A COMPARATIVE QUANTITATIVE AND MORPHOLOGICAL STUDY OF AGEING IN THE MOUSE NEOSTRIATUM, INDUSIUM GRISEUM AND ANTERIOR COMMISSURE

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Abstract
The glia:neuron ratio increased between 5 and 9 mo. in the neostriatum and indusium griseum and thereafter remained constant until 18 mo. old. Between 18 and 22 mo. 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 mo. 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. In the anterior commissure, the pattern of glial change was almost identical in both limbs with oligodendrocytes increasing between 6 and 9 mo. then decreasing between 9 and 18 mo. Astrocytes decreased between 6 and 18 mo. Between 18 and 22 mo. 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 mo. in all regions. Astrocytes first contained lipofuscin at 6 mo. in the neostriatum, at 9 mo. in the indusium griseum and at 15 mo. in the anterior commissure. Oligodendrocytes first contained lipofuscin at 12 mo. in the anterior commissure, at 18 mo. in the indusium griseum and at 18 mo. in the neostriatum. Ependymal cells adjacent to the neostriatum contained lipofuscin and osmiophilic lipid at 6 mo. Foamy pericytes were found in all regions: from 6 mo. in the neostriatum; from 9 mo. in the indusium griseum and from 15 mo. 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 aging varies in different regions of gray matter, but is similar in 2 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.