The ultrastructural identification of vagal terminals in the solitary nucleus of the cat after anterograde labelling with horseradish peroxidase.

Horseradish peroxidase (HRP) was injected into the nodose ganglion of the cat in order to label the axon terminals of vagal afferent fibres in the solitary nucleus. HRP reaction product was seen in axons, the majority of which were unmyelinated. Axon terminals containing round clear vesicles and an occasional dense-core vesicle were also labelled. These terminals synapsed upon both large and small dendritic elements, the majority of which were less than 1.0 micrometers in diameter. The labeling method appears to affect adversely the normal ultrastructural characteristics of terminals or their postsynaptic relationships and in these respects is superior to electron microscopic degeneration methods.