Morphine hyperthermia in rats: role of neurochemical substances in brain.

Central neurochemical mechanism underlying the hyperthermic effect of morphine has been investigated in rats. 200 micrograms morphine hydrochloride, when administered through cerebroventricular route at different seasonal air temperature, caused a rise in rectal temperature of rats. This hyperthermia was not affected by prior administration of antiserotonergic (pCPA, 5.6-DHT) or anticatecholaminergic (PBZ, 6-OHDA) drugs, as well as by PGE synthetase inhibitor, indomethacin. Similarity, cholinergic muscarinic or nicotinic receptor blockers, such as atropine and pentolinium/ D-tubocurarine respectively, were ineffective to modify it. Whereas, the depletion of acetylcholine in brain by pretreating the animals with hemicholinium profoundly delayed the hyperthermia, suggesting a central cholinergic involvement in morphine induced hyperthermia in rats.