Effect of des-Tyr1-[gamma]-endorphin and des-enkephalin-[gamma]-endorphin on active and passive avoidance behavior of rats; A dose-response relationship study

Abstract

The potency of two β-endorphin fragments, des-Tyr1-γ-endorphin (DTγE, βE-(2–17)) and des-enkephalin-γ-endorphin (DEγE, βE-(6–17)) was compared on extinction of pole-jumping avoidance behavior and on retention of a one-trial step-through passive avoidance procedure. Both peptides facilitated the extinction of pole-jumping avoidance behavior and attenuated passive avoidance behavior. The γ-type endorphins exhibited an inverted U-shaped dose-response curve on passive avoidance behavior but not on extinction of pole-jumping avoidance behavior. DEγE appeared to be approximately three times more potent than DTγE on extinction of pole-jumping avoidance behavior but one hundred times more potent on passive avoidance behavior. It is suggested that DEγE rather than DTγE represents the endogenous neurolepticlike neuropeptide derived from β-endorphin.