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M.J. Roux, S. Picaud, J.A. Sahel, Y. Schwab; Gaba Transmission in the Mice Outer Retina: Receptors But No Ligand . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3450.
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Purpose: To determine if mouse cone photoreceptors express functional GABA receptors, and what may be the role of GABA in the mammalian outer retina. Methods: Localization of various elements involved in GABAergic transmission (GAD, GABA and other inhibitory amino–acids, the vesicular transporter VIAAT, synaptic proteins and GABA receptors) were determined in three common inbred mice strains using immunohistochemistry. Whole–cell patch–clamp recordings were obtained from rods and cones on mouse retinal slices. Cells were identified according to their morphology, revealed by the Alexa dye added to the recording pipette solution. Results: Major differences were found for GAD and GABA labeling in the outer retina from the different strains. Horizontal cells were immuno–negative for GAD65/67 and GABA in C57BL/6J mice, but positive in Balb/c mice. Surprisingly, VIAAT was highly expressed in horizontal cell processes contacting rod photoreceptors, while it could hardly be detected in processes contacting cone photoreceptors. GABA–positive interplexiform cells were found in all strains. Cones (but not rods) recorded on retinal slices responded to GABA applied on their pedicle with a current reversing at ECl, that was nearly fully blocked by bicuculline. Conclusions: Though the source of their endogenous ligand remained enigmatic, functional GABA receptors were expressed at mouse cone terminals.
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