Saccharin Fading Research Articles

Saccharin fading is not required for the acquisition of alcohol self-administration, and can alter the dynamics of cue-alcohol memory reconsolidation

RationaleAnimal models of alcohol-seeking are useful for understanding alcohol addiction and for treatment development, but throughput in these models is limited by the extensive pretraining required to overcome the aversive taste of ethanol. Work by Augier et al. (Psychopharmacology 231: 4561–4568, 2014) indicates that Wistar rats will self-administer alcohol without water deprivation, exposure to sweetened ethanol solutions or intermittent access to ethanol.Objectives and methodsWe sought to replicate and extend the work of Augier et al. by comparing the acquisition of instrumental self-administration of ethanol in Lister-Hooded rats that had been previously saccharin faded (SF group) or not (NSF group). We also aimed to determine whether NMDA receptor antagonism with MK-801, given at memory reactivation, reduced subsequent ethanol-seeking behaviour in both groups of animals. Finally, we assessed the ethanol preference of SF and NSF rats using the two-bottle choice procedure.ResultsBoth SF and NSF groups acquired instrumental self-administration of ethanol, though SF rats consumed fewer of the earned reinforcers. MK-801, given at memory reactivation, had different effects on NSF and SF rats: impairing the capacity of an ethanol-paired conditioned stimulus (CS) to support reinstatement in NSF rats, and enhancing it in SF rats. Finally, neither SF nor NSF rats showed a preference for ethanol.ConclusionsOur data support those of Augier et al. (Psychopharmacology 231: 4561–4568, 2014) that pretraining is unnecessary for rats to acquire instrumental self-administration of ethanol. Indeed, saccharin fading may produce a weaker memory that extinguishes more readily, thus accounting for the different effects of MK-801 on SF and NSF rats.

Inactivation of the Prelimbic Cortex Impairs the Context-Induced Reinstatement of Ethanol Seeking.

Evidence indicates that drug relapse in humans is often provoked by exposure to the self-administered drug-associated context. An animal model called “ABA renewal procedure” has been used to study the context-induced relapse to drug seeking. Here, we reported a new and feasible training procedure for the ABA renewal method to explore the role of the prelimbic cortex in context-induced relapse to ethanol seeking. By using a saccharin fading technique, we trained rats to self-administer ethanol (10%). The drug delivery was paired with a discrete tone-light cue. Lever pressing was subsequently extinguished in a non-drug-associated context in the presence of the discrete cue. Rats were subsequently tested for reinstatement in contexts A or B, under extinction conditions. Ethanol-associated context induced the reinstatement of ethanol seeking and increased the expression of Fos in the prelimbic cortex. The rate of neural activation in the prelimbic cortex was 3.4% in the extinction context B and 7.7% in the drug-associated context A, as evidenced by double-labeling of Fos and the neuron-specific protein NeuN. The reversible inactivation of the neural activity in the prelimbic cortex with gamma-Aminobutyric acid (GABA) receptor agonists (muscimol + baclofen) attenuated the context-induced reinstatement of ethanol self-administration. These results demonstrated that the neuronal activation of the prelimbic cortex is involved in the context-induced reinstatement of ethanol seeking.

A Method for Evaluating the Reinforcing Properties of Ethanol in Rats without Water Deprivation, Saccharin Fading or Extended Access Training

A Method for Evaluating the Reinforcing Properties of Ethanol in Rats without Water Deprivation, Saccharin Fading or Extended Access Training

A Method for Evaluating the Reinforcing Properties of Ethanol in Rats without Water Deprivation, Saccharin Fading or Extended Access Training.

Operant oral self-administration methods are commonly used to study the reinforcing properties of ethanol in animals. However, the standard methods require saccharin/sucrose fading, water deprivation and/or extended training to initiate operant responding in rats. This paper describes a novel and efficient method to quickly initiate operant responding for ethanol that is convenient for experimenters and does not require water deprivation or saccharin/sucrose fading, thus eliminating the potential confound of using sweeteners in ethanol operant self-administration studies. With this method, Wistar rats typically acquire and maintain self-administration of a 20% ethanol solution in less than two weeks of training. Furthermore, blood ethanol concentrations and rewards are positively correlated for a 30 min self-administration session. Moreover, naltrexone, an FDA-approved medication for alcohol dependence that has been shown to suppress ethanol self-administration in rodents, dose-dependently decreases alcohol intake and motivation to consume alcohol for rats self-administering 20% ethanol, thus validating the use of this new method to study the reinforcing properties of alcohol in rats.

Morphine intake and the effects of naltrexone and buprenorphine on the acquisition of methamphetamine intake

Some common genetic factors appear to influence risk for drug dependence across multiple drugs of abuse. In previous research, mice that were selectively bred for higher amounts of methamphetamine consumption, using a two-bottle choice methamphetamine drinking procedure, were found to be less sensitive to the locomotor stimulant effects of morphine and of the more selective μ-opioid receptor agonist fentanyl, compared to mice that were bred for low methamphetamine consumption. This suggested that μ-opioid receptor-mediated pathways may influence genetic risk for methamphetamine consumption. We hypothesized that these differences in opioid sensitivity would impact opioid intake in the methamphetamine drinking lines and that drugs with μ-opioid receptor activity would impact methamphetamine intake. Consumption of morphine was examined in 2, two-bottle choice studies, one that compared morphine to quinine consumption and another that used a saccharin fading procedure. Next, naltrexone (0, 0.5, 1, 2, 5, 10 and 20 mg/kg), a μ-opioid receptor antagonist, and buprenorphine (0, 1, 2 or 4 mg/kg), a μ-opioid receptor partial agonist, were each examined for their effects on the acquisition of methamphetamine consumption. Low methamphetamine drinking mice consumed more morphine compared to high methamphetamine drinking mice. Naltrexone did not alter methamphetamine consumption in either selected line; however, buprenorphine reduced methamphetamine intake in the high methamphetamine drinking line. These data show that greater sensitivity to opioids is associated with greater opioid intake and warrant further investigation of drugs with μ-opioid receptor-specific agonist activity in genetically determined differences in methamphetamine consumption.

Deep brain stimulation of the nucleus accumbens reduces ethanol consumption in rats

Recent studies have shown that deep brain stimulation (DBS) of the nucleus accumbens (NAcc) has an inhibitory effect on drug-seeking behaviors including reinstatement responding for cocaine. The objective of the present study was to expand on these findings by assessing the effects of DBS on behaviors related to alcohol consumption. The specific aim of this study was to determine whether DBS delivered to either the shell or core of the NAcc would reduce ETOH intake in rats using a two-bottle choice limited access procedure. Long Evans rats were induced to drink a 10% ethanol solution using a saccharin fading procedure. Bipolar electrodes were implanted bilaterally into either the core or shell of the NAcc. During testing animals received DBS 5 min prior to and during a 30-minute test session in which both ETOH and water bottles were accessible. Current was delivered at amplitudes ranging from 0 to 150 µA. ETOH consumption was significantly reduced from baseline levels at the 150 µA current for both shell and core electrode placements. A significant current effect was not found for water consumption for either site. These results provide evidence that DBS delivered either to the nucleus accumbens core or shell subregions can significantly reduce ethanol intake in the rat.

Neurosteroid Modulators of GABAA Receptors Differentially Modulate Ethanol Intake Patterns in Male C57BL/6J Mice

Allopregnanolone (ALLO) and structurally related endogenous neurosteroids are potent modulators of gamma-aminobutyric acid A (GABA(A)) receptor function at physiologically relevant concentrations. Accumulating evidence implicates a modulatory role for ALLO in behavioral processes underlying ethanol self-administration, discrimination, and reinstatement. The purpose of this study was to evaluate the impact of exogenous neurosteroid challenges with the agonist ALLO and the partial agonist/antagonist epipregnanolone (EPI) on the microarchitecture of ethanol drinking patterns. Male C57BL/6J mice were initiated to consume an unsweetened 10% v/v ethanol solution (10 E) by a saccharin fading procedure during daily 2-hr limited-access sessions beginning 1-hr after dark-phase onset. Cumulative lick responses were recorded for 10 E and water by lickometer circuits. After establishing 10 E intake baselines, mice were habituated to vehicle injection (VEH; 20% w/v beta-cyclodextrin ip), and then were treated with either VEH or neurosteroid immediately before the drinking session. Each mouse received a series of ALLO doses (3.2, 10, 17, and 24 mg/kg) alone and EPI doses (0.15, 1, 3, and 10 mg/kg) alone in a counterbalanced within-group design. The GABA(A) receptor-positive modulator ALLO dose-dependently modulated overall ethanol intake throughout the 2-hr session with the 3.2 mg/kg dose eliciting a significant increase, whereas the 24 mg/kg dose produced a significant suppression of ethanol intake versus VEH pretreatment. ALLO-evoked alterations in intake corresponded to significant, dose-dependent alterations in bout frequency and interbout interval. ALLO also elicited robust, dose-dependent elevations in 10 E licks during the initial 5 min of access but subsequently produced in a dose-dependent suppression of 10 E licks during session minutes 20-80. In contrast, the partial agonist/antagonist neurosteroid EPI exhibited no influence on any consumption parameter evaluated. The present findings suggest that GABA(A) receptor-active neurosteroids may modulate the regulatory processes that govern the onset, maintenance, and termination of drinking episodes. The differential influence of ALLO and EPI on ethanol intake patterns may reflect an alteration in GABA-ergic inhibitory tone that is likely due to each neurosteroid's pharmacological profile at GABA(A) receptors. Manipulation of endogenous ALLO may prove a useful strategy for diminishing excessive intake and protecting against the loss of regulatory control over drinking.

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.

Pairings of ethanol sipper with food induces Pavlovian autoshaping of ethanol drinking in rats: evidence of long-term retention and effects of sipper duration.

This study asks if repeated Pavlovian pairings of a sipper tube (conditioned stimulus, CS) with food (unconditioned stimulus, US) will induce Pavlovian autoshaping conditioned responses (CRs), consisting of drinking of either 6% ethanol or water from the sipper CS. This study also tests predictions derived from the autoshaping model by asking if sipper CS-directed drinking will be retained, despite the absence of training for several weeks, and, in addition, if drinking rate is a negative function of sipper CS duration. Autoshaping procedures, conducted in two daily sessions, consisted of the brief insertion of the sipper tube CS followed by the response-independent presentation of food US. For the Ethanol group (n = 8), the sipper CS contained 6% ethanol, whereas for the Water group (n = 8), the sipper CS contained tap water. Saccharin fading procedures were employed, whereas for both groups, during days 1-19, the sipper CS contained 0.1% saccharin, and thereafter across training days the concentration of saccharin was gradually reduced (0.07, 0.035, 0.0%). Following elimination of saccharin, both groups were maintained in their home cages during a 27-day retention interval, and then re-evaluated for autoshaping of drinking of unsweetened ethanol and water. Thereafter, across days, the duration of access to the sipper CS (5.0, 7.5, 10.0, 15.0 s) during each autoshaping trial was increased. Both groups increased drinking across the first 19 days of training with sipper CS-food US pairings, and, at 0.0% saccharin, the Ethanol group consumed 14.76 ml of 6% ethanol per day, resulting in a daily ethanol consumption of 2.77 g/kg. For both groups, daily levels of drinking before and after the 27-day retention interval were comparable, attesting to the durability of the acquired drinking effects. At each CS duration, the Ethanol group consumed more millilitres of fluid per day than did the Water group, and for the Ethanol group, peak drinking of 24.0 ml of 6% ethanol per day was observed at the 10 s CS duration. For both groups, drinking rate (millilitres of fluid consumed per second of CS duration), was a declining monotonic function of CS duration, resulting in a daily ethanol consumption of approximately 4.2 g/kg for the Ethanol group. These data reveal that these sipper CS-food US autoshaping procedures induce drinking in rats that is durable and negatively related to increasing CS duration. The effects of both variables are consistent with the hypothesis that drinking from the sipper CS is a Pavlovian autoshaping CR. Autoshaping of drinking in the Water group is observed despite the absence of water deprivation, and even more fluid is consumed by the Ethanol group than by the Water group. The high volumes of ethanol consumed during brief daily sessions suggest that Pavlovian autoshaping procedures may provide an animal learning model of binge drinking.

Suppression of ethanol responding by centrally administered CTOP and naltrindole in AA and Wistar rats.

Both mu- and delta-opioid receptors have been implicated in the reinforcing actions of ethanol. However, selective opioid receptor antagonists have not altered ethanol intake in all rodent strains consistently, which suggests that genotype may modulate their suppressive effects. Therefore, we tested the effects of the selective mu-antagonist D-Pen-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) and the selective delta-antagonist naltrindole in both high-drinking AA (Alko, Alcohol) and heterogeneous Wistar rats. AA and Wistar rats were trained to respond for ethanol (10% w/v) in a two-lever operant condition by using a saccharin fading procedure. After stable baseline responding was established, rats were implanted stereotaxically either with a guide cannula above the lateral ventricle or with bilateral cannulas above the nucleus accumbens, basolateral amygdala, or ventral tegmental area. After postoperative recovery, AA and Wistar animals were tested after intracerebroventricular microinjections of either CTOP (0-3 microg) or naltrindole (0-30 microg) or subcutaneous injections of naloxone (0-1 g/kg), which was used as a reference antagonist. Effects of intracerebral microinjections of CTOP and naltrindole (both 0-500 ng) were tested only in Wistar rats. Subcutaneous naloxone and intracerebroventricular CTOP and naltrindole suppressed ethanol self-administration in a similar manner in AA and Wistar rats. Cumulative response patterns indicated that naloxone and naltrindole had no effect on the initiation of responding but suppressed it later during the session, whereas CTOP also affected initiation. In Wistar rats, naltrindole microinjections into both the nucleus accumbens and basolateral amygdala decreased ethanol responding, whereas CTOP was effective only in the amygdala. Injections of these antagonists into the ventral tegmental area had little effect on ethanol intake. The results confirm previous results which showed that both mu- and delta-opioid receptors are involved in the regulation of ethanol self-administration and indicate that genetic differences between AA and Wistar rats produced by selection do not modify the effects of opioid antagonists. The nucleus accumbens and the basolateral amygdala may be important central sites for the mediation of their suppressive effects.

Ethanol Reinforcement in Nondeprived Mice: Effects of Abstinence and Naltrexone

Background: Operant experiments which indicate that ethanol can serve as a reinforcer to maintain lever responding during limited periods of access have not been conducted on non-food-deprived mice, as they have for rats and monkeys. Furthermore, there are no reports of the effects of chronic ethanol and subsequent abstinence on ethanol reward in mice. Finally, although naltrexone reduces responding for ethanol in food-deprived mice, the effects of the drug on ethanol reward for non-food-deprived mice have not been reported. Methods: In three experiments, lever responding for ethanol (10–12%) was established in C57BL/6 (B6) mice by using either sucrose or saccharin fading procedures commonly used for rats. Experiment 1 examined both appetitive and consummatory responses while sucrose was faded from the ethanol solutions. Experiment 2 examined lever responding and ethanol intake (1) during saccharin fading; (2) when reinforcement schedules, reward availability, and primary conditioned reinforcers were manipulated; and (3) when mice were allowed chronic ethanol consumption followed by forced abstinence. Experiment 3 examined the effects of low doses of naltrexone on ethanol reward. Results: Lever responding for ethanol can be established in non-food-deprived mice with the sucrose and saccharin fading procedures commonly used for rats. Lever responses increased with decreases in the reinforcer and increases in schedule demand, which indicated the reward value of the ethanol solution. Removal of ethanol from the solution reduced consumption with no change in the appetitive, instrumental response, which indicated that the two responses were under control of different stimuli, perhaps mediated by different neural mechanisms. Forced abstinence after chronic ethanol exposure increased responding for the drug, which suggested increased reward value. Naltrexone reduced responding as previously reported for food-deprived B6 mice. Conclusions: Ethanol appears to serve as a reinforcer for non-food-deprived or non-water-deprived B6 mice. Its reinforcing effects are increased by forced abstinence after chronic exposure and are decreased by naltrexone.

Ethanol Reinforcement in Nondeprived Mice: Effects of Abstinence and Naltrexone

Operant experiments which indicate that ethanol can serve as a reinforcer to maintain lever responding during limited periods of access have not been conducted on non-food-deprived mice, as they have for rats and monkeys. Furthermore, there are no reports of the effects of chronic ethanol and subsequent abstinence on ethanol reward in mice. Finally, although naltrexone reduces responding for ethanol in food-deprived mice, the effects of the drug on ethanol reward for non-food-deprived mice have not been reported. In three experiments, lever responding for ethanol (10-12%) was established in C57BL/6 (B6) mice by using either sucrose or saccharin fading procedures commonly used for rats. Experiment 1 examined both appetitive and consummatory responses while sucrose was faded from the ethanol solutions. Experiment 2 examined lever responding and ethanol intake (1) during saccharin fading; (2) when reinforcement schedules, reward availability, and primary conditioned reinforcers were manipulated; and (3) when mice were allowed chronic ethanol consumption followed by forced abstinence. Experiment 3 examined the effects of low doses of naltrexone on ethanol reward. Lever responding for ethanol can be established in non-food-deprived mice with the sucrose and saccharin fading procedures commonly used for rats. Lever responses increased with decreases in the reinforcer and increases in schedule demand, which indicated the reward value of the ethanol solution. Removal of ethanol from the solution reduced consumption with no change in the appetitive, instrumental response, which indicated that the two responses were under control of different stimuli, perhaps mediated by different neural mechanisms. Forced abstinence after chronic ethanol exposure increased responding for the drug, which suggested increased reward value. Naltrexone reduced responding as previously reported for food-deprived B6 mice. Ethanol appears to serve as a reinforcer for non-food-deprived or non-water-deprived B6 mice. Its reinforcing effects are increased by forced abstinence after chronic exposure and are decreased by naltrexone.

Central Administration of an Opiate Antagonist Decreases Oral Ethanol Self‐Administration in Rats

Opioid peptides have been implicated in various behavioral actions of alcohol, including its reinforcing effects; however, the role of specific brain sites for these actions remains to be explored. The present study examined the effects of intracerebroventricular (ICV) or intracerebral injections of an opiate antagonist (methylnaloxonium) on ethanol self-administration. The nucleus accumbens and amygdala were selected as intracerebral sites because these regions have been implicated in the reinforcing effects of drugs of abuse. Male Wistar rats were trained in a limited-access paradigm (30 min/day) to respond for ethanol (10% w/v) or water in a two-lever free-choice condition using a saccharin fading procedure. After the establishment of stable baseline responding for ethanol, animals were implanted stereotaxically with a guide cannula above the lateral ventricle or with bilateral guide cannulae either above the nucleus accumbens or amygdala. After postoperative recovery of stable baseline responding, the rats were tested 15 min after ICV or intracerebral microinjections of methylnaloxonium (0-2000 ng). Injections of methylnaloxonium into the amygdala significantly reduced responding for ethanol at doses of 250-500 ng. Injections of methylnaloxonium into the nucleus accumbens significantly reduced responding for ethanol at doses of 500-1000 ng, whereas higher doses were needed ICV. These results provide evidence that opioid receptors located in the amygdala and nucleus accumbens may be involved in the regulation of ethanol self-administration.

Operant Self‐Administration of Sweetened Versus Unsweetened Ethanol: Effects on Blood Alcohol Levels

Sweeteners are often added to ethanol solutions to increase ethanol intake. However, literature on studies that use human subjects and laboratory animals suggests that sucrose, other sugars, and carbohydrate-rich foods alter ethanol absorption and metabolism, which leads to lower blood alcohol levels (BAL) relative to ethanol absorbed alone. This experiment was designed to test whether the addition of the nutritive sweetener sucrose, or the nonnutritive sweetener saccharin, to a 10% ethanol solution, self-administered in an oral operant paradigm, affected BAL in rats relative to self-administration of an unsweetened 10% ethanol solution. All rats were trained to lever press for ethanol by use of a saccharin fading procedure. Half of the rats then received 30-min sessions in which ethanol + 2% sucrose and water were available and were alternated daily with sessions in which ethanol + 0.2% saccharin and water were available. The other half of the rats went on to receive daily sessions of unsweetened ethanol and water. BAL were taken after these standard daily sessions as well as after a 1-week period of alcohol deprivation (to enhance ethanol intake). Rats responded for more ethanol + sucrose than unsweetened ethanol, but had lower BAL per gram ethanol consumed in both the baseline test and alcohol deprivation effect test. No effect of saccharin on BAL was detected. An additional experiment that examined the effects of four concentrations of both sucrose and saccharin on self-administration of ethanol and BAL showed that, whereas rats consumed more ethanol + sucrose than ethanol + saccharin, BAL were significantly lower per gram ethanol consumed in the sucrose group. These results confirm previous reports and suggest that the addition of sucrose to an ethanol solution can result in lower BAL relative to unsweetened ethanol in an oral operant self-administration paradigm.

Estrous Cycle Effects on Operant Responding for Ethanol in Female Rats

Human females have been reported to be uniquely sensitive to the deleterious effects of ethanol, thus it is important to study the characteristics of and mechanisms underlying alcohol consumption that may be specific to females. Models of ethanol self-administration in female rats that take into consideration the estrous cycle have the potential to provide important information concerning these characteristics and mechanisms. The purpose of this study was to explore the effect of the cycle on ethanol self-administration using a limited access operant paradigm. Female Wistar rats were trained to lever press for 10% ethanol versus water using a saccharin fading procedure. Responses were examined across the four phases of the estrous cycle. No effects of estrous cycle phase were observed when these rats were allowed to cycle freely. Subsequently, estrous phase effects were investigated in females whose cycles had been synchronized. Under this condition, an effect of estrous phase was present, with lower ethanol intake observed in estrus (and in some cases proestrus). Synchronized rats all showed at least one very clear 4-day estrous cycle, whereas free-running rats' cycles ranged from 3 to 5 days. Thus, it is more likely that synchronized rats were tested in the identical portion of each phase, when hormone levels were less variable. These results suggest that ethanol may be more reinforcing during diestrus than proestrus and estrus in female rats.

Increased Ethanol Self-Administration after a Period of Imposed Ethanol Deprivation in Rats Trained in a Limited Access Paradigm

A predominant feature in human alcohol abuse is the reported desire or “craving” to consume ethanol along with frequent episodes of drinking after periods of abstinence. These and other factors may be responsible for relapse to uncontrolled ethanol drinking. When relapse occurs after a period of abstinence, ethanol drinking has been shown to be temporarily increased. Two aspects of drug dependence could contribute to these increases. One may be the development of a need state; the other may involve changes in the perception of the positive reinforcing effects of ethanol when reinforcer access is limited. To investigate this phenomenon further, the present study was conducted to examine in nondependent rats the effect of forced time-off on oral ethanol self-administration in a limited access paradigm (30 mid/day). Male Wistar rats were trained to respond for ethanol (10% w/v) or water in a two-lever, free-choice condition using a saccharin fading procedure. After the establishment of stable baseline responding for ethanol, various ethanol deprivation periods (3, 5, 7, 14, or 28 days) were imposed, during which no ethanol was available. Responding for ethanol increased as a function of the duration of the deprivation period when compared with baseline levels. This increase was temporary and returned to baseline levels within 2 to 3 days. Given that the shortest time-off period was 5 days and the rats showed no signs of withdrawal, this transient increase in ethanol responding does not seem to be related to the manifestation of dependence and withdrawal, and may be related to changes in ethanol's reinforcement properties. These results with rats may provide a useful tool to elucidate mechanisms underlying human alcohol seeking behavior and relapse.

Increased Ethanol Self‐Administration after a Period of Imposed Ethanol Deprivation in Rats Trained in a Limited Access Paradigm

A predominant feature in human alcohol abuse is the reported desire or "craving" to consume ethanol along with frequent episodes of drinking after periods of abstinence. These and other factors may be responsible for relapse to uncontrolled ethanol drinking. When relapse occurs after a period of abstinence, ethanol drinking has been shown to be temporarily increased. Two aspects of drug dependence could contribute to these increases. One may be the development of a need state; the other may involve changes in the perception of the positive reinforcing effects of ethanol when reinforcer access is limited. To investigate this phenomenon further, the present study was conducted to examine in nondependent rats the effect of forced time-off on oral ethanol self-administration in a limited access paradigm (30 min/day). Male Wistar rats were trained to respond for ethanol (10% w/v) or water in a two-lever, free-choice condition using a saccharin fading procedure. After the establishment of stable baseline responding for ethanol, various ethanol deprivation periods (3, 5, 7, 14, or 28 days) were imposed, during which no ethanol was available. Responding for ethanol increased as a function of the duration of the deprivation period when compared with baseline levels. This increase was temporary and returned to baseline levels within 2 to 3 days. Given that the shortest time-off period was 5 days and the rats showed no signs of withdrawal, this transient increase in ethanol responding does not seem to be related to the manifestation of dependence and withdrawal, and may be related to changes in ethanol's reinforcement properties. These results with rats may provide a useful tool to elucidate mechanisms underlying human alcohol seeking behavior and relapse.

GABA A receptor antagonism in the extended amygdala decreases ethanol self-administration in rats

The present experiments examined the role of the extended amygdala GABA A receptors in the regulation of ethanol consumption in rats. The areas of the extended amygdala studied included the central nucleus of the amygdala, the bed nucleus of the stria terminalis, and the shell of the nucleus accumbens. The effects of bilateral microinjections of a competitive GABA A receptor antagonist, 2-(3-carboxypropyl)-3-amino-6-(4-methoxyphenyl)pyridazinium bromide (SR 95531), on ethanol consumption were assessed in Wistar rats that were trained to respond for oral ethanol (10% w/v) in a two-lever, free-choice operant task during 30-min sessions using a saccharin fading procedure. Injections of SR 95531 into the central amygdaloid nucleus decreased ethanol responding significantly at doses of 2 and 4 ng without affecting water responding. SR 95531 injections into the bed nucleus of the stria terminalis reduced ethanol responding significantly at the 8 ng and 16 ng dose, while only the 16 ng dose produced a significant effect in the shell of the nucleus accumbens. Cumulative response patterns showed that intra-amygdaloid injections did not disrupt the initiation of responding. Injections into the bed nucleus of the stria terminalis and the nucleus accumbens, however, suppressed both ethanol and water responding at the highest SR 95531 doses during the first minutes. These findings suggest that GABA A receptors in the extended amygdala may be involved in the mediation of some aspects of ethanol reward.