STRAIN DIFFERENCES IN THE ANALGESIC AND REINFORCING ACTION OF MORPHINE IN MICE

The analgesic and reinforcing effects of morphine were compared in fou r strains of mice (C57BL/6, BALB/c, DBA, CBA). The analgesic action of morphine was measured in tail immersion (49 degrees C), hot plate (60 degrees C), and tail clip (four-point scale of nociceptive response) tests. The reinforcing action of morphine was studied in IV self-admin istration and conditioned place preference techniques. The results dem onstrate strain differences in the analgesic and reinforcing action of morphine in mice. The relative rank order of the strains varied for t he several tests as well as for the morphine effects. The lack of corr elation between analgesic and reinforcing action of morphine in inbred strains supports the conclusion that analgesia and reinforcement are separate processes with different genetic control.