consume 0.5 g/kg of a 1% (w/v) ethanol plus 4% (w/v) Tang solution in 1-hr limited-access sessions without the requirement of an operant response. Once consumption was stable at a particular concentration (%) and/or amount (g/kg), animals were given access to higher concentrations and/or amounts of ethanol. Animals were tested on a bimanual motor skill (BMS) task 20 and 90 min after consumption to assess behavioral impairment. Blood alcohol levels (BALs) were assessed after a session in which animals had the opportunity to consume up to 3.0 g/kg of 6% (w/v) ethanol.

RESULTS

The gradual fading up of higher concentrations and amounts of ethanol resulted in controlled and robust levels (>2.0 g/kg) of ethanol intake in half of the subjects. Increasing the concentration of the sweetener from 4 to 6% (w/v) was effective in initiating consumption in three animals. Two monkeys required the additional step of presenting the increased-sweetener solutions after a meal (postprandial consumption) to initiate significant ethanol intake. Animals were significantly impaired on the BMS task after consumption of 2.0, 2.5, and 3.0 g/kg of ethanol. Individual consumption ranging from 0.8 to 3.0 g/kg of ethanol produced BALs of 18 to 269 mg/dl.

CONCLUSIONS

The flavorant-fading procedure was effective in producing behaviorally relevant levels of ethanol consumption in rhesus macaques. This model facilitated a randomized-dose procedure to determine the behavioral effects of 0.5 to 3.0 g/kg of ethanol. This procedure therefore is of significant utility in determining behavioral or physiologic effects of specific doses of consumed ethanol in monkeys.

Oral cocaine seeking by rats: action or habit?

Having established that the presence of cocaine in a 10% (wt/vol) sucrose solution enhanced the reinforcing properties of the solution in a dose-dependent manner, the authors investigated the susceptibility of oral cocaine seeking to outcome devaluation. Rats were trained to perform different instrumental responses for a cocaine-sucrose and a lemon-sucrose solution. An aversion was then conditioned from either the cocaine-sucrose or the lemon-sucrose solution by pairing consumption with lithium chloride. When instrumental performance was subsequently tested in extinction, the rats performed the lemon-sucrose response less if this solution, rather than cocaine-sucrose, had been devalued by aversion conditioning. By contrast, performance of the cocaine-sucrose response was unaffected by whether the cocaine-sucrose or the lemon-sucrose solution had been devalued.

Pavlovian Conditioning With Ethanol: Sign-Tracking (Autoshaping), Conditioned Incentive, and Ethanol Self-Administration

BACKGROUND

Conditioned incentive theories of addictive behavior propose that cues signaling a drug's reinforcing effects activate a central motivational state. Incentive motivation enhances drug-taking and drug-seeking behavior. We investigated the behavioral response to cues associated with ethanol and their interaction with operant self-administration of ethanol.

METHODS

In two experiments, rats received operant training to press a lever for a sweetened ethanol solution. After operant training, the animals were given Pavlovian pairings of a brief and localized cue light with the sweetened ethanol solution (no lever present). Lever pressing for ethanol was then re-established, and the behavioral effects of the cue light were tested during an ethanol self-administration session.

RESULTS

The conditioned responses resulting from pairing cue lights with the opportunity to ingest ethanol had three main effects: (1) induction of operant behavior reinforced by ethanol, (2) stimulation of ethanol-seeking behavior (magazine entries), and (3) signal-directed behavior (i.e., autoshaping, or sign-tracking). Signal-directed behavior interacted with the other two effects in a manner predicted by the location of the cue light. These conditioned responses interact with operant responding for ethanol reinforcement.

CONCLUSIONS

These findings demonstrate the importance of Pavlovian conditioning effects on ethanol self-administration and are consistent with conditioned incentive theories of addictive behavior.

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.

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

BACKGROUND

The purpose of these experiments was to provide an initial investigation into ethanol self-administration elicited in the schedule-induced polydipsia (SIP) paradigm.

METHODS

Mature male mice were food deprived to between 80 and 85% of their baseline weight and received 20 daily 1 hr SIP test sessions in which a food pellet (20 mg) was delivered on a fixed-time 60 sec schedule. In different groups, the acquisition of drinking 5% (v/v) ethanol solution (experiment 1) or water (experiment 2) was recorded along with other behaviors that occurred in the test chambers.

RESULTS

Results indicated that C57BL/6J mice drank significantly more ethanol than DBA/2J mice and that C57 mice achieved blood alcohol concentrations as high as 300 mg/dl. Blood alcohol concentrations were consistently correlated with g/kg ethanol intake. The groups did not differ in consumption of water. SIP test sessions using higher concentrations of ethanol (10-20% v/v, experiment 1) or sucrose solutions (0.1-2% w/v, experiment 2) then were performed. Group differences in ethanol consumption were maintained at all ethanol concentrations. Although DBAs drank more of a low concentration of sucrose (0.1%), when expressed as g/kg, sucrose intake was equivalent in the two strains at all concentrations. Analysis of the time course of drinking clearly showed that this behavior was adjunctive in nature.

CONCLUSION

These results demonstrate the effectiveness of this procedure in inducing ethanol self-administration and its utility for investigating the genetic bases of vulnerability toward excessive ethanol consumption.

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.

Overexpression of dopamine D2 receptors reduces alcohol self-administration

The mechanism(s) underlying predisposition to alcohol abuse are poorly understood but may involve brain dopamine system(s). Here we used an adenoviral vector to deliver the dopamine D2 receptor (DRD2) gene into the nucleus accumbens of rats, previously trained to self-administer alcohol, and to assess if DRD2 levels regulated alcohol preference and intake. We show that increases in DRD2 (52%) were associated with marked reductions in alcohol preference (43%), and alcohol intake (64%) of ethanol preferring rats, which recovered as the DRD2, returned to baseline levels. In addition, this DRD2 overexpression similarly produced significant reductions in ethanol non-preferring rats, in both alcohol preference (16%) and alcohol intake (75%). This is the first evidence that overexpression of DRD2 reduces alcohol intake and suggests that high levels of DRD2 may be protective against alcohol abuse.

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.

An investigation into the effects of 5-HT agonists and receptor antagonists on ethanol self-administration in the rat

Pharmacological manipulation leading to altered 5-HT function has been widely demonstrated to reduce ethanol intake in free choice tests. The aim of the present study was to examine the effects of a range of compounds known to influence 5-HT neurotransmission, including selective 5-HT receptor agonists and antagonists, on ethanol ingestion and maintained behaviour in an operant self-administration paradigm. Female Sprague-Dawley rats were trained to respond for 8% ethanol (v/v) in a 60-min test by a previously described technique. The number of responses and ethanol reinforcers (dipper deliveries), ethanol consumption (g/kg of body weight), and locomotor activity (LMA) were measured following administration of 5-HT agonists (5-HT, d-fenfluramine, fluoxetine, buspirone, TFMPP, and DOI) and antagonists (metergoline, ritanserin, and ondansetron) 30 min prior to testing. d-Fenfluramine, fluoxetine, buspirone, TFMPP, and DOI all produced a reduction in ethanol ingestion and maintained behaviour at doses that failed to reduce LMA. Conversely, metergoline and ritanserin only reduced ethanol self-administration at doses that concomitantly reduced LMA. 5-HT and ondansetron were without effect on any measure. These results demonstrate that, under the present experimental conditions, activation of central 5-HT1A, 5-HT1B, and 5-HT2 receptors reduced ethanol intake and reinforced behaviour in an operant paradigm.

Genetic selection of alcohol preference can be countered by conditioning processes

Twenty-four P rats and 24 NP rats were conditioned to consume 10% w/v alcohol in daily 0.5-h limited access periods using a modified version of Samson's sucrose fading procedure. Both P and NP rats demonstrated a strikingly similar day-to-day pattern of alcohol intakes. For the most part, P rats drank more than NP rats, but by the middle of the fourth month of drinking, P and NP rats were drinking equivalent amounts of alcohol. Both P and NP rats consumed alcohol in amounts similar to two outbred strains of rats (Wistar and Sprague-Dawley) previously conditioned to drink alcohol in this laboratory.

Effects of sucrose-substitution initiation on patterns of drinking by Lewis rats during continuous alcohol access

Initiation of alcohol drinking using the sucrose-substitution procedure was studied in inbred Lewis rats. One group of animals was initiated to self-administer alcohol prior to being placed in the continuous-access condition, whereas the second group of animals did not undergo initiation. During the continuous-access period, the animals were housed in operant chambers where they had continuous access to alcohol (10% v/v), food, and water during daily 23-h experimental sessions. After 5 weeks of baseline conditions, the response, requirement for food was increased over weeks. This was followed by weekly increases in the ethanol response requirement with the food response requirement returned to baseline conditions. In the continuous-access condition, both groups consumed similar amounts of alcohol by the end of the 4-week baseline period and showed similar numbers of dippers presented per alcohol bout and number of alcohol bouts per day. During the food response requirement manipulation, alcohol consumption increased for both groups but intake increased significantly more for the noninitiated group. The difference between groups was accounted for by a larger number of alcohol drinking bouts per day for the noninitiated group. Alcohol consumption decreased at each increase in ethanol reinforcement response requirement for both groups. Alcohol-reinforced responding per session increased for the noninitiated animals but remained unchanged for the initiated group during this condition. Responding increased substantially for both groups when the alcohol reinforcement response requirement was returned to baseline conditions. These results suggest that alcohol may serve more as a food source for noninitiated animals during the food reinforcement manipulation and that initiation may result in more resistance to change during the alcohol reinforcement manipulation. These data show that the type of initial exposure to alcohol can impact future drinking patterns.

Alcohol, GABAA-benzodiazepine receptor complex, and aggression

Neurobiological investigations have become productive since experimental protocols were developed that engender large increases in aggressive behavior after acute alcohol challenges in individual experimental animals. Recent developments extended the heightened aggressive behavior to rats that self-administered alcohol shortly before the social confrontation. Quantitative ethological analysis revealed that alcohol prolongs "bursts" of aggressive acts and displays and disrupts communication between the aggressive animal and the opponent who defends, submits, or flees. Pharmacological modulation of the GABAA receptor with benzodiazepine agonists and neuroactive steroids results in dose-dependent biphasic changes in aggressive behavior that mimic the dose-effect function of alcohol; benzodiazepines potentiate the aggression-heightening effects of alcohol as well as the behaviorally suppressive effects; and antagonists at benzodiazepine receptors prevented the aggression-heightening effects of alcohol. The maturational and experiential origins for potentially distinctive GABAA receptor characteristics in individuals who exhibit heightened aggressive behavior await identification.

The 5-HT1A receptor agonist 8-OH-DPAT reduces ethanol intake and maintained behavior in female Sprague-Dawley rats

Agents affecting serotonergic (5-hydroxytryptamine, 5-HT) function influence ethanol consumption in rats and primates. In the present study female Sprague-Dawley rats were trained to orally self-administer 8% ethanol (v/v) in a large operant chamber in a 60-min test period by a prandial drinking technique. The number of response, ethanol reinforcers (dipper deliveries), and ethanol consumption (g/kg) were measured following administration of the 5-HT1 A agonist 8-OH-DPAT (0.001 1.0 mg/kg, ip) 30 min prior to testing. Locomotor activity (LMA) was also measured to assess activity changes induced by 8-OH-DPAT. 8-OH-DPAT selectively reduced ethanol ingestion from 17.1 +/- 3.2 dipper deliveries under vehicle conditions to 6.6 +/- 3 at a dose of 0.1 mg/kg. Higher doses of 8-OH-DPAT (0.5 and 1.0 mg/kg) significantly reduced both ethanol ingestion and LMA. Lower doses of 0.001-0.01 mg/kg of 8-OH-DPAT were without effect on ethanol intake and maintained behavior. These results demonstrate that, under the present experimental conditions, the 5-HT1A receptor agonist 8-OH-DPAT reduced ethanol self-administration in the rat, and support a role for 5-HT1A receptors in the mediation of ethanol reinforcement.

Genetic differences in naloxone enhancement of ethanol-induced conditioned taste aversion

The influence of the opioid system on acquisition of an ethanol-induced conditioned taste aversion was examined in alcohol-preferring and avoiding inbred strains of mice (C57BL/6J and DBA/2J). Fluid-deprived mice from each strain received either ethanol alone, naloxone alone, or both ethanol and naloxone immediately after access to a novel tasting fluid. Naloxone alone (1 or 3 mg/kg) did not induce a conditioned taste aversion in either strain of mice. Administration of ethanol (1.5 g/kg) to DBA/2J mice produced a moderate taste aversion that was not affected by co-administration of naloxone. Although ethanol administered alone (3 g/kg) did not cause a taste aversion in C57BL/6J mice, the combination of ethanol and the higher dose of naloxone produced a significant taste aversion that increased across trials. A second experiment addressed the possibility that naloxone failed to enhance the ethanol-induced condition taste aversion in DBA/2J mice due to a "floor" effect on consumption. A lower ethanol dose (1 g/kg) was given alone or in combination with naloxone (1 or 3 mg/kg). Again, ethanol produced a moderate conditioned taste aversion that was not potentiated by naloxone. Subsequent conditioning with a high ethanol dose produced further suppression of intake, confirming that naloxone's failure to enhance aversion on earlier trials was not due to a "floor" effect. These data demonstrate a strain specific interaction between the aversive effect of ethanol and naloxone. More specifically, the results indicate that blockade of opioid receptors enhances the aversive effect of ethanol in C57BL/6J but not DBA/2J mice, suggesting that genetically determined differences in the endogenous opioid system of alcohol-preferring mice may mitigate ethanol's aversive effect.

Initiation of ethanol self-administration by the sucrose-substitution method with HAS and LAS rats

This study was performed to examine ethanol self-administration in rats bred for different sensitivities to the sedative effects of alcohol [the Colorado High Alcohol Sensitive (HAS) and Low Alcohol Sensitive (LAS) rats]. Four rats from each replicate line of the HAS and LAS rats (n = 16) were obtained from the University of Colorado, and initiation to self-administer ethanol by the sucrose-substitution procedure was attempted. Before the initiation procedure was conducted, home-cage ethanol intake and preference ratio did not differ between LAS and HAS rats. During the initiation procedure, the LAS rats came to self-administer 10% ethanol (v/v) at similar levels as outbred Wistar rats initiated with the same procedure (approximately 0.4 g/kg/session). The HAS rats, however, failed to initiate (approximately 0.08 g/kg/ session after completing the sucrose-substitution procedure) and lever pressing was reduced even more in the HAS rats when the ethanol concentration presented was > 10% (v/v). Three of the eight HAS rats stopped lever pressing completely when the ethanol concentration was raised to 15%. After initiation, home-cage preference ratio differed significantly between the LAS and HAS rats (LAS > HAS, p < 0.03). That the LAS rats did not consume greater amounts of ethanol compared with outbred Long-Evans or Wistar rats is contrary to our hypothesis, based on recent human data suggesting that a lower sensitivity to ethanol could result in increased alcohol intake. The finding that the HAS rats could not be initiated, while selectively bred ethanol nonpreferring rats can, is also contrary to our hypothesis. Further studies related to ethanol self-administration with the HAS line could provide important information related to the genetics of alcohol nonacceptance.

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.

Family history of alcoholism and the mediation of alcohol intake by catalase: further evidence for catalase as a marker of the propensity to ingest alcohol

Earlier studies have suggested that catalase activity (CA) may represent a biological marker of alcohol intake in animals and in humans. An initial study was designed to rule out the possibility that CA is induced as a function of acute alcohol intake. Subjects (n = 80) were presented with either an alcohol (0.5 g/kg of body weight) or control solution, and asked to provide four 100-microliters blood samples at 0.0, 0.5, 2.0, and 24.0 hr. Results showed no differences in CA between individuals who had received alcohol, and controls, even when the effects of previous drinking history were covaried out. This lack of effect of acute alcohol intake on the possible induction of CA further supported the notion that CA may be a viable marker of alcohol intake, rather than the converse. In the second study, the relation between CA and alcohol intake was investigated in individuals with a family history (FH) of alcoholism (FH+), and in those without a family history of alcoholism (FH-). Subjects (n = 607) completed the Michigan Alcoholism Screening Questionnaire, the MacAndrew Scale, and the Concordia University Alcohol Screening Questionnaire; answered questions concerning their FH for alcoholism; and provided a 100-microliters blood sample. Results showed that FH+ individuals had higher mean CA compared with FH- individuals. When individuals with FH+ were compared with those with FH-, differences in the pattern of relation between CA and alcohol intake were observed. Although a significant relation between CA and alcohol intake was obtained for both FH- and FH+ individuals, this relation was significantly higher (p < 0.001) for individuals with FH+.(ABSTRACT TRUNCATED AT 250 WORDS)

Sucrose, ethanol, and sucrose/ethanol reinforced responding under variable-interval schedules of reinforcement

Adding sweeteners to ethanol solutions is a common method of inducing rats to consume ethanol. However, it has usually been assumed that it is the sweet taste and/or the calories contained in the sweet solution that controls consumption. The present experiment examined the role of ethanol in controlling responding reinforced by ethanol or an ethanol/sucrose mixture compared with sucrose solutions of various concentrations. After initiation to self-administer 10% (v/v) ethanol using the sucrose-substitution method, rats were trained to respond under a concurrent VI 5" VI 5" schedule. During one condition, responding on one lever was reinforced by the presentation of 10% ethanol, and responding on a second lever was reinforced by water or one of the following sucrose solutions: 1% (w/v), 1.5%, 2%, 2.5%, 3%, and 5%. During a subsequent condition, responding reinforced by a 10% ethanol/2% sucrose mixture was compared under the concurrent schedule with responding reinforced by water, 2%, 2.5%, 3%, 5%, or 10% sucrose (w/v). The results indicated that the ethanol or ethanol/sucrose mixture maintained more responding than did sucrose solutions that were sweeter. Data support the conclusion that, after initiation, the taste and/or pharmacological effects of ethanol had become an important component of the reinforcing stimulus independent of the sweetener.

Conditioned reinforcing effects of capsules associated with high versus low monetary payoff

The ability of a placebo drug capsule to serve as a conditioned reinforcer as a function of being paired with money reinforcement was evaluated. Volunteers were administered two differently colored capsules that presumably contained two different drugs. Although the volunteers were told they might contain a stimulant, sedative, or placebo, both capsules contained only a placebo. During sessions, volunteers participated in performance tasks. The tasks were programmed so that following one capsule, the amount of money obtained contingent upon responding was greater (high frequency of reinforcement) than following the other capsule (low frequency of reinforcement). During experiment 1, participants were exposed twice each to the two reinforcement conditions (sampling). During these choice sessions, 9 of 12 participants chose the capsule associated with the high frequency of reinforcement 2 or 3 times. Experiment 2 was designed to explore further whether the differential mood effects observed during sampling sessions could be conditioned. Although this could not be demonstrated, the self-administration results demonstrating the control of choice behavior even in the absence of pharmacological effects suggest that drugs may function as conditioned reinforcers. This finding has implications for broadening our understanding of the determinants of initiation and continued drug use.

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.

Ethanol self-administration by alcohol-nonpreferring (NP) rats in a continuous access situation

Male rats, from the alcohol nonpreferring (NP) line, were studied in operant chambers in which food pellets, water, and 10% ethanol (v/v) were available continuously for 23 h/d. The NP rats consumed less ethanol per day following 7 weeks under these conditions than did either alcohol-preferring (P) rats or Long-Evans (LE) studied previously under the same conditions for 4 weeks. The NP rats consumed 0.2 g/kg per day during the first week of the experiment, 0.72 g/kg per day during the fourth week, and 1.03 g/kg per day during the seventh week compared to 2.2 g/kg per day for LE rats and 4.8 g/kg per day for P rats following 4 weeks. These data indicate that NP rats will slowly initiate ethanol self-administration under continuous access conditions, but to a lesser extent and at a slower rate than other lines of rats studied previously.

Effects of ethanol concentration and fixed-ratio requirement on ethanol self-administration by P rats in a continuous access situation

Rats, from the alcohol preferring (P) line, were placed in operant chambers in which food pellets, water, and 10% ethanol (v/v) were available continuously for 23 hr/day. During Experiment 1, the effects of changing ethanol concentration and response requirement for ethanol were examined. Ten percent and 20% ethanol (v/v) were available on two fixed ratio (FR) schedules, FR 1 and FR 4, for 2 weeks each. During Experiment 2, the effects of increasing the response requirement for ethanol were investigated. Starting with FR 4, the FR requirement for ethanol doubled during 2-week intervals until FR 32 was in effect. For the final phase of these studies, water was placed in the dipper for 1 week followed by a return to 10% ethanol in the dipper. The results from Experiment 1 indicated that when the FR requirement was decreased from FR 4 to FR 1, ethanol-reinforced responding decreased but total daily intake increased. Lowering the FR requirement did not affect the number of ethanol bouts per day but bout size increased. Ethanol concentration had no effect on bout size but the number of bouts per day decreased when the concentration was increased to 20%. Since bout size was unchanged by increasing the ethanol concentration, intake per bout increased at 20% ethanol. The results from Experiment 2 indicated that increasing the response requirement for ethanol decreases ethanol intake. When water was placed in the dipper, responding decreased to the lowest levels observed in the experiment. When ethanol was returned to the dipper, responding returned to baseline levels.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Effects of oral ethanol self-administration on the EEG of alcohol preferring and -nonpreferring rats

EEG measures have been shown to differ in human subjects who are at genetically increased risk for the development of alcoholism. In the present study, EEG was recorded in rats that were selectively bred for alcohol-preferring (P) and nonpreferring (NP) behaviors during an ethanol self-administration paradigm. In this paradigm, rats initially learned to press a lever for a 0.2% saccharin solution. Ethanol was then added to the saccharin solution in increasing concentrations while saccharin was faded progressively. EEG recordings were analyzed under three different conditions: baseline, 0.2% saccharin and 10% ethanol. Statistical analyses were carried out within each group of rats for three 10-min intervals in each condition. NP rats showed increases in EEG power in the 6-32 Hz frequency ranges 20-30 min following ethanol availability. In contrast, no significant EEG effects were found for P rats in the 10% ethanol condition with respect to time. EEG power in the three time periods (0-10, 10-20, 20-30 min) was also compared between conditions (baseline, saccharin, 10% ethanol). For NP rats, a significant increase in EEG power during the 20-30 min time interval was found in the 10% ethanol session for the 16-32 Hz frequency range as compared to baseline and saccharin. In P rats, a significant increase in the power of the EEG was found during the first 10 min in the 10% ethanol session in the 8-16 Hz frequency range as compared to baseline and saccharin. The two rat lines also differed in their behavioral responses to the self-administration paradigm.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol self-administration in a nonrestricted access situation with alcohol-preferring (P) rats

Genetic variables have been implicated as contributing factors in the development of alcoholic behavior. Rats bred selectively for alcohol preference have been used in laboratory studies to investigate the role of such variables. In the present study, rats from the alcohol preferring (P) line were placed in operant chambers in which food pellets, water, and 10% ethanol (v/v) were available continuously for 23 hr/day. Food pellets (45 mg) were presented on an FR 1 schedule of reinforcement, while ethanol was presented in a 0.1 ml dipper on an FR 4 schedule of reinforcement. Water was available in a drinking tube with licks monitored by a drinkometer. Data were analyzed in terms of both total daily intakes and computer defined bouts. The P rats showed greater daily ethanol intakes compared with Long-Evans (LE) animals previously studied under similar access conditions. The major difference in intake was a result of the P rats having a greater number of daily ethanol drinking bouts, while having only a slight increase in individual bout size. These data indicate that genetic selection for ethanol preference may result in the regulation of ethanol intake by means of changes in the frequency of ethanol drinking bouts but not by changes in bout size.

Alcohol Self-Administration: Role of Mesolimbic Dopamine

It appears clear that ethanol reinforcement, like that of many abused drugs, utilizes the mesolimbic DA pathways. From the data presented on microinjection of DA agonists and antagonists, it would seem that only part of the regulatory process controlling ethanol drinking is directly involved with this pathway. Once drinking has begun, the DA antagonist raclopride results in a rapid termination of drinking. This appears to be a blocking effect of what may be conditioned reinforcement resulting from prior ethanol reinforcement initiation procedures. Microinjection of the DA agonists d-amphetamine and quinpirole prolonged drinking, with little signs of normal termination apparent in the 30-min session in many animals. This appeared to be the result of interference with normal termination processes. While it remains to be demonstrated that oral ethanol consumption results in the release of DA in the nucleus accumbens, evidence from prior work and the present studies support a role for the mesolimbic DA system in ethanol reinforcement.

Drinking of high concentrations of ethanol versus palatable fluids in alcohol-preferring (P) rats: valid animal model of alcoholism

A genetically based animal model of alcoholism has been characterized in Wistar-derived rats in terms of their preference (P rats) or lack of preference (NP rats) for 10% ethanol over water. The present experiments were designed to determine: 1) whether a 10% solution of ethanol is the optimal concentration for differentiation of these lines; 2) what concentrations of ethanol are maximally preferred by P and NP rats; and 3) whether highly palatable fluids presented simultaneously with each rat's preferred solution of ethanol would alter the patterns of drinking by either the P or NP or both lines of rats. A three-bottle procedure was used to establish preference for ethanol in the presence of water as well as highly palatable solutions. The results showed that, when concentrations ranging from 3-30% were presented over a 12-day test interval, the mean absolute intake of ethanol of the P rats was 6.7 g/kg per day, with a maximum intake of 10.9 g/kg per day at the 25% concentration. These levels of intake were significantly higher than the 4.3 g/kg per day consumed during the presentation of the commonly used constant concentration of 10%. Similarly, the mean absolute intake of ethanol by the NP rats was also elevated significantly at concentrations of 15-30% (2.0 g/kg per day) above that consumed at the 10% concentration (0.4 g/kg).(ABSTRACT TRUNCATED AT 250 WORDS)