Stress prevents the chronic ethanol-induced delta opiod receptor supersensitivity in the rat brain.

The effects of ethanol administration on binding characteristics of the highly selective mu and delta opioid receptor agonists 8H-[D-Ala2-MePhe4-Gly5-ol]enkephalin (3H-DAGO) and 3H-[D-Pen2, D-Pen5] enkephalin (3H-DPDPE), respectively, were investigated in the rat brain. Chronic but not acute ethanol administration profoundly increased affinity of 3H-DPDPE without changing the number of delta receptors. Stress, applied before each ethanol administration, prevents the above changes. On the other hand, chronic treatment with ethanol did not affect the binding characteristics of 3H-DAGO. These results suggest particular sensitivity of the delta opioid receptor to chronic ethanol administration. Furthermore, a possible involvement of endogenous opioid peptide systems in the enhancement of delta opioid receptor sensitivity is postulated.