INVOLVEMENT OF MU-OPIOID AND DELTA-OPIOID RECEPTORS IN THE ETHANOL-ASSOCIATED PLACE PREFERENCE IN RATS EXPOSED TO FOOT SHOCK STRESS

The purpose of this study was to establish the ethanol-induced place p reference in rats exposed to foot shock stress using the conditioned p lace preference paradigm. We also investigated the role of the endogen ous opioid system in the development of the ethanol-induced place pref erence. The administration of ethanol (300 mg/kg, i.p.) with foot shoc k stress, but not without such stress, induced a marked and significan t place preference. Naloxone (1 and 3 mg/kg, s.c.), a non-selective op ioid receptor antagonist, significantly attenuated the ethanol-induced place preference. Moreover, the selective mu-opioid receptor antagoni st beta-funaltrexamine (3 and 10 mg/kg, i.p.) and selective delta-opio id receptor antagonist naltrindole (1 and 3 mg/kg, s.c.), but not the selective K-opioid receptor antagonist nor-binaltorphimine (1 and 3 mg /kg, i.p.), significantly attenuated the ethanol-induced place prefere nce. Furthermore, 150 mg/kg ethanol (which tended to produce a place p reference, although not significantly) combined with each dose (that d id not produce a place preference) of the mu-opioid receptor agonist m orphine (0.1 mg/kg, s.c.) or selective delta-opioid receptor agonist 2 -methyl-4a alpha-(3-hydroxyphenyl)-1,2,3,4,4 a,5,12,12 a alpha-octahyd roquinolino [2,3,3-g] isoquinoline (TAN-67; 20 mg/kg, s.c.), but not t he selective kappa-opioid receptor agonist ro-N-(2-(1-pyrrolidinyl)cyc lohexyl)benzenacetamide methanesulfonate (U50,488H; 1 mg/kg, s.c.), pr oduced a significant place preference. These data indicate that stress may be important for development of the rewarding effect of ethanol, and that mu- and delta-opioid receptors may be involved in the rewardi ng mechanism of ethanol under stressful conditions. (C) 1998 Published by Elsevier Science B.V. All rights reserved.