Nitric oxide synthase in the glossopharyngeal and vagal afferent pathway of a teleost, Takifugu niphobles - The branchial vascular innervation

To examine the presence of nitric oxide synthase (NOS) in the sensory syste m of the glossopharyngeal and vagus nerves of teleosts, nicotinamide adenin e dinucleotide phosphate diaphorase (NADPHd) activity and immunoreactivity for NOS were examined in the puffer fish Takifugu niphobles. The nitrergic sensory neurons were located in the ganglia of both the glossopharyngeal an d the vagal nerves. In the vagal ganglion, positive neurons were found in t he subpopulations for the branchial rami and the coelomic visceral ramus, b ut not for the posterior ramus or the lateral line ramus. In the medulla, n itrergic afferent terminals were found in the glossopharyngeal lobe, the va gal lobe, and the commissural nucleus. In the gill structure, the nitrergic nerve fibers were seen in the nerve bundles running along the efferent bra nchial artery of all three gill arches. These fibers appeared to terminate in the proximal portion of the efferent filament arteries of three gill arc hes. On the other hand, autonomic neurons innervating the gill arches were unstained. These results suggest that nitrergic sensory neurons in the glos sopharyngeal and vagal ganglia project their peripheral processes through t he branchial rami to a specific portion of the branchial arteries, and they might play a role in baroreception of this fish. A possible role for nitri c oxide (NO) in baroreception is also discussed.