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

Adolescent alcohol binge drinking and withdrawal: behavioural, brain GFAP-positive astrocytes and acute methamphetamine effects in adult female rats

RATIONALE

Alcopop beverages are generally the first alcoholic beverage that young females drink which contain high levels of sugar and alcohol. The over-consumption of these drinks may encourage alcohol co-administration with methamphetamine (METH) impacting on drinking behaviour and glial function.

AIMS

The aims of this study were to evaluate the effect of adolescent binge alcohol exposure on consumption level, anxiety-like behaviour, cross-sensitization with METH and on astrocyte expression in reward related brain regions.

METHODS

Adolescent female Sprague-Dawley rats had daily 1-hour oral alcohol consumption of alcopop (ALCP; with sucrose) or ethanol-only (ETOH; without sucrose), transitioned from 5 to 15% (v/v) ethanol content for 34 days. Water and sucrose groups act as controls. During alcohol withdrawal, rats were tested for anxiety on the elevated plus maze (EPM) and locomotor activity following saline or METH (1 mg/kg i.p) treatment. Brains were then collected to assess astrocyte immunofluorescence for glial fibrillary acidic protein (GFAP) in reward-related brain regions.

RESULTS

Rats pretreated with 5% ALCP consumed significantly more volume and ethanol intake when compared to 5% EtOH rats. Both ALCP and EtOH groups had a higher preference ratio for 5% than 15% alcohol solutions and ALCP rats had greater ethanol intake at 15% than EtOH rats. Alcohol withdrawal showed no significant differences between groups on anxiety, METH cross-sensitization effects or GFAP intensity in the regions studied.

CONCLUSIONS

Overall, the addition of sucrose to alcoholic solutions encouraged female rats to consume larger volumes and greater ethanol intake compared to ethanol-only solutions, yet did not have long lasting effects on behaviour and astrocytes.

Ethanol self-administration in free-flying honeybees (Apis mellifera L.) in an operant conditioning protocol

BACKGROUND

This study examines the effect of ethanol (EtOH) on continuous reinforcement schedules in the free-flying honeybee (Apis mellifera L.). As fermented nectars may be encountered naturally in the environment, we designed an experiment combining the tools of laboratory research with minimal disturbance to the natural life of honeybees.

METHODS

Twenty-five honeybees were trained to fly from their colonies to a fully automated operant chamber with head poking as the operant response. Load size, intervisit interval, and interresponse times (IRTs) served as the dependent variables and were monitored over the course of a daily training session consisting of many visits. Experimental bees were tested using an ABA design in which sucrose only was administered during condition A and a 5% EtOH sucrose solution was administered during condition B. Control bees received sucrose solution only.

RESULTS

Most bees continued to forage after EtOH introduction. EtOH significantly reduced the load size and the intervisit interval with no significant effect on IRTs. However, a look on individual data shows large individual differences suggesting the existence of different kinds of behavioral phenotypes linked to EtOH consumption and effects.

CONCLUSIONS

Our results contribute to the study of EtOH consumption as a normal phenomenon in an ecological context and open the door to schedule-controlled drug self-administration studies in honeybees.

A limited access mouse model of prenatal alcohol exposure that produces long-lasting deficits in hippocampal-dependent learning and memory

BACKGROUND

It has been estimated that approximately 12% of women consume alcohol at some time during their pregnancy, and as many as 5% of children born in the United States are impacted by prenatal alcohol exposure (PAE). The range of physical, behavioral, emotional, and social dysfunctions that are associated with PAE are collectively termed fetal alcohol spectrum disorder (FASD).

METHODS

Using a saccharin-sweetened ethanol solution, we developed a limited access model of PAE. C57BL/6J mice were provided access to a solution of either 10% (w/v) ethanol and 0.066% (w/v) saccharin or 0.066% (w/v) saccharin (control) for 4 h/d. After establishing consistent drinking, mice were mated and continued drinking during gestation. Following parturition, solutions were decreased to 0% in a stepwise fashion over a period of 6 days. Characterization of the model included measurements of maternal consumption patterns, blood ethanol levels, litter size, pup weight, maternal care, and the effects of PAE on fear-conditioned and spatial learning, and locomotor activity.

RESULTS

Mothers had mean daily ethanol intake of 7.17 ± 0.17 g ethanol/kg body weight per day, with average blood ethanol concentrations of 68.5 ± 9.2 mg/dl after 2 hours of drinking and 88.3 ± 11.5 mg/dl after 4 hours of drinking. Food and water consumption, maternal weight gain, litter size, pup weight, pup retrieval times, and time on nest did not differ between the alcohol-exposed and control animals. Compared with control offspring, mice that were exposed to ethanol prenatally displayed no difference in spontaneous locomotor activity but demonstrated learning deficits in 3 hippocampal-dependent tasks: delay fear conditioning, trace fear conditioning, and the delay nonmatch to place radial-arm maze task.

CONCLUSIONS

These results indicate that this model appropriately mimics the human condition of PAE and will be a useful tool in studying the learning deficits seen in FASD.

Chronic intermittent ethanol exposure in early adolescent and adult male rats: effects on tolerance, social behavior, and ethanol intake

BACKGROUND

Given the prevalence of alcohol use in adolescence, it is important to understand the consequences of chronic ethanol exposure during this critical period in development. The purpose of this study was to assess possible age-related differences in susceptibility to tolerance development to ethanol-induced sedation and withdrawal-related anxiety, as well as voluntary ethanol intake after chronic exposure to relatively high doses of ethanol during adolescence or adulthood.

METHODS

Juvenile/adolescent and adult male Sprague-Dawley rats were assigned to one of five 10-day exposure conditions: chronic ethanol (4 g/kg every 48 hours), chronic saline (equivalent volume every 24 hours), chronic saline/acutely challenged with ethanol (4 g/kg on day 10), nonmanipulated/acutely challenged with ethanol (4 g/kg on day 10), or nonmanipulated. For assessment of tolerance development, duration of the loss of righting reflex (LORR) and blood ethanol concentrations (BECs) upon regaining of righting reflex (RORR) were tested on the first and last ethanol exposure days in the chronic ethanol group, with both saline and nonmanipulated animals likewise challenged on the last exposure day. Withdrawal-induced anxiety was indexed in a social interaction test 24 hours after the last ethanol exposure, with ethanol-naïve chronic saline and nonmanipulated animals serving as controls. Voluntary intake was assessed 48 hours after the chronic exposure period in chronic ethanol, chronic saline and nonmanipulated animals using an 8-day 2 bottle choice, limited-access ethanol intake procedure.

RESULTS

In general, adolescent animals showed shorter durations of LORR and higher BECs upon RORR than adults on the first and last ethanol exposure days, regardless of chronic exposure condition. Adults, but not adolescents, developed chronic tolerance to the sedative effects of ethanol, tolerance that appeared to be metabolic in nature. Social deficits were observed after chronic ethanol in both adolescents and adults. Adolescents drank significantly more ethanol than adults on a gram per kilogram basis, with intake uninfluenced by prior ethanol exposure at both ages.

CONCLUSIONS

Adolescents and adults may differ in their ability and/or propensity to adapt to chronic ethanol exposure, with adults, but not adolescents, developing chronic metabolic tolerance. However, this chronic exposure regimen was sufficient to disrupt baseline levels of social behavior at both ages. Taken together, these results suggest that, despite the age-related differences in tolerance development, adolescents are as susceptible as adults to consequences of chronic ethanol exposure, particularly in terms of disruptions in social behavior. Whether these effects would last into adulthood remains to be determined.

The influence of selection for ethanol withdrawal severity on traits associated with ethanol self-administration and reinforcement

BACKGROUND

Several meta-analyses indicate that there is an inverse genetic correlation between ethanol preference drinking and ethanol withdrawal severity, but limited work has characterized ethanol consumption in 1 genetic animal model, the Withdrawal Seizure-Prone (WSP) and-Resistant (WSR) mouse lines selected for severe or mild ethanol withdrawal, respectively.

METHODS

We determined whether line differences existed in: (i) operant self-administration of ethanol during sucrose fading and under different schedules of reinforcement, followed by extinction and reinstatement of responding with conditioned cues and (ii) home cage drinking of sweetened ethanol and the development of an alcohol deprivation effect (ADE).

RESULTS

Withdrawal Seizure-Prone-1 mice consumed more ethanol than WSR-1 mice under a fixed ratio (FR)-4 schedule as ethanol was faded into the sucrose solution, but this line difference dissipated as the sucrose was faded out to yield an unadulterated 10% v/v ethanol solution. In contrast, WSR-1 mice consumed more ethanol than WSP-1 mice when a schedule was imposed that procedurally separated appetitive and consummatory behaviors. After both lines achieved the extinction criterion, reinstatement was serially evaluated following oral ethanol priming, light cue presentation, and a combination of the 2 cues. The light cue produced maximal reinstatement of responding in WSP-1 mice, whereas the combined cue was required to produce maximal reinstatement of responding in WSR-1 mice. There was no line difference in the home cage consumption of a sweetened ethanol solution over a period of 1 month. Following a 2-week period of abstinence, neither line developed an ADE.

CONCLUSIONS

Although some line differences in ethanol self-administration and reinstatement were identified between WSP-1 and WSR-1 mice, the absence of consistent divergence suggests that the genes underlying these behaviors do not reliably overlap with those that govern withdrawal severity.

Chronic binge-like moderate ethanol drinking in rats results in widespread decreases in brain serotonin, dopamine, and norepinephrine turnover rates reversed by ethanol intake

This research was initiated to assess the turnover rates (TORs) of dopamine (DA), norepinephrine (NA), serotonin (5-HT), aspartate, glutamate, and GABA in brain regions during rodent ethanol/sucrose (EtOH) and sucrose (SUC) drinking and in animals with a history of EtOH or SUC drinking to further characterize the neuronal systems that underlie compulsive consumption. Groups of five male rats were used, with two trained to drink EtOH solutions, two to drink SUC and one to serve as a non-drinking control. When stable drinking patterns were obtained, rats were pulse labeled intravenously and killed 60 or 90 min later and the TORs of DA, norepinephrine, 5-HT, aspartate, glutamate, and GABA determined in brain regions. Changes in the TOR of 5-HT, DA, and NA were detected specific to EtOH drinking, SUC drinking or a history of EtOH or SUC drinking. An acute EtOH deprivation effect was detected that was mostly reversed with EtOH drinking. These results suggest that binge-like drinking of moderate amounts of EtOH produces a deficit in neuronal function that could set the stage for the alleviation of anhedonic stimuli with further EtOH intake that strengthen EtOH seeking behaviors which may contribute to increased EtOH use in at risk individuals.

Vapor inhalation of alcohol in rats

Alcohol dependence constitutes a neuroadaptive state critical for understanding alcoholism, and various methods have been utilized to induce alcohol dependence in animals, one of which is alcohol vapor exposure. Alcohol vapor inhalation provides certain advantages over other chronic alcohol exposure procedures that share the ultimate goal of producing alcohol dependence in rats. Chronic alcohol vapor inhalation allows the experimenter to control the dose, duration, and pattern of alcohol exposure. Also, this procedure facilitates testing of somatic and motivational aspects of alcohol dependence. Chronic exposure to alcohol vapor produces increases in alcohol-drinking behavior, increases in anxiety-like behavior, and reward deficits in rats. Alcohol vapor inhalation as a laboratory protocol is flexible, and the parameters of this procedure can be adjusted to accommodate the specific aims of different experiments. This unit describes the options available to investigators using this procedure for dependence induction, when different options are more or less appropriate, and the implications of each.

Time course of elevated ethanol intake in adolescent relative to adult rats under continuous, voluntary-access conditions

BACKGROUND

Adolescence is a period of elevated alcohol consumption in humans as well as in animal models. Previous studies in our laboratory have shown that adolescent Sprague-Dawley rats consume approximately 2 times more ethanol on a gram per kilogram basis than adult animals in a 2-bottle choice free-access situation. The purpose of the present study was to examine the time course and pattern of elevated ethanol intake during adolescence and the adolescent-to-adult transition, contrast this intake with ontogenetic patterns of food and water intake, and determine whether adolescent access to ethanol elevates voluntary consumption of ethanol in adulthood.

METHODS

Adolescent [postnatal day (P)27-28] and adult (P69-70) male Sprague-Dawley rats were singly housed with continuous access to both water and 1 of 3 experimental solutions in ball-bearing-containing sipper tubes: unsweetened ethanol (10% v/v), sweetened ethanol (10% v/v+0.1% w/v saccharin), and saccharin alone (0.1% w/v).

RESULTS

Ethanol consumption plateaued at approximately 7.5 g/kg/d during the first 2 weeks of measurement (i.e., P28-39) in early adolescence, before declining sharply at approximately P40 to levels that were only modestly elevated compared with adult-typical consumption patterns that were reached by approximately P70. In contrast, intake of food and total calories showed a more gradual decline into adulthood with no distinguishable plateaus in early adolescence. When adolescent-initiated and adult-initiated animals were tested at the same chronological age in adulthood, animals drank similar amounts regardless of the age at which they were first given voluntary access to ethanol.

CONCLUSIONS

Taken together, these data suggest that the elevated ethanol intake characteristic of early-to-mid adolescence is not simply a function of adolescent-typical hyperphagia or hyperdipsia, but instead may reflect age-related differences in neural substrates contributing to the rewarding or aversive effects of ethanol, as well as possible modulatory influences of ontogenetic differences in sensitivity to novelty or in ethanol pharmacokinetics. Voluntary home cage consumption of ethanol during adolescence, however, was not found to subsequently elevate ethanol drinking in adulthood.

The gamma-aminobutyric acid-B receptor agonist baclofen attenuates responding for ethanol in ethanol-dependent rats

BACKGROUND

Gamma-aminobutyric acid-B (GABA(B)) receptor agonists have been shown to suppress operant self-administration of ethanol in nondependent rats. However, little work has focused on the effects of GABA(B) receptor agonists on self-administration of ethanol in dependent animals.

METHODS

In the present experiment, the GABA(B) receptor agonist baclofen was tested for the ability to modulate both fixed- (FR) and progressive-ratio (PR) responding for ethanol in rats while nondependent and subsequently after ethanol dependence induction. Following the acquisition and stabilization of baseline operant ethanol self-administration and after dependence induction, baclofen [0.0, 0.5, 1, 2, and 4 mg/kg, intraperitoneal (IP)] was tested on FR-1 responding for ethanol. The ability of baclofen (2.0 mg/kg) to affect responding under a PR schedule of reinforcement was also evaluated. Dependence was induced in the animals by subjecting them to a 1-month intermittent vapor-exposure period in which animals were exposed to ethanol vapor for 14 h/d. Following the 1-month period, the vapor-exposed animals resumed FR-1 and PR baclofen drug testing (doses as described above) in the operant chambers at a time point corresponding to the animals being 6 hours into withdrawal (i.e., 6 hours after the ethanol vapor had been discontinued for that day).

RESULTS

Baclofen (0.0, 0.5, 1, 2, and 4 mg/kg, IP) dose-dependently decreased ethanol self-administration in both nondependent and dependent rats on a FR schedule of reinforcement. However, the dose of baclofen that significantly reduced responding for ethanol was shifted to the left in the ethanol vapor-exposed animals, indicating an increased sensitivity to baclofen in animals that were chronically exposed to ethanol. When tested using a PR schedule of reinforcement, there was a significant increase in the breakpoint for the vapor-exposed animals (i.e., the animals were willing to work more in a dependent state). Baclofen (2.0 mg/kg, IP) suppressed intake for both nondependent and dependent animals.

CONCLUSIONS

Ethanol dependence produced increased self-administration of ethanol as reflected in increased ethanol intake and increased responding on a PR schedule of reinforcement. As baclofen suppressed ethanol self-administration and showed evidence of increased potency in dependent animals, the present experiment suggests that the GABA(B) receptor could be a potential pharmacotherapeutic target for the treatment of chronic alcoholism.

Effects of gamma-hydroxybutyric acid and flunitrazepam on ethanol intake in male rats

Both gamma-hydroxybutyric acid (GHB) and flunitrazepam are often used illicitly in combination with ethanol. Nevertheless, the effects that these and other drugs of abuse have on the reinforcing effects of ethanol remain inconclusive. To test the effects of GHB and flunitrazepam on contingent ethanol intake, twelve male Long-Evans rats were trained to orally consume ethanol using a saccharin-fading procedure. After training, all animals preferentially consumed ethanol instead of water at each of five ethanol concentrations (0-32%) when tested with a two-bottle preference test in the homecage. Animals then received a noncontingent dose of ethanol (0.32, 0.56, 1, and 1.33 g/kg), flunitrazepam (0.032, 0.1, and 0.32 mg/kg), or GHB (100, 180, 320, and 560 mg/kg) prior to each subject's daily access to ethanol (18% v/v). Noncontingent doses of ethanol decreased ethanol intake, however, the subjects consumed enough ethanol to maintain a consistent total ethanol dose in g/kg. Flunitrazepam did not affect ethanol intake at any dose tested, whereas GHB only affected intake at the highest dose (560 mg/kg), a dose that also produced sedation. These data suggest that there are perceptible or qualitative differences between GHB, flunitrazepam, and ethanol in terms of their capacity for modulating oral ethanol intake in outbred rats.

Individual differences in ethanol self-administration following withdrawal are associated with asymmetric changes in dopamine and serotonin in the medial prefrontal cortex and amygdala

BACKGROUND

Ethanol withdrawal alters brain neurochemistry, causes asymmetric activation of neurons in the medial prefrontal cortex (mPFC) and amygdala (AMY), and increases ethanol craving and drinking. Rats with intrinsic rightward-turning preferences drink more ethanol than those with left or no preferences; they also exhibit an ethanol-induced neurochemical activation that favors the right side of the mPFC. Our experiments used rats with different turning preferences to assess differences in withdrawal effects on mPFC and AMY neurochemistry as well as ethanol self-administration.

METHODS AND RESULTS

Rats with left-turning, right-turning, and nonturning preferences were fed a 6% ethanol-containing liquid diet (WD) or a pair-fed control diet for 14 days. Differences in dopamine (DA), serotonin (5HT), norepinephrine (NE), and metabolite [3,4-dihydroxphenylacetic acid, homovanillic acid (HVA), and 5-hydroxyindoleacetic acid) concentrations were assessed in each side of the mPFC and AMY during acute withdrawal. Similar groups were fed the same diets and tested for consumption of 10% ethanol versus water and 1% sucrose versus water. WD increased HVA/DA in the mPFC and caused depletions of DA and 5HT in the mPFC and 5HT in the AMY. These effects were greater in the right than in the left side of these structures in rats with right-turning preferences. WD reduced ethanol drinking but right turners drank significantly more than left turners on day 2 of testing and drank more on days 2 and 3 than on day 1. No effects were observed on sucrose drinking. Similar groups were also trained to self-administer ethanol using a sucrose-fade sipper tube procedure that separated measures of ethanol seeking (bar pressing) and consumption. Following 14 days of vapor chamber exposure to ethanol, rats of all turning preferences had a lower rate of bar pressing on the first postwithdrawal day and shorter latencies to begin bar pressing on the third withdrawal day versus prewithdrawal baseline. Only right-turning-preference rats consumed more ethanol following withdrawal.

CONCLUSIONS

These studies show that individual rats differ in postwithdrawal brain neurochemistry and ethanol consumption and that these differences are associated with differences in functional brain asymmetry.

Evaluation of a simple model of ethanol drinking to intoxication in C57BL/6J mice

Because of intrinsic differences between humans and mice, no single mouse model can represent all features of a complex human trait such as alcoholism. It is therefore necessary to develop partial models. One important feature is drinking to the point where blood ethanol concentration (BEC) reaches levels that have measurable affects on physiology and/or behavior (>1.0 mg ethanol/ml blood). Most models currently in use examine relative oral self-administration from a bottle containing alcohol versus one containing water (two-bottle preference drinking), or oral operant self-administration. In these procedures, it is not clear when or if the animals drink to pharmacologically significant levels because the drinking is episodic and often occurs over a 24-h period. The aim of this study was to identify the optimal parameters and evaluate the reliability of a very simple procedure, taking advantage of a mouse genotype (C57BL/6J) that is known to drink large quantities of ethanol. We exchanged for the water bottle a solution containing ethanol in tap water for a limited period, early in the dark cycle, in the home cage. Mice regularly drank sufficient ethanol to achieve BEC>1.0 mg ethanol/ml blood. The concentration of ethanol offered (10%, 20% or 30%) did not affect consumption in g ethanol/kg body weight. The highest average BEC ( approximately 1.6 mg/ml) occurred when the water-to-ethanol switch occurred 3 h into the dark cycle, and when the ethanol was offered for 4 rather than 2 h. Ethanol consumption was consistent within individual mice, and reliably predicted BEC after the period of ethanol access. C57BL/6J mice from three sources provided equivalent data, while DBA/2J mice drank much less than C57BL/6J in this test. We discuss advantages of the model for high-throughput screening assays where the goal is to find other genotypes of mice that drink excessively, or to screen drugs for their efficacy in blocking excessive drinking.

Suppression of ethanol self-administration by the neuropeptide Y (NPY) Y2 receptor antagonist BIIE0246: evidence for sensitization in rats with a history of dependence

Evidence from genetically modified mice suggests a role for NPY in regulation of ethanol intake, but results of pharmacological studies have been more variable. We have previously shown that potentiation of NPY signaling through antagonism at NPY-Y2 receptors decreases operant responding for ethanol in Wistar rats without a history of dependence. Here, we examined the effects of Y2-antagonism in animals with a history of dependence induced by long-term intermittent exposure to ethanol vapor. The Y2-receptor antagonist BIIE0246 suppressed operant responding for ethanol (approximately 50%, p=0.01), at a dose (0.5 nmol i.c.v.) which was ineffective in subjects without a history of dependence. Responding for the ethanol-free control solution was unaffected. These data confirm that antagonism at central NPY-Y2 receptors selectively suppresses motivation to self-administer ethanol, and indicate that the NPY system is sensitized in animals with a history of dependence. This may render the NPY system, and Y2 receptors in particular, an attractive target for treatment of alcohol dependence.

Sugar-dependent rats show enhanced intake of unsweetened ethanol

Rats show signs of dependence on sugar when it is available intermittently, including bingeing, withdrawal, and cross-sensitization with amphetamine. In the current study, we sought to determine whether sugar-dependent rats would show increased intake of unsweetened ethanol and, conversely, whether intermittent access to ethanol would augment sugar consumption. In Experiment 1, with intermittent versus ad libitum access to ethanol, Sprague-Dawley rats were given escalating concentrations of ethanol (1%, 2%, 4%, 7%, and 9%) over the course of 20 days. Rats in the intermittent ethanol access group, with 12-h daily access, consumed more 4%, 7%, and 9% ethanol during the first hour of access, and more 9% ethanol daily, than did rats in the ad libitum ethanol access group. In Experiment 2, with ethanol as a gateway to sugar intake, the rats from Experiment 1 were switched to 10% sucrose with 12-h daily access for 1 week. Rats in the intermittent ethanol access group consumed significantly more sugar than was consumed by rats in a control group with no prior ethanol experience. In Experiment 3, with sugar as a gateway to ethanol to determine whether sugar dependence leads to increased ethanol intake, four groups were maintained for 21 days according to the following designations: intermittent access to sugar and chow, ad libitum access to sugar and chow, intermittent access to chow, or ad libitum access to chow. Four days later, all groups were switched to intermittent ethanol access, as described in Experiment 1. The group with intermittent access to sugar and chow consumed the most 9% ethanol, supporting the suggestion that sugar dependence alters a rat's proclivity to drink ethanol. These results may relate to the co-morbidity between binge-eating disorders and alcohol intake and the tendency of people abstaining from alcohol to consume excessive amounts of sugar. In conclusion, bingeing on either ethanol or sugar fosters intake of the other.

Flavor preferences conditioned by intragastric ethanol with limited access training

In a prior study, ad libitum fed rats learned a strong preference (90%) for a flavored saccharin solution (conditioned stimulus, CS+) paired with concurrent intragastric (IG) infusions of 5% ethanol over another flavor (CS-) paired with water infusions in unlimited access sessions (22 h/day). The present study expanded the investigation of ethanol-conditioned preferences to limited access sessions (30 min/day). Experiment 1 revealed that ad lib or food-restricted rats failed to develop a CS+ preference using the same CS solutions (0.05% Kool-Aid+0.2% saccharin) and IG infusions that were effective with long-term training. Experiments 2 and 3 mimicked the parameters from a report of successful ethanol conditioning in deprived rats: ethanol (0.5 g/kg) or water was infused intragastrically 5 min before access to sweetened CS solutions flavored with HCl or NaCl. Rats learned to prefer the ethanol-paired CS+ when the flavors were mixed with 5% sucrose but not when mixed with 0.2% saccharin. Experiment 4 revealed that 5% sucrose solutions flavored with 0.25% Kool Aid also supported flavor preference conditioning by IG ethanol (0.5 g/kg). CS+ preferences were obtained in rats trained with ethanol infused 5 min before or concurrent with CS+ intake, but not in rats trained with ethanol infused 30 min before CS+ intake. These data confirm that flavor preferences can be conditioned by IG ethanol using a limited access procedure. However, in contrast to 22 h/day training, 30 min/day training requires more intense CS flavors and a nutritive sweetener. The preference reinforcing actions of ethanol may develop slowly and are thus most effective with long training sessions or when intense CS flavors are used in short training sessions.

Ethanol flavor preference conditioned by intragastric carbohydrate in rats

The unpalatable flavor of ethanol solutions greater than approximately 6% may limit their consumption by rats. We determined if ethanol flavor avoidance, like bitter or sour taste avoidance, can be reversed by intragastric (IG) carbohydrate conditioning. Ad lib fed rats drank 5% ethanol and a matched flavor (0.05% citric acid+0.5% maltodextrin, CM) on alternate days. For control rats, postingestive effects were equated: when they drank one solution they were infused IG with the other. Conditioned rats were also infused with 5% ethanol when they drank CM, but when they drank 5% ethanol they were infused with CM + 16% maltodextrin, a potent reward in flavor preference learning. In choice tests, only the conditioned rats preferred ethanol to CM; both groups preferred 5% ethanol to water. Conditioned rats but not controls preferred ethanol to water when the concentration was raised to 10%, and sustained their preference when the infusate carbohydrate was gradually removed. When ethanol concentration was gradually raised to 25%, ethanol preference declined from 48% to 30% in the control rats and from 84% to 50% in the conditioned rats. Thus, ethanol flavor avoidance can be reversed or reduced by postingestive nutritive conditioning, which may combine with the pharmacological effects of ethanol to produce the acquired appetite for the flavor of alcoholic beverages.

Flavor quality and ethanol concentration affect ethanol-conditioned flavor preferences

A previous report showed that outbred rats acquired preferences for a sweetened conditioned stimulus (CS) flavor paired with intragastric ethanol. To evaluate the role of sweet taste in ethanol conditioning, this study compared training with sweetened and unsweetened flavors. In Experiment 1, nondeprived rats were trained to drink one flavored solution (CS+, e.g., grape) paired with intragastric infusion of 5% ethanol and another (CS-, e.g., cherry) paired with intragastric water on alternate days. The volume of ethanol solution infused was matched to the volume of flavored solution the rats consumed. The sweet group's flavors initially contained 0.2% saccharin, reduced to 0.1%, 0.05%, and 0% over days; the plain group's flavors were unsweetened. The sweet group drank more and self-infused more ethanol during training and its preference for the CS+ over the CS- (without saccharin) exceeded that of the plain group (75% versus 62%). Experiment 2 equated total ethanol intake in rats trained with two combinations of flavor quality and ethanol concentration. The Sweet5 group drank flavors with 0.2% saccharin throughout training and tests and received 5% ethanol when they drank CS+, while the Plain10 group drank unsweetened flavors and the CS+ was paired with 10% ethanol. Despite equal daily ethanol doses, the Sweet5 group strongly preferred the CS+ (89%) while the Plain10 group avoided it (31%). The two groups continued to show opposite CS+ preference profiles even when both were tested with sweet CS flavors and 10% ethanol infusions. Thus, sweet taste contributes to the development of ethanol-conditioned flavor preferences, and this effect is not explained by a simple enhancement of ethanol intake.

Long-lasting increase in voluntary ethanol consumption and transcriptional regulation in the rat brain after intermittent exposure to alcohol

Prolonged exposure of the brain to ethanol is a prerequisite for developing ethanol dependence, but the underlying neural adaptations are unknown. Here we demonstrate that rats subjected to repeated cycles of intoxication and withdrawal develop a marked and long-lasting increase in voluntary ethanol intake. Exposure-induced but not spontaneous alcohol intake is antagonized by acamprosate, a compound clinically effective in human alcoholism. Expression analysis of cingulate cortex and amygdala reveals a set of long-term up-regulated transcripts in this model. These include members of pathways previously implicated in alcohol dependence (glutamatergic, endocannabinoid, and monoaminergic neurotransmission), as well as pathways not previously thought to be involved in this disorder (e.g., members of the mitogen-activated protein kinase pathway). Thus, alternating periods of ethanol intoxication and withdrawal are sufficient to induce an altered functional brain state, which is likely to be encoded by long-term changes in gene expression. These observations may have important implications for how alcoholism is managed clinically. Novel clinically effective treatments may be possible to develop by targeting the products of genes found to be regulated in our model.

Effects of adolescent ethanol exposure on ethanol consumption in adult rats

Ethanol exposure during early development could predispose an individual to increased ethanol consumption. Given the high prevalence of adolescent ethanol abuse, it is important to assess the potential impact of adolescent ethanol exposure on the development of alcohol drinking. The following study was designed to assess the initiation of ethanol consumption in adult rats after exposure to ethanol vapors during adolescence. Male Sprague-Dawley rats (n = 23) were exposed to ethanol vapor for 12 h per day for 10 consecutive days between postnatal days 30 and 40. Ethanol vapor exposure maintained blood ethanol levels averaging 250 mg/dl. All rats were subsequently trained to self-administer ethanol after a 52-day withdrawal period. When ethanol consumption was assessed in the adult rats (>3 months old) there were no significant differences in initiation or maintenance of ethanol self-administration between ethanol-exposed and control rats. In addition, there were no group differences in the ability of a noise stressor presented before the drinking session to transiently decrease ethanol intake. Overall, these findings indicate that forced exposure to ethanol vapor during adolescence does not seem to be sufficient to alter initiation or maintenance of limited-access ethanol self-administration.

Persistent suppression of ethanol self-administration by brief social stress in rats and increased startle response as index of withdrawal

Excessive alcohol drinking is often linked to the experience of stress, but experimental approaches using animal models of alcohol self-administration have had widely varying outcomes. The objective was to determine how daily exposure to brief, predictable social stress would change alcohol self-administration in rats in a daily limited access protocol. Male Long-Evans rats had either access to a 10% ethanol solution for 15 min in the home cage setting (n=20) or were reinforced with 15% ethanol deliveries for every fifth lever press (n=10). Subsequently, all rats were subjected to brief social stress for five consecutive days. Social stress consisted of attacks by an opponent for 5 min followed by exposure to threats while in a protective cage for 30 min. In both the home cage drinking and operant conditioning groups, social stress exposure significantly decreased alcohol intake or rate of alcohol reinforcements, respectively. When alcohol intake was scheduled immediately before social stress (i.e., 24 h after the previous social stress episode), a decrease was observed with a delay of 1 or 2 days. When alcohol intake was scheduled 4 h after stress, no changes in intake or alcohol reinforcements were observed. Animals that consumed a low dose of ethanol displayed less defensive behavior during social stress compared to water-drinking animals, and showed an increased startle reflex at 8 and 56 h after discontinuation of daily ethanol access. The current experimental protocols of social defeat stress reveal a transient suppression rather than a facilitation of alcohol consumption.