GRADUAL INHIBITION OF INDUCIBLE NITRIC-OXIDE SYNTHASE BUT NOT OF INTERLEUKIN-1-BETA PRODUCTION IN RAT MICROGLIAL CELLS OF ENDOTOXIN-TREATEDMIXED GLIAL-CELL CULTURES

In cultures of purified microglial cells and astrocytes from newborn r ats, the immunocytochemical localization of interleukin-1 beta (IL-1 b eta) and inducible nitric oxide synthase (iNOS) using recently develop ed antibodies, as well as the release of IL-1 beta and nitric oxide (N O), was studied following exposure of the cells to endotoxin [lipopoly saccharide (LPS)]. In the absence of LPS, IL-1 beta- and iNOS-immunore active microglial cells and IL-1 beta or NO release were not observed, whereas in the presence of the endotoxin, the production of NO and IL -1 beta by microglial cells dramatically exceeded their synthesis and release by astrocytes. Interestingly, microglial cells cultured for 4- 8 days in the presence of astrocytes appeared to lose their ability to produce iNOS, whereas the release of IL-1 beta remained unaltered. Mo reover, endotoxin-stimulated microglial cells appeared to regain their ability to synthesize iNOS following their separation from astrocytes . These data show that microglia are primarily responsible for NO and IL-1 beta production in mixed glial cell cultures upon endotoxin stimu lation. Moreover, in the presence of astrocytes the induction of iNOS, but not that of IL-1 beta in microglial cells is gradually inhibited. (C) 1996 Wiley-Liss, Inc.