Narcotic antagonist potentiation of apomorphine drug effect: a stereospecific, centrally mediated drug action.

Systemic pretreatment with naloxone but not its (+)-enantiomer significantly potentiated apomorphine-induced stereotypic climbing activity in mice. Systemic or central pretreatment with naltrexone also significantly potentiated the apomorphine drug effect. The N-methyl derivative of naltrexone had no influence when administered systemically but significantly potentiated the apomorphine drug effect when administered centrally. These findings suggest that narcotic antagonist potentiation of apomorphine-induced stereotypic climbing in mice is a stereospecific phenomenon that originates in the central nervous system.