Hydrogen Sulfide Modulates Adult and Reparative Neurogenesis in the Cerebellum of Juvenile Masu Salmon, Oncorhynchus masou

Abstract

Fish are a convenient model for the study of reparative and post-traumatic processes of central nervous system (CNS) recovery, because the formation of new cells in their CNS continues throughout life. After a traumatic injury to the cerebellum of juvenile masu salmon, Oncorhynchus masou, the cell composition of the neurogenic zones containing neural stem cells (NSCs)/neural progenitor cells (NPCs) in the acute period (two days post-injury) changes. The presence of neuroepithelial (NE) and radial glial (RG) neuronal precursors located in the dorsal, lateral, and basal zones of the cerebellar body was shown by the immunohistochemical (IHC) labeling of glutamine synthetase (GS). Progenitors of both types are sources of neurons in the cerebellum of juvenile O. masou during constitutive growth, thus, playing an important role in CNS homeostasis and neuronal plasticity during ontogenesis. Precursors with the RG phenotype were found in the same regions of the molecular layer as part of heterogeneous constitutive neurogenic niches. The presence of neuroepithelial and radial glia GS+ cells indicates a certain proportion of embryonic and adult progenitors and, obviously, different contributions of these cells to constitutive and reparative neurogenesis in the acute post-traumatic period. Expression of nestin and vimentin was revealed in neuroepithelial cerebellar progenitors of juvenile O. masou. Patterns of granular expression of these markers were found in neurogenic niches and adjacent areas, which probably indicates the neurotrophic and proneurogenic effects of vimentin and nestin in constitutive and post-traumatic neurogenesis and a high level of constructive metabolism. No expression of vimentin and nestin was detected in the cerebellar RG of juvenile O. masou. Thus, the molecular markers of NSCs/NPCs in the cerebellum of juvenile O. masou are as follows: vimentin, nestin, and glutamine synthetase label NE cells in intact animals and in the post-traumatic period, while GS expression is present in the RG of intact animals and decreases in the acute post-traumatic period. A study of distribution of cystathionine β-synthase (CBS) in the cerebellum of intact young O. masou showed the expression of the marker mainly in type 1 cells, corresponding to NSCs/NCPs for other molecular markers. In the post-traumatic period, the number of CBS+ cells sharply increased, which indicates the involvement of H2S in the post-traumatic response. Induction of CBS in type 3 cells indicates the involvement of H2S in the metabolism of extracellular glutamate in the cerebellum, a decrease in the production of reactive oxygen species, and also arrest of the oxidative stress development, a weakening of the toxic effects of glutamate, and a reduction in excitotoxicity. The obtained results allow us to consider H2S as a biologically active substance, the numerous known effects of which can be supplemented by participation in the processes of constitutive neurogenesis and neuronal regeneration.

Mechanical Brain Injury Increases Cells’ Production of Cystathionine β-Synthase and Glutamine Synthetase, but Reduces Pax2 Expression in the Telencephalon of Juvenile Chum Salmon, Oncorhynchus keta

“…Due to the high efficiency of the regenerative process in the fish brain, it can be concluded with confidence that the increased production of H 2 S in the NE cells of the juvenile chum salmon brain after the injury is directly related to the processes of reparative neurogenesis. The results of the study on the telencephalon of juvenile O. keta are consistent with the previously obtained results on O. masou which also revealed the effects of increased H 2 S production in the cerebellum 3 days after injury [16]. Unlike trout [18], no RG-type CBS + NPCs were detected in the pallium of O. keta.…”

“…The activation of neurons in the brain causes neurotransmitters, including glutamate, to be released, thus, activating NMDA receptors, which, in turn, leads to an increase in astrocytic intracellular calcium [43,44]. Therefore, the presence of two levels of CBS activity in cells and granules of the juvenile chum salmon telencephalon indicates mediator-modulatory intercellular interactions, which is consistent with the previously obtained data on fish [16,17,45].…”

“…As a result of injury to the O. keta telencephalon, the number of H 2 S-producing cells increases sharply, which leads to an increase in the total production of hydrogen sulfide in the brain. Taking into account the fact that the rates of such processes as proliferation, cell migration, and neuronal differentiation in PVZ after traumatic injury increase multifold, we may consider hydrogen sulfide as a factor contributing to reparative processes, which is consistent with the previously obtained results of a study of unilateral eye injury in trout [17,18] and cerebellum of masu salmon [16]. Due to the high efficiency of the regenerative process in the fish brain, it can be concluded with confidence that the increased production of H 2 S in the NE cells of the juvenile chum salmon brain after the injury is directly related to the processes of reparative neurogenesis.…”

“…There are multiple interplays between H 2 S and other gasotransmitters both on the level of their generation and as targets [15]. Previous studies on traumatic injury to the cerebellum in juvenils of masu salmon Oncorhynchus masou demonstrated sharply increasing the number of CBS + cells after 3 days, which indicates the involvement of H 2 S in the post-traumatic response [16]. Similar results were observed after optic nerve injury in trout, which showed a significant increase in the number of H 2 S-producing cells in the integrative centers of the brain: telencephalon, optic tectum, and cerebellum [17].…”

“…Juvenile Pacific salmon is a convenient model for the study of postembryonic neurogenesis, since the intensive neurogenesis in its brain is provided by neuroepithelial progenitors [6,16,28]. The brain of Pacific salmon largely retains the features of a primitive (ancestral) organization, while maintaining the high proliferative activity of neuroepithelial (NE) cells, which is characteristic of embryonic development.…”