In this study, we have used noradrenergic histofluorescence and selective neurectomies of the vidian, ethmoid and caudal nasal nerves to evaluate the distribution of postganglionic sympathetic fibers in the canine nasal mucosa. In conjunction with the histochemical localization of the noradrenergic fibers in the nasal mucosa after vidian neurectomy, the norepinephrine content of the mucosa was also evaluated using high-performance liquid chromatography. Unilateral neurectomy of the superior cervical ganglion (SCG) resulted in the unilateral disappearance of all noradrenergic histofluorescence in the nasal mucosa, while no morphological changes in noradrenergic fibers could be identified after neurectomy of the cervical sympathetic trunk 1 cm below the SCG. Ethmoid neurectomy caused the disappearance of noradrenergic fibers of the upper third of the nasal mucosa, while vidian neurectomy resulted in a partial loss of noradrenergic fibers in the lower two-thirds of the nasal mucosa. The loss was chiefly in the area adjacent to venous sinusoids and was responsible for 50% of the norepinephrine content of this tissue. We concluded that all the postganglionic sympathetic fibers are from the ipsilateral SCG. Some of them travel via the ethmoid nerve and innervate the upper third of the nasal mucosa. The remaining fibers travel via the vidian nerve and perhaps the vessel walls of the supplying arteries and innervate the lower two-thirds of the nasal mucosa. The vidian nerve chiefly innervates the venous sinusoids of the lower two-thirds of the nasal mucosa.
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