NITRIC-OXIDE DOES NOT MEDIATE THE NEUROTROPHIC EFFECTS OF EXCITATORY AMINO-ACIDS IN CULTURED CEREBELLAR GRANULE NEURONS

Excitatory amino acids, such as N-methyl-D-aspartate (NMDA) and kainate, promote neuritogenesis and viability in primary cultures of cerebellar granule cells. In view of the recent demonstration that excitatory amino acids activate the synthesis of nitric oxide, the present study examined a potential role of nitric oxide in mediating the neurotrophic effects of excitatory amino acids. NMDA enhanced the viability of 8-day-old cerebellar granule cell cultures in a concentration-dependent fashion, whereas kainate showed a concentration-dependent biphasic effect. A specific inhibitor of nitric oxide synthase, N(G)-nitroarginine (0.5 mM), did not antagonize the neurotrophic effects of NMDA (0.5 mM) or kainate (0.05 mM). The concentration of N(G)-nitroarginine was sufficient to inhibit NMDA or kainate stimulated nitric oxide synthesis and was stable in the culture media throughout the 8-day culture period. Using a specific chemiluminescence detection method, endogenous nitric oxide was directly measured in the headspace gas phase of homogenized cultured cerebellar granule cells, and was not detected when homogenates were incubated with N(G)-nitroarginine (0.5 mM). Furthermore, addition of a nitric oxide precursor, S-nitroso-N-acetylpenicillamine (1-200-mu-M), was not neurotrophic, but rather, was neurotoxic in granule cells. These findings indicate that nitric oxide is not a neurotrophic factor in primary cultures of cerebellar granule cells.