Development of nitric oxide neurons in the chick embryo retina

Nitric oxide (NO) is a gas involved in neurotransmission in the central ner vous system (CNS) and in vertebrate retinas. This paper describes five type s of nitrergic neurons in developing and adult chick retina using the nicot inamide adenine dinucleotide phosphate diaphorase (NADPHd) reaction. Three of them, nitrergic types 1, 2 and 3, were observed in the inner nuclear lay er, while nitrergic type 4 was observed in the ganglion cell layer; nitrerg ic type 5 were the retinal photoreceptors. Cell processes formed four nitre rgic networks, which could be observed in the inner plexiform layer (IPL), at sublayers 1, 3a, 3b and 4. Another nitrergic network was observed in the outer plexiform layer (OPL). From hatching, the dendritic branches were co mpletely developed in the IPL and in the OPL, forming the mentioned network s. Current evidence suggests that NO is coexpressed with other neurotransmi tters in neurons of the CNS. Double-staining procedures, using NADPHd and 5 HT immunohistochemistry in chicken retina, in a sequential or in an alterna tive manner, did not reveal the coexistence of these two neurotransmitters in the same neurons, but their networks matched in sublayers 1 and 4 of the IPL. (C) 2000 Published by Elsevier Science B.V.. All rights reserved.