Vagal preganglionic innervation of the cat heart--an attempt to identify the medullary "heart area" by the retrograde axoplasmic transport of horseradish peroxidase.

The medullary "heart area", origins of the vagal preganglionic fibers innervating the heart, were identified in 19 cats with the use of horseradish peroxidase (HRP) as a retrograde axonal tracer. When HRP was injected in the A-V node area, S-A node area, right atrial wall and right ventricular wall, the labeled neurons were principally found in the lateral half of the dorsal motor nucleus (DMN) and in the medial solitary nucleus (MSN), were almost the same in number bilaterally, and were chiefly from the calamus scriptorius to the upper cervical cord. They showed no anatomical proof for asymmetric distribution. When HRP was injected in the left ventricular wall or the apex, few labeled neurons were identified in the DMN. Labeled neurons were not found in the nucleus ambiguus. This study suggests the labeled neurons in the DMN and MSN are origins of the dually innervating vagal preganglionic fibers to the heart.