Hydrogen Sulfide-, Parvalbumin-, and GABA-Producing Systems in the Masu Salmon Brain

Abstract

Using immunohistochemical techniques, we determined localization of the zones of positivity with respect to cystathionine-β-synthase (CBS, the enzyme mediating production of hydrogen sulfide, H2S), GABA, and parvalbumin (PA) in the brain of the masu salmon (Oncorhynchus masоu). The corresponding positivity was found in neurons of the ventral spinal column (VSC), medial reticular formation (RF) of the myelencephalon, fibers and cells of the cerebellum, in the mesencephalic tegmentum, optic tectum, periventricular diencephalon, hypothalamus, and telencephalon. The heterogeneity of immunopositive CBS-, GABA-, and PA-containing neuronal subpopulations in all cerebral regions of the masu salmon is, obviously, related to the fact that the above-mentioned groups belong to different neurochemical and electrophysiological systems. In caudal magnocellular cerebral systems (dorsomedial nuclei of the tegmentum, medullary parts of the medial RF, and also in the VSC), we found high levels of colocalization of CBS, GABA, and PA. We hypothesize that hydrogen sulfide, which is produced by CBS-containing cells, can play a role of the modulator of GABAergic neurotransmission, while the presence of PA in neuronal elements is indicative of a high level of energy metabolism and/or high electrical activity. In the periventricular parts of the diencephalon of the masu salmon, we found cells with high levels of CBS-, GABA-, and PA-positivity. It seems possible that these cells are involved in the processes of growth and physiological regeneration of neurons in diencephalic cerebral structures of fishes.