The effects of aminotriazole and acetaldehyde on an ethanol drug discrimination with a conditioned taste aversion procedure.

The present study was designed to investigate whether acetaldehyde shares stimulus properties with ethanol using the conditioned taste aversion (CTA) baseline of drug discrimination learning. Animals were trained to discriminate ethanol (0.8 g/kg, i.p.) from saline using 11 consecutive cycles consisting of a pairing day and three nonpairing days. On pairing days, all animals were injected with ethanol 30 min prior to a 20-min limited access to a saccharin solution (0.1% w/v) and then immediately injected with either LiCl (0.15 M, 1.8 meq) or distilled water. On the three following nonpairing days, animals were injected with saline and 30 min later presented with the same saccharin solution for 20 min. No injections followed on these nonpairing days. Results showed that animals acquired discriminative stimulus control for ethanol after seven pairings. Pretreatment with the catalase inhibitor did not alter the discriminative control for ethanol. Generalization tests revealed that acetaldehyde substituted for ethanol at a dose of 0.3 g/kg. The results of the present study suggest that catalase inhibition did not reverse or alter the discriminative stimulus effects of ethanol. However, generalization tests showed that acetaldehyde (0.3 g/kg) will substitute for ethanol suggesting that these two drugs share some similar properties.     

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.     

Methylnaltrexone attenuates taste aversion conditioned by low-dose ethanol

Previous research has shown that activation of a subset of peripheral opioid receptors located in the gut produce aversive effects as measured in the place and taste conditioning (CTA) paradigms. Endogenous opioid activity and tetrahydroisoquinolines (TIQs) are stimulated or formed after ethanol (EtOH) administration and both are known to activate opioid receptors. We therefore examined the hypothesis that a portion of the aversive effects of EtOH may be mediated through peripheral opioid receptors, activated by EtOH-induced opioids or TIQs. EtOH CTAs were slightly attenuated when animals were pretreated with the putative peripheral opioid receptor antagonist methylnaltrexone. By itself MNTX did not condition a taste preference or aversion. However, blood EtOH levels (BELs) in animals pretreated with MNTX were lower than those of saline-pretreated subjects, an effect that just reached statistical significance and was not present at specific EtOH doses. The results indicate that a portion of the aversive conditioning effects of EtOH (using a two-bottle CTA paradigm) may be receptor-mediated effects, exerted by an action on peripheral opioid receptors, but the specific mechanism of attenuation is unclear.     

Genetic differences in ethanol-induced conditioned taste aversion after ethanol preexposure

The present studies examined the development of ethanol-induced conditioned taste aversion in C57BL/6J (B6) and DBA/2J (D2) mice with a history of ethanol preexposure. In Experiment 1, adult male B6 and D2 mice received four preexposure injections of either saline or 4 g/kg ethanol over an 8-day period. After preezposure, all mice were given five conditioning trials consisting of 1-h access to 0.15% w/v saccharin solution followed immediately by ethanol injections (4 g/kg, IP) on all but the last trial. Drug-naive D2 mice showed greater reductions in saccharin intake. Ethanol preexposure reduced the development of ethanol-induced taste aversion in each strain. However, B6 mice showed little taste aversion overall, hindering the characterization of genetic differences in ethanol's preexposure effect. To address this problem, the parameters for taste conditioning were changed in Experiment 2 to more closely match degree of taste aversion in drug-naive mice across both strains. B6 and D2 mice received four preezposure injections of either saline, 2 g/kg ethanol, or 4 g/kg ethanol. Subsequently, mice received five conditioning trials consisting of 1-h access to 0.2 M NaCl flavor followed by 4 g/kg ethanol (B6 mice) or 2 g/kg ethanol (D2 mice) on trials 1–4. Ethanol-naive mice of each strain developed similar levels of conditioned taste aversion. Ethanol preexposure produced greater retardation of conditioned aversion in B6 mice than in D2 mice. These results demonstrate genetic differences in the ability of ethanol preezposure to reduce the development of ethanol-induced conditioned taste aversion.     

Effects of haloperidol or SCH-23390 on ethanol-induced conditioned taste aversion.

Dopaminergic systems are thought to play an important role in the motivational effects of ethanol. The present experiments examined the effects of haloperidol (a D2 antagonist) and SCH-23390 (a D1 antagonist) on the acquisition of ethanol-induced conditioned taste aversion. In four separate experiments, adult male Swiss-Webster mice were acclimated to a 2-h/day water restriction regimen. Subsequently they received four conditioning trials consisting of 1-h access to either 0.2 M NaCl (experiments 1-3) or 0.15 % w/v saccharin (experiment 4). After flavor access on trials 1-3, subjects received either haloperidol (0.1, 0.15, or 0.3 mg/kg), SCH-23390 (0.05 mg/kg), or saline followed 30 min later by 0, 2, or 4 g/kg ethanol. Ethanol-flavor pairings reduced subsequent flavor intakes, indicating the development of conditioned taste aversion. Neither haloperidol of SCH-23390 reduced flavor intakes in the absence of ethanol. However, both haloperidol and SCH-23390 reduced ethanol-conditioned aversion depending on ethanol dose and conditioned flavor. These results are consistent with the notion that dopaminergic processes are important for the development of ethanol-induced conditioned taste aversion, and the notion that dopaminergic receptor systems influence both positive and negative motivational effects of ethanol.     

Effect of perinatal dexamethasone treatment on conditioned taste aversion in rats.

Effect of perinatal dex Rats received a single subcutaneous injection of 1 mg/kg dexamethasone at the age of seven days. One hundred days after the treatment, conditioned taste aversion was determined in the adult animals. Perinatally applied dexamethasone did not affect water consumption but caused a significant attenuation of conditioned taste aversion. These findings may be explained by dexamethasone effects upon brain development which cause impairment of memory functions or, alternatively, decreased responsiveness to aversive stimuli.     

Role of conditioned taste aversion in the development of activity anorexia

Activity anorexia (AA) occurs when rats are restricted to one meal period (60-90 min) each day and have unlimited access to a running wheel the rest of the time. This AA procedure also contains the conditions necessary for conditioned taste aversion (CTA). The food eaten during the meal period is the conditioned stimulus paired with the unconditioned stimulus produced by wheel running. Thus, CTA to food may account in part for the decreased eating in AA. To test this possibility, male rats were subjected to the AA procedure. They had daily 90-min exposures to their familiar chow and spent the rest of the day in running wheels (experimental condition) or home cages (control condition). A second, concurrent experiment had the same procedure except that novel, rather than familiar, food was used. In both experiments, AA occurred; the rats allowed to wheel run ate less than those in the control condition. Several days after AA training, a two-food preference test assessed whether CTA occurred. Wheel running induced CTA when food was novel but not when it was familiar. Since AA is typically studied with procedures using familiar food, the present findings indicate that CTA plays little or no role in AA.     

Differences in ethanol-induced conditioned taste aversion in Sardinian alcohol-preferring and Sardinian alcohol-nonpreferring rats.

In the present study, we investigated whether aversion to the pharmacological effects of ethanol developed to a differential extent in selectively bred Sardinian alcohol-preferring (sP) and Sardinian alcohol-nonpreferring (sNP) rats, and whether this different response was consistent with their genetically determined differences in ethanol preference and consumption. To this purpose, a conditioned taste aversion paradigm was used. Male sP and sNP rats were exposed to five sessions in which a 20-min availability of a saccharin solution (1 g/l) was paired to the injection of ethanol (0, 0.5, or 1 g/kg, i.p.), delivered immediately after removal of the saccharin bottle (conditioning phase). Subsequently, the choice between saccharin solution and water was offered for 18 consecutive daily 20-min sessions (postconditioning phase). Ethanol at 1g/kg produced a marked aversion to saccharin in sNP rats: The reduction in saccharin intake was already evident on the second day of the conditioning phase and lasted for 15 days of the postconditioning phase. In contrast, this dose of ethanol elicited a modest, if any, conditioned taste aversion in sP rats, although blood ethanol levels were comparable to those assessed in sNP rats. These results indicate the existence of a differential degree of aversion to the postingestional effects of ethanol between sP and sNP rats, and support the suggestion that it may contribute, at least in part, to the opposite preference for and consumption of ethanol monitored in these rat lines.     

Testing taste sensitivity and aversion in very young children: development of a procedure

Taste perception in 45 3- to 6-year-old children was tested using procedures specifically designed for this age group. Detection thresholds for sucrose and urea were measured by a staircase method and aversion to urea was assessed hedonically, using drawings of facial expressions. All children understood the task and could perform the necessary actions. A subgroup of 20 children participated in a second measurement after a mean interval of 9.5 days: there was a satisfactory degree of stability between the sessions. However, a third measurement, on a subgroup of 13 children after a somewhat longer interval, showed a marked drop in the stability of the urea thresholds. This drop was thought to arise from a decrease in the children's motivation, leading to increased distractibility. Mean threshold estimates were 31 mmol/l for sucrose detection, 59 mmol/l for urea detection and 134 mmol/l for urea aversion, but some children were extremely sensitive to the taste of urea. The findings show that it is possible to study taste perception in very young children if their age is taken into consideration in developing the test procedure. Valid data can be obtained if the procedures are short, easy to understand and intrinsically motivating.     

Ethanol tolerance developed during intoxicated operant performance in rats prevents subsequent ethanol-induced conditioned taste aversion.

Four groups of Sprague-Dawley rats (n = 10 per group) were trained in a two-phase conditioning experiment. All rats were initially trained in an FR30 operant task (phase 1), and subsequently trained in a conditioned taste aversion (CTA) task. The groups of rats differed in their ETOH exposure. All rats received 2-week chronic exposure in phase 1. Two groups received chronic presession ETOH and, therefore, the opportunity for intoxicated practice; another group, yoked to this latter group, received postsession ETOH; the final group received presession saline injections. The presession ETOH groups were conditioned in the CTA task with either ETOH or saline; both increased their intakes of the conditioned tastant. The presession saline and the postsession ETOH groups received ETOH CTA; both developed a robust CTA. Thus, prior history of intoxicated practice under the operant task prevented the development of ETOH-induced CTA. We argue that ETOH exposure may be a necessary but not sufficient condition for tolerance to develop to the aversive attributes of ETOH.     

Ethanol-induced conditioned taste aversion in the rat: effects of 5,7-dihydroxytryptamine lesion of the dorsal raphe nucleus.

The effects of lesions of 5-hydroxytryptamine (5-HT) neurons in the dorsal raphe nucleus (DRN) on ethanol-induced conditioned taste aversion were studied in male Wistar rats. Biochemical analysis revealed that a serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), infused into the DRN produced selective depletion of serotonin (i.e., 5-HT) in the frontal cortex and striatum. Conditioned taste aversion to saccharin solution induced by 2 g/kg of ethanol was not affected by the lesion. In contrast, aversion conditioning produced by a lower dose of ethanol (1 g/kg) was slightly but significantly attenuated by the 5,7-DHT administration. Taken together with our previous observations, the results of the present study may indicate that central serotonergic projections do not have a primary role in the aversive effects of high doses of ethanol (>1 g/kg) in the rat. On the other hand, it seems that serotonergic neurons of the DRN may play some modulatory role in the formation of the aversive-stimulus properties of moderate doses of ethanol.     

Effects of chronic ethanol exposure on acetaldehyde and free radical production by astrocytes in culture.

In a previous study, the production of acetaldehyde and free radicals derived from ethanol was characterized in astrocytes in primary culture. In the present study, the effects of chronic exposure on the production of both compounds as well as on the main antioxidant system were compared with those of an acute exposure. This was done to better understand the different ways the brain reacts to these modes of exposure. Under these conditions, both a time-dependent increase in the accumulation of acetaldehyde and a decreased formation of the alpha-hydroxyethyl radical were shown. This was associated with increased activities of catalase, superoxide dismutase (SOD), and glutathione peroxidase (GPX) and with decreased glutathione (GSH) content. These effects, which counteract reactive oxygen species (ROS) formation by stimulating the main enzymes of the antioxidant system, were also associated with the reduced amount of radicals derived from ethanol. This could be a beneficial effect, but this was counter-balanced by the increased rate of acetaldehyde accumulation, whose high toxicity is well known. All these effects underline the crucial role played by catalase which, on one hand converts hydrogen peroxide to water and, on the other hand, ethanol to acetaldehyde.     

Summation of overshadowing and latent inhibition in rats' conditioned taste aversion: scapegoat technique works for familiar meals

In rats' taste aversion learning, presentation of another taste with a target taste alleviates aversion for the target taste (overshadowing), and exposure of a target taste prior to its conditioning alleviates aversion for that taste (latent inhibition). The present study demonstrated summation of these effects, resulting in the least aversion in the rats that had received both overshadowing and latent inhibition treatments. The finding that overshadowing and latent inhibition summate is contrary to the prediction by the comparator hypothesis that they counteract, as recently reported in conditioned suppression of licking in thirsty rats. The present result supports the employment of the so-called "scapegoat technique" in cancer patients receiving chemotherapy after taking familiar meals.     

Effects of calcium channel blockers on pentylenetetrazol drug discrimination in rats.

The effects of the dihydropyridine L-type calcium channel blockers nitrendipine and nimodipine on the pentylenetetrazol (PTZ) drug discrimination, an operant model of anxiety, were investigated. Male Long-Evans rats were trained to discriminate PTZ (16 mg/kg, i.p.) from saline. Both nitrendipine (5.0-25 mg/kg, i.p.) and nimodipine (5.0-25 mg/kg, i.p.) partially substituted for the PTZ discriminative stimulus. However, pretreatment with nitrendipine (25 mg/kg, i.p.) or nimodipine (25 mg/kg, i.p.) produced no change in the PTZ dose-effect function. Rats were given a nutritionally balanced liquid diet containing 6.5% ethanol for 10 days. Rats selected the PTZ drug lever during withdrawal. Subchronic coadministration of nitrendipine (1.25-5.0 mg/kg, i.p., b.i.d.) with ethanol failed to dose-dependently reduce PTZ-lever responding, but it did reverse withdrawal signs. Acute administration of nitrendipine (5, 10, and 20 mg/kg, i.p.) produced marked suppression of lever responding, but it failed to significantly reduce levels of PTZ-lever responding. Although calcium channel blockers reduce signs of ethanol withdrawal, they also markedly reduce rates of behavior and produce no clear effects on anxiety-like behaviors induced by ethanol withdrawal.     

Effects of acetaldehyde on c-fos mRNA induction in the paraventricular nucleus following ethanol administration

AIMS: The effect of acetaldehyde on c-fos mRNA expression in the paraventricular nucleus (PVN) of the rat was examined using in situ hybridization histochemistry. METHODS: Increases in acetaldehyde concentrations were induced using cyanamide (a potent inhibitor of aldehyde dehydrogenase), in the presence of two different doses of ethanol. Concentrations of blood ethanol and acetaldehyde were determined by head space gas chromatography. RESULTS: Neither cyanamide alone nor the low dose of ethanol (1 g/kg) alone increased c-fos expression in the PVN. However, the combination of cyanamide and low dose ethanol resulted in a significant and maximal increase in c-fos mRNA in the PVN. High dose ethanol (3 g/kg) resulted in a significant increase in c-fos mRNA. This stimulation also appeared maximal as there was no further increase in c-fos expression in the presence of cyanamide. CONCLUSIONS: These data suggest that acetaldehyde accumulation in blood has an important stimulatory effect on c-fos expression in the PVN at low ethanol concentrations. Furthermore, this stimulation of c-fos mRNA appears to be an either/or response: not activated in response to low dose ethanol, but maximally to high dose ethanol. These data also provide further evidence for a dissociation between the activation of c-fos and corticotrophin-releasing factor (CRF) mRNA in the PVN, as we have previously demonstrated that this dose of cyanamide alone is sufficient to evoke a sustained increase in plasma corticosterone and an increase in CRF mRNA.     

Effects of ethanol, acetaldehyde, and acetic acid on histamine secretion in guinea pig lung mast cells.

We studied the direct effects of ethanol and its metabolites on the guinea pig lung mast cell, and the alterations caused in the histamine release induced by different stimuli. Guinea pig lungs cells dispersed by collagenase were used throughout. High concentrations of ethanol (100 mg/ml), acetaldehyde (0.3-3 mg/ml) and acetic acid (3 mg/ml) induced histamine release that was not inhibited by sodium cyanide (0.3 mM). Lower concentration of ethanol (10 mg/ml) and acetic acid (0.3 mg/ml), but not acetaldehyde, inhibited the histamine release induced by antigen and ionophore A23187. The histamine release induced by phorbol 12-miristate 13-acetate (1 microM) was also inhibited by ethanol (10 mg/ml). Changes in the levels of calcium, glucose and phosphatidic acid did not influence the effect of ethanol. We conclude that high doses of ethanol, acetaldehyde, and acetic acid cause a cytotoxic histamine release by independent mechanisms. Low concentrations of acetic acid inhibit the histamine release by pH reduction. Ethanol acts by a generalized effect that is independent of calcium and glucose suggesting a nonspecific effect that, nevertheless, is not cytotoxic since it can be reversed by washing the cells.     

Failure of a schedule-induction procedure to increase ethanol intake in an established limited-access self-administration condition.

Determining mechanisms that can increase ethanol consumption during a single drinking bout is central to understanding alcohol abuse. When rodents are used as models to study excessive drinking, most often limited and transient increases in bout size are found with various manipulations. In a variety of studies, investigators have reported that schedule-induced drinking can result in excessive consumption of either water or alcohol (ethanol) during a single drinking period in food-restricted rats. The question examined in this experiment was, Could a schedule-induction paradigm increase bout size in nondeprived rats already self-administering ethanol? After the rats were trained to self-administer a 10% (volume/volume) ethanol solution in a fixed daily drinking session, non-response-contingent presentation of a 10% (weight/volume) sucrose solution, on a fixed-time, 120-s schedule, was used to determine whether additional ethanol consumption could be induced. This was followed by the use of a fixed-time, 300-s schedule and then, by using the fixed-time, 120-s schedule, with the presentation of a 2% (weight/volume) sucrose solution. None of these conditions induced an increase in ethanol self-administration. The results indicate that factors that control ethanol bout size in the nondeprived rat are such that the standard schedule-induction condition seems to be ineffective if an ethanol bout has occurred in the recent past.     

Classically conditioned ethanol stimulus control of a motor behavior

Rats with extensive unilateral 6-hydroxydopamine lesions of substantia nigra rotate (turn in circles) in response to administration of dopamine agonists. Here apomorphine administration, but not single or repeated administrations of ethanol, resulted in rotation in such lesioned animals. When apomorphine and ethanol were administered simultaneously to lesioned animals, rapid contralateral rotation resulted. After five of these conditioning trials in which ethanol and apomorphine were paired, ethanol alone elicited apomorphine-like rotation. Saline administration did not result in rotation in the conditioned animals, indicating that ethanol rather than the injection procedure exerted stimulus control over the behavior. Control animals which were treated five times with apomorphine and ethanol in an unpaired manner showed no conditioned rotation to ethanol.     

Effects of 5,7-dihydroxytryptamine lesion of the dorsal raphe nucleus on ethanol discrimination in the rat.

It has been shown that ethanol produces a complex interoceptive cue in rodents with distinct GABAergic, glutamatergic, and serotonergic (5-hydroxytryptamine, 5-HT) components. The present study aimed to examine the contribution of the 5-HT system originating in the dorsal raphe nucleus (DRN) to the discriminative stimulus effects of ethanol in male Wistar rats. Therefore, selective lesions of 5-HT neurons in the DRN were induced by microinfusions of 5,7-dihydroxytryptamine. The DRN- and sham-lesioned rats were trained to discriminate ethanol (1.0 g/kg) from saline in a standard two-lever drug discrimination procedure. Acquisition of ethanol discrimination and discrimination performance after consumption of lower doses of ethanol did not differ between the groups. In substitution tests, diazepam (0.5-2.5 mg/kg), a nonselective benzodiazepine receptor agonist, partially generalized from the ethanol cue in both groups. In contrast, m-chlorophenylpiperazine (0.1-0.9 mg/kg), a mixed 5-HT(1B/2C) receptor agonist, did not mimic the ethanol cue. The drug decreased response rates in both groups, but this effect was more evident in the sham-lesioned group. A 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propyloamino)-tetraline (0.05-0.4 mg/kg), did not produce significant increase in ethanol-appropriate responding in either group. These results may indicate that 5-HT neurons of the DRN are not critically involved in ethanol discrimination in the rat.