High-alcohol-drinking rats exhibit persistent freezing responses to discrete cues following Pavlovian fear conditioning

We previously reported that high-alcohol-drinking (HAD) rats exhibited selective deficits in active avoidance learning and that those deficits were partially reversed by moderate doses of ethanol under certain training conditions [Pharmacol. Biochem. Behav. 75 (2003) 89]. In that study, we hypothesized that HAD deficits resulted from exaggerated fear in the conditioning context and that the anxiolytic properties of ethanol, along with prior exposure to the conditioning apparatus, were responsible for the facilitated avoidance learning that was observed in HAD rats following moderate doses of ethanol. The current study was designed to test whether HAD rats exhibit behaviors consistent with increased fear in aversive learning contexts. We used a standard Pavlovian fear conditioning paradigm to assess behavioral freezing in HAD (HAD-1 and HAD-2) and low-alcohol-drinking (LAD; LAD-1 and LAD-2) rats. No significant differences were observed between HAD-1 and HAD-2 or between LAD-1 and LAD-2 rats, indicating that the replicate lines performed similarly in this study. Both HAD and LAD rats exhibited robust fear conditioning during training. Although no differences were observed between HAD and LAD rats during fear training, HAD rats failed to extinguish freezing behavior in response to the discrete tone conditional stimulus during subsequent fear retention tests. Thus, HAD rats demonstrated prolonged cue-elicited fear that was resistant to extinction.     

LAD rats learn a three-key drug discrimination more rapidly and achieve a higher level of performance than HAD rats.

High-alcohol drinking (HAD1) and low-alcohol drinking (LAD1) rats were trained to discriminate among 0.75 g/kg ethanol, 1.5 g/kg ethanol and saline under a fixed-ratio 10 schedule. LAD rats learned the discrimination more rapidly than HAD rats, and asymptotic performance by LAD rats was better than that of HAD rats. The 0.75 g/kg dose of ethanol failed to control the responding of HAD rats, both when baseline responding stabilized and during the determination of an ethanol dose-response curve. These differences between LAD and HAD rats in ethanol discrimination were not observed in previous experiments using a two-choice procedure. The three-choice procedure may be useful for establishing strain differences in ethanol discrimination. These and previous experiments with alcohol-preferring rats suggest that the learning of an ethanol discrimination may be dissociable from voluntary ethanol consumption in rat strains bred selectively to consume ethanol.     

Interactive effects of ethanol and nicotine on learning in C57BL/6J mice depend on both dose and duration of treatment

Objective and rationale Alcohol and nicotine are commonly co-abused; one possible explanation for co-abuse is that each drug ameliorates the aversive effects of the other. Both drugs have dose-dependent effects on learning and memory. Thus, this study examined the interactive effects of acute ethanol and acute, chronic, or withdrawal from chronic nicotine on fear conditioning in C57BL/6J mice. Materials and methods Conditioning consisted of auditory conditioned stimulus-foot-shock unconditioned stimulus pairings. For acute studies, saline or ethanol, then saline or nicotine was administered before training, and saline or nicotine was also administered before testing. For chronic and withdrawal studies, saline or nicotine was administered chronically, and ethanol or saline was administered before training. Results Acute nicotine (0.09 mg/kg) reversed ethanol-induced deficits (1.0 and 1.5 g/kg) in contextual and cued fear conditioning, whereas a low dose of ethanol (0.25 g/kg) reversed nicotine (6.3 mg kg⁻¹ day⁻¹) withdrawal-induced deficits in contextual conditioning. Tolerance developed for the effects of nicotine on ethanol-induced deficits in conditioning and cross-tolerance between chronic nicotine and acute ethanol was seen for the enhancing effects of ethanol on conditioning. Conclusions The complex and sometimes polar actions of ethanol and nicotine on behavior may contribute to co-abuse of these drugs. Specifically, smoking may initially reduce the aversive effects of ethanol, but tolerance develops for this effect. In addition, low doses of alcohol may lessen nicotine withdrawal symptoms.     

Lack of difference between HAD and LAD rats in the stimulus generalization of ethanol to nicotine

High alcohol drinking (HAD) and low alcohol drinking (LAD) rats were trained to discriminate 0.5 g/kg ethanol from saline. HAD and LAD rats learned the discrimination at the same rate and to the same level of asymptotic performance. In substitution tests, increasing doses of ethanol produced increased responding on the ethanol lever with dose-effect curves that were very similar in HAD and LAD rats. There was no generalization from ethanol to nicotine, or d-amphetamine, in either HAD or LAD rats. These data may be contrasted with data obtained with alcohol preferring rats (P rats) and alcohol non-preferring rats (NP rats), where the ethanol discrimination was learned more rapidly, asymptotic performance was better in P than in NP rats, and ethanol discriminative stimulus generalized to nicotine and partially to d-amphetamine in P, but not in NP rats. These data suggest that the differences in ethanol consumption reported previously by P and HAD rats relative to NP and LAD rats is not necessarily related to strain differences in ethanol discrimination as the differences in ethanol discrimination previously observed between P and NP rats do not occur in HAD and LAD rats.     

Ethanol disrupts fear conditioning in C57BL/6 mice

Ethanol has been demonstrated to disrupt numerous forms of learning. For example, ethanol disrupts fear conditioning in rats. Surprisingly, the opposite result was reported for mice. Because of the importance of mouse models in ethanol research and the predominance of transgenic mice generated on a C57BL/6 background, the present study examined the effects of acute ethanol administration on fear conditioning in C57BL/6 mice. Fear conditioning was chosen because of the apparent contradiction in results between mice and rats, because of its popularity in assessing forebrain-dependent learning and because the task examines two types of learning: (i) the hippocampus-dependent contextual learning and (ii) the hippocampus-independent conditioned stimulus-unconditioned stimulus learning. Dose-response curves were generated for ethanol (0.5, 1.0 and 1.5 g/kg) given on either training day, testing day, or both days. Ethanol, in a dose-dependent manner, disrupted fear conditioning when given on training day or given on both training and testing days. Ethanol given on testing day only did not disrupt fear conditioning. The present results demonstrate that ethanol disrupts fear conditioning in C57BL/6 mice.     

Variable interval schedules of timeout from avoidance: effects of ethanol, naltrexone, and CGS 8216

Four rats were trained on concurrent schedules of shock avoidance and timeout from avoidance, where responses on one lever postponed shock and responses on another lever occasionally (VI 45 sec schedule) produced a 2-min timeout during which the avoidance schedule was suspended. These procedures maintained stable rates of responding on both levers, providing a baseline for studying the effects of drugs on behavior under different types of aversive control (shock avoidance and timeout from avoidance). In the first experiment the effects of ethanol (0.5, 1.0, 1.5, and 2.0 g/kg) and an opiate antagonist, naltrexone (1 mg/kg) were assessed alone and in combination. Ethanol produced a dose-dependent decrease in avoidance characterized by increased shock rates and decreased response rates. At the same time, however, responding on the timeout lever generally increased relative to avoidance lever rates. All of these effects were largely confined to the early parts of the 2-hr session, when blood-ethanol levels were relatively high. Naltrexone had no effect on performances and did not interact with ethanol. In a second experiment, the effects of the benzodiazepine antagonist CGS 8216 were studied alone, and in combination with ethanol. CGS 8216 (5 mg/kg) generally disrupted both avoidance and timeout responding but did not reverse ethanol actions.     

Early maternal separation affects ethanol-induced conditioning in a nor-BNI insensitive manner, but does not alter ethanol-induced locomotor activity

Early environmental stress significantly affects the development of offspring. This stress has been modeled in rats through the maternal separation (MS) paradigm, which alters the functioning of the HPA axis and can enhance ethanol intake at adulthood. Infant rats are sensitive to ethanol's reinforcing effects, which modulate ethanol seeking and intake. Little is known about the impact of MS on sensitivity to ethanol's appetitive and aversive effects during infancy. The present study assessed ethanol-induced conditioned place preference established through second-order conditioning (SOC), spontaneous or ethanol-induced locomotor activity and ethanol intake in preweanling rats that experienced normal animal facility rearing (AFR) or daily episodes of maternal separation (MS) during postnatal days 1-13 (PDs 1-13). Low-ethanol dose (0.5 g/kg) induced appetitive conditioned place preference (via SOC) in control rats given conventional rearing but not in rats given maternal separation in early infancy, whereas 2.0 g/kg ethanol induced aversive conditioned place preference in the former but not the latter. The administration of a kappa antagonist at PD 1 or immediately before testing did not alter ethanol-induced reinforcement. High (i.e., 2.5 and 2.0 g/kg) but not low (i.e., 0.5 g/kg) ethanol dose induced reliable motor stimulation, which was independent of early maternal separation. Ethanol intake and blood alcohol levels during conditioning were unaffected by rearing conditions. Pups given early maternal separation had lower body weights than controls and showed an altered pattern of exploration when placed in an open field. These results indicate that, when assessed in infant rats, earlier maternal separation alters the balance between the appetitive and aversive motivational effects of ethanol but has no effect on the motor activating effects of the drug.     

The psychopharmacology of impulsive behaviour in rats VIII: effects of amphetamine,methylphenidate, and other drugs on responding maintained by a fixed consecutive number avoidance schedule

Rationale Impulsive behaviour is a component of psychiatric disorders such as bipolar disorder, attention deficit hyperactivity disorder (ADHD), or personality disorders. Most experimental studies on impulsive behaviour punish impulsive choices by loss or delay of reward. In the present study, impulsive behaviour was punished by an explicitly aversive stimulus, using a novel fixed consecutive number (FCN) schedule of electric shock avoidance.Objectives This study was conducted to demonstrate stable performance using the FCN avoidance procedure, and examine the effects of drugs previously shown to affect impulsive behaviour using a conventional FCN schedule.Methods First, rats were trained in the appetitive FCN procedure. Pressing the right lever in an operant conditioning chamber after having pressed the left lever at least six times delivered a food pellet (FCN6). Responses on the right lever before completing this ratio resulted in a time out and restarted the ratio. The rats were then switched to FCN avoidance. Responses on the right lever made before completion of the ratio also resulted in food delivery, but were accompanied by an electric shock.Results Chlordiazepoxide (10.0 mg/kg), ethanol (1.0 g/kg), and haloperidol (0.1 mg/kg) increased impulsive behaviour by reducing the number of left lever responses made before the right lever was pressed. Imipramine (1.0–10.0 mg/kg) and desipramine (1.0–10.0 mg/kg) had no effect on impulsive choice. Amphetamine (0.4 and 0.8 mg/kg) and methylphenidate (6.0 mg/kg) significantly increased the mean chain length, and the proportion of very long chains, indicative of reduced impulsivity, although this did not improve efficiency.Conclusions The increases in impulsivity produced by chlordiazepoxide, ethanol, and haloperidol were similar to those under appetitive FCN schedules. In contrast, amphetamine and methylphenidate, by reducing impulsivity in the FCN avoidance, induced effects opposite to those observed in an appetitive FCN procedure. These results suggest that the therapeutic actions of stimulants, to reduce impulsive behaviour in ADHD, may arise in part by increasing the control of behaviour by aversive stimuli.     

Role of dopamine D3 receptors in the expression of conditioned fear in rats

There has been considerable interest in the role of dopamine D(3) receptors in appetitive conditioning but few studies have examined their role in aversive conditioning. The present study examined the effect of the dopamine D(3) receptor-preferring partial agonist BP 897 (1-(4-(2-naphthoyl-amino)butyl)-4-(2-methoxyhenyl)-1A-piperazine hydrochloride) and the selective dopamine D(3) receptor antagonist SB-277011A (trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]syclohexyl]4-quinolininecarboxamide]) on the expression and acquisition of fear conditioning. Rats (N=143) received 3 conditioned stimulus-shock pairings and then received 15 conditioned stimulus-alone presentations (3 per day) while lever pressing for food. Response suppression was taken as the behavioral measure of fear. Rats showed strong suppression to the conditioned stimulus after it had been paired with shock and suppression progressively weakened over conditioned stimulus-alone presentations. In experiment 1, rats that received BP 897 (1.0, 2.0 mg/kg i.p.) or SB-277011A (10.0 mg/kg i.p.) prior to conditioned stimulus-alone presentation sessions showed reduced suppression to the conditioned stimulus as compared to rats that received vehicle or lower doses of drug (0, 0.1 mg/kg BP 897; 0, 0.5, 5.0 mg/kg SB-277011A). Injections of BP 897 (1.0, 2.0 mg/kg) or SB-277011A (10.0 mg/kg) prior to conditioned stimulus-shock pairings did not significantly affect subsequent response suppression. Thus, BP 897 and SB-277011A dose-dependently attenuated the expression but not the acquisition of conditioned fear. These findings suggest that BP 897 and SB-277011A reduce the control of responding by aversively conditioned stimuli.     

Chronic alcohol consumption in alcohol-preferring P rats attenuates subsequent conditioned taste aversion produced by ethanol injections

Rats of the P line were tested for the development of tolerance to the aversive effects of ethanol during 33 days of continuous availability of food, water and a 10% (v/v) ethanol solution. Beginning on the day following the removal of ethanol, five daily conditioned taste aversion (CTA) trials were administered to the ethanol-drinking P rats and an ethanol-naive control group. The CTA trials consisted of a 20-min access to a Polycose solution, followed by IP injection of saline, 0.5, 1.0, or 1.5 g ethanol/kg. The ethanol-drinking rats developed a preference for the Polycose solution when it was paired with 0.5 g ethanol injections, but the control rats did not. Both control and ethanol groups had similar CTAs at the 1.5 g dose. However, at the 1.0 g dose, the ethanol group had an attenuated CTA compared with the water control group. The results suggest that P rats develop tolerance to aversive effects of ethanol during chronic drinking. This tolerance could contribute to the high ethanol intake in these selectively-bred rats.     

Conditioned stimulus preference after acetaldehyde but not ethanol injections

Acetaldehyde, the first ethanol metabolite, has been suggested to mediate some of the behavioral effects of ethanol and particularly its reinforcing properties, although this later hypothesis remains extremely controversial. While several studies demonstrated the reinforcing effects of brain acetaldehyde, blood acetaldehyde accumulation is believed to be primarily aversive. In the present study, a conditioned reinforcement procedure has been used to investigate the reinforcing and/or aversive effects of intraperitoneal injections of both acetaldehyde and ethanol in Wistar rats. An olfactory stimulus was paired with daily injections of either ethanol (0, 0.25, 0.5, 1 and 2 g/kg) or acetaldehyde (0, 10, 20, 100 and 150 mg/kg). After eight conditioning sessions, all rats were tested for their stimulus preference or aversion. The results show that conditioning with small, 0.25 and 0.5 g/kg, ethanol doses induced neither preference nor aversion for the olfactory cue. In contrast, higher ethanol doses (1.0 and 2.0 g/kg) resulted in significant stimulus aversions. Acetaldehyde conditioning led to a biphasic stimulus preference, with a maximal preference around 20 mg/kg acetaldehyde. No evidence of aversive effects was found with increasing doses of acetaldehyde, even with concentrations close to the lethal limit. The present study clearly shows that systemic acetaldehyde injections induced significant stimulus preferences. This suggests that acetaldehyde may be, at least in part, responsible for the reinforcing effects of alcohol intake.     

Brief exposure to a mild stressor enhances morphine-conditioned place preference in male rats

Rationale Exposure to moderate tail shock [3, 0.75 s, 1 mA, 20 s interstimulus interval (ISI)] can enhance pain reactivity (hyperalgesia) in rats. This hyperalgesia reflects an unconditioned response that transfers across contexts and is associated with enhanced Pavlovian fear conditioning to aversive unconditioned stimuli (US). It is possible that moderate shock also enhances learning about appetitive stimuli such as a reinforcing drug.Objectives The present study examined the effect of moderate shock exposure on unconditioned psychomotor activation and appetitive conditioning using a morphine place-preference task.Methods During training, rats were given moderate shock or restraint and then received subcutaneous morphine at one of four doses (0.0, 0.2, 1.0, or 5.0 mg/kg) and were transferred to a conditioning apparatus. Five hours later, animals were given discrimination training in a different context. Animals received 2 days of training, each separated by a day of testing for preference. To test the impact of shock on psychomotor activation, subjects were given shock or restraint and one of two doses of morphine (0.0 mg/kg or 5.0 mg/kg) and placed in a box to monitor activity.Results Vehicle-treated shocked rats showed a conditioned place aversion. Subjects that received morphine showed a dose-dependent place preference that was facilitated by moderate shock exposure. Shock also enhanced the motor activation produced by morphine.Conclusions These results indicate that the affective state produced by moderate shock has a negative valence that is sufficient to support a conditioned place aversion. This state is associated with a general sensitization that enhances processing of appetitive US.     

Effect of diazepam on successive negative contrast in one-way avoidance learning.

The effect of administration of diazepam on successive negative contrast in one-way avoidance learning was examined in rats. Contrast was induced by shifting rats from a large reward, 30 s spent in the safe compartment, to a small reward, 1 s spent in the safe compartment. IP administration of 2 mg/kg diazepam eliminated this negative contrast. Moreover, this effect is dose dependent, with doses of 2 and 2.5 mg/kg, but not 0.5 mg/kg, effective in reliably reducing contrast. These results suggest the existence of similar or common underlying mechanisms in both aversive and appetitive contrast effects; they are discussed in light of the current theories of frustrative nonreward and as a mean of studying the behavioral and biological mechanisms of anxiety.     

The maternal separation paradigm and adult emotionality and cognition in male and female Wistar rats

A single 24-h maternal separation (MS) in the rat during the stress hyporesponsive period alters adult behavior and neuroendocrine stress response. The age of the animal at MS might be a crucial factor for effects in adulthood. We report here on adult behavioral effects of MS performed on postnatal day 4 (MS4), 9 (MS9), or 18 (MS18) in male and female Wistar rats. Unrelated subjects were used to avoid confounding litter effects. Subjects were tested on paradigms of unconditioned fear/anxiety, i.e., open field and elevated plus-maze, and on paradigms involving learning in an aversive situation, i.e., conditioned freezing, active avoidance, and water maze. In line with our predictions we obtained (a) sex differences that were consistent with enhanced fear/anxiety in males relative to females, (b) evidence that MS4 yielded deficits in active avoidance learning and conditioned freezing (trend level), whereas MS9 yielded enhanced active avoidance and water maze learning, (c) evidence (at trend level) that these effects of MS are greater in males than in females. There was no evidence for an effect of MS on paradigms of unconditioned fear/anxiety. We conclude that MS, irrespective of the age at separation, does not provide a robust environmental model of modified behavior in aversive situations.     

Low dose quetiapine reverses deficits in contextual and cued fear conditioning in rats with excitotoxin-induced hippocampal neuropathy

Previous studies have demonstrated that adult rats with excitotoxic lesions of the hippocampus display deficits in memory-related behaviors similar to the memory deficits associated with schizophrenia. In this study, we assessed the sub-chronic effects of quetiapine, risperidone and haloperidol on performance deficits after intracerebroventricular administration of the excitotoxin, kainic acid, using paradigms for contextual and cued fear conditioning and spatial reversal learning in rats. The effects of three doses of quetiapine (5, 10 and 20 mg/kg) and single doses of risperidone (0.5 mg/kg) and haloperidol (0.15 mg/kg) were compared. Quetiapine administration at the lowest dose (5 mg/kg) reversed deficits in contextual and cued fear conditioning, but not deficits in spatial reversal learning, in kainic acid-treated animals. However, the two higher doses of quetiapine, and the single doses of risperidone and haloperidol, did not reverse any of the kainic acid-induced behavioral deficits. These results may be relevant to the effects of quetiapine and other antipsychotic drugs on memory deficits in patients with schizophrenia.     

Scopolamine and Pavlovian fear conditioning in rats: dose-effect analysis.

Muscarinic-cholinergic antagonism produces learning and memory deficits in a wide variety of hippocampal-dependent tasks. Hippocampal lesions produce both acquisition deficits and retrograde amnesia of contextual fear (fear of the place of conditioning), but do not impact fear conditioning to discrete cues (such as a tone). In order to examine the effects of muscarinic antagonism in this paradigm, rats were given 0.01 to 100 mg/kg of scopolamine (or methylscopolamine) either before or after a fear conditioning session in which tones were paired with aversive footshocks. Fear to the context and the tone were assessed by measuring freezing in separate tests. It was found that pretraining, but not post-training, scopolamine severely impaired fear conditioning; methylscopolamine was ineffective in disrupting conditioning. Although contextual fear conditioning was more sensitive to cholinergic disruption, high doses of scopolamine also disrupted tone conditioning. Scopolamine did not affect footshock reactivity, but did produce high levels of activity. However, hyperactivity was not directly responsible for deficits in conditioning. It was concluded that scopolamine disrupts CS-US association formation or CS processing, perhaps through an attenuation of hippocampal theta rhythm.     

Neural mechanisms of extinction learning and retrieval.

Emotional learning is necessary for individuals to survive and prosper. Once acquired, however, emotional associations are not always expressed. Indeed, the regulation of emotional expression under varying environmental conditions is essential for mental health. The simplest form of emotional regulation is extinction, in which conditioned responding to a stimulus decreases when the reinforcer is omitted. Two decades of research on the neural mechanisms of fear conditioning have laid the groundwork for understanding extinction. In this review, we summarize recent work on the neural mechanisms of extinction learning. Like other forms of learning, extinction occurs in three phases: acquisition, consolidation, and retrieval, each of which depends on specific structures (amygdala, prefrontal cortex, hippocampus) and molecular mechanisms (receptors and signaling pathways). Pharmacological methods to facilitate consolidation and retrieval of extinction, for both aversive and appetitive conditioning, are setting the stage for novel treatments for anxiety disorders and addictions.     

A neurotensin agonist and antagonist decrease and increase activity, respectively, but do not preclude discrete cue conditioning

There is evidence to suggest that neurotensin (NT) may enhance cognitive function. For example, in aversive trace conditioning, the NT agonist PD149163 selectively increased trace conditioning (Grimond-Billa, et al., 2008). The present study, therefore, examined the role of NT in associative learning, tested using an appetitive trace conditioning procedure (0-s or 10-s inter-stimulus-interval [ISI]) with a mixed frequency noise as a conditioned stimulus (CS) and food delivery as the unconditioned stimulus (UCS). The effects of an NT agonist (PD149163, 0.125 and 0.25 mg/kg, Experiment 1) and an NT antagonist (SR142948A, 0.01 and 0.1 mg/kg, Experiment 2) were compared. To take nonspecific effects of these compounds into account, conditioning to the CS was measured as a percentage of total responding, during UCS deliveries and in the inter-trial-interval (ITI). In both experiments, associative learning to the contiguously (0-s) presented CS was demonstrated, although there was a relative reduction in this learning under 0.125 mg/kg PD149163. Counter to prediction, the only effect on trace conditioning was some overall reduction in responding to the CS in the 10-s group conditioned under 0.25 mg/kg PD149163. The NT antagonist was without any effect on appetitive conditioning. However, these NT compounds were not ineffective: decreases and increases in responding in the ITI, ISI and during UCS deliveries seen under PD149163 and SR142948A were dissociable from effects on discrete cue conditioning.     

Parameters of low-dose ethanol intravenous self-administration in the rat

Male Wistar rats were able to press on an operant lever 24 hr/day for intravenous infusions of saline or ethanol at doses of 0.5, 1.0 or 5.0 mg/kg/infusion. Only the 1.0 mg/kg/infusion group showed a significant increase in responding on the lever as a function of days, whereas the 5.0 mg/kg/infusion group showed a significant decrease in responding as a function of days. The results suggest that the reinforcing value of intravenous ethanol changes from rewarding to neutral or aversive in valence at a dose-level below that expected to produce signs of intoxication.     

Dissociation of the effects of ethanol on memory, anxiety, and motor behavior in mice tested in the plus-maze discriminative avoidance task

Rationale Several studies have shown the amnestic effects of ethanol (ETOH). However, while memory tasks in rodents can be markedly influenced by anxiety-like behavior and motor function, ETOH induces anxiolysis and different effects on locomotion, depending on the dose. Objective Verify the effects of ETOH in mice tested in the plus-maze discriminative avoidance task (PMDAT) concomitantly evaluating memory, anxiety-like behavior, and motor behavior. Methods ETOH acutely or repeatedly treated mice were submitted to the training session in a modified elevated plus-maze with two open and two enclosed arms, aversive stimuli in one of the enclosed arms, and tested 24 h later without aversive stimuli. Learning/memory, locomotion, and anxiety-related behavior were evaluated by aversive arm exploration, number of entries in all the arms and open arms exploration, respectively. Results Acute ETOH: (1) either increased (1.2–1.8 g/kg) or decreased (3.0 g/kg) locomotion; (2) decreased anxiety levels (1.2–3.0 g/kg); and (3) induced learning deficits (1.2–3.0 g/kg) and memory deficits (0.3–3.0 g/kg). After repeated treatment, sensitization and tolerance to hyperlocomotion and anxiolysis induced by 1.8 g/kg ETOH were observed, respectively, and tolerance to the amnestic effect of 0.6 (but not 1.8) g/kg ETOH occurred. Conclusion Neither the anxiolytic nor the locomotor effects of ETOH seem to be related to its amnestic effect in the PMDAT. Additionally, data give support to the effectiveness of the PMDAT in simultaneously evaluating learning, memory, anxiety-like behavior, and motor activity by different parameters. Possible relationships between the behavioral alterations found are discussed.