Anti-nociceptive effects of calcitonin gene-related peptide in nucleus raphe magnus of rats: an effect attenuated by naloxone

The present study investigated the role of calcitonin gene-related peptide (CGRP) on nociception in nucleus raphe magnus (NRM) and the interaction bet ween CGRP and opioid peptides in NRM of rats. CGRP-like immunoreactivity wa s found at a concentration of 6.0+/-0.17 pmol/g in NRM tissue of ten sample s of rats, suggesting that it may contribute to physiological responses orc hestrated by the NRM. The hindpaw withdrawal latency (HWL) to thermal and m echanical stimulation increased significantly after intra-NRM administratio n of 0.5 or 1 nmol of CGRP in rats, but not 0.25 nmol. The anti-nociceptive effect induced by CGRP was antagonized by following intra-NRM injection of 1 nmol of the CGRP receptor antagonist CGRP8-37. Furthermore, the CGRP-ind uced anti-nociceptive effect was attenuated by following intra-NRM administ ration of 6 nmol of naloxone. The results indicate that CGRP and its recept ors play an important role in anti-nociception, and there is a possible int eraction between CGRP and opioid peptides in NRM of rats. (C) 2000 Elsevier Science B.V. All rights reserved.