Developmental expression of nitric oxide synthase isoform I and III in chick retina.

During our studies on the multiple possible functions of nitric oxide (NO) in chick retinal development and physiology, we have demonstrated the presence and the activity of NO synthase (NOS-I and III) in certain neuronal populations (photoreceptors, amacrine cells in the inner nuclear and ganglion cells) and also in synaptic-rich regions in the developing chick retina. Both enzymes, detected by nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase, immunohistochemistry and Western blotting, appeared between embryonic days 6 and 12, and followed a spatial and temporal pattern of expression which correlated with the differentiation of the neuronal layers. Evaluation of the conversion of [3H]-labeled arginine to [3H]-citrulline, confirmed the presence of a calcium-dependent NOS activity in the cytosolic and particulate retinal extracts during the development. This pattern of NOS expression suggests that the regulated release of NO during key phases of development might be one mechanism involved in the regulation of retinal differentiation.