Surface complexity of human neocortical astrocytic cells: changes with development, aging, and dementia

Astrocytes from area 11 of the human neocortex were Golgi-impregnated. The material was taken from four human subjects, (1) a neonate without obvious CNS damage, (2) a middle-aged adult serving as control, (3) an aged individual without apparent mental disturbances, and (4) an aged patient with dementia. Camera-lucida drawings of 7 to 26 astrocytic cells from each donor were digitized into a personal computer, and analyzed for their fractal dimension D which is an objective and quantitative measure of the complexity of the cell's borders. Both radial and multipolar astrocytes from neonatal cortex showed a comparatively low fractal dimension (D approximately 1.39), that is, low surface complexity. Adult ("control") astrocytes were characterized by a high fractal dimension (D = 1.57), corresponding to their large surface complexity. Astrocytes from the aged subject showed a somewhat smaller fractal dimension (D = 1.51) and, thus, surface complexity; this difference was however not highly significant. In contrast, astrocytes from the subject with dementia showed a significant reduction in surface complexity (D = 1.47). Parallel changes were observed in the brain volume compartment occupied by the process of individual astrocytes. These data suggest that formation and maintenance of astrocytic processes and/or side branches correlate positively with the degree of information processing within their neuronal environment.