Reconsideration of the autonomic cranial ganglia: An immunohistochemical study of mid-term human fetuses

The cranial parasympathetic ganglia have been reported to paradoxically contain the sympathetic nerve marker, tyrosine hydroxylase (TH), in addition to neurons expressing parasympathetic markers such as vasoactive intestinal peptide (VIP) and neuronal nitric oxide synthase (nNOS). However, the distribution of these molecules in the cranial ganglia of human fetuses has not yet been examined. Using paraffin sections from 10 mid-term human fetuses (12-15 weeks), we performed immunohistochemistry for TH, VIP, and nNOS in the parasympathetic ciliary, pterygopalatine, otic, and submandibular ganglia, and for comparison, the sensory inferior vagal ganglion. The ciliary and submandibular ganglia contained abundant TH-positive neurons. In the former, TH-positive neurons were much more numerous than nNOS-positive neurons, whereas in the latter, nNOS immunoreactivity was extremely strong. No or a few cells in the pterygopalatine, otic, and inferior vagal ganglia expressed TH. Ciliary TH neurons appeared to compensate for classically described sympathetic fibers arising from the superior cervical ganglion, whereas in the submandibular ganglion, nNOS-positive neurons as well as TH neurons might innervate the lingual artery in addition to the salivary glands. Significant individual variations in the density of all these markers suggested differences in sensitivity to medicine affecting autonomic nerve function. Consequently, in the human cranial autonomic ganglia, it appears that there is no simple dichotomy between sympathetic and parasympathetic function.