Induction of Nitric Oxide Synthase in Glial Cells

: Primary astrocyte cultures, C6 glioma cells, and N18 neuroblastoma cells were assayed for nitric oxide synthase (NOS) activity with a bioassay of cyclic GMP production in RFL‐6 fibroblasts. Treatment of astrocyte cultures for 16–18 h with lipopolysaccharide (LPS) induced NOS‐like activity that was l‐arginine and NADPH dependent, Ca2+ independent, and potentiated by superoxide dismutase. Induction was evident after 4 h, was dependent on the dose of LPS, and required protein synthesis. Treatment of astrocyte cultures with leucine methyl ester reduced microglial cell contamination from 7 to 1%, with a loss of 44% of NOS‐like activity. C6 cells treated with LPS also showed Ca2+‐independent and l‐arginine‐dependent NOS‐like activity. N18 cells demonstrated constitutive Ca2+‐dependent NOS‐like activity that was not enhanced by LPS induction. These data indicate that NOS‐like activity can be induced in microglia, astrocytes, and a related glioma cell line as it can in numerous other cell types, but not in neuron‐like N18 cells.