The development of NADPH-diaphorase and nitric oxide synthase in the visual system of the cichlid fish, Tilapia mariae

The pattern of NADPH-diaphorase expression was studied in the retina and op tic tectum of the cichlid fish Tilapia mariae during the first developmenta l stages. NADPH-diaphorase activity was seen early, at hatching. In the ret ina a few cell bodies of the retinal inner nuclear layer showed a faint lab eling. Scattered labeled cells were found in the stratum periventriculare o f the optic tectum, while the optic nerve was unlabeled. Two days after hat ching, the number of labeled neurons increased in the inner nuclear layer a nd a few stained cell bodies were also scattered in the ganglion cell layer . Both the inner and outer plexiform layers showed a diffuse staining and t he optic nerve was devoid of labeling. In the optic tectum several positive cells in the periventricular layer, with their dendritic trees extending i n the superficial fibrous layer, were found. In 1-month-old Tilapia, NADPH- diaphorase staining and nitric oxide synthase immunoreactivity were found t o overlap in both the retina and optic tectum, The density of NADPH-diaphor ase labeled neurons in the inner nuclear layer of the retina and in the str atum periventriculare of the optic tectum was largely reduced in comparison with 2 days posthatching embryos. These findings indicated an early and tr ansient production of nitric oxide in the retina and optic tectum of Tilapi a, suggesting a functional role for nitric oxide in the development of visu al structures in aquatic vertebrates. (C) 2001 Elsevier Science Inc.