The origin of the hypothalamic-vagal descending pathway: an experimental ultrastructural study.

Placing uni- and bilateral electrolytic lesions in the rat hypothalamic paraventricular nuclei was followed by the degradation of presynaptic profiles in the medullary dorsal vagal nuclei. Unilateral lesions resulted in degeneration of the dorsal vagal nuclei presynaptic profiles on the side of the lesion and on the site opposite. Our results seem to afford the first experimental proof that descending hypothalamic axons synapsing in the medulla on the neurons of the dorsal vagal nuclei arise in the paraventricular nuclei and intersect at some level of the lower brain stem.