Enhancement of pavlovian conditioned suppression by mild ethanol intoxication

Effect of Alcohol and Tobacco Smoke on Long-Term Memory and Cell Proliferation in the Hippocampus of Rats

INTRODUCTION

Alcohol is frequently used in combination with tobacco and few studies explore interactions between these two drugs of abuse. Here, we evaluated the effect of chronic alcohol administration and concomitant exposure to tobacco smoke on long-term memory and on cell proliferation in the hippocampus of rats.

METHODS

Forty male Wistar rats were assigned to four groups and treated with alcohol (2g/kg by gavage) and/or exposed to tobacco smoke (from six cigarettes, by inhalation) twice a day (at 9:00 AM and 2:00 PM) for 30 days. Long-term memory was evaluated in the inhibitory avoidance test and hippocampal cell proliferation was analyzed for bromodeoxyuridine immunohistochemistry.

RESULTS

Our results showed that alcohol, tobacco smoke, or their combination improved the long-term memory evaluated by the memory index in rats. Moreover, alcohol and tobacco coadministration decreased bromodeoxyuridine-labeled cells by 60% when compared to the control group, while alcohol treatment decreased labeled cells by 40%. The tobacco group showed a nonsignificant 26% decrease in labeled cells compared to the control group.

CONCLUSIONS

Chronic alcohol and tobacco coadministration improves the long-term memory in rats in the inhibitory avoidance test. However, coadministration decreases the cell proliferation in the hippocampus of rats, suggesting a deleterious effect by the combined use of these drugs of abuse.

Immediate and delayed voluntary ethanol effects on motor performance, learning and inhibition in rats

The effects of prolonged voluntary ethanol consumption on psychomotor performance, operant conditioning and inhibition were examined in adult male Wistar rats. Animals were food deprived and alcohol or control solution was available 1 h/day during 15 days, with free water for the rest of the day. Then, rats were tested in a two-bottle paradigm (solution and water available) for 1 h/day during 19 days, and subjects were tested daily for psychomotor performance and operant conditioning immediately or 6 h after (delayed) the solution access. Psychomotor performance was tested in an 80 degrees -inclined screen. Successive conditioning phases were: free shaping (FS), continuous reinforcement (CRF), operant extinction (EXT), successive discrimination (DIS) and two-stimuli test (TST). Alcohol consumption deteriorated psychomotor performance and improved the animal's ability to learn simple associations between stimuli and responses (free shaping and extinction), in immediate and delayed groups. Finally, alcohol deteriorated behavioral inhibition (DIS and TST) tested immediately after drinking. Taken together, results suggest that prolonged voluntary ethanol intake could induce permanent psychomotor impairment and associative learning facilitation, and also an impairment of the inhibition related to the intoxication state.

EtOH self-administration on shuttle box avoidance learning and extinction in rats

The effects of ethanol on the acquisition and extinction of the two-way active avoidance response were examined in adult, male Wistar rats from two treatment groups, oral self-administration of alcohol solution (10% v/v ethanol and 3% w/v glucose in distilled water) and oral self-administration of control solution (3% w/v glucose in distilled water). Alcohol or control solutions were available 1 h per day during 15 days simultaneously with food, with free water for the rest of the day. Blood was drawn in the last day of this phase to evaluate blood ethanol levels (BEL). After this period, rats were tested in a two-bottle paradigm for 1 h per day and placed in a shuttle box immediately afterwards. This phase went lasted for 10 days. Subjects were trained to avoid an electric foot shock in the first 5 days (15 trials per day). Following this, half of the subjects were tested in an "easy extinction with punishment" (EEP) and the other half in a "difficult extinction with punishment" (DEP) of the avoidance response for the last 5 days. Alcohol accelerates the avoidance responding acquisition, and no significant effects of alcohol were seen in the extinction phase. Data are discussed in terms of the specificity of the effects of alcohol on learning.

Context and tone conditioning are selectively impaired by ethanol in the preweanling rat: effects of dose and time of administration

Depending on dose and task requirements, ethanol can have either a facilitative or an impairing influence on learning. Some explanations for this dichotomy have considered ethanol's suppression of behavioral variability and processing of incidental stimuli (e.g., context). The present study examined the effect of ethanol on context and conditioned stimulus (CS) learning in the preweanling rat. To assess state-dependent effects, a drug dissociation design was used. Learning to both context and CS were analyzed within each dose of ethanol (0, 1.2, 1.6, or 2.0 g/kg) and a trend analysis was conducted to determine dose-response relationships as a function of train-test state. The 1.2 g/kg dose of ethanol did not affect conditioning to either the context or the CS. A 1.6 g/kg dose tended to disrupt context, but not CS, conditioning. The influence of 2.0 g/kg ethanol depended on train-test conditions. Ethanol administration prior to training resulted in the stronger impairment of CS learning while context conditioning was most disrupted if ethanol was given only prior to testing. The results suggest that ethanol selectively attenuates processing of stimuli, possibly dependent on relative saliency at the time of testing.

Enhancement of sensory preconditioning by a moderate dose of ethanol in infant and juvenile rats

Little is known regarding the effects of acute ethanol on learning and memory among infant and juvenile rats. Two experiments were designed to evaluate the influence of various doses of ethanol administration on sensory preconditioning and primary conditioning in preweanling (16-day-old) and postweanling (28-day-old) rats. Moderate doses of ethanol facilitated conditioning at both ages. In the absence of ethanol, sensory preconditioning was not statistically significant among postweanlings in Experiment 1, although the phenomenon was clear and robust among preweanlings. Sensory preconditioning was facilitated by administration of doses of 0.8 and 1.2 g/kg ethanol in preweanlings and a dose of 1.6 g/kg ethanol in postweanlings, whereas sensory preconditioning was impaired in preweanlings by a high dose (2.4 g/kg) of ethanol. This reflected a shift to the right, between the preweaning and the postweaning periods, in the dose-response curve. It was determined in Experiment 2 that the effect of ethanol on sensory preconditioning could not be explained by stimulus generalization or an effect of ethanol on first-order conditioning, confirming the effect of ethanol on learning of the odor-odor association in the preexposure phase. The basis for a dose-dependent biphasic effect of ethanol on sensory preconditioning is discussed.