CHRONIC ADMINISTRATION OF ORG2766 AND MORPHINE COUNTERACTS ISOLATION-INDUCED INCREASE IN SOCIAL INTEREST - IMPLICATION OF ENDOGENOUS OPIOIDSYSTEMS

In complex behaviors, like social behavior, the MSH/ACTH (4-9) analog Org2766 is found to counteract changes in social interest caused by pr eceding housing or test conditions. Previous studies have indicated an involvement of endogenous opioid systems in these outcomes. In the pr esent study we have counteracted isolation-induced enhanced social int erest by chronic treatment (7 x every 48 h) with Org2766 or with the o piate morphine. These effects were blocked by previous administration of naloxone. However, in group-housed animals, both Org2766 and morphi ne treatment did not result in changes in social activity as compared to saline-treated group-housed controls. Chronic administration of nal oxone in group-housed rats resulted in an increase in social interest. These results are discussed in relation to possible function of Org27 66 and morphine as a substitute for the release of endogenous opioids caused by social contact.