Localization of ascending inotropic and chronotropic pathways in the cat.

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Abstract
The locations and organization of spinal pathways controlling the cardiac vagi were studied in 3 groups of cats. In all animals .beta.-adrenergic blockade was induced and the L4 spinal segment was exposed. The right carotid sinus nerves (RCSN) and right peroneal nerves (RPN) were sectioned and the central ends prepared for stimulation. In 1 group of cats, hearts were paced and indices of ventricular contractility were monitored. In another group heart rate and blood pressure were recorded and cardiac pacing was not induced. RCSN stimulation produced negative inotropic and chronotropic responses. These responses were attenuated by simultaneous RPN stimulation. Unilateral spinal lesions at L4 placed in the area of the dorsolateral sulcus (DLS) attenuated, whereas such bilateral lesions abolished, the effects of RPN stimulation. Afferent fibers entering 1 side of the spinal cord probably excite a bilateral ascending pathway that inhibits the cardiac vagi. A 3rd group of cats was studied to determine whether the left and right limbs of the pathway affect bilateral cardiac vagal preganglionic somata or only the complementary ipsilateral cardiac vagus. These animals were instrumented for monitoring either heart rate or contractility and the left vagus was sectioned. Functional cardiac innervation was provided solely by the right vagus. RCSN stimulation produced negative inotropic and chronotropic responses which were attenuated by RPN stimulation. A right DLS lesion at L4 abolished the effects of RPN stimulation. The spinal ascending afferent pathway apparently affects principally the ipsilateral cardiac vagal preganglionic somata.