ACUTE IPSILATERAL HYPERALGESIA AND CHRONIC CONTRALATERAL HYPOALGESIA AFTER UNILATERAL 6-HYDROXYDOPAMINE LESIONS OF THE SUBSTANTIA-NIGRA

The effect of unilateral 6-hydroxydopamine lesions on flinch-jump thresholds to footshock was investigated during 3 months postoperative in rats. Preoperatively, the ipsilateral-contralateral thresholds were closely matched but postoperatively for flinch-jump thresholds to footshock applied to the body surface contralateral to the lesion hemisphere increased, whereas ipsilateral thresholds decreased. The ipsilateral decrease in threshold was maximal at postoperative day 1 but the contralateral increase persisted throughout testing. In control rats no ipsilateral-contralateral differences in the threshold were obtained. In both the control and 6-hydroxydopamine-treated groups there was an additional bilateral decline in jump threshold during the course of the experiment. These results suggest a role for dopaminergic and nondopaminergic participation in an animal''s response to nociceptive stimulation.