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The oxidative damage induced by continuous illumination (CI) of the retina produces the degeneration of photoreceptors. In previous studies we observed an increase of NO signal in the exposed retinas after 2 hours peaking at 24 hours of CI by using Electron Paramagnetic Resonance. Western blot also showed a peak of iNOS expression in the retinas after 24hs of CI. Electron microscopy showed apoptotic nuclei in outer nuclear layer after 2 and 5 days of CI. We think that NO may be one of the free radicals involved in the oxidative stress induced by CI, so its increase could be involved in the observed photoreceptor degeneration. In order to study the oxidative effect of NO in retinal tissue we determined the nitration of proteins by immunocytochemistry and Western blot. Sprague Dawley rats were continuously illuminated (CI) with white light (12,000 lux) for 24hs, 48hs, 5 and 7 days while control rats (CTL) were maintained at light/dark cycles of 12/12 h. The eyes of CTL and CI rats were fixed in a solution containing 4 % paraformaldehyde. The sections were processed with the PAP immunocytochemical technique using a nitrotyrosine (Ntyr) antibody generously provided by J. Rodrigo, Inst. Cajal, Madrid. Other eyes of CTL and CI rats were processed by Western blot analysis. Retinal homogenates (15 ìg) were separated by SDS-PAGE and transferred to PVDF membranes. Membranes were blocked and incubated with anti rabbit nitrotyrosine (1:250) for 120 min. Then, membranes were washed and incubated with peroxidase-labeled goat anti-rabbit IgG (1:2000) for 90 min and visualized using DAB. Densitometric analysis was performed using Image J. Densitometry analyses. Nitrotyrosine immunoreactivity was observed in Inner Nuclear Layer (INL) and Ganglion Cell Layer (GCL) in CTL rats. After CI a change of nitrotyrosine immunostaining pattern was detected. Ntyr immunoreactivity was observed in Outer Nuclear Layer (ONL) as well as in INL and GCL. Western blots analysis showed multiple bands of nitrotyrosine proteins. The band profile differed among control, 5 and 7 days of illumination. The band of 29KD was present in CTL, 24 and 48hs lanes and disappeared afterwards while 120KD band appeared in 48hs, 5 and 7 days lanes with increasing intensity. The observed results showed a change of nitration patterns in IC rats both by immunocytochemistry and Western blot. It may be that the increase of NO nitrates tyrosine residues in proteins which alter their structures and functions leading, probably with other free radicals, to the damage of the retina. Nitrotyrosine immunoreactivity was observed in Inner Nuclear Layer (INL) and Ganglion Cell Layer (GCL) in CTL rats. After CI a change of nitrotyrosine immunostaining pattern was detected. Ntyr immunoreactivity was observed in Outer Nuclear Layer (ONL) as well as in INL and GCL. Western blots analysis showed multiple bands of nitrotyrosine proteins. The band profile differed among control, 5 and 7 days of illumination. The band of 29KD was present in CTL, 24 and 48hs lanes and disappeared afterwards while 120KD band appeared in 48hs, 5 and 7 days lanes with increasing intensity. The observed results showed a change of nitration patterns in IC rats both by immunocytochemistry and Western blot. It may be that the increase of NO nitrates tyrosine residues in proteins which alter their structures and functions leading, probably with other free radicals, to the damage of the retina. Sprague Dawley rats were continuously illuminated (CI) with white light (12,000 lux) for 24hs, 48hs, 5 and 7 days while control rats (CTL) were maintained at light/dark cycles of 12/12 h. The eyes of CTL and CI rats were fixed in a solution containing 4 % paraformaldehyde. The sections were processed with the PAP immunocytochemical technique using a nitrotyrosine (Ntyr) antibody generously provided by J. Rodrigo, Inst. Cajal, Madrid. Other eyes of CTL and CI rats were processed by Western blot analysis. Retinal homogenates (15 ìg) were separated by SDS-PAGE and transferred to PVDF membranes. Membranes were blocked and incubated with anti rabbit nitrotyrosine (1:250) for 120 min. Then, membranes were washed and incubated with peroxidase-labeled goat anti-rabbit IgG (1:2000) for 90 min and visualized using DAB. Densitometric analysis was performed using Image J. Densitometry analyses. Nitrotyrosine immunoreactivity was observed in Inner Nuclear Layer (INL) and Ganglion Cell Layer (GCL) in CTL rats. After CI a change of nitrotyrosine immunostaining pattern was detected. Ntyr immunoreactivity was observed in Outer Nuclear Layer (ONL) as well as in INL and GCL. Western blots analysis showed multiple bands of nitrotyrosine proteins. The band profile differed among control, 5 and 7 days of illumination. The band of 29KD was present in CTL, 24 and 48hs lanes and disappeared afterwards while 120KD band appeared in 48hs, 5 and 7 days lanes with increasing intensity. The observed results showed a change of nitration patterns in IC rats both by immunocytochemistry and Western blot. It may be that the increase of NO nitrates tyrosine residues in proteins which alter their structures and functions leading, probably with other free radicals, to the damage of the retina. Nitrotyrosine immunoreactivity was observed in Inner Nuclear Layer (INL) and Ganglion Cell Layer (GCL) in CTL rats. After CI a change of nitrotyrosine immunostaining pattern was detected. Ntyr immunoreactivity was observed in Outer Nuclear Layer (ONL) as well as in INL and GCL. Western blots analysis showed multiple bands of nitrotyrosine proteins. The band profile differed among control, 5 and 7 days of illumination. The band of 29KD was present in CTL, 24 and 48hs lanes and disappeared afterwards while 120KD band appeared in 48hs, 5 and 7 days lanes with increasing intensity. The observed results showed a change of nitration patterns in IC rats both by immunocytochemistry and Western blot. It may be that the increase of NO nitrates tyrosine residues in proteins which alter their structures and functions leading, probably with other free radicals, to the damage of the retina. Sprague Dawley rats were continuously illuminated (CI) with white light (12,000 lux) for 24hs, 48hs, 5 and 7 days while control rats (CTL) were maintained at light/dark cycles of 12/12 h. The eyes of CTL and CI rats were fixed in a solution containing 4 % paraformaldehyde. The sections were processed with the PAP immunocytochemical technique using a nitrotyrosine (Ntyr) antibody generously provided by J. Rodrigo, Inst. Cajal, Madrid. Other eyes of CTL and CI rats were processed by Western blot analysis. Retinal homogenates (15 ìg) were separated by SDS-PAGE and transferred to PVDF membranes. Membranes were blocked and incubated with anti rabbit nitrotyrosine (1:250) for 120 min. Then, membranes were washed and incubated with peroxidase-labeled goat anti-rabbit IgG (1:2000) for 90 min and visualized using DAB. Densitometric analysis was performed using Image J. Densitometry analyses. Nitrotyrosine immunoreactivity was observed in Inner Nuclear Layer (INL) and Ganglion Cell Layer (GCL) in CTL rats. After CI a change of nitrotyrosine immunostaining pattern was detected. Ntyr immunoreactivity was observed in Outer Nuclear Layer (ONL) as well as in INL and GCL. Western blots analysis showed multiple bands of nitrotyrosine proteins. The band profile differed among control, 5 and 7 days of illumination. The band of 29KD was present in CTL, 24 and 48hs lanes and disappeared afterwards while 120KD band appeared in 48hs, 5 and 7 days lanes with increasing intensity. The observed results showed a change of nitration patterns in IC rats both by immunocytochemistry and Western blot. It may be that the increase of NO nitrates tyrosine residues in proteins which alter their structures and functions leading, probably with other free radicals, to the damage of the retina. Nitrotyrosine immunoreactivity was observed in Inner Nuclear Layer (INL) and Ganglion Cell Layer (GCL) in CTL rats. After CI a change of nitrotyrosine immunostaining pattern was detected. Ntyr immunoreactivity was observed in Outer Nuclear Layer (ONL) as well as in INL and GCL. Western blots analysis showed multiple bands of nitrotyrosine proteins. The band profile differed among control, 5 and 7 days of illumination. The band of 29KD was present in CTL, 24 and 48hs lanes and disappeared afterwards while 120KD band appeared in 48hs, 5 and 7 days lanes with increasing intensity. The observed results showed a change of nitration patterns in IC rats both by immunocytochemistry and Western blot. It may be that the increase of NO nitrates tyrosine residues in proteins which alter their structures and functions leading, probably with other free radicals, to the damage of the retina. Nitrotyrosine immunoreactivity was observed in Inner Nuclear Layer (INL) and Ganglion Cell Layer (GCL) in CTL rats. After CI a change of nitrotyrosine immunostaining pattern was detected. Ntyr immunoreactivity was observed in Outer Nuclear Layer (ONL) as well as in INL and GCL. Western blots analysis showed multiple bands of nitrotyrosine proteins. The band profile differed among control, 5 and 7 days of illumination. The band of 29KD was present in CTL, 24 and 48hs lanes and disappeared afterwards while 120KD band appeared in 48hs, 5 and 7 days lanes with increasing intensity. The observed results showed a change of nitration patterns in IC rats both by immunocytochemistry and Western blot. It may be that the increase of NO nitrates tyrosine residues in proteins which alter their structures and functions leading, probably with other free radicals, to the damage of the retina.