DIFFERENCES BETWEEN 2 SUBSTRAINS OF AB MICE IN THE OPIOID SYSTEM

Animals from two substrains of AB mice, i.e., ABH/Md and ABG/Md, diffe r in the occurrence of aggressive behavior. After maturation, male ABH mice regularly exhibited abnormal aggressive behavior making group-ho using impossible. In contrast, ABG animals never showed such behaviora l patterns. To elucidate the role of opioid mechanisms, we tested the reaction of these animals to morphine in the hot plate test. Moreover, specific DAMGO binding was measured. It was shown that mice from cont rol groups differed significantly in reaction to the thermal stimulus. ABH mice had significantly longer reaction times. With increasing dos es of morphine this difference disappeared, suggesting different level s of basal activity in endogenous opioid systems. This is underlined b y significantly lower DAMGO binding in aggressive ABH mice. The result s suggest that differences in endogenous opioid systems may account fo r differences in aggressiveness. (C) 1997 Elsevier Science Inc.