Electrical self-stimulation in the central amygdaloid nucleus after ibotenic acid lesion of the lateral hypothalamus.

This experiment was carried out in order to investigate the involvement of lateral hypothalamus (LH) in electrical self-stimulation of the central amygdaloid nucleus (CeA). Adult male Sprague-Dawley rats were bilaterally implanted with a guide cannula situated above each LH and with two electrodes in the CeA. Self-stimulation was subsequently obtained separately from both right and left electrodes. The LH was then lesioned unilaterally by ibotenic acid (IBO) injection. Eight days later, the effect of this unilateral lesion on self-stimulation of the ipsilateral and contralateral CeA was tested. Then the neurons of the remaining non-lesioned LH side were lesioned with IBO and self-stimulation was tested 15 days after the second lesion. Both unilateral as well as bilateral lesions of LH produced a significant decrease in CeA self-stimulation rates but had no significant effect on the reward effectiveness. The unilateral lesions did not produce any modification of the rate-intensity function in the contralateral CeA. This lesion-induced depression in performance was reversed by treatment with phenobarbital. These results provide clear evidence that the rewarding effects of CeA electrical stimulation do not result from the activation of the LH outputs and that the apparent decrease in CeA self-stimulation may result from the LH lesion-induced increase in the frequency of epileptiform manifestations that occur following amygdaloid stimulation.