In vitro interaction between cerebellar astrocytes and granule cells: a putative role for nitric oxide

In primary cultures of astrocytes and granule cells from neonatal rat cerebellum, the activity and function of nitric oxide (NO) synthase were measured by the conversion of [3H]arginine to [3H]citrulline and the accumulation of cyclic guanosine monophosphate (cGMP), respectively. The glutamate receptor agonist N-methyl-D-aspartate (NMDA) and the Ca2+ ionophore A23187 stimulated NO synthase activity in cerebellar granule cells but not in astrocytes. In granule cells, NMDA, A23187, and sodium nitroprusside (SNP) elicited an accumulation of cGMP, whereas only SNP was active in astrocytes. However, in astrocytes that were incubated together with granule cells, NMDA induced a more than 3-fold increase in the concentration of cGMP; this increase was blocked by both the NO synthase inhibitor NG-monomethyl-L-arginine (MeArg) and the allosteric NMDA receptor antagonist (+)5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine maleate (MK-801). Thus, cerebellar astrocytes do not appear to express NO synthase but do contain guanylate cyclase, which can be activated by an NO-like factor produced by cerebellar granule cells after stimulation by NMDA.