Oral Self-Administration Of EtOH In Transgenic Mice Lacking Beta-Endorphin

Abstract

EtOH modifies the production and/or release of endogenous opioid peptides, including -endorphin (Gianoulakis, 2004; Przewlocka et al., 1994; Schulz et al., 1980). Opioids subsequently influence the reinforcing properties of EtOH and the development of alcoholism (Terenius, 1996; Van Ree, 1996). In this study, beta-endorphin deficient mutant mice were used to examine the effects of a specific opioid peptide on EtOH consumption. Mice were obtained from The Jackson Laboratory, Bar Harbor, ME, USA. Male and female, adult naïve mice were single housed in Plexiglas cages with corn cob bedding and ad lib access to food (mouse chow) and water. A two-bottle free choice EtOH oral self-administration paradigm was administered to homozygous mutant mice (void of all beta-endorphin), heterozygous mice (50% beta-endorphin expression), and sibling wildtype mice (C57BL/6J). Subjects received increasing concentrations of EtOH (0%, 3%, 6%, 12%, and 15%) each given over an eight day span, and were evaluated for preference and consumption each day. Bottles were switched every other day to avoid the development of a side preference. Overall, females drank more than males. Homozygous mutant mice (KO) showed decreased preference for EtOH at all concentrations, and self-administered significantly less than heterozygous mice (HT) and wildtype mice (C57). The HTs had a tendency to drink the most followed by the C57s, and the KOs drank the least. These data support the hypothesis that beta-endorphin influences the reinforcing effects of EtOH.

Keywords

• Ethanol
• β-endorphin
• self-administration
• transgenic mice