Immunocytochemical localization of neuronal and inducible nitric oxide synthase in the retina of zebrafish, Brachydanio rerio

Several previous studies have revealed the distribution of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) in the retina of various species. However, nothing has been reported on the nNOS and iNOS expression in zebrafish retina, even though it has been used as an effective model for developmental studies. In this study on nNOS and iNOS immunoreactivity (IR) in the zebrafish retina, iNOS-IR signals were detected in the ganglion cell layer (GC), the inner plexiform layer (IP), the outer plexiform layer (OP) and the photoreceptor layer (PR). nNOS-IR signals were also intensely detected in the GC, IP, OP and PR. These signals were very similar to the iNOS-IR signals, except for some minor differences in relative intensities. This could be explained by the speculation that the synthesis of nitric oxide by iNOS may represent a compensatory mechanism in the absence of nNOS. We described for the first time the distribution of nNOS and iNOS-IR cells in zebrafish retina. This could provide the basis for further study on the nNOS and iNOS properties of zebrafish retina.