Low doses of beta-endorphin increase social contacts of rats tested in dyadic encounters

Social isolation for 7 days increases the frequency of social interactions of rats, when they are tested with non-isolated partners in dyadic encounters. Subcutaneous administration of beta-endorphin enhances the social interactions of the isolated animals. Especially contact behavior, which includes crawl over, mounting and social grooming is stimulated by beta-endorphin, whereas social explorative behavior and approaching/following are less or not changed by peptide treatment. Already 10 ng/kg of the peptide increases the social interactions, especially social contacts of the rats. Treatment with naltrexone does not interfere with the social interactions of the isolated animals, but completely antagonizes the beta-endorphin-induced increase of social behavior, suggesting that this effect of beta-endorphin is mediated by opiate receptor systems. It is postulated that beta-endorphin modulates close and intimate social contacts probably by its reward-inducing properties.