Chronic morphine-induced hyperactivity in rats is altered by nucleus accumbens and ventral tegmental lesions

Lesions of the nucleus accumbens (NA) and the ventral tegmental area (VTA) attenuated and delayed the onset of the locomotor excitatory effects of morphine following chronic administration. Neither lesion, however, totally prevented the increase in locomotor excitation. These findings suggest that while the NA and VTA seem to play a role in mediating the excitatory effects of morphine, other regions and brain circuits must also be involved.