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C. Mora–Ferrer, R.B. Schmidt–Hoffmann, B. Weirich; Glycinergic Mechanisms for Chromatic and Achromatic Retinal Coding Investigated in Behavioral Experiments . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5383.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the contribution of inhibitory mechanisms to the retinal coding for direction and color, i.e. both chromatic and achromatic coding mechanisms, in behavioral experiments.
Directional coding was investigated with the optomotor response behavior using sinewave patterns (4 cm/cycle) of varied contrasts (10, 20, 40, 60, and 80%) and 3 or 10 RPM pattern velocity. The chromatic coding properties were investigated by measuring the wavelength discrimination ability with a two–choice forced procedure (e.g. Mora–Ferrer & Neumeyer, 1996). All experiments were performed under photopic illumination conditions and animals exhibited stable responses. Drugs injected, into the vitreous of both eyes, were strychnine (glycine antagonist; directional and color coding; 0.05–5 microM), bicuculline (GABAa–receptor antagonist; directional coding; 10 microM), and bicuculline and strychnine (directional coding; 10/1 microM). All experiments were approved by state and university councils and are in accordance with ARVO guidelines.
The contrast–dependent optomotor response is velocity independent and similar for 40–80% contrast. A threshold contrast of approx. 25% can be defined. Strychnine had little to no effect on full–field motion behavior using 40–80% and 10% contrast stimuli and significantly elevated the behavioral response to a 20% contrast stimulus by about 60%. Bicuculline significantly reduced the optomotor response by 40–50% for 20–80% stimulus contrast and had no effect for 10% stimulus contrast. The combined blockade of GABAa– and glycine–receptors resulted in an significantly stronger reduction of the optomotor response if compared to bicuculline alone for all contrasts tested except 10%. Wavelength discrimination was not affected by strychnine.
Blockade of glycine receptors alone does not seem to have any major effect on goldfish achromatic or chromatic coding mechanisms. Based on the full–field motion detection data, it could be argued that glycine is involved in a narrow range sensitivity–control mechanism. The effect of both GABAa– and glycine–receptor blockade in the full–field motion perception experiment superseded the GABAa–receptor blockade significantly. This indicates either an interaction of glycine and GABA at GABA/glycine binding sites or some synergistic inhibitory mechanism. Whether similar mechanisms, i.e. synergistic inhibition and/or control of sensitivity increase, also exists for chromatic coding mechanisms remains to be investigated.
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