The Nitric Oxide (NO) is an essen­tial regulatory molecule in vascular tone and integrity ²⁶. previous studies has supported the role of NO in re­modeling of axons arbors and acts as an activity dependent retrograde sig­nal during the refinement of visual connections ¹⁴> ⁴& ⁵.
Recently, it was found that NO has been implicated in retinal pathogene-sis of retinal vasculogenesis in devel­opment of retinal neovascularization (NV) in ischemic retinopathies ¹¹.
NADPH-diaphorase reaction re­flects NOS activity in the retina and neural tissue ³- ¹⁷-¹- ²- ¹³' ⁶' ¹⁶ - ^{20 & 7}. NADPH-diaphorase staining neu­rons, have been localized with neu­rons in the brain and peripheral tissue
containing nitric oxide synthase, which generates NO. NADPH- dia-phorase staining are localized in the pedunculopontine nucleus and colocalized in amacrine cells of the inner nuclear layer and ganglion cells of the retina ⁷. NADPH-diaphorase has been shown to be a reliable marker of nNOS activity in neuronal tissue ^{16& 1}.
NADPH-diaphorase reaction was, therefore used in this study for localiz­ing the development of retinal vascu-lature as well as any related neuronal