Lipopolysaccharide-induced nitric oxide synthase activity in cultured cerebellar granule neurons

We examined the inducible form of nitric oxide synthase (iNOS) activity in cerebellar primary cultures enriched with granule neurons. Treatment with lipopolysaccharide (LPS) for 24 h was performed in two different cultures in which the survival of neurons was controlled by the levels of extracellular K+. Treatment of the granule neurons with the contaminating non-neuronal cells (< 5%) in a high K+ (25 mM) -containing culture medium with LPS induced four-fold NOS activity compared to that of the control, and the induced NOS activity was calcium-independent. LPS did not induce the NOS activity at all in the contaminating non-neuronal cells alone which were obtained by eliminating all the granule neurons from the culture by lowering the K+ concentration (5 mM). We conclude that the LPS-activated granule neurons can express iNOS activity and that this induction is not attributable to the contaminating nonneuronal cells.