Afferent projections of the cervical vagus and nodose ganglion in the dog.

The distribution within the brain stem of the afferent projections of the cervical vagus and the nodose ganglion was studied with horseradish peroxidase (HRP) and HRP-wheat germ agglutinin conjugate. Two to eight days after application of tracer into the cervical vagosympathetic trunk or the nodose ganglion the brain stems and ganglia were perfused and processed by the tetramethyl benzidine method. Vagal afferent fibers entered the lateral medulla as a distinct bundle spatially separate from the vagal efferent rootlets which were caudal and ventral to the afferents. Labeled axons in the solitary tract began to enter the nucleus tractus solitarii (nTS) 4.5 mm anterior to obex and were seen throughout the ipsilateral nTS as far as 3.5 mm caudal to obex. Label density varied within the nTS, with heaviest labeling in the dorsal and dorsolateral portions. Label was also seen in the ipsilateral area postrema (ap) and dorsal motor nucleus of the vagus. Labeled fibers crossed in the commissural portions of ap and nTS to enter the contralateral ap and nTS.