Neural projections from paraventricular nucleus that subserve vasomotor functions.

Descending projections from the paraventricular nucleus of the hypothalamus (PVN) either terminate in the dorsal medulla or pass through the ventrolateral medulla to terminate in the intermediolateral column of the spinal cord. We sought to determine whether a cardiovascular function is subserved by these pathways. Electrical stimulation of the PVN in urethan-anesthetized rats produced increases in blood pressure and mesenteric and renal vascular resistances while hindquarter resistance decreased. This integrated cardiovascular response appeared to be neurogenically mediated because it was virtually abolished by ganglionic blockade and unaffected by blockade of peripheral vascular vasopressin receptors. Adrenal catecholamines appeared to contribute since adrenalectomy reduced the response, especially the hindquarter vasodilation. Interruption with a knife cut of the PVN-dorsal medullary pathway did not affect the response to PVN stimulation except for hindquarter vasodilation, which was reduced significantly. Interruption of the PVN-ventrolateral medullary pathway by local microinjection of lidocaine blocked the pressor and vasoconstrictor responses to PVN stimulation but enhanced the hindquarter vasodilation. These data suggest that fibers descending from the PVN responsible for skeletal muscle vasodilation pass to or through the dorsal medulla, whereas efferent vasoconstrictor pathways from the PVN appear to course through, or synapse in, the ventrolateral medulla.