[Effect of morphine and naloxone on the biorhythm of pain sensitivity of mice after unilateral inactivation of cerebral hemispheres].

The effects of morphine (5 mg/kg, i.p.) and naloxone (1 mg/kg, i.p.) on the formation of pain sensitivity biorhythms was studied in the tail-flick test on adult male SHR mice upon unilateral inactivation of cerebral hemispheres by Leao's method of spreading potassium depression. It was established that morphine changed the rhythmogenic properties of both left and right hemispheres, inverted the phase of circadian rhythm, and produced the most pronounced analgesic action in the stage of maximum pain sensitivity (minimum pain threshold). Naloxone affected the pain rhythm predominantly in the operated and right-hemisphere-active animals, which confirmed the increased role of opioids in the process of rhythm regulation in mice.