Body temperature effects of opioids administered into the periaqueductal grey area of rat brain.

The ability of opioids to influence rectal temperature after injection into the periaqueductal grey region (PAG) of rat brain was investigated. Both morphine and beta-endorphin caused a dose-dependent increase in rectal temperature of up to 2 degrees C. By using selective ligands of the subclasses of opiate receptor such as [D-Ala2,D-Leu5]enkephalin for delta-receptors and ethylketocyclazocine, dynorphin(1-17) and dynorphin(1-8) for kappa-receptors, it was possible to show that neither the delta- nor the kappa-opiate receptor was involved in the hyperthermic response. However, [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO), a mu-receptor ligand, did produce a dose-dependent hyperthermia. The ability of naltrexone, an opiate receptor antagonist, to reverse the hyperthermia induced by beta-endorphin and DAGO suggests that the opioid-stimulated increase in body temperature via the PAG is mediated through the mu-opiate receptor. Since the application of opioids to the PAG produces a hyperthermic response, it is possible that this brain site may have a role in the peptidergic control of body temperature.