Sucrose-fading Procedure Research Articles

Mouse strain differences in punished ethanol self-administration.

Determining the neural factors contributing to compulsive behaviors such as alcohol-use disorders (AUDs) has become a significant focus of current preclinical research. Comparison of phenotypic differences across genetically distinct mouse strains provides one approach to identify molecular and genetic factors contributing to compulsive-like behaviors. Here we examine a rodent assay for punished ethanol self-administration in four widely used inbred strains known to differ on ethanol-related behaviors: C57BL/6J (B6), DBA/2J (D2), 129S1/SvImJ (S1), and BALB/cJ (BALB). Mice were trained in an operant task (FR1) to reliably lever-press for 10% ethanol using a sucrose-fading procedure. Once trained, mice received a punishment session in which lever pressing resulted in alternating ethanol reward and footshock, followed by tests to probe the effects of punishment on ethanol self-administration. Results indicated significant strain differences in training performance and punished attenuation of ethanol self-administration. S1 and BALB showed robust attenuation of ethanol self-administration after punishment, whereas behavior in B6 was attenuated only when the punishment and probe tests were conducted in the same contexts. By contrast, D2 were insensitive to punishment regardless of context, despite receiving more shocks during punishment and exhibiting normal footshock reactivity. Additionally, B6, but not D2, reduced operant self-administration when ethanol was devalued with a bitter tastant. B6 and D2 showed devaluation of sucrose self-administration, and punished suppression of sucrose seeking was context dependent in both the strains. While previous studies have demonstrated avoidance of ethanol in D2, particularly when ethanol is orally available from a bottle, current findings suggest this strain may exhibit heightened compulsive-like self-administration of ethanol, although there are credible alternative explanations for the phenotype of this strain. In sum, these findings offer a foundation for future studies examining the neural and genetic factors underlying AUDs.

Differences in the reinstatement of ethanol seeking with ganaxolone and gaboxadol

The endogenous neuroactive steroid allopregnanolone (ALLO) has previously been shown to induce reinstatement of ethanol seeking in rodents. ALLO is a positive allosteric modulator at both synaptic and extrasynaptic GABAA receptors. The contribution of each class of GABAA receptors in mediating reinstatement of ethanol seeking is unknown. The first aim of the present study was to determine whether ganaxolone (GAN), a longer-acting synthetic analog of ALLO, also promotes reinstatement of ethanol seeking. The second aim was to examine whether preferentially activating extrasynaptic GABAA receptors with the selective agonist gaboxadol (THIP) was sufficient to reinstate responding for ethanol in mice. Male C57BL/6J mice were trained to lever press for access to a 10% ethanol (v/v) solution (10E), using a sucrose-fading procedure. Following extinction of the lever-pressing behavior, systemic THIP (0, 4 and 6mg/kg) and GAN (0, 10, and 15mg/kg) were tested for their ability to reinstate ethanol-appropriate responding in the absence of 10E access. GAN significantly increased lever pressing on the previously active lever, while THIP did not alter lever-pressing behavior. The results of this study suggest that direct activation of extrasynaptic GABAA receptors at the GABA site is not sufficient to induce ethanol seeking in the reinstatement procedure. Future studies are necessary to elucidate the mechanisms and brain areas by which differences in the pharmacological activity of GAN and THIP at the GABAA receptor contribute to the dissimilarity in their effect on the reinstatement of ethanol seeking. Nonetheless, based on the increased use of these drugs in clinical trials across multiple disease states, the effects of GAN or THIP on alcohol seeking may be an important consideration if these drugs are to be used clinically in a population with a co-occurring alcohol use disorder.

Induction of multiple reinstatements of ethanol- and sucrose-seeking behavior in Long–Evans rats by the α-2 adrenoreceptor antagonist yohimbine

Developing models to efficiently explore the mechanisms by which stress can mediate reinstatement of drug-seeking behavior is crucial to the development of new pharmacotherapies for alcohol use disorders. We examined the effects of multiple reinstatement sessions using the pharmacological stressor, yohimbine, in ethanol- and sucrose-seeking rats in order to develop a more efficient model of stress-induced reinstatement. Long-Evans rats were trained to self-administer 10% ethanol with a sucrose-fading procedure, 20% ethanol without a sucrose-fading procedure, or 5% sucrose in 30-min operant self-administration sessions, followed by extinction training. After reaching extinction criteria, the animals were tested once per week with yohimbine vehicle and yohimbine (2 mg/kg), respectively, 30 min prior to the reinstatement sessions or blood collection. Levels of reinstatement and plasma corticosterone (CORT) were determined each week for four consecutive weeks. Yohimbine induced reinstatement of ethanol- and sucrose-seeking in each of the 4 weeks. Interestingly, the magnitude of the reinstatement decreased for the 10% ethanol group after the first reinstatement session but remained stable for the 20% ethanol group trained without sucrose. Plasma CORT levels in response to injection of both vehicle and yohimbine were significantly higher in the ethanol-trained animals compared to sucrose controls. The stable reinstatement in the 20% ethanol group supports the use of this training procedure in studies using within-subject designs with multiple yohimbine reinstatement test sessions. Additionally, these results indicate that the hormonal response to stressors can be altered following extinction from self-administration of relatively modest amounts of ethanol.

Acupuncture Inhibits GABA Neuron Activity in the Ventral Tegmental Area and Reduces Ethanol Self‐Administration

Withdrawal from chronic ethanol enhances ventral tegmental area (VTA) GABA neuron excitability and reduces mesolimbic dopamine (DA) neurotransmission, which is suppressed by acupuncture at Shenmen (HT7) points (Zhao et al., 2006). The aim of this study was to evaluate the effects of HT7 acupuncture on VTA GABA neuron excitability, ethanol inhibition of VTA GABA neuron firing rate, and ethanol self-administration. A role for opioid receptors (ORs) in ethanol and acupuncture effects is also explored. Using electrophysiological methods in mature rats, we evaluated the effects of HT7 stimulation and opioid antagonists on VTA GABA neuron firing rate. Using behavioral paradigms in rats, we evaluated the effects of HT7 stimulation and opioid antagonists on ethanol self-administration using a modification of the sucrose-fading procedure. HT7 stimulation produced a biphasic modulation of VTA GABA neuron firing rate characterized by transient enhancement followed by inhibition and subsequent recovery in 5 minutes. HT7 inhibition of VTA GABA neuron firing rate was blocked by systemic administration of the nonselective μ-opioid receptor antagonist naloxone. HT7 stimulation significantly reduced ethanol suppression of VTA GABA neuron firing rate, which was also blocked by naloxone. HT7 acupuncture reduced ethanol self-administration without affecting sucrose consumption. Systemic administration of the δ-opioid receptor (DOR) antagonist naltrindole blocked ethanol suppression of VTA GABA neuron firing rate and significantly reduced ethanol self-administration without affecting sucrose consumption. These findings suggest that DOR-mediated opioid modulation of VTA GABA neurons may mediate acupuncture's role in modulating mesolimbic DA release and suppressing the reinforcing effects of ethanol.

The effects of pre-pubertal gonadectomy and binge-like ethanol exposure during adolescence on ethanol drinking in adult male and female rats

The pubertal surge in gonadal hormones that occurs during adolescence may impact the long-term effects of early alcohol exposure and sex differences in drinking behavior in adulthood. We investigated this hypothesis by performing sham or gonadectomy surgeries in Long-Evans rats around post-natal day ( P) 20. From P35–45, males and females were given saline or 3.0 g/kg ethanol using a binge-like model of exposure (8 injections total). As adults (P100), they were trained to self-administer ethanol via a sucrose-fading procedure and then given access to different unsweetened concentrations (5–20%, w/v) for 5 days/concentration. We found that during adolescence, ethanol-induced intoxication was similar in males and females that underwent sham surgery. In gonadectomized males and females, however, the level of intoxication was greater following the last injection compared to the first. During adulthood, females drank more sucrose per body weight than males and binge-like exposure to ethanol reduced sucrose consumption in both sexes. These effects were not seen in gonadectomized rats. Ethanol consumption was higher in saline-exposed females compared to males, with gonadectomy reversing this sex difference by increasing consumption in males and decreasing it in females. Exposure to ethanol during adolescence augmented ethanol consumption in both sexes, but this effect was statistically significant only in gonadectomized females. Together, these results support a role for gonadal hormones during puberty in the short- and long-term effects of ethanol on behavior and in the development of sex differences in consummatory behavior during adulthood.

Alcohol self-administration in rats: Modulation by temporal parameters related to repeated mild social defeat stress

Clinical evidence often points to stress as a cause or an antecedent to the development of drinking problems. Yet, animal models of alcohol drinking have yielded inconsistent evidence for a direct contribution of stress, and many studies have shown that stress suppresses alcohol consumption. The aim of the present study was to examine alcohol reward in animals exposed to repeated, mild social stress, and to determine whether alcohol drinking changes as a function of the temporal parameters of alcohol access relative to the stressor. Male Long-Evans rats, trained to self-administer a 6% (wt/vol) alcohol solution using a sucrose-fading procedure, were exposed to five brief (5 min) episodes of contact with an aggressive male. Full contact with the resident was limited to a single episode of defeat, whereas the following four encounters occurred with the subjects behind a protective wire mesh cage. Alcohol self-administration was measured 1 week prior to stress (baseline), on each day of stress exposure, and 1 week following stress. Separate groups of animals were randomly assigned to self-administer alcohol immediately prior, immediately following, or 2 h following defeat stress. Stress preferentially increased alcohol drinking on stress-exposure days, and further elevated the amount consumed 1 week following stress. Temporal parameters of alcohol access relative to the stressor were found to be important. Average alcohol consumption was greatest for animals drinking 2 h postdefeat, whereas animals drinking immediately prior to or following the stressor did not show a significant increase in alcohol consumption. Results suggest that mild social defeat stress is sufficient to elicit increases in alcohol consumption in nonpreferring strains of rodents, provided alcohol access occurs at an optimal time interval after the social defeat experience.

Long-Evans Rats Acquire Operant Self-Administration of 20% Ethanol Without Sucrose Fading

A major obstacle in the development of new medications for the treatment of alcohol use disorders (AUDs) has been the lack of preclinical, oral ethanol consumption paradigms that elicit high consumption. We have previously shown that rats exposed to 20% ethanol intermittently in a two-bottle choice paradigm will consume two times more ethanol than those given continuous access without the use of water deprivation or sucrose fading (5-6 g/kg every 24 h vs 2-3 g/kg every 24 h, respectively). In this study, we have adapted the model to an operant self-administration paradigm. Long-Evans rats were given access to 20% ethanol in overnight sessions on one of two schedules: (1) intermittent (Monday, Wednesday, and Friday) or (2) daily (Monday through Friday). With the progression of the overnight sessions, both groups showed a steady escalation in drinking (3-6 g/kg every 14 h) without the use of a sucrose-fading procedure. Following the acquisition phase, the 20% ethanol groups consumed significantly more ethanol than did animals trained to consume 10% ethanol with a sucrose fade (1.5 vs 0.7 g/kg every 30 min) and reached significantly higher blood ethanol concentrations. In addition, training history (20% ethanol vs 10% ethanol with sucrose fade) had a significant effect on the subsequent self-administration of higher concentrations of ethanol. Administration of the pharmacological stressor yohimbine following extinction caused a significant reinstatement of ethanol-seeking behavior. Both 20% ethanol models show promise and are amenable to the study of maintenance, motivation, and reinstatement. Furthermore, training animals to lever press for ethanol without the use of sucrose fading removes a potential confound from self-administration studies.

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.

The impact of moderate daily alcohol consumption on aggression and the formation of dominance hierarchies in rats

Group-housed male rats form social hierarchies, and under these conditions, it has been reported that subordinate (SUB) rats consume more alcohol than dominant (DOM) rats. We tested the hypothesis that a history of drinking alcohol would cause SUB rats to consume even greater amounts of alcohol. Male Long-Evans rats were trained to drink 10% alcohol or a sucrose/quinine solution equal in calories for 1 h/day using a sucrose-fading procedure. Subsequently, rats were housed in colonies (four males, two females) in a visible burrow system (VBS) for 14 days. Individual control male rats were housed in a tub cage with one female. Rats were removed from the VBS (or control environment) daily and given 1 h to drink alcohol or sucrose/quinine. Colonies given daily access to sucrose/quinine formed clear DOM/SUB relationships in all measured parameters. Alcohol-drinking colonies failed to establish a dominance hierarchy and displayed little aggression, with an average of 14.6 +/- 6.1 offensive attacks compared with 58.5 +/- 12.3 attacks carried out by DOM sucrose/quinine rats. During VBS housing, alcohol and sucrose/quinine intake decreased independent of housing environment or social status. Contrary to prior reports of the effect of alcohol on aggressive behavior, moderate daily alcohol intake before and during VBS housing reduced aggression and precluded the formation of a dominance hierarchy in rats.

The mGluR5 antagonist MPEP decreases operant ethanol self-administration during maintenance and after repeated alcohol deprivations in alcohol-preferring (P) rats.

Recent research indicates that blockade of mGluR5 modifies the reinforcing properties of ethanol. The present studies examined the effects of mGluR5 receptor blockade in a genetic model of high ethanol intake, the alcohol-preferring (P) rat, on the maintenance of operant ethanol self-administration. In addition, we determined the effect of 2-methyl-6-(phenylethyl)-pyridine (MPEP) on the repeated alcohol deprivation effect. Twelve male (P) rats were trained in experimental sessions to self-administer 10% w/v ethanol via a sucrose-fading procedure. After the establishment of operant ethanol self-administration, subjects were treated with various metabotropic glutamate receptor (mGluR) subtype antagonists immediately prior to experimental sessions: the mGluR5 antagonist MPEP (1, 3, and 10 mg/kg); the mGluR2--3 antagonist LY-341495 (1, 3, and 10 mg/kg); and the mGluR1 antagonist CPCCOEt (1, 3, and 10 mg/kg). After determining the role of mGluR5 in the maintenance of operant ethanol self-administration, we examined the role of this receptor in relapse following repeated periods of alcohol deprivation by depriving subjects of ethanol exposure for three 2-week deprivation periods. The mGluR5 antagonist MPEP dose-dependently decreased operant ethanol self-administration. In addition, rats that received saline immediately prior to repeated alcohol deprivation sessions self-administered ethanol at increasing levels that were above those achieved in the last operant-conditioning session prior to the initial 2-week deprivation period. This repeated alcohol deprivation effect was prevented in subjects pretreated with MPEP (10 mg/kg). These findings suggest that mGluR5 receptors may modulate both the maintenance of operant ethanol self-administration and abstinence-induced increases in ethanol intake.

S.03.03 Paracapsular cells of the amygdala: an inhibitory gate modulated by D1 dopamine receptors

The endogenous neuroactive steroid allopregnanolone (ALLO) has previously been shown to induce reinstatement of ethanol seeking in rodents. ALLO is a positive allosteric modulator at both synaptic and extrasynaptic GABAA receptors. The contribution of each class of GABAA receptors in mediating reinstatement of ethanol seeking is unknown. The first aim of the present study was to determine whether ganaxolone (GAN), a longer-acting synthetic analog of ALLO, also promotes reinstatement of ethanol seeking. The second aim was to examine whether preferentially activating extrasynaptic GABAA receptors with the selective agonist gaboxadol (THIP) was sufficient to reinstate responding for ethanol in mice. Male C57BL/6J mice were trained to lever press for access to a 10% ethanol (v/v) solution (10E), using a sucrose-fading procedure. Following extinction of the lever-pressing behavior, systemic THIP (0, 4 and 6 mg/kg) and GAN (0, 10, and 15 mg/kg) were tested for their ability to reinstate ethanol-appropriate responding in the absence of 10E access. GAN significantly increased lever pressing on the previously active lever, while THIP did not alter lever-pressing behavior. The results of this study suggest that direct activation of extrasynaptic GABAA receptors at the GABA site is not sufficient to induce ethanol seeking in the reinstatement procedure. Future studies are necessary to elucidate the mechanisms and brain areas by which differences in the pharmacological activity of GAN and THIP at the GABAA receptor contribute to the dissimilarity in their effect on the reinstatement of ethanol seeking. Nonetheless, based on the increased use of these drugs in clinical trials across multiple disease states, the effects of GAN or THIP on alcohol seeking may be an important consideration if these drugs are to be used clinically in a population with a co-occurring alcohol use disorder.

Increased Ethanol Drinking After Repeated Chronic Ethanol Exposure and Withdrawal Experience in C57BL/6 Mice

The development of dependence may have significant motivational consequences regarding continued use and abuse of ethanol. We have developed a mouse model of ethanol dependence and repeated withdrawals that demonstrates sensitization of seizures and other symptoms of withdrawal. It is unclear whether such experience influences ethanol drinking behavior. The present series of experiments were designed to examine whether repeated cycles of chronic ethanol exposure and withdrawal has an impact on subsequent motivation to voluntarily self-administer ethanol. With the use of a modified sucrose-fading procedure, adult male C57BL/6J mice were trained to drink 15% (v/v) ethanol in a limited access procedure (2 hr/day). The animals were not food or water deprived at any time during the experiments. Once stable baseline intake was established, mice were exposed to four cycles of 16 hr of ethanol vapor (or air) in inhalation chambers separated by 8-hr periods of withdrawal. At 32 hr after the last cycle of ethanol exposure, all mice were tested for ethanol intake under limited access conditions for 5 consecutive days. The animals then received a second series of chronic ethanol exposure and withdrawal followed by another 5-day test period for ethanol drinking. Stable daily baseline intake was established in mice that drank 15% ethanol combined with 5% sucrose (experiment 1), 15% ethanol alone (experiment 2), 5% sucrose alone (experiment 3), or 15% ethanol when presented as a choice with water (experiment 4). After repeated cycles of chronic ethanol exposure and withdrawal experience, consumption of ethanol solutions increased over baseline levels and in comparison with control (air-exposed) groups. However, sucrose consumption did not change in mice that were trained to drink 5% sucrose. The increase in ethanol consumption after chronic ethanol exposure and withdrawal experience resulted in a significant increase in resultant blood ethanol levels. Once the positive reinforcing properties of ethanol were established, chronic ethanol exposure and withdrawal experience resulted in a significant increase in voluntary ethanol drinking that yielded a >2-fold increase in resultant blood ethanol levels. This increase in ethanol intake occurred whether ethanol was presented in combination with sucrose, alone (unadulterated), or as a choice with tap water. Furthermore, this effect seems to be selective for ethanol in that animals that were trained to drink a sucrose solution did not exhibit a change in their intake after similar chronic ethanol exposure. As such, this model may be useful in studying the mechanisms and conditions in which chronic ethanol treatment influences motivation to resume drinking after a period of abstinence (relapse).

Ethanol-reinforced behaviour predicts acquisition but not extinction of cocaine self-administration in the rat.

The aim of the present study was to evaluate the relationship between operant oral ethanol self-administration and intravenous (i.v.) cocaine self-administration in male Wistar rats. Twenty-four rats were trained to lever press for 8% v/v ethanol in the sucrose-fading procedure. The subjects with the highest (high ethanol responders [HER], n = 7) and lowest (low ethanol responders [LER], n = 7) ethanol intakes were selected for further experiments. After a wash-out period, during which i.v. catheters were implanted, the HER and LER were trained to nose-poke for cocaine infusions (0.33 mg/kg/infusion, a FR1 schedule) for nine daily sessions. The HER emitted more 'active' nose-pokes and obtained more cocaine infusions during sessions 2-4. Drug-seeking behaviour in the absence of cocaine reinforcement was then assessed for three consecutive extinction sessions. No between-group differences were found in terms of extinction of cocaine seeking. Locomotor responses to a novel environment were also similar in both groups. The present results suggest that a propensity to self-administer ethanol predicts more rapid acquisition of cocaine self-administration behaviour but does not influence subsequent behaviour during extinction.

Relationship between dopamine D2 receptor-associated responses and operant ethanol self-administration in the rat: a factor analysis.

To characterize the relationship between dopamine D(2) receptor-associated responses and operant ethanol self-administration in Wistar rats. Thirty-two rats were first tested for apomorphine-induced sniffing and raclopride-induced catalepsy. Subsequently, the same subjects were initiated to lever press for ethanol in the sucrose-fading procedure. The subjects were allowed to respond for 8% v/v ethanol for 20 days. A factor analysis was used to characterize the relationship between D(2)-associated responses and parameters of sucrose and ethanol self-administration. The analysis revealed three factors accounting for 88.3% of the total variability. The first factor comprised only parameters of ethanol-reinforced behaviour. Parameters of sucrose self-administration and cataleptic responses to raclopride loaded heavily on the second and third factors, respectively. None of the factors comprised apomorphine-induced stereotypy. It appears that there is no relationship between apomorphine-induced sniffing, raclopride-induced catalepsy and operant responding for ethanol in Wistar rats. Our results, combined with previous reports, suggest that D(2) receptors are not primarily involved in the regulation of ethanol reinforcement.

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

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

Short or continuous social stress: suppression of continuously available ethanol intake in subordinate rats

We explored the effects of short, intermediate, and continuous social stress on daily ethanol and water intake in rats. The study was designed to: (1) detect increases in intake during hours when animals were not stressed; and (2) detect shifts in preference from solutions with high to low alcohol content. Male Long-Evans rats acquired ethanol self-administration using a sucrose-fading procedure, which was followed by continuous access to 10% and 3% ethanol solutions and water. After intake stabilized, rats were exposed to three periods of five consecutive days of social stress, with 8-10 days without stress in between. Short social stress consisted of being attacked and defeated by an aggressive opponent, followed by 30 min exposure to threats by the aggressive male while in a protective cage. Intermediate and continuous social stress consisted of a 6 h or 24 h 'threat of attack' exposure, respectively. All stress exposures reduced daily intake of 10% ethanol, did not cause changes in intake of 3% ethanol, and caused increases in water intake. No compensatory ethanol consumption was observed on stress days or after stress exposure was discontinued. These results are at variance with the hypothesis for increased alcohol consumption during or following social stress episodes.

Moderate, long-term, alcohol consumption potentiates normal, age-related spatial memory deficits in rats.

A modified "Samson" sucrose fading procedure was used to establish voluntary consumption of a 20% ethanol (EtOH) solution in male Sprague-Dawley rats for 18 consecutive months. Intakes were stable over the life span, and corresponded to the moderate to high levels of intake typically observed in human "social" drinkers and alcoholics. The Morris Water Maze (WM), Olton Radial Arm Maze (RM), and a "balance beam" test were used to assess the effects of alcohol and aging on spatial memory and motor function. Aged EtOH-consuming rats (AGED/ALC) demonstrated impaired task acquisition, relative to aged controls (AGED), not reaching criterion performance in either spatial memory task even when given four additional days of training. AGED/ALC rats scored significantly lower on percent correct out of the first eight arm entries, and committed more perseverative errors in the RM. There were no significant performance differences between AGED and AGED/ALC rats on a balance beam test of fine motor coordination and equilibrium, suggesting that deficits observed in the RM and WM were not related to differential motor functioning. These results demonstrated that long-term, moderate, oral self-administration of EtOH, within the range typically consumed by humans, had adverse effects on spatial memory in rats, and that such a pattern of EtOH consumption seemed to exacerbate the decline in cognitive functioning associated with normal aging.

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.

Dorsal lesions of the prefrontal cortex: effects on alcohol consumption and subcortical monoaminergic systems

Male Wistar rats were subjected to either bilateral aspiration lesions of the dorsal regions of the prefrontal cortex (PFC) or sham lesions and placed on a 6-week, modified sucrose-fading procedure. At the time of sacrifice, the size of the lesion, both in anterior-posterior and medial-lateral dimensions, was measured. Following sacrifice, levels of dopamine (DA), serotonin (5-HT), norepinephrine (NE), and their metabolites were measured in the midbrain (raphe) and nucleus accumbens (NA). Lesioned animals had reductions in 5-HT in the NA, and DA and NE in the raphe. The lesioned group drank more of a solution of 5% alcohol than controls early in the sucrose fading, and less during the later stages. In the lesioned group, the size of the left- and right-hemisphere lesions predicted 5-HIAA levels in the NA, and 5-HT and 5-HIAA levels in the raphe. A laterality effect was noted, such that the size of left-hemisphere lesions were positively associated with raphe 5-HT and 5-HIAA levels, and negatively associated with 5-HT levels in the NA, while right-hemisphere lesions showed the opposite relationships. In addition, the width of the left-hemisphere lesion predicted some measures of alcohol intake. These results suggest that, in the rat, the dorsal PFC is involved in the regulation of monoamines in subcortical regions known to be important in the regulation of reinforced behaviors, and that this regulation differs between hemispheres and shows a laterality effect. In addition, the dorsal PFC appears to have a subtle involvement in the regulation of alcohol intake.

Specific decreases in ethanol- but not water-reinforced responding produced by the 5-HT 3 antagonist ICS 205-930

The serotonin 5-HT 3 antagonist ICS 205–930 has been shown to block the discriminative stimulus properties of ethanol and decrease voluntary intake, suggesting a possible role for 5-HT 3 systems in the reinforcing effects of ethanol. ICS 205–930 (0.56, 1.0, 3.0, 10.0, and 17.0 mg/kg i.p.) was examined on ethanol and water self-administration in an operant paradigm. Following a sucrose-fading procedure, two groups of nondeprived rats responded on either a concurrent fixed ratio 4 schedule for ethanol (10% v/v) and water (CONC FR4 FR4), or a single FR4 schedule for ethanol (10% v/v). ICS 205–930 dose-dependently decreased ethanol-reinforced responding in the concurrent condition without decreasing water-reinforced responding, suggesting a specific effect on ethanol. Ethanol-reinforced responding was also dose-dependently decreased in the single FR4 condition, but the dose effect curve was shifted to the left. These data support the conclusions that 5-HT 3 systems may play a specific role in ethanol self-administration that is independent of general appetitive and motor processes, and that 5-HT 3 antagonists may have therapeutic efficacy in the treatment of alcohol abuse when multiple reinforcers are available.