Cardiovascular reflexes following lesions in medullary reticular formation

Abstract

In 19 anesthetized cats acute destruction of large portions of the medullary reticular formation was achieved with the aid of a radio-frequency lesion maker. Midline structures were spared by confining the lesions to the dorsolateral medulla. Tissue injury extended from a level rostral to the inferior olivary complex to the obex. These lesions in the medullary vasomotor area did not alter significantly the cardiovascular reflex adjustments to bilateral occlusion of the carotid arteries or to the stimulation of the central end of the cut sciatic nerve. In addition, an increase in contractile force, heart rate, and blood pressure evoked by stimulation of pressor areas in the posterior hypothalamus could be obtained following the lesions. The preparations were critically dependent upon supramedullary connections to maintain vascular tone and circulatory reflex adjustments, for decerebration in the lesioned animal brought about a reduction in blood pressure and a loss of vascular reflex responses. These findings suggest that supramedullary centers exert tonic as well as phasic influences on vascular and cardiac activity that is independent of the medullary vasomotor area.