Identification of peroxidase-positive astrocytes by combined histochemical and immunolabeling techniques in situ and in cell culture.

A subpopulation of astrocytes in the vertebrate brain and in cysteamine-treated brain cell cultures contain cytoplasmic granules which exhibit an affinity for Gomori stains, orange-red autofluorescence, and non-enzymatic endogenous peroxidase activity. Visualization of these cells at the light microscopic level is confounded by the nonspecificity of the various histochemical methods routinely employed. In an attempt to circumvent this problem, we assayed for peroxidase-positive astrocytes using various combinations of diaminobenzidine (DAB) histochemistry and immunolabeling for the astrocyte-specific marker glial fibrillary acidic protein (GFAP). We determined that (a) DAB histochemistry in conjunction with avidin-biotin-immunoperoxidase labeling for GFAP specifically detects peroxidase-positive astrocytes in situ and (b) DAB histochemistry combined with indirect immunofluorescence for GFAP effectively demonstrates these cells in cysteamine-treated brain cell cultures.