HIPPOCAMPUS GROWTH IN BANK VOLES (CLETHRIONOMYS GLAREOLUS, RODENTIA) FROM DIFFERENT SEASONAL GENERATIONS

Age-related variations in the hippocampus mass in the late postnatal ontogeny of bank voles (Clethrionomys glareolus) from the spring and autumn generations are considered in a comparative aspect. The mass of the hippocampus of the spring voles is increased regularly over their short life cycle and approaches the values maximum for the species at two-months age. In the autumn voles, a two-peak growth curve is detected, the hippocampus increasing until September, after which an autumn-winter regression of the mass of this brain region was observed. The hippocampal growth of autumn voles resumed at the age of 7-9 months and coincided with the beginning of the reproduction period. The hippocampus of autumn voles reached the definitive size at the age of 10-11 months. The results obtained characterize specific features of hippocampal growth in spring and autumn voles. The mechanisms that switch the alternative types of ontogeny of the seasonal generations are discussed.