Ethanol oral self-administration is increased in mutant mice with decreased beta-endorphin expression

The relationship between ethanol (EtOH) administration and the endogenous o pioid system has been studied for many years and a considerable body of evi dence supports the contention that EtOH modulates the production and/or rel ease of endogenous opioid peptides. However, substantially less is known ab out the converse influence: the effect that opioids have on EtOH sensitivit y. In this study, we used the beta-endorphin deficient mutant mouse Line C5 7BL/6-Pomc1(tm1Low) to investigate the possible role of a specific opioid p eptide on EtOH consumption. Homozygous knockout mice (entirely lacking beta -endorphin), heterozygous mice (50% beta-endorphin expression) and sibling wildtype mice from the same strain were evaluated in a two-bottle free choi ce paradigm for oral self-administration of EtOH. Across varying EtOH conce ntrations only the heterozygous mice were found to consistently drink more than wildtype mice. These data support the hypothesis that beta-endorphin m odulates the response to EtOH. (C) 1999 Elsevier Science B.V. All rights re served.