Paradoxical effects of amphetamine on preweanling and postweanling rats.

In adult rats amphetamine acts as a strong behavioral stimulant leading to a marked increase in random, nondirected locomotor activity. In contrast we report that amphetamine administered to preweanling rats in the presence of an anesthetized adult rat produces no visible increase in motor activity. Instead, it appears to enhance the normal tendency of neonatal rats to approach and maintain contact with conspecifics. In postweanling rats amphetamine disrupts the tendency to aggregate and produces an increase in behavioral activity comparable to that seen in adult rats. These findings may constitute the basis for an animal model of minimal brain dysfunction hyperkinesis.