Light-adaptive role of nitric oxide in the outer retina of lower vertebrates: a brief review

The role of nitric oxide (NO) as a novel neurochemical mechanism controllin g light adaptation of the outer retina is discussed by considering mainly p ublished results. The emphasis is on the retinae of fishes and amphibia, bu t some data from the mammalian (rabbit) retinae have also been included for completeness. In the fish retina, application of NO donors in the dark cau sed light-adaptive photomechanical movements of cones. The normal effect of light adaptation in inducing cone contractions was suppressed by pretreatm ent of retinae with all NO scavenger. NO donors modulated horizontal cell a ctivity by uncoupling the cells' lateral gap junctional interconnections an d enhancing negative feedback to cones, again consistent with a light-adapt ive role of NO. Direct evidence for light adaptation-induced release of NO has been obtained in fish (carp) and rabbit retinae. The results strongly s uggest that control of retinal light adaptation is. under multiple neuroche mical control, with NO and dopamine having an interactive role.