Naloxone blockade of apomorphine-induced stereotyped behavior: interaction of endogenous opiates with dopamine

The specific opiate antagonist, naloxone, inhibits the in vivo and in vitro activity of the endogenous opiate compounds which have heretofore been identified. In this study systemic naloxone administration successfully blocked the production of stereotyped behavior induced by the direct dopamine agonist apomorphine. This implies that the endogenous opiates contribute to the production of stereotyped behavior initiated by dopaminergic stimulation and that endogenous opiates may function as central neurotransmitters with dopaminergic activity.