Sympathetic and parasympathetic neurons are likely to be absent in the human vestibular and geniculate ganglia: an immunohistochemical study using elderly cadaveric specimens.

The vestibular and geniculate ganglia of the ear in experimental animals carry both of the tyrosine hydroxylase (TH)-positive sympathetic neurons and the neuronal nitric oxide synthase (nNOS)-positive parasympathetic neurons. With an aid of immunohistochemistry, we examined these ganglia as well as the horizontal part of the facial nerve using specimens from 10 formalin-fixed elderly cadavers. The submandibular ganglion from the same cadavers was used for the positive control for both markers. Although there was a nonspecific reaction in nuclei for the present antibody of nNOS, these ganglia were unlikely to contain either nNOS- or TH-positive neurons. However, we did not deny a possibility that the absence was a result of degeneration with aging. In contrast, the facial nerve horizontal part consistently contained both of TH-positive- and nNOS-positive fibers. These fibers might regulate blood supply to the facial nerve and the dysregulation leads to edema to elevate pressure on the nerve within its osseous canal.