The immunocytochemical localization of neuronal nitric oxide synthase in the developing rat retina

The localization of nitric oxide synthase (NOS) was investigated in the dev eloping rat retina by immunocytochemistry and western blot analysis, using an antiserum directed against neuronal NOS. NOS-labeled cells were first de tected at postnatal day 5 (P5) in the inner row of the neuroblastic layer. These cells were considered to correspond to the type 1 cell of the adult r at retina. Type 2 cells, characterized by a small soma and weak immunoreact ivity, and a class of displaced amacrine cells were detected at P9 and P7, respectively. By P14 or P15, the time of eye opening, NOS immunoreactivity appeared in some bipolar cells. NOS was first expressed at the protein leve l at P9. Thereafter, quantitative evaluation by immunoblotting confirmed th at the intensity of the immunoreactive bands increased abruptly, reaching t he same Value as is found in the adult retina at P21. Our results demonstra te that differentiation of NOS-labeled cells follows a discrete development al pattern and is most active during the 2nd postnatal period in the rat re tina.