A comparative quantitative and morphological study of ageing in the mouse neostriatum, indusium griseum and anterior commissure.

The glia:neuron ratio increased between 5 and 9 months in the neostriatum and indusium griseum and thereafter remained constant until 18 months-of-age. Between 18 and 22 months the glia:neuron ratio did not change in the neostriatum, but increased significantly in the indusium griseum due to a combination of a loss of neurons and an increase in glia. The 6--9 months rise was mainly due to an increase in the number of astrocytes in both regions although there was some increase in oligodendrocytes at this time. The increase in glia in the indusium griseum between 18 and 22 months was due to an increase in both astrocytes and microglia. In the anterior commissure, the pattern of glial change was almost identical in both limbs with oligodendrocytes increasing between 6 and 9 months then decreasing between 9 and 18 months. Astrocytes decreased between 6 and 18 months. Between 18 and 22 months oligodendrocytes and microglia both increased in number. There was a decrease in glioblasts in both limbs with age. The age at which lipofuscin appeared was different in each type of glial cell and in each region studied. Microglia contained lipofuscin at 6 months in all regions. Astrocytes first contained lipofuscin at 6 months in the neostriatum, at 9 months in the indusium griseum and at 15 months in the anterior commissure. Oligodendrocytes first contained lipofuscin at 12 months in the anterior commissure, at 18 months in the indusium griseum and at 18 months in the neostriatum. Ependymal cells adjacent to the neostriatum contained lipofuscin and osmiophilic lipid at 6 months but by 12 months the latter had become much less osmiophilic. Foamy pericytes were found in all regions: from 6 months in the neostriatum; from 9 months in the indusium griseum and from 15 months in the anterior commissure. These contained lipid droplets, were only found adjacent to arterioles or venules, and were likely Ibrahim's neurolipomastocytes. The response of glia to ageing varies in different regions of grey matter, but is similar in two different regions of white matter. These age changes may be related to different levels of metabolic activity of glia in different parts of the brain.