Neuronal and glial cell types revealed by NADPH-diaphorase histochemistry in the retina of a teleost fish, the grass goby (Zosterisessor ophiocephalus, Perciformes, Gobiidae)

The grass goby is a mud-burrowing fish with a rich retinal vasculature appr opriate to its hypoxic habitat. NADPH-diaphorase histochemistry was perform ed on retinal sections and wholemounts to reveal cells that contain nitric oxide synthase and so may be presumed to synthesise nitric oxide, a gaseous intercellular messenger with many roles including vasodilation. Structures that were consistently stained by this method included cone ellipsoids, ho rizontal cells, Muller cells and their processes, large displaced ganglion cells in the inner nuclear layer (identified by their axons), large interst itial ganglion cells in the inner plexiform layer, and capillary endothelia l cells. In wholemounts, horizontal cells were seen to form a regular patte rn, contacting each other at their dendritic terminals. Some cells in the g anglion cell layer were weakly stained, but stained bipolar and amacrine ce lls were not seen. The diaphorase-positive large gan ganglion cells all for med large, sparsely branched dendritic trees, arborizing near the scleral b order of the inner plexiform layer. The displaced and interstitial cells se emed to belong to distinct morphological types, the interstitial cells havi ng smaller somata and trees. Analysis of their spatial distributions in one representative retina confirmed this: the displaced cells formed a highly regular mosaic with a mean spacing (nearest-neighbour distance) of 303 mu m , whereas the interstitial cells formed a separate mosaic, almost as regula r but with a smaller mean spacing of 193 mu m, rising to 217 mu m in a samp le that excluded the area retinae temporalis. Spatial correlogram analysis showed that these two mosaics were spatially independent. Nitric oxide prob ably has many roles in the retina. The presence of its synthetic enzyme in Muller cells, which communicate with retinal blood vessels, is consistent w ith a role in the control of retinal blood flow. Its function in large, mos aic-forming retinal ganglion cells is unknown.