Distribution of glial fibrillary acidic protein and glutamine synthetase in human cerebral cortical astrocytes--a light and electron microscopic study.

Human cerebral cortex was studied immunocytochemically by light and electron microscopy using antibodies against glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS). Glial fibrillary acidic protein-positive cells and processes were present in both cortex and white matter, but in contrast glutamine synthetase-positive cells and processes were present only in cortex. Cell bodies which contained glutamine synthetase had typical ultrastructural features of protoplasmic astrocytes. Glutamine synthetase-positive processes were often present near asymmetrical synapses in the neuropil. These processes often contained mitochondria, but not glial filaments, and were different from unlabelled astrocytic processes, which seldom contained mitochondria, but had large numbers of glial filaments. Glutamine synthetase immunoreactivity therefore affords a means of distinguishing between these two types of astrocytic processes in the human cerebral cortex.