Age-dependent changes in the glial cell nests of the canine rhinencephalic allocortex. A morphometric study.

In the present study, the morphological features as well as the age-dependent changes of the glial cell nests (GCN) within the rhinencephalic allocortex of the dog are described. A combination of two stereological methods, i.e., Cavalieri's principle and the optical disector, was used to obtain unbiased estimates of the volumes of the whole brain, the allocortex, and the GCN. Furthermore, the numerical densities and total number of the two prevailing populations of undifferentiated cells within these nests were determined. Cells with medium-sized dark nuclei (CMD) and cells with large pale nuclei (CLP) were distinguished. The volume of the GCN in relation to the volume of the allocortex decreased with increasing age. The numerical density and the total number of all cells of the GCN and of the CMD were reduced with age, whereas the numerical density and number of the CLP increased with advancing age. Similar morphological features as well as age-dependent changes have already been described of the cell populations in the subependymal layer. Therefore, in analogy, we presume that the glial cells of the GCN have emigrated from the subependymal layer. The significance of these age-dependent changes remains as obscure as does the function of the GCN.