Alcohol and taste-mediated learning

Drug discrimination learning: Interoceptive stimulus control of behavior and its implications for regulated and dysregulated drug intake

Drug discrimination research has generated rich evidence for the capacity of interoceptive drug stimuli to control behavior by serving as discriminative cues. Owing to its neuropharmacological specificity, drug discrimination learning has been widely used to characterize the stimulus effects and neuropharmacological underpinning of drugs. Apart from such utility, discriminative drug stimuli may help regulate drug use by disambiguating conditioned associations and post-intake outcomes. First, this review summarizes the evidence supporting interoceptive regulation of drug intake from the literature of exteroceptive discriminative control of drug-related behavior, effects of drug priming, and self-titration of drug intake. Second, an overview of interoceptive control of reward-seeking and the animal model of discriminated goal-tracking is provided to illustrate interoceptive stimulus control of the initiation and patterning of drug intake. Third, we highlight the importance of interoceptive control of aversion-avoidance in the termination of drug-use episodes and describe the animal model of discriminated taste avoidance that supports such a position. In bridging these discriminative functions of drug stimuli, we propose that interoceptive drug stimuli help regulate intake by disambiguating whether intake will be rewarding, nonrewarding, or aversive. The reflection and discussion on current theoretical formulations of interoceptive control of drug intake may further scientific advances to improve animal models to study the mechanisms by which interoceptive stimuli regulate drug intake, as well as how alterations of interoceptive processes may contribute to the transition to dysregulated drug use.

Chemogenetic inhibition of locus coeruleus to rostromedial tegmental nucleus noradrenergic pathway increases light cycle ethanol drinking in male and female mice and blunts ethanol-induced CTA

We recently showed that chemogenetic activation of the locus coeruleus (LC) to the rostromedial tegmental nucleus (RMTg) noradrenergic (NE) pathway significantly blunted binge-like ethanol drinking and induced aversive-like behaviors in mice. The aim of the present study is to determine if silencing this TH + LC → RMTg noradrenergic pathway promotes increased levels of binge-like ethanol intake and reduced ethanol-induced conditioned taste aversion (CTA). To this end, both male and female TH-ires-cre mice on a C57BL/6 J background were cannulated in the RMTg and injected in the LC with rAVV viruses that encode cre-dependent Gi-expressing designer receptor exclusively activated by designer drugs (DREADDs), or its control, to directly control the activity of NE neurons. Inhibition of the LC to RMTg pathway had no effect on the binge-ethanol drinking in a "drinking-in-the-dark" (DID) paradigm. However, when using this paradigm during the light cycle, silencing of this circuit significantly increased ethanol intake without altering sucrose drinking. Moreover, we found that inhibition of this circuit significantly attenuated an ethanol-induced CTA. In addition, when compared to control animals, pairing RMTg-directed Clozapine N-oxide (CNO) with an i.p. injection of 1.5 g/kg ethanol reduced c-Fos activation in the LC, and increased c-Fos expression in the ventral tegmental area (VTA) in Gi-expressing mice. Our data show that inhibition of the TH + LC to the RMTg pathway significantly increased ethanol drinking as well as attenuated ethanol-induced CTA, supporting the involvement of the LC to RMTg noradrenergic circuit as an important protective mechanism against excessive ethanol consumption.

Male and female C57BL/6 mice display drug-induced aversion and reward in the combined conditioned taste avoidance/conditioned place preference procedure

BACKGROUND

Drugs of abuse have rewarding and aversive effects that, in balance, impact abuse potential. Although such effects are generally examined in independent assays (e.g., CPP and CTA, respectively), a number of studies have examined these effects concurrently in rats in a combined CTA/CPP design. The present study assessed if similar effects can be produced in mice which would allow for determining how each is affected by subject and experiential factors relevant to drug use and abuse and the relationship between these affective properties.

METHODS

Male and female C57BL/6 mice were exposed to a novel saccharin solution, injected (IP) with saline or 5.6, 10 or 18 mg/kg of the synthetic cathinone, methylone, and placed on one side of the place conditioning apparatus. The following day, they were injected with saline, given access to water and placed on the other side of the apparatus. After four conditioning cycles, saccharin avoidance and place preferences were assessed in a final two-bottle CTA test and a CPP Post-Test, respectively.

RESULTS

In the combined CTA/CPP design, mice acquired a significant dose-dependent CTA (p = 0.003) and a significant CPP (p = 0.002). These effects were independent of sex (all p's > 0.05). Further, there was no significant relationship between the degree of taste avoidance and place preference (p > 0.05).

CONCLUSIONS

Similar to rats, mice displayed significant CTA and CPP in the combined design. It will be important to extend this design in mice to other drugs and to examine the impact of different subject and experiential factors on these effects to facilitate predictions of abuse liability.

Impact of the Aversive Effects of Drugs on Their Use and Abuse

Drug use and abuse are complex issues in that the basis of each may involve different determinants and consequences, and the transition from one to the other may be equally multifaceted. A recent model of the addiction cycle (as proposed by Koob and his colleagues) illustrates how drug-taking patterns transition from impulsive (acute use) to compulsive (chronic use) as a function of various neuroadaptations leading to the downregulation of DA systems, upregulation of stress systems, and the dysregulation of the prefrontal/orbitofrontal cortex. Although the nature of reinforcement in the initiation and mediation of these effects may differ (positive vs. negative), the role of reinforcement in drug intake (acute and chronic) is well characterized. However, drugs of abuse have other stimulus properties that may be important in their use and abuse. One such property is their aversive effects that limit drug intake instead of initiating and maintaining it. Evidence of such effects comes from both clinical and preclinical populations. In support of this position, the present review describes the aversive effects of drugs (assessed primarily in conditioned taste aversion learning), the fact that they occur concurrently with reward as assessed in combined taste aversion/place preference designs, the role of aversive effects in drug-taking (in balance with their rewarding effects), the dissociation of these affective properties in that they can be affected in different ways by the same manipulations, and the impact of various parametric, experiential, and subject factors on the aversive effects of drugs and the consequent impact of these factors on their use and abuse potential.

Ethanol pre-exposure differentially impacts the rewarding and aversive effects of α-pyrrolidinopentiophenone (α-PVP): Implications for drug use and abuse

RATIONALE

Exposure to a drug can subsequently impact its own reactivity as well as that of other drugs. Given that users of synthetic cathinones, i.e., "bath salts", typically have extensive and varied drug histories, an understanding of the effects of drug history on the behavioral and physiological consequences of synthetic cathiones may be important to their abuse liability.

OBJECTIVES

The goal of the current work was to assess the effects of an ethanol pre-exposure on the rewarding and aversive effects of α-PVP.

METHODS

Adult male Sprague Dawley rats were exposed to ethanol prior to combined conditioned taste avoidance/conditioned place preference training in which rats were injected with 1.5, 3 or 5 mg/kg of racemic α-PVP or vehicle. Following a 7-day washout period, rats were then tested for thermoregulatory effects of α-PVP using subcutaneous probes to measure body temperature changes over the course of 8 h. This was followed 10 days later by assessments for α-PVP-induced locomotor activity and stereotypies over a 1-h session.

RESULTS

α-PVP induced significant dose- and trial-dependent taste avoidance that was significantly attenuated by ethanol history and dose- and time-dependent increases in locomotor activity that were significantly increased by ethanol. α-PVP also induced place preferences and dose- and time-dependent increases in body temperature, but these measures were unaffected by ethanol history.

CONCLUSIONS

α-PVP's aversive effects (as measured by taste avoidance) were attenuated, while its rewarding effects (as indexed by place preference conditioning) were unaffected, by ethanol pre-exposure. Such a pattern may indicate increased α-PVP abuse liability, as changes in the balance of aversion and reward may impact overall drug effects and likelihood of drug intake. Future self-administration studies will be necessary to explore this possibility.

Sex as a biological variable: Drug use and abuse

The study of sex as a biological variable is a necessary emphasis across a wide array of endpoints, including basic neuroscience, medicine, mental health, physiology and behavior. The present review summarizes work from clinical and preclinical populations on sex differences in drug use and abuse, ranging from initiation to escalation/dysregulation and from drug cessation/abstinence to relapse. These differences are analyzed in the context of the addiction cycle conceptualization of Koob and his colleagues and address patterns of drug use (binge/intoxication), motivation underlying its use (withdrawal/negative affect) and likelihood and causes of craving and relapse of drug taking (preoccupation/anticipation). Following this overview, an assessment of the basis for the reported sex differences is discussed in the context of the affective (rewarding and aversive) properties of drugs of abuse and how such properties and their balance vary with sex and contribute to drug intake. Finally, the interaction of sex with several experiential (drug history) and subject (age) factors and how these interactions affect reward and aversion are discussed to highlight the importance of understanding such interactions in predicting drug use and abuse. We note that sex as a biological variable remains one of critical evaluation and that such investigations of sex differences in drug use and abuse continue and be expanded to assess all facets of their mediation, including these affective properties, how their balance may be impacted by the multiple conditions under which drugs are taken and how this overall balance affects drug use and addiction vulnerability.

Exposure to nicotine during periadolescence or early adulthood alters aversive and physiological effects induced by ethanol

The majority of smokers begin their habit during adolescence, which often precedes experimentation with alcohol. Interestingly, very little preclinical work has been done examining how exposure to nicotine during periadolescence impacts the affective properties of alcohol in adulthood. Understanding how periadolescent nicotine exposure influences the aversive effects of alcohol might help to explain why it becomes more acceptable to this preexposed population. Thus, Experiment 1 exposed male Sprague Dawley rats to either saline or nicotine (0.4mg/kg, IP) from postnatal days 34 to 43 (periadolescence) and then examined changes in the aversive effects of alcohol (0, 0.56, 1.0 and 1.8g/kg, IP) in adulthood using the conditioned taste aversion (CTA) design. Changes in blood alcohol concentration (BAC) as well as alcohol-induced hypothermia and locomotor suppression were also assessed. To determine if changes seen were specific to nicotine exposure during periadolescence, the procedures were replicated in adults (Experiment 2). Preexposure to nicotine during periadolescence attenuated the acquisition of the alcohol-induced CTAs (at 1.0g/kg) and the hypothermic effects of alcohol (1.0g/kg). Adult nicotine preexposure produced similar attenuation in alcohol's aversive (at 1.8g/kg) and hypothermic (1.8g/kg) effects. Neither adolescent nor adult nicotine preexposure altered BACs or alcohol-induced locomotor suppression. These results suggest that nicotine may alter the aversive and physiological effects of alcohol, regardless of the age at which exposure occurs, possibly increasing its overall reinforcing value and making it more likely to be consumed.

The paradox of drug taking: the role of the aversive effects of drugs

In 1991, Woods described the paradoxical nature of eating, specifically, that it produced aversive and negative effects. He noted in this analysis the multiple physiological and behavior adaptations, both learned and unlearned, that were aimed at regulating food intake and reducing its aversive, disruptive effects. From this position, he argued that consumption reflected a balance of the positive and aversive effects of eating. The present review extends this analysis to drug use and abuse, i.e., that drug taking itself also is a balance of reward and aversion. Although traditionally the analysis of drug use and abuse has focused on a drug's positive and negative rewarding effects, the present review highlights the aversive effects of these same drugs, e.g., cocaine, morphine, alcohol, and describes such effects as protective in nature. This balance and the manner by which it can be impacted by subject and experiential factors are described with a focus on genetic models of drug abuse using the Lewis and Fischer inbred rat strains.

Conditioned taste aversion learning: implications for animal models of drug abuse

Drugs of abuse are typically discussed in terms of their rewarding effects and how these effects mediate drug taking. However, these drugs produce aversive effects that could have an important role in the overall acceptability of a drug and its likelihood of being self-administered. Rewarding and aversive effects, then, could be interpreted as separate behavioral effects, with the balance of the two determining overall drug acceptability. Interestingly, the role of aversive effects on drug acceptability in the self-administration preparation has received limited attention in this context. This chapter examines the aversive effects of drugs and discusses their role in drug taking. If these aversive effects serve a protective function, manipulations that alter or decrease these effects could have implications for drug taking. Several factors have been reported to alter conditioned taste aversion (CTA) learning, a preparation used in the assessment of the aversive effects of drugs in general. Two of these factors, drug history and strain, are reviewed here. By reviewing these, we intend to demonstrate the protective nature of aversive effects in the initiation and escalation of drug taking and to provide evidence that reductions in aversive effects could produce changes in patterns of drug self-administration that could lead to an increased vulnerability to abuse drugs by altering the reward-aversion balance. The aim of this chapter is not to question the importance of rewarding effects in self-administration but rather to provide evidence that aversive effects are an important factor that needs to be considered in discussions of drug-taking behavior.

Conditioned flavor aversions: assessment of drug-induced suppression of food intake

Administration of a drug following ingestion of a novel food or solution often suppresses subsequent intake of the new food or solution. This suppression is associative, in that consumption is not suppressed when there is no temporal relationship between consumption and drug administration. The robust nature of aversion learning has made this procedure a sensitive and widely used behavioral index of drug side effects. The procedures described in this unit are suitable for work with rodents, and may require modifications, e.g., in presentation of the ingesta and drug for other species. Familiar and novel foods may be used instead of solutions, with similar results.

The effects of nicotine on ethanol-induced conditioned taste aversions in Long-Evans rats

RATIONALE

Overall drug acceptability is thought to be a function of the balance between its rewarding and aversive effects, the latter of which is reportedly affected by polydrug use.

OBJECTIVES

Given that nicotine and alcohol are commonly co-used, the present experiments sought to assess nicotine's impact on ethanol's aversive effects within a conditioned taste aversion design.

MATERIALS AND METHODS

Experiment 1 examined various doses of nicotine (0, 0.4, 0.8, 1.2 mg/kg) to determine a behaviorally active dose, and experiment 2 examined various doses of ethanol (0, 0.5, 1.0, 1.5 g/kg) to determine a dose that produced intermediate aversions. Experiment 3 then examined the aversive effects of nicotine (0.8 mg/kg) and ethanol (1.0 g/kg) alone and in combination. Additionally, nicotine's effects on blood alcohol concentrations (BAC) and ethanol-induced hypothermia were examined.

RESULTS

Nicotine and ethanol combined produced aversions significantly greater than those produced by either drug alone or the summed aversive effects of the individual compounds. These effects were unrelated to changes in BAC, but nicotine and ethanol combined produced a prolonged hypothermic effect which may contribute to the increased aversions induced by the combination.

CONCLUSIONS

These data demonstrate that nicotine may interact with ethanol, increasing ethanol's aversive effects. Although the rewarding effects of concurrently administered nicotine and ethanol were not assessed, these data do indicate that the reported high incidence of nicotine and ethanol co-use is unlikely due to reductions in the aversiveness of ethanol with concurrently administered nicotine. It is more likely attributable to nicotine-related changes in ethanol's rewarding effects.

Conditioned taste aversion: a database

The present commentary describes the availability of a database on conditioned taste aversion learning, the avoidance of fluids and foods previously associated with the aversive effects of a variety of drugs. The database includes articles as early as 1955 by Garcia and his colleagues [Science 122 (1955) 127] (reporting such avoidance in rats) and papers just published given that the database is ongoing and constantly updated. At the printing of this announcement, approximately 2600 papers are included in the database. The database allows the user to search for articles by author(s), key word(s), date, title and journal. These terms can be used as single entries or multiple combinations. Finally, the full database can be viewed by performing the search function without entering any terms in the query window. The database can be accessed at http://www.CTALearning.com.

Studies on the role of nicotinic acetylcholine receptors in the discriminative and aversive stimulus properties of ethanol in the rat

The role of the nicotinic acetylcholine receptor (nAChR) in the discriminative and aversive stimulus effects of ethanol was studied in rats. In the operant drug discrimination procedure the rats were trained to discriminate between 1.0 g/kg ethanol and saline under the FR10 schedule of sweetened milk reinforcement. Neither the nAChR agonist, nicotine (0.1-0.6 mg/kg) nor the nAChR antagonist, mecamylamine (3.0-6.0 mg/kg) substituted for the ethanol stimulus. Moreover, mecamylamine (0.5-6.0 mg/kg) did not antagonise the ethanol stimulus. The cross-familiarisation conditioned taste aversion procedure was used as an alternative method to study stimulus resemblance between ethanol and nicotine. Six daily injections of nicotine (0.6 mg/kg) significantly decreased a subsequent ethanol-induced taste aversion conditioning. The aversive stimulus effects of ethanol were investigated with the conditioned taste aversion (CTA) paradigm. Mecamylamine (1.0-3.0 mg/kg) did not attenuate an ethanol-induced CTA. These results suggest that: (1) nAChRs are not primarily involved in the discriminative stimulus effects of ethanol when studied with the operant drug discrimination test; (2) nAChRs are not critically involved in the ethanol-induced CTA.

5,7-dihydroxytryptamine lesion does not affect ethanol-induced conditioned taste and place aversion in rats

The effect of the lesion of central serotonergic neurons by 5,7-dihydroxytryptamine (5,7-DHT), on ethanol-induced taste and place aversion conditioning was studied in male Wistar rats. Control biochemical analysis revealed that 5,7-DHT (250 micrograms per rat, free base, i.c.v.) produced marked and selective depletion of serotonin (5-HT) in the hippocampal formation and the limbic forebrain complex. Ethanol-induced (1.5 g/kg, i.p.) conditioned taste aversion (CTA) to saccharin solution was unaffected by the lesion of central serotonergic neurons. The 5,7-DHT-lesioned and sham-lesioned rats showed comparable ethanol-induced CTA even 30 days after the last ethanol injection. Similarly, ethanol-induced (1.5 g/kg, i.p.) conditioned place aversion (CPA) was unaffected by 5,7-DHT administration. These results suggest that central serotonergic pathways are not primarily involved in the aversive effects of high ethanol doses in rats.

Conditioned taste aversions induced by alcohol and lithium in rats selectively bred for ethanol neurosensitivity

Rats that were selectively bred for differences in alcohol-induced sleep time (alcohol neurosensitivity) were tested for differences in formation and extinction of alcohol- and LiCl-induced conditioned taste aversions. Male rats bred for high, control, or low alcohol sensitivity (HAS, CAS, and LAS rats, respectively) were deprived of water and given daily 30 min access to water for a baseline period of 7 days. Rats were then given a novel 0.125% sodium saccharin solution, followed by an intraperitoneal injection of either saline, 2 g/kg of ethanol (at 10% w/v), or 50.9 mg/kg of LiCl (0.15 M) on 3 conditioning days. Each saccharin exposure was followed by a recovery day of access to water. The ethanol-induced saccharin aversion extinguished more rapidly in LAS rats than in CAS or HAS rats (p < 0.05), but LiCl conditioned equivalent aversions in each group. Also, ethanol injection results in large differences in observed resting behavior in these rats (HAS > CAS > LAS), but LiCl injection produced no reliable group differences in resting. The weaker alcohol-induced taste aversion in LAS rats accords with their previously measured higher oral consumption of alcohol (Kulkosky et al., Alcoholism 17:545-551, 1993) and the idea that alcohol intake is limited by an expectancy of postingestive consequences. The weaker ethanol-induced aversion in LAS rats reflects selective breeding of an alcohol-specific trait and not a general difference in aversive conditioning or chemical neurosensitivity.

Ethanol self-administration patterns and taste aversion learning across inbred rat strains

Initial self-administration of high doses of EtOH is shown to be associated in some inbred rat strains with the eventual development of a low preference for EtOH, presumably as a consequence of taste aversion learning occurring during initial intake. Only modest support was obtained for the hypothesis that strain differences in the aversiveness of EtOH affects taste aversion learning. The instrinsic palatability of EtOH and the salience of EtOH as a conditioned stimulus may also affect EtOH preference, but there do not appear to be differences among strains in their general ability to form taste-toxicosis associations.

Ethanol self-administration in deprived rats: effects of Ro15-4513 alone, and in combination with flumazenil (Ro15-1788)

Previous work in our laboratory demonstrated that Ro15-4513, a partial inverse benzodiazepine agonist, decreases self-administration of ethanol (ETOH) in rats maintained on a two-bottle regmine of a saccharin ethanol solution (ES) and water over a 35-day consumption period. The present study extended the consumption period to 60 days and examined the effects of Ro15-4513 (2.5 mg/kg), flumazenil (Ro15-1788) (8.0 mg/kg), and Ro15-4513 in combination with Ro15-1788 on the time course of ETOH self-administration. High initial intake of ES observed during the first 4 weeks declined significantly over subsequent weeks. Ro15-4513 pretreatment, however, resulted in significant reduction of ES, while significantly preventing the "normal" reduction of consumption as was observed under control conditions. The antagonistic actions of Ro15-4513 were blocked/attenuated by the benzodiazepine receptor antagonist, Ro15-1788, independent of whether consumption of the ES was low or high. Both Ro15-4513 and Ro15-1788 affected water intake differentially compared with vehicle-injected controls. The results suggest that GABA-benzodiazepine mechanisms may be important in altering chronic ETOH drinking patterns depending upon experience with ETOH, tolerance, or learning.

Assessment of ethanol's hedonic effects in mice selectively bred for sensitivity to ethanol-induced hypothermia

Mice selectively bred for sensitivity (COLD) or insensitivity (HOT) to the hypothermic effect of ethanol were tested in three tasks purported to assess ethanol's hedonic properties: place conditioning, taste conditioning, and ethanol drinking. In the place conditioning task, distinctive tactile (floor) stimuli were differentially paired with injection of ethanol (2.25 g/kg) or saline, and preference for the tactile stimuli was assessed during a choice test without ethanol. In the taste conditioning task, fluid-deprived mice were given repeated access to saccharin followed by injection of ethanol (2.25 g/kg). In the drinking task, mice were given access on alternate days to a single drinking tube containing water or ethanol in a concentration that gradually increased from 1 to 12% (v/v) over days. HOT mice showed greater conditioned preference for ethanol-paired flavor cues, and greater aversion for ethanol-paired flavor cues, and drank less ethanol at concentrations above 5% than COLD mice. HOT mice also showed higher levels of ethanol-stimulated activity than COLD mice. Control experiments indicated that the lines did not differ in initial preference for the tactile and flavor stimuli used in the conditioning tasks. Because the same line differences were seen in mice selected from two genetically independent populations, these studies offer strong evidence of genetic correlations between ethanol's thermal effect and its effect on activity, place conditioning and taste conditioning. Evidence of a genetic correlation between ethanol's thermal effect and ethanol drinking, however, is weaker since it is based on a line difference observed in only one of the genetic replicates. (ABSTRACT TRUNCATED AT 250 WORDS)

The conditioning of aversions to familiar and preferred flavours: a new aversion therapy model

The present study examined the ability of rats to develop aversions to familiar flavours and to flavours that they had previously acquired a preference for. Rats were first conditioned to prefer a CS+ flavour over a CS- flavour by pairing CS+ intake with the consumption of a starch solution (16% Polycose). A second group was exposed to the same training but preference conditioning was prevented by inhibiting starch digestion with the drug acarbose. The rats were next given aversion training; the CS+ flavour was now paired with toxicosis (LiCl injection) while the CS- flavour paired with a control treatment (NaCl injection). The results of two-choice tests revealed that aversion training produced significant avoidance of the CS+ flavours in both the group that had acquired a preference for this flavour as well as in the no-preference group. The value of using conditioned flavour preferences as targets for aversions to model the aversion therapy approach to alcoholism is discussed.

Cholecystokinin and satiation with alcohol

Release of the brain-gut peptide cholecystokinin (CCK) is stimulated by intragastric instillation of ethanol, and peripheral administration of CCK inhibits ethanol consumption. To assess the temporal specificity of the inhibitory effect of CCK on alcohol intake, water-deprived rats were given 5% ethanol at 20, 10 or 0 min after intraperitoneal injections of CCK octapeptide. Delaying access to ethanol for 20 min prevented a significant effect of CCK on intake. CCK's temporally constrained inhibitory action on alcohol consumption is consistent with an ethanol satiation effect. To test the motivational specificity of CCK's effect on fluid intake, rats were allowed a 2-bottle choice of 2% ethanol and water after CCK injections. Ethanol solution intake was suppressed by CCK, and total water intake was unaffected. The putative alcohol satiation action of CCK is appropriately specific to ethanol solution in free-choice tests. Hungry, but not fluid-deprived rats that were either ethanol experienced or naive received a 2-bottle choice of 4% ethanol or water after CCK or saline injections. CCK again specifically inhibited ethanol intake, but this effect required prior ethanol experience. Doses of CCK and naloxone, an opioid receptor blocker, combined to inhibit ethanol intake in an infra-dose-additive manner in water-deprived rats. CCK may act endogenously, in part on opioid receptor-mediated processes, as a preabsorptive satiety signal of ethanol. The full expression of this action appears to depend on prior conditioning of nutritive expectancy of the postingestive effects of alcohol.

Conditioned taste aversions as a behavioral baseline for drug discrimination learning: an assessment with phencyclidine

When PCP was given prior to the pairing of saccharin with LiCl (and the PCP vehicle prior to a nonpoisoned exposure to the same saccharin solution), rats rapidly acquired the discrimination, avoiding saccharin consumption following PCP and consuming saccharin following the vehicle after only three conditioning trials. Conversely, when the PCP vehicle was given prior to the saccharin-LiCl pairing and PCP prior to a nonpoisoned exposure to saccharin, other subjects avoided saccharin consumption following the vehicle injection and readily consumed saccharin after an injection of PCP. During dose substitution sessions, animals displayed greater drug-appropriate responding as the dose of PCP increased. When a range of doses of ketamine was given in place of PCP prior to saccharin access, subjects displayed dose-dependent PCP-appropriate responding. When a range of doses of d-amphetamine was substituted for PCP, subjects displayed vehicle-appropriate responding at all doses. The relative efficacy of the taste aversion procedure as a baseline for drug discrimination learning is discussed.

Rat strain differences in ethanol self-administration and taste aversion learning

Taste aversion learning was investigated in two inbred strains of rats known to differ in amount of ethanol (EtOH) they will self-administer orally. The "low EtOH preference" strain, WKYs, acquired an aversion to an EtOH solution during self-administration; but a "high preference" strain, M520s, did not. It was shown that a lower dose of EtOH will condition saccharin aversion in WKYs than in M520s, suggesting EtOH is a more effective US in the low preference strain. Analysis of patterns of EtOH self-administration indicates the pattern of the low preference strain is more likely to result in taste aversion learning. The implications of these results for the presumed relation between EtOH preference and other EtOH-related phenotypes is discussed.

Effect of taste aversion learning on ethanol self-administration

Ethanol (EtOH) oral self-administration studies using rats have had inconsistent outcomes: studies in which rats are fluid deprived report decreasing EtOH intake over trials, whereas studies not employing fluid deprivation report increasing intake over trials. The present study supports the hypothesis that differential taste aversion learning may account for some of this discrepancy. This study indicates that taste aversion learning is maximized under fluid deprivation conditions and that "latent inhibition," i.e., exposure to non-intoxicating amounts of the EtOH solution prior to conditioning, reduces taste aversion learning. It is suggested that the effect of fluid deprivation on taste aversion resulting from EtOH self-administration may be at least in part due to the development of latent inhibition in non-deprived animals during initial exposure to the EtOH solution.

An experimental model of self-intoxication in C57 mice

Male C57BL/6J mice offered unrestricted access to food, water and 10% ethanol, exhibited obvious intoxication when treated with the alcohol dehydrogenase inhibitor, 4-methylpyrazole (4MP) by chronic infusion. Plasma concentrations of ethanol ranged from 156 +/- 43 mg/dl at midday to 254 +/- 31 mg/dl at midnight producing a twenty-fold increase in the total exposure to blood alcohol. Illness sufficiently severe to require intervention occurred in five of the ten mice in the experimental group, while controls treated with 4MP and offered only water to drink displayed no adverse effects. The continuation of drinking despite life-threatening toxicity suggests these mice failed to make an association between the consumption of ethanol and its consequences.

Bombesin and litorin inhibit ethanol intake

Twenty-three hr water-deprived rats received access to 5% ethanol solution for 30 min daily. Intraperitoneal injection of bombesin (4.0-16.0 micrograms/kg) or litorin (16.0 micrograms/kg) significantly inhibited ethanol intake. Litorin (32.0 micrograms/kg) equivalently suppressed the intakes of 5% ethanol and 8.9% dextrose solutions. The results are consistent with previous reports that administration of bombesin-like peptides selectively inhibits caloric intake in the rat. Injection of bombesin-like peptides may affect ethanol and dextrose intake by eliciting a satiety signal that governs caloric intake.

Brain-gut neuropeptides and the limitation of ethanol consumption

Recent studies have clearly shown powerful control of ingestive behavior by certain peptides known to be present in both brain and gut tissues. These "brain-gut neuropeptides" are thought to constitute endogenous factors responsible for the normal regulation of food intake. This review explores the potential for a role of these peptides in the limitation of ethanol intake, which shares several features with the control of food intake. The putative satiety role of the neuropeptides cholecystokinin and bombesin, and other brain-gut peptides is briefly described. The conclusion that voluntary ethanol intake is partially controlled as a function of the energy ethanol provides, and the rate of its utilization, is illustrated with data from recent studies of rat and hamster ethanol consumption. The possibility of neuropeptide influence on ethanol intake is presented in light of new findings that cholecystokinin and bombesin inhibit ethanol consumption in the rat. If neuropeptides are demonstrated to modulate ethanol intake by eliciting satiety, this information may be useful in the identification and understanding of the endogenous factors which regulate human alcohol intake, and will suggest possible peptide-based therapeutic interventions for control of alcohol abuse and alcoholism.

Ethanol-induced conditioned taste aversion to ethanol

A single injection of 2.5 g/kg ethanol one hr after drinking a 10% ethanol-0.05% saccharin solution produced a persistent conditioned taste aversion to the ethanol-saccharin solution. Twelve pairings produced a still stronger aversion that generalized to an aversion to a 10% ethanol solution without saccharin. Unpaired presentations of ethanol-saccharin solution and ethanol injections prevented the subsequent development of an aversion from a single pairing. Twelve pairings of access to saccharin solution with ethanol injections produced an aversion that generalized to an ethanol-saccharin solution. All groups receiving 12 alternate-day ethanol injections developed tolerance to the hypothermic effect of ethanol, but the tolerance was not conditioned to the drinking fluids previously paired with ethanol injections and it was unrelated to the subsequent drinking behaviors.

Effect of cholecystokinin octapeptide on ethanol intake in the rat

Water-deprived rats received 3%, 6% or 9% ethanol solution or water for 30 min daily. Intraperitoneal injection of cholecystokinin octapeptide (CCK-8, 2.0-4.0 micrograms/kg) significantly and specifically inhibited ethanol intake. The findings are consistent with previous reports of specificity of the inhibition of caloric intake by CCK-8. Administration of CCK-8 may influence ethanol intake by modulating a satiety signal that ordinarily controls ethanol intake.