Behavioral effects of the beta-endorphin fragment 2-9.

The non-opiate beta-endorphin (beta E) fragment des-Tyr-alpha-endorphin (beta E 2-16) delays extinction of pole jumping avoidance behavior and potentiates apomorphine-induced stereotyped sniffing. Structure-activity relationship studies revealed that the active moiety mediating these psychostimulant effects resides in the sequence beta E 2-9. The interaction between beta E 2-9 and apomorphine was also present following intrastriatal injection of both substances. These data provide evidence for a selective interference of the fragment beta E 2-9 with brain mechanisms, which can be distinguished from the opiate- and neuroleptic-like activity of beta-endorphin fragments. This further demonstrates the importance of beta-endorphin and its fragments for modulation of behavioral processes.