Distribution of carotid sinus and depressor nerves in cat brain stem

Abstract

Compound action potentials evoked antidromically by electrical stimulation with microelectrodes in the medulla oblongata of anesthetized paralyzed cats were recorded distally in the carotid sinus nerve (CSN) and aortic depressor nerve (DN). The mean latency of the CSN response was 0.9 msec. with a calculated conduction velocity of contributing fibers ranging from 66 to 12 m/sec. The mean latency of DN response was 1.6 msec with conduction velocities of 40-16 m/sec. All contributing fibers were therefore myelinated. Responses followed repetitive stimulation above 900 cycles/sec. Positive points for evoked responses were less than 300 [mu] in diameter and threshold currents less than 5 [mu]a. Positive points for CSN and DN were found in nucleus tractus solitarius and in subnuclei of the medial reticular formation corresponding to the so-called depressor area. DN alone was represented in the nucleus cuneatus. Repetitive stimulation at positive points dropped the blood pressure and slowed the heart. The fibers studied were probably baroreceptor in origin and thus primary afferent fibers of baroreceptors project directly into both the nucleus tractus solitarius and medial reticular formation.