Nitric oxide-mediated death of cultured neonatal retinal ganglion cells: neuroprotective properties of glutamate and chondroitin sulfate proteoglycan.

The release of nitric oxide and stimulation of glutamate receptors by excitatory amino acids has been linked to neuronal degeneration and toxicity. In the rat retina approximately 60% of retinal ganglion cells (RGCs) die during the first postnatal week. In this study we examined the effects of nitric oxide synthase blockers and glutamate on the survival of neonatal RGCs in vitro over a 16 h assay period. Less than 10% of P1 RGCs survived in serum free defined media alone (control), however survival was increased, in a dose-dependent manner, when L-glutamate (10 microM-10 mM) was added to the media; a maximum of 70% of RGCs could be maintained with the addition of 5 mM glutamate. This effect was blocked by the NMDA and non-NMDA receptor blockers APV and DNQX and was age dependent; the survival of RGCs from P5 but not P7 rats was enhanced by the addition of glutamate even in high calcium concentrations (10 mM). When the nitric oxide synthase blockers L-NAME (5 mM) or haemoglobin (25 microM) were added to the culture media, up to 61% of P1 RGCs survived. The addition of the 480 kDa chondroitin sulfate proteoglycan (SCCP) previously shown to enhance RGC survival in vivo and in vitro, potentiated the action of glutamate and L-NAME and increased RGC survival to over 90% with almost all RGCs expressing a profusion of processes. These results suggest that the release of nitric oxide and glutamate by cells within the retina may contribute to the regulation of RGC numbers in vivo during development.