Nitric oxide as a regulatory molecule in the processing of the visual stimulus.

Nitric oxide (NO) is a highly reactive gas with considerable diffusion power that is produced pre- and post synaptically in the central nervous system (CNS). In the visual system, it is involved in the processing of the visual information from the retina to superior visual centers. In this review we discuss the main mechanisms through which nitric oxide acts, in physiological levels, on the retina, lateral geniculate nucleus (LGN) and primary visual cortex. In the retina, the cGMP-dependent nitric oxide activity initially amplifies the signal, subsequently increasing the inhibitory activity, suggesting that the signal is "filtered". In the thalamus, on dLGN, neuronal activity is amplified by NO derived from brainstem cholinergic cells, in a cGMP-independent mechanism; the result is the amplification of the signal arriving from retina. Finally, on the visual cortex (V1), NO acts through changes on the cGMP levels, increasing signal detection. These observations suggest that NO works like a filter, modulating the signal along the visual pathways.