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BA Ekesten, P Gouras; Stimulating Dark Adapted Opsins In Light Adapted Cones . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3752.
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Purpose: The common house mouse has two cone opsins, one with maximal absorbtion in the ultraviolet (UV) and one in the green part of the spectrum. Some cones co-express both opsins. UV stimuli are supressed by long wavelength adapting lights not absorbed by UV cone opsin. We have studied whether this suppression occurs in the cones or is due to postsynaptic interactions. Methods: The retina from normal C57B mice in a superfused eyecup preparation was examined. ERGs from these retinas were obtained in response to UV and green flashes. A 750 cd/m2 yellow background light was used to light adapt the retina. Responses were amplified and averaged by a computerized data acquisition system (PowerLab, AD Instruments, CA). Posynaptic transmission was blocked adding 2.5 mM kynurenic acid (KYN) and 1.5 mM aminophosphonobutyric acid (APB) to the superfusion fluid. Results: ERG responses to UV and green flashes could be obtained from the eyecups in the chamber for up to 10 hours. The steady yellow background eliminated responses to green stimuli and greatly reduced UV cone responses for at least 8-10 minutes. UV responses recovered in the yellow light within 10 minutes. KYN and APB blocked postsynaptic transmission resulting in a negative photoreceptor response. The addition of KYN and APB did not prevent the suppression or the recovery of the UV responses in presence of the yellow background but the responses to green flashes were completely eliminated. Conclusion: Postsynaptic interaction through second order retinal neurons is not involved in the supression of the UV response by yellow background light. The interaction between the UV and green mechanisms must occur within the same cone implying that cone desensitization occurs before transducin activation.
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