Gradual inhibition of inducible nitric oxide synthase but not of interleukin‐1β production in rat microglial cells of endotoxin‐treated mixed glial cell cultures

Abstract

In cultures of purified microglial cells and astrocytes from newborn rats, the immunocytochemical localization of interleukin-1β (IL-1β) and inducible nitric oxide synthase (iNOS) using recently developed antibodies, as well as the release of IL-1β and nitric oxide (NO), was studied following exposure of the cells to endotoxin [lipopolysaccharide (LPS)]. In the absence of LPS, IL-1β- and iNOS-immunoreactive microglial cells and IL-1β or NO release were not observed, whereas in the presence of the endotoxin, the production of NO and IL-1β 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-1β remained unaltered. Moreover, 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-1β production in mixed glial cell cultures upon endotoxin stimulation. Moreover, in the presence of astrocytes the induction of iNOS, but not that of IL-1β in microglial cells is gradually inhibited. © 1996 Wiley-Liss, Inc.