A quantitative histological study of the indusium griseum and neostriatum in elderly mice.

A quantitative histological examination of brains from mice aged 25, 28 and 31 months of age showed that there was no loss of neurons from the indusium griseum and the number of glia per 100 neurons also remained constant. In contrast the number of glia per 100 neurons in the neostriatum fell between 25 and 28 months. The percentage of oligodendrocytes was significantly higher than in younger mice but the percentage of microglia fell in both regions from 25 to 31 months. Unlike the indusium griseum, in which there was a significant variation in the mitotic and pyknotic indices with age, the neostriatum showed no variation in the mitotic and pyknotic indices between 6 and 31 months. The mitotic index was always lower in the neostriatum.