Seasonal Variability of the Hippocampus’s Architectonics in Bank Voles (Clethrionomys glareolus, Rodentia)

Resumo

Seasonal and age-related variability of the hippocampus in the bank vole (Clethrionomys glareolus) was monitored in a natural population from Moscow oblast. Autumn-born animals were compared at three stages of their life cycle: in autumn (1–3 months old), during the winter decrease of brain weight (5–7 months old), and after the spring “growth spurt” (9–11 months old). The winter sample exhibited significantly smaller (p < 0.05) section areas of ​​both the dentate gyrus and the CA3 field of the hippocampus. All studied divisions of the hippocampal complex—molecular and granule layers of the dentate gyrus, pyramidal cell layers, and fibers of the CA3 field of the hippocampus—exhibited a similar winter decrease (9.4–13.3%). In spring, hippocampal complex showed regrowth. In overwintered voles, the size of hippocampal divisions in summer surpassed that in the winter sample by 5.4–27.3%. The results indicate a considerable morphological plasticity of the main hippocampal structures in response to seasonal factors in nonwinter-sleeping rodents.