An immunohistochemical quantification of fibrous astrocytes in the aging human cerebral cortex

In order to determine whether cortical fibrous astrocytes increase with age, we studied 25 patients ranging in age from 24 to 100 years with no clinical or pathological evidence of dementia or other cerebral disorder. Paraffin sections of mid-frontal cortex were obtained and stained with the avidin-biotin immunolabeling procedure for glial intermediate filament protein. The resulting immunolabeled fibrous astrocytes were then counted in the molecular and cellular (cortical laminae 2-6) layers. Populations of fibrous astrocytes in both layers varied widely among individuals, and in the molecular layer their numbers were not significantly correlated with advancing age. In the cellular layer, however, despite widely ranging cell counts among individuals within the same decades of life, there was a significant linear increase with age. Our data suggest that the increase occurs or accelerates significantly after age 70, but the case numbers preclude reaching such a conclusion with statistical confidence. However, when the patients are divided into those less than 70 and those older, fibrous astrocytes in the cellular layer are shown to be significantly increased in the latter group compared to the former.