Human brainstem preganglionic parasympathetic neurons localized by markers for nitric oxide synthesis

Identification of human parasympathetic preganglionic neurons in pontomedullary regions has been largely based on studies using cholinesterase histochemical procedures, and so far there is no adequate account of the location of these cells. Nitric oxide synthase (NOS) is present in brainstem parasympathetic preganglionic salivatory neurons in the rabbit (Zhu et al., 1996). In the present study we have used histochemical and immunohistochemical staining for NOS to examine possible preganglionic parasympathetic neurons in the human brainstem. We examined, in five human brains, the distribution, through the caudal pons and rostral medulla, of NOS-positive neurons in serial sections stained with NADPH diaphorase for histochemistry, and with antibodies against neuronal NOS peptide for immunohistochemistry. In scattered pontomedullary regions (rostral to the dorsal motor nucleus and the nucleus ambiguus) known to contain parasympathetic preganglionic neurons in animals, we observed groups of NOS-positive neurons which correspond in morphology and distribution with NOS-positive parasympathetic preganglionic neurons in rabbits. These neurons are probably parasympathetic preganglionic neurons in the human brainstem, involved in the control of lacrimation, salivation, oral and nasopharyngeal secretion, as well as the control of the dilation of extra- and intracranial blood vessels.