Purpose: To investigate the neurotoxic outcome in the rat retina exposed to nitric oxide (NO) released from an NO donor and to evaluate the effects of neurotrophic factors on the survival of NO-damaged retinal cells.
Methods: An NO releasing compound, N-ethyl-2-(1-ethyl-2-hydroxy-2-nitrosohydrazino) ethanamine (NOC 12), was intravitreously injected into a rat's right eye. The influences of NOC 12 on retinal neurons and the neuroprotective effects of ciliary neurotrophic factor (CNTF) or brain-derived neurotrophic factor (BDNF) on NOC 12-mediated damage were estimated by counting cells in the ganglion cell layer (GCL) and by measuring the thickness of retinal layers. The exact count of retinal ganglion cells (RGCs) was also confirmed by means of retrograde labeling with a fluorescent tracer.
Results: Morphometric analyses of retinal damage in the NOC 12-exposed eyes demonstrated a significant and dose-dependent decrease in cell density in the GCL and a reduction in thickness of the inner plexiform layer and inner nuclear layer, but not of the outer nuclear layer. TdT-dUTP terminal nick-end labeling of retinal sections after intravitreous injection of NOC 12 demonstrated that NO could trigger apoptotic cell death. The counting of the RGCs labeled with a fluorescent tracer suggested that a decrease in GCL cell density induced by NOC 12 reflects a loss in RGCs. Treatment with CNTF (1 microg) or BDNF (1 microg) before the intravitreous injection of NOC 12 (400 nmol) demonstrated that these trophic factors have protective effects against NO-induced neuronal cell death in the retina.
Conclusions: Exogenous NO induces retinal neurotoxicity, suggesting that NO plays a pathogenic role in degenerative retinal diseases. BDNF and CNTF protect retinal neurons from NO-mediated neurotoxicity.