An intraspinal sympathetic preganglionic pathway: physiologic evidence in the cat.

Electrical stimulation of the zona intermedia of the lower thoracic/upper lumbar cat spinal cord resulted in increases of heart rate (HR), blood pressure (BP) and cardiac contractility (dp/dt). Sites of maximal cardiovascular response (SMCR) were localized histologically to the intermediolateral nucleus (ILN). The inotropic and chronotropic responses were abolished by spinal cord transection or hemisection two to three segments rostral to the site of stimulation. Discrete electrolytic lesions in the white matter adjacent to the ILN were also shown to markedly decrease or abolish the chronotropic and inotropic responses elicited by stimulation of a more caudal SMCR. Longitudinal spinal section resulted in decreased cardiovascular responses from an SMCR; these changes were larger on the left side and greatest for BP as compared to HR and dp/dt. These findings indicate the existence of an ascending intraspinal cardiovascular pathway located in the deep white matter adjacent to the ILN. They further suggest that this is the intraspinal sympathetic preganglionic pathway recently described anatomically.