Structural specializations of human retinal glial cells.

Electron microscopy and immunohistochemistry have been used to study the structural specializations of astrocyte and Müller glia cells in human retinas. The astrocytes and Müller cells contribute to the formation of the internal limiting membrane, the retina, the blood vessel glial limiting membranes and the glial sheaths of the ganglion cells. Two types of junctions were observed among retinal glial cells. Adherent junctions were found between astrocytes and Müller cells, and between adjacent astrocytes. Gap junctions were only observed between astrocyte processes. These similarities suggest that astrocytes and Müller cells can perform the same functions in human retinas. Finally, the "perivascular astrocyte of Wolter", related only to the blood vessels, was not found. All the retinal astrocytes have the same ultrastructural characteristics, confirming the absence of these astroglial cells in human retinas observed by immunohistochemical techniques.