Behavioral effects of low, acute doses of morphine in nontolerant groups of rats in an open-field test.

Groups of eight rats were treated with low, acute doses of morphine (2, 3.5, and 5 mg/kg body weight) or a corresponding volume of isotonic NaCl solution. The formation of groups, certain other features of social interaction, plus some individual items were recorded. Morphine induced an increase in the frequency of group formations without disruption of grooming and rearing patterns. The total picture of morphine-induced behavior changes at the dose levels used might be characterized as a polyactivation (or a varied stimulation); different from the selective stimulation reported for d-amphetamine.