EFFECTS OF CALCITONIN-GENE-RELATED PEPTIDE ON ACUTE AND CHRONIC EFFECTS OF MORPHINE

Calcitonin gene-related peptide (CGRP), which has been observed in dif ferent parts of the nervous system, is known to modify pain sensitivit y to different stimuli in rats and mice. The aim of this study was to investigate the possible interaction of CGRP with morphine on nocicept ion in adult male NMRI mice after central administration of the peptid e. CGRP (20 or 200 ng) did not itself modify pain sensitivity in the t ail-flick test and did not affect the acute antinociceptive action of a single dose of morphine in the same test. However, CGRP suppressed t he development of rapid tolerance to morphine in a dose-dependent mann er, but had no action on the development of chronic tolerance to morph ine and on manifestations of naloxone-precipitated withdrawal syndrome .