Protoplasmic astrocytes in CA1 stratum radiatum occupy separate anatomical domains

Protoplasmic astrocytes are increasingly thought to interact extensively with neuronal elements in the brain and to influence their activity. Recent reports have also begun to suggest that physiologically, and perhaps functionally, diverse forms of these cells may be present in the CNS. Our current understanding of astrocyte form and distribution is based predominantly on studies that used the astrocytic marker glial fibrillary acidic protein (GFAP) and on studies using metal-impregnation techniques. The prevalent opinion, based on studies using these methods, is that astrocytic processes overlap extensively and primarily share the underlying neuropil. However, both of these techniques have serious shortcomings for visualizing the interactions among these structurally complex cells. In the present study, intracellular injection combined with immunohistochemistry for GFAP show that GFAP delineates only approximately 15% of the total volume of the astrocyte. As a result, GFAP-based im...