Electrical self-stimulation in the parabrachial area is depressed after ibotenic acid lesion of the lateral hypothalamus

Abstract

The involvement of lateral hypothalamic intrinsic neurons on electrical self-stimulation of the parabrachial area was analyzed. Rats were bilaterally implanted in the parabrachial area and with a guide cannula located above each lateral hypothalamus. They were subsequently tested for intracranial self-stimulation. Then, the lateral hypothalamus on one side of the brain was injected with ibotenic acid. The effect of the induced lesion was tested 8 days later on self-stimulation of the ipsilateral and contralateral parabrachial areas. The intrinsic neurons of the non-lesioned lateral hypothalamus were then destroyed with ibotenic acid. Self-stimulation was then tested 8, 12 and 30 days later. The unilateral lesion produced a significant decrease of self-stimulation using the electrode ipsilateral to the lesion, without any modification of the stimulation using the contralateral electrode. After bilateral lesion, self-stimulation was greatly reduced bilaterally. The results suggest that the main effect of the lesion was to increase the self-stimulation threshold. Given that the parabrachial area is a relay station for the gustatory inputs and that the intrinsic neurons of the lateral hypothalamus project back to the parabrachial area, the present results are tentatively interpreted as an indication that self-stimulation in this pontine area results from the activation of feedback loops between the lateral hypothalamus and the parabrachial area.