Morphology and response to vagus nerve section of the intra-epithelial axons of the rat trachea. A quantitative ultrastructural study.

The fine structure and distribution of the axons in the epithelium of the left and right sides of the trachea were studied in control rats and in rats subjected to unilateral cervical vagotomy. In control rats, the axons possessed similar ultrastructural features to the vesicle-containing axons which have been identified in the cornea and in the submucous plexus of the ureter. Stereological analysis showed that there are considerable differences in the degree of orientation of the axons and in the density of the intra-epithelial plexus on the two sides of the trachea. Degenerating axons were most numerous in the epithelium one day after vagotomy and degeneration and elimination of the axons by phagocytosis by the epithelial cells was completed within three days of section of the nerve. Comparison of the figures for the numbers of axons/grid hole obtained from specimens taken three days after vagotomy with those obtained from control specimens indicated that almost all the axons are derived directly from the vagus and that, although the majority of the axons in the epithelium on one side of the trachea are derived from the ipsilateral nerve, approximately one fifth are derived from the nerve on the contralateral side.