NOCICEPTIVE STIMULUS INDUCES RELEASE OF ENDOGENOUS BETA-ENDORPHIN IN THE RAT-BRAIN

The hypothesis that the naturally occurring analgesic peptide, beta-en dorphin, is released in the brain in response to pain had never been d irectly validated. In this study, we applied a brain microdialysis met hod for monitoring beta-endorphin release in vivo, to test this hypoth esis in the brains of conscious, freely moving rats. Herein we first s how that endogenous beta-endorphin can be measured in vivo in the brai n under physiological conditions. Upon induction of a nociceptive stim ulus by injection of formalin into the hind-paws of rats, the extracel lular levels of beta-endorphin in their arcuate nucleus increased by 8 8%, corresponding to their nociceptive response, This direct evidence for the release of endogenous beta-endorphin in the brain in response to nociceptive stimulus indicates a possible mechanism for organisms t o cope with pain. (C) 1998 IBRO. Published by Elsevier Science Ltd.