Gaseous transmitters in the brain of the masu salmon, <Emphasis Type="Italic">Oncorhynchus masou</Emphasis> (Salmoniformes,Salmonidae)

Distribution of nitroxidergic and H₂S-producing neurons in the brain of the masu salmon Oncorhynchus masou was studied by methods of histochemical labeling of NADPH-diaphorase and by immunohistochemical labeling of the neuronal nitric oxide synthase and cystathionine β-synthase (CBS). The established distribution of CBS and nNOS/NADPH-d of neurons and fibers in the masu salmon telencephalon, optic tectum, and cerebellum allows suggesting that the NO- and H₂S-producing systems represent individual, non-overlapping neuronal complexes performing specialized functions in the activity of local neuronal networks. In the medullar part, the nNOS-ir and NADPH-d-positive neurons were detected in the composition of viscerosensory (V, VII, and IX–X) and visceromotor (III, IV, and VI) nuclei of craniocerebral nerves, octavolateral afferent complex, reticulospinal neurons, and medial reticular formation. CBS in the masu salmon medulla was revealed in neurons of the nerve X nucleus, reticulospinal neurons, and ventrolateral reticular formation. Distribution of NO-ergic and H₂S-producing neurons in the masu salmon medullar nuclei indicates that NO in masu salmon is the predominant neuromodulator of the medullar viscerosensory systems, while H₂S seems to modulate only the descending motor systems. The results of the performed study allow suggesting that NO in the masu salmon medulla periventricular area can act as a regulator of postnatal ontogenesis.