ANTINOCICEPTIVE ACTIVITY OF D-ALA2-D-LEU5-ENKEPHALIN (BW 180C) IN THE RAT AFTER MODIFICATION TO CENTRAL 5-HYDROXYTRYPTAMINE FUNCTION

The antinociceptive activities of intracerebroventricular (icv.) injections of morphine and the synthetic enkephalin BW 180C have been assessed in the rat, using the tail immersion test. Intracerebroventricularly injected BW 180C was found to be several times less potent than icv morphine. Intracerebroventricularly injected 5-HT and peripherally administered clomipramine potentiated, whilst peripherally administered cyproheptadine attenuated, the effects of both morphine and B W 180C. In contrast, reserpine pretreatment abolished the anticociceptive activity of both opiate substances but this was subsequently restored after an icv injection of 5-HT. These results suggest that intact 5-HT pathways positively modulate the antinociceptive activity of morphine and the enkephalins, although a more precise nature of its involvement needs to be determined. © 1979.