The Opioid Peptides Enkephalin and β-Endorphin in Alcohol Dependence

BackgroundExperimental evidence indicates that the endogenous opioid system influences stress responses as well as reinforces effects of addictive drugs. Because stress is an important factor contributing to drug dependence and relapse, we have now studied ethanol preference in enkephalin– and β-endorphin–deficient mice under baseline conditions and after stress exposure.MethodsIn the present study we used a two-bottle choice paradigm to study ethanol consumption and stress-induced ethanol preference. To examine alcohol withdrawal symptoms the forced drinking procedure was employed. We performed an association analysis in two case-control samples of alcohol addicts to determine whether these opioid peptides also contribute to ethanol dependence in humans.ResultsEthanol consumption was significantly reduced in the absence of β-endorphins, particularly in female knockout animals. Stress exposure results in an increased ethanol consumption in wild-type mice but did not influence ethanol-drinking in β-endorphin knockouts. Enkephalin-deficient mice showed no difference from wild-type mice in baseline ethanol preference but also showed no stress-induced elevation of ethanol consumption. Interestingly, we found a two-marker haplotype in the POMC gene that was associated with alcohol dependence in females in both cohorts.ConclusionsTogether these results indicate a contribution of β-endorphin to ethanol consumption and dependence.