THE CALCITONIN-GENE-RELATED PEPTIDE ANTAGONIST CGRP(8-37) INCREASES THE LATENCY TO WITHDRAWAL RESPONSES IN RATS

The present study explored the effects of calcitonin gene-related peptide (CGRP) and its antagonist CGRP(8-37) on the latency to hindpaw withdrawal responses induced by both thermal and mechanical stimulation in rats. (1) Intrathecal injection of 10 nmol of CGRP had no effects on the latency to hindpaw withdrawal; intrathecal injection of 5 nmol of substance P (SP) decreased the latency to both withdrawal responses. (2) Intrathecal administration of 5 nmol or 10 nmol of CGRP(8-37), but not 1 nmol, induced a significant increase in hindpaw withdrawal latency. (3) Intrathecal administration of CGRP(8-37) not only reversed the SP-induced decrease in latency to both withdrawal responses but also mediated a significant increase in response latency compared to basal levels. The demonstrated results suggest that intrathecal administration of CGRP(8-37) has a possible antinociceptive effect, and CGRP receptors in the spinal cord may be involved.