Proliferation, Neuro- and Gliogenesis in Normal and Mechanically Damaged Mesencephalic Tegmentum in Juvenile Chum Salmon, Oncorhynchus keta
Processes of proliferation, constitutive neuro- and gliogenesis in the mesencephalic tegmentum of intact juvenile chum salmon, Oncorhynchus keta, and at 3 days after a traumatic injury were studied by immunohistochemistry (IHC) labeling of PCNA, HuCD, and GFAP. In the chum tegmentum, the proliferative activity was revealed both in separate cells and in small cell clusters of the periventricular zone (PVZ). The presence of constitutive neurogenic zones provides the processes of persistent brain growth. After a damage to the tegmentum, proliferation in PVZ is activated, the constitutive neurogenic zones reactivate, and reactive neurogenic niches form in the parenchyma, and also the proliferative activity is initiated in the centers of secondary proliferation (basal tegmentum). It was first found that a traumatic damage to the tegmentum leads to accelerated differentiation of neurons in the subventricular zone (SVZ) and dorsomedial tegmentum, as well as to the appearance of HuCD+ cells with the ependymo- and radioglial phenotype in SVZ, which are absent in intact animals. It was first shown that the local foci of posttraumatic neurogenesis, located in the reticular formation parenchyma, and the zones of posttraumatic gliosis, contributing to a more efficient process of cell migration to the injury area, are formed as a result of tegmentum damage. The data obtained provide new information on the constitutive biology of neural stem cells and their involvement in brain regeneration.