Non-opiate [beta]-endorphin fragments and dopamine--II [beta]-endorphin 2-9 enhances apomorphine-induced stereotypy following subcutaneous and intra-striatal injection

Abstract

The non-opiate β-endorphin (βE) fragment 2–16 (des Tyr1-α-endorphin) enhanced apomorphine-induced stereotyped sniffing in rats, but did not interfere with the hypoactivity elicited by small doses of apomorphine. Structure-activity relationship studies revealed that the active moiety of α-endorphin fragments with respect to their potentiating effects on apomorphine-induced stereotyped sniffing resides in the βE fragment 2–9. Subsequent studies showed that the potentiating influence of βE 2–9 was dependent on the dose of the peptide and that the interaction between this peptide and apomorphine may be non-competitive in nature. The stereotyped sniffing elicited by apomorphine, injected bilaterally into the striatal area of the brain, was dose-dependently enhanced by intra-striatal pretreatment with βE 2–9. It is concluded that the influence of α-type endorphins and βE 2–9 on apomorphine-induced behavioural changes, is in some aspects opposite to that of γ-type endorphins, but may be mediated by quite different mechanisms.