EFFECTS OF MORPHINE HYDROCHLORIDE ON SOCIAL ENCOUNTERS BETWEEN MALE-MICE

The effects of a single injection of morphine hydrochloride (0.3, 0.6, or 1.25 mg/kg) or physiological saline (0.9% NaCl) on the agonistic b ehaviour elicited by isolation in male mice were examined. Individuall y housed mice were exposed to anosmic ''standard opponents'' 30 minute s after the drug administration, and the encounters were videotaped an d evaluated using an ethologically based analysis. Morphine (at 0.6 an d 1.25 mg/kg) significantly and dose-dependently decreased time spent in offensive (''threat'' and ''attack'') and ''digging'' behaviours bu t markedly increased ''non-social exploration'' without a significant increase of ''immobility.'' The lowest dose was completely ineffective in producing changes in any of the behaviours studied. It is conclude d that these results present a specific ethopharmacological profile ch aracterized by suppression of aggressive behaviour, increase in non-so cial exploration, and no evident impairment of motor activity. (C) 199 3 Wiley-Liss, Inc.