Differential effects of localized lesions of n. accumbens on morphine- and amphetamine-induced locomotor hyperactivity in the C57BL/6J mouse.

Mice of the C57BL/6J strain became hyperactive to increasing doses of morphine sulfate. This response was similar to locomotor hyperactivity induced by amphetamine. Lesions and chemical blockade of posterior n. accumbens abolished amphetamine-induced hyperactivity and reduced but did not abolish the morphine response. These experiments demonstrate that the response to the two drugs is mediated by overlapping but noncongruent neural systems.