HISTOCHEMISTRY OF NADPH-DIAPHORASE - A MARKER FOR NEURONAL NITRIC-OXIDE SYNTHASE - IN THE CARP RETINA

The nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase his tochemical technique was used as a marker to assess the distribution o f nitric oxide synthase activity in the carp retina. NADPH-diaphorase activity was found to be present in photoreceptors (rods and cones), h orizontal cells, amacrine cells, bipolar cells, Muller cells and gangl ion cells. Staining was most prominent in the photoreceptor ellipsoids bur was not confined to any particular subtype. The density of the st aining within the inner plexiform layer (IPL) was determined by image analysis. There was a broad peak of activity in each sublamina of the IPL, but sublamina h appeared to be relatively more heavily stained. T he results taken together suggest that the nitric oxide signalling sys tem could have a broader involvement in retinal function than previous ly thought. Furthermore, nitric oxide may have a novel mode of action in the retina whereby it could be effective on cells (photoreceptors) that also synthesize it.