Behavioral abnormalities induced by frontal cortical and nucleus accumbens lesions.

In previous studies, we have demonstrated that in male rats, unilateral right hemisphere lesions of either the frontolateral cortex or the nucleus accumbens (NAS) result in significant postoperative locomotor hyperactivity. In the present study we carried out two experiments to assess whether the production of hyperactivity in response to these two lesions is mediated through a common mechanism. In the first experiment, male Sprague-Dawley rats received either unilateral frontocortical suction and/or unilateral electrolytic lesions of the NAS. Only rats with lesions of the right hemisphere (suction and/or electrolytic) developed locomotor hyperactivity. Similar lesions in the left hemisphere did not result in behavioral changes. While both right cortical and NAS lesions alone produced hyperactivity, there was no additive effect of both lesions. In the second experiment, the effect of cortical lesions on NAS dopaminergic activity was assessed. Male Sprague-Dawley rats received either a right, left or sham frontocortical suction lesion, and were sacrificed 1, 2, and 4 weeks after surgery. Right hemisphere suction lesions produced a significant bilateral increase in NAS and caudate nucleus dopamine turnover (as measured by DOPAC/DA ratio) 4 weeks post-lesion, while similar left hemisphere lesions did not. These findings suggest that lesions in the dorsolateral frontal cortex and NAS may affect locomotor activity through a common mechanism mediated through the NAS.