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REEM TAHA, Ido Perlman; Nitric Oxide (NO) affects neuronal adaptation in the turtle retina. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5520.
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Visual adaptation was divided into two major categories; receptoral and neuronal (post-receptoral) adaptation. While receptoral adaptation is well understood, neuronal adaptation mechanisms are still unclear. Nitric Oxide (NO) was suggested to act as a neuromodulator in the vertebrate retina. This study tested the working hypothesis that NO plays a role in neuronal adaptation.
Electroretinogram (ERG) recordings from turtle eyecups were done under different background conditions while raising retinal NO level with L-arginine (Nitric Oxide Synthase (NOS) substrate) or lowering it with L-NAME (a competitive NOS inhibitor). Small-amplitude ERG responses were used to derive sensitivity to light. P-III and P-II components of the ERG were isolated in order to assess the function of photoreceptors (PRs) and ON-center bipolar cells (ON-BCs) respectively. Similar experiments were conducted on horizontal cells by intracellular recordings.
With bright light stimuli, raising NO increased the amplitude of P-III and P-II while lowering NO reduced these responses. In contrast, raising/lowering NO increased/decreased light sensitivity of PRs (P-III), and decreased/increased that of ON-BCs (P-II) respectively. When we measured light sensitivity for dark-adapted state and different background lights, we found that background desensitization of ON-BCs started at lower background levels compared to PRs. This is the manifestation of neuronal adaptation. When NO level was raised, this difference between ON-BCs and PRs was eliminated, while lowering NO made the difference more pronounced, indicating that neuronal adaptation is affected by NO. NO effects upon horizontal cells light sensitivity were similar to those of PRs.
Our data indicate that NO plays a major role in neuronal adaptation. The opposing effects of NO upon light sensitivity of PRs and ON-BCs probably reflect NO-dependent increase in guanylate cyclase activity in the PRs and additional effect of NO on post-synaptic signal transduction pathway in ON-BCs. This latter NO effect needs further studies, but may involve S-nitrosylation, and not activation of guanylate cyclase.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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