Postulated Vasodilator Center in the Medulla Oblongata

Abstract

Depressor reactions were elicited by electrical stimulation in the distal part of the medulla oblongata. The following observations were made. The depressor area is larger than previously assumed. Depressor responses are accompanied by vasodilatations in the muscles and the skin. Vasodilatations are not due to vasodilator nerve impulses, at least not in the sympathetic, parasympathetic or dorsal root fibers. Consequently, relaxation of the vessels must be due solely to inhibition of prevailing vasoconstrictor tone. Ventral to and accompanying the depressor area there is a pressor area. Bilateral superficial cauterization in the area postulated to contain the vasodilator center abolishes depressor reactions to vagus and sinus nerve stimulation, but not those to stimulation of an afferent spinal nerve. The depressor area does not constitute a vasodilator center, either in the sense that it governs vasodilator activity or in the sense that it is an integrative area relaying inhibitory impulses to vasoconstrictor neurons. The depressor area probably consists of fibers mediating inhibitory vagus and sinus nerve impulses to vasoconstrictor neurons. The pressor layer ventral to the depressor area consists either of fibers carrying excitatory impulses from the vagus and sinus nerves to vasoconstrictor neurons or of such neurons connecting with the depressor fibers.