Nitric oxide synthase in the autonomic and sensory ganglia innervating the submandibular salivary gland

This article reviews the neuroanatomical studies on the distribution of nitric oxide synthase (NOS) in neurons and nerve fibers innervating the submandibular gland. Specificity of NADPH‐diaphorase activity as a histochemical marker of neuronal NOS is discussed in light of corresponding NOS immunoreactivity. Anatomical data suggest that nitric oxide may affect neural regulation of the submandibular gland through both sympathetic, parasympathetic and sensory divisions of the autonomic nervous system. NOS‐containing nerve terminals in the gland parenchyme are mainly vascular and either parasympathetic and/or sensory in nature, while sympathetic terminals lack NOS. Most postganglionic parasympathetic neurons are intensely NOS‐immunoreactive. Some of the preganglionic parasympathetic neurons show vague reactivity, while their terminals in the submandibular ganglia stain heavily. The postganglionic sympathetic neurons normally show only barely visible reactivity, while manipulations interrupting axonal continuity increase neuronal NOS content. A subpopulation of the preganglionic sympathetic neurons and their terminals are intensely reactive. The observations summarized here suggest that nitric oxide participates in the control of blood flow through the gland, while direct effect on secretion is unlikely. © 1996 Wiley‐Liss, Inc.