Age-Related Changes in Neurons and S100-, GFAP-Immunoreactive Cells in the Motor Cortex of Cats

Morphological changes of neurons and S100-,GFAP-immunoreactive cells in the motor cortex of young adult and older cats were comparatively investigated, and the correlation of these changes and motor function degradation during senescence was discussed. Nissl staining was applied to show cortical layers and neurons. Immunohistochemical method was employed to exhibit S100-immunoreactive (S100-IR) and GFAP-immunoreactive (GFAP-IR) cells. Under an Olympus microscope, Moitcam 5000 Digital Image Acquisition and Analysis System was used to statistically count the number of total cortical neurons, GFAP-IR cells and S100-IR cells in each cortical layer, and the cell-body diameter of GFAP-IR cells and S100-IR cells were randomly sampled and measured. The density of total neurons in layer V and VI of the motor cortex showed a significant decrease in older cats (P < 0.01). Furthermore, the density and the cell-body diameter of GFAP-IR and S100-IR cells in the motor cortex of old cats were significantly increased when compared to that in young adults (P < 0.01). In addition，the S100 and GFAP immunoreactivity in the motor cortex of older cats was stronger than in younger ones. The density of total neurons in layer V and VI of the motor cortex was significantly reduced during aging, which might lead to a decreased motion mediation capacity of the motor cortex in older individuals. Moreover, with age, astrocytes in the motor cortex were significantly activated and increased, which is of great significance in maintaining normal neuronal activities, signalling between neurons and therefore slowing down age-dependent motor function degradation.