CHRONIC ETHANOL TREATMENT - EFFECTS ON THE ACTIVATION OF BRAIN BETA-ENDORPHIN SYSTEM BY NOVELTY

Chronic ethanol ingestion in rats abolishes novelty-induced antinociception, as measured by a tailflick method. This treatment also inhibited the posttraining facilitatory effect of naloxone and the posttraining amnesic effect of beta-endorphin in a step-down inhibitory avoidance task. Measurement of hypothalamic beta-endorphin-like immunoreactivity (beta-EPLIR) shows that there is a decrease in the levels of this peptide in chronic ethanol-treated rats. Exposure to a novel situation, which causes a decrease of beta-EPLIR in control (water-treated) rats, had no effect in ethanol-treated rats. Taken together, these results suggest that chronic ethanol treatment decreases hypothalamic beta-endorphin levels and makes this system unresponsive to novelty.