Dissociation of antinociceptive and motor effects of supraspinal opioid agonists in the rat

This study compared the antinociceptive and motor effects produced by intracerebroventricular administration of selective mu- (DAMGO) and delta- (DPDPE) opioid receptor agonists in the rat. Changes in nociceptive thresholds were measured using the Randall-Selitto paw-withdrawal test and changes in motor coordination were evaluated using the rotarod treadmill test. Both DAMGO and DPDPE produced statistically significant, dose-dependent increases in mechanical nociceptive thresholds compared to vehicle controls. However, in the motor coordination studies, neither opioid agonist produced statistically significant changes in rotarod performance scores. The dissociation of antinociceptive and motor effects at this supraspinal site differs from the strong association between antinociceptive and motor effects produced by intrathecal administration of the same opioid agonists.