The calcitonin gene-related peptide antagonist CGRP8-37 increases the latency to withdrawal responses in rats

The present study explored the effects of Calcitonin gene-related peptide (CGRP) and its antagonist CGRP8-37 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 CGRP8-37, but not 1 nmol, induced a significant increase in hindpaw withdrawal latency. (3) Intrathecal administration of CGRP8-37 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 CGRP8-37 has a possible antinociceptive effect, and CGRP receptors in the spinal cord may be involved.