Non-opiate [beta]-endorphin fragments and dopamine--III [gamma]-type endorphins and various neuroleptics counteract the hypoactivity elicited by injection of apomorphine into the nucleus accumbens

Abstract

The hypoactivity in rats induced by small doses of apomorphine, injected bilaterally into the nucleus accumbens area of the brain, could be antagonized by pretreatment with the neuroleptic-like neuropeptide des-enkephalin-γ-endorphin (DEγE, β-endorphin 6–17) as well as with the neuroleptic drugs haloperidol, sulpiride and clozapine injected into the accumbens. Dose-response studies revealed that a dose of 100 pg DEγE completely inhibited the apomorphine-induced hypomotility. p ]The influence of DEγE appeared to be specific for γ-type endorphins, since α-type endorphins were inactive in this respect. Treatment with DEγE injected into the accumbens for 4 days resulted in an enhancement of apomorphine-induced hypoactivity. It is concluded that γ-type endorphins may control the activity of dopaminergic transmission in the nucleus accumbens, a suggestion which may be of significance for the purported neuroleptic-like and antipsychotic action of γ-type endorphins.