Localization of ascending inotropic and chronotropic pathways in the cat.

SUMMARY We studied the locations and organization of spinal pathways controlling the cardiac vagi in three groups of cats. In all animals, /?-adrenergic blockade was induced and the L4 spinal segment was exposed. The right carotid sinus nerves (RC9N) and right peroneal nerves (RPN) were sectioned and the central ends were prepared for stimulation. In one 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. The data suggest that afferent fibers entering one side of the spinal cord excite a bilateral ascending pathway that inhibits the cardiac vagi. A third group of cats then 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. Thus, 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. These data suggest that the spinal ascending afferent pathway affects principally the ipsilateral cardiac vagal preganglionic somata. SINCE the original work by Kerr and Alexander (1964), studies have been performed to identify spinal pathways involved in cardiovascular control. Descending pressor (Foreman and Wurster, 1973), descending depressor (Ulert and Seller, 1969), ascending pressor, and ascending depressor (Chung and Wurster, 1976) pathways were localized bilaterally in the dorsolateral funiculi (DLF), ventrolat-eral funiculi (VLF), dorsolateral sulci, and DLF, respectively. Since most studies were performed on vagotomized animals, the roles of the pathways in cardiac vagal control were not determined (Bilateral sciatic nerve stimulation produces tachycardia and abolishes the bradycardia in response to carotid sinus nerve stimulation or physiological baroreceptor activation in cats with /?-adrenergic blockade (Quest and Gebber, 1972). Electrical activation of the cut central ends of various peripheral nerves produces evoked responses in single units or slips of the cardiac vagal branches Cardiac vagal preganglionic somata are organized according to physiological function in the cat. So-mata of …