Localization of nitric oxide synthase in the goldfish retina

The localization of nitric oxide synthase and NADPH-diaphorase was studied in the goldfish retina by means of immunohistochemistry or tetrazolium salt technique. Nitric oxide synthase was found in some small neurons of the inner nuclear layer and in large neurons of the ganglion cell layer. The reaction product was localized in the outer plexiform layer and a diffuse labeling was also observed in the inner plexiform layer. In addition to the outer segments of photoreceptors, NADPH-diaphorase labeled several neurons of the inner nuclear layer and some neurons scattered in the ganglion cell layer. Both outer and inner plexiform layers were labeled. Ultrastructural observations showed that the reaction product was found to be bound to the endoplasmic membranes of positive neurons. In the outer plexiform layer the formazan precipitate labeled prevailingly the presynaptic terminals of rods and cones, in the inner plexiform layer both pre- and postsynaptic profiles showed the reaction product.