Localization Of Zinc In The Carp Retina: A Light-and Electron-microscopic Study

Many lines of evidence suggest that zinc may play an important neuromodulatory role in the CNS, including retina. In this work, localization of zinc in the carp retina was studied using the silver amplification method, by light and electron microscopy. Reaction products (silver grains) were widely distributed throughout the retina, including photoreceptors, the outer and inner nuclear layers (ONL and INL), the ganglion cell layer (GCL), as well as in both outer and inner plexiform layers (OPL and IPL) . Generally, staining for zinc was stronger in the outer retina than in the inner retina, and grains were aggregated with the greatest density in the OPL and the outer limiting membrane (OLM). Silver precipitates were detected in the inner segments but not the outer segments of photoreceptors. At the ultrastructural level, zinc was localized to myoid regions, mitochondria in the inner segments of photoreceptors, internuclear space and nuclei of photoreceptors. Silver grains were found in the terminals of photoreceptors: cone pedicles and rod spherules as well as in processes of horizontal cells in the OPL. In the INL and GCL, zinc was associated with the Golgi apparatus and / or the cytoplasm. The presence of zinc in the terminals of photoreceptors suggests that zinc might be released from photoreceptor terminals and play modulatory roles in the retina.