Imaging of nitric oxide in the retina

Abstract

Nitric oxide (NO) is the most widespread signaling molecule found in the retina in that it can be made by every retinal cell type. NO is able to influence a wide variety of synaptic mechanisms ranging from increasing or decreasing neurotransmitter release to the modulation of gap junction conductivity. Although biochemical methods can analyze overall levels of NO, such methods cannot indicate the specific cell types involved. In the last few years, fluorescent imaging methods utilizing diaminofluorescein have allowed the real-time visualization of neurochemically or light stimulated NO-induced fluorescence (NO-IF) in specific retinal cells. Recent experiments have shown that this NO-IF can be stabilized using paraformaldehyde fixation. This aldehyde stabilization has allowed the imaging of NO production in the dark and in response to light, as well as the neurochemical modulation of light stimulated NO production. The results of these studies indicate that NO is not always freely diffusible and that NO is largely retained in many cells which make it. The NO production in retina is highly damped in that in the absence of stimulation, the endogenous levels of NO production are extremely low. Finally, different neurochemical or light stimulation protocols activate NO production in specific cells and subcellular compartments. Therefore, although the NO signaling is widespread in retina, it is very selectively activated and has different functions in specific retinal cell types. The use of NO imaging will continue to play a critical role in future studies of the function of NO in retina and other neural systems.

Nitrosative Stress in the Rat Retina at the Onset of Streptozotocin-Induced Diabetes

“…Since we determined cGMP levels in the whole retina, our results might suggest that changes in cGMP occurred in different cell populations, which may have differed in their synthesis and degradation activities. Although several groups have concluded that the NO-cGMP pathway modulates the neural circuitry in the inner retina [40-42], the most pronounced effect of dark adaptation in the rat retina is an enhancement of NADPH-d activity in Müller cells. Moreover, Müller cells were reported to be immunonegative for sGC [22], which may explain our results.…”

Role of acetylcholine in nitric oxide production in the salamander retina

“…In future studies we will directly localize NO increases in response to mAChR activation using NO imaging (Eldred and Blute, 2005). Given the potential interactions with the both glycinergic and GABAergic transmitter systems and the widespread localization of these receptors in both the inner and outer retina, mAChR-stimulated NO production will certainly have many physiological functions in visual processing.…”

“…Since it is a gas it is potentially capable of functioning as an intercellular messenger to affect cellular metabolism, although imaging studies suggest that diffusion of NO from cells is much more limited and controlled than had been previously thought (Eldred and Blute, 2005). NO acts through several different biochemical mechanisms to effect downstream targets, including S-nitrosylation (Ignarro and Gruetter, 1980), ADP ribosylation (Brune and Lapetina, 1989), and interaction with heme groups of many proteins (Craven and DeRubertis, 1978).…”

Ambient Light Regulates Sodium Channel Activity to Dynamically Control Retinal Signaling

“…However, our preliminary experiments showed that the muscarinic receptor antagonist atropine did not alter the effects of bright illumination on sodium currents, ruling out this possibility. Nitric oxide (NO) may also be released by light and/or dopamine application in the retina (Eldred and Blute, 2005;Sekaran et al, 2005) and could have modulated the bipolar cell sodium currents. However, in other parts of the CNS, NO increases voltage-gated sodium currents (Hammarstrom and Gage, 1999), which is opposite to our results.…”