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W. Shen; GLYCINERGIC INTERPLEXIFORM CELLS REGULATE SPATIAL SENSITIVITY IN THE DISTAL RETINA . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1318.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Glycine feedback from interplexiform cells affects signals in the distal retina by increasing glutamate input to horizontal cells (HCs). This study investigated the function of glycinergic feedback on spatial properties of HCs during dark adaptation. Light to dark adaptation is known to initiate a cascade of molecular events in photoreceptors. Dopaminergic pathways affect communication from photoreceptors during light adaptation. Less is known about the effects of dark adaptation on neural circuits in the distal retina. Methods: Tiger salamander retinal slices were prepared in the dark, then light adapted for 20–30 minutes before whole cell recordings. HCs light responses were studied in the dark after the light adaptation. A 250 nm diameter spot (S–) and full–field (F–) white light stimuli were used to stimulate the center and surround inputs of the HCs. The HCs spatial sensitivity was calculated by measuring the amplitude ratio of a F– to a S– light response (RF/S). Results: After light adaptation, the HC membrane potential gradually depolarized in the dark. The F– light response became greater than the S– light response, indicating an increase in coupling between HCs. The RF/S was around 1.9 under these conditions. Application of 50µM glycine further depolarized HCs and preferentially increased the F– light response. In glycine presence, the RF/S increased to 3.3, suggesting that glycine can modify spatial sensitivity of HCs. 1µM strychnine, a glycine receptor antagonist, suppressed the light responses to both F– and the S– stimuli. The suppression was much pronounced on the F– light stimuli. The RF/S ratio was reduced to 1.2 in the strychnine solution, indicating that endogenous glycine increases surround input during the light to dark adaptation. Dopamine receptor antagonist, SCH23390, could not block the glycine effect on F– light responses. However, GABA receptor antagonist, picrotoxin, blocked 70% of the enhancement of the F– light response, and the RF/S was changed to 1.3, suggesting that blocking GABA input could attenuate surround input and alter HCs spatial sensitivity. Conclusions: The experiments suggest that glycinergic feedback control neural network adaptation. Endogenous glycine alters spatial sensitivity of HCs. It is possible that glycinergic feedback enhances surround GABA input by increasing glutamate input in the dark. The F– light stimuli reduced glutamate input to the HCs, which also reduce surround GABA input. That could be the mechanism by which glycine feedback enhances F– light response in HCs. The concerted effect might be a factor in the visual adjustment from daylight to the dark room condition.
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