Carotid sinus nerve projections to the brain stem in the cat

The distribution of carotid sinus nerve (CNS) afferent and efferent fibers in the brain stem was examined in eight cats using horseradish peroxidase (HRP) neurohistochemistry. The transganglionic transport of HRP yielded dense extraperikaryal labeling within the nucleus of the tractus solitarius (nTS). Labeling was also present in the area postrema (ap) and in the region of the nucleus ambiguus (nA). The nTS labeling was bilateral, the ipsilateral side being more intense. Within the nTS, the labeling was not uniform, being heaviest in the dorsal, dorsolateral and commissural subnuclei. Moderate labeling was seen in the ventrolateral nTS. In the region of the obex, HRP labeled fibers could be followed from the nTS to the region of the nA, where extraperikaryal labeling could be seen. HRP labeled perikarya were found in the rostral pole of nA. In two controls, the CSN was sectioned close to its junction to the glossopharyngeal nerve just prior to HRP injection. In both cases, no labeling was found in either the petrosal ganglion or brain stem.