Vagal cardiomotor mechanisms in the hindbrain of the dog and cat

Abstract

Hindbrain-stereotaxic explorations in 28 cats and 24 dogs disclosed 3 areas where stimulating electrodes produced vagal cardiac inhibition. Stimulation in or near the nucleus ambiguus regularly evoked vagal potentials and slowed the heart in the cat and dog. Stimulation of the dorsal nucleus of vagus occasionally resulted in vagal activation and cardiac slowing in the dog, but never in the cat. This species difference may account for some of the confusion in the literature. In both species, stimulation of the afferent solit-arius nuclei evoked vagal potentials with longer latencies, brady-cardia, variable blood pressure response, and respiratory effects including the diving reflex. The bulbar cardioinhibitory mechanisms project to the ipsilateral and contralateral vagus. Both must be cut to abolish bradycardia. Stimulating central vagal mechanisms, especially the ambiguus area, frequently incited a stimulus-bound atrial fibrillation. These experiments point to discrete vagal afferent and efferent cardiomotor mechanisms in hindbrain with species differences. They re-emphasize a CNS [central nervous system] facility for inducing cardiac arrhythmias including atrial fibrillation directly related to CNS-vagal stimulation.