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C Zhou, RF Dacheux; Inhibitory Currents of Rabbit Off-Cone Bipolar Cell Axon Terminals . Invest. Ophthalmol. Vis. Sci. 2002;43(13):737.
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Purpose: The experimental aim was to characterize the GABA- and glycine-activated currents for the axon terminals of morphologically identified off-cone bipolar cells in the rabbit retina and to determine their differential contribution to the inhibitory input of the cell. Methods: Whole-cell currents were recorded from off-cone bipolar cells in the rabbit retinal slice preparation that was superfused with a Ringer’s solution containing 2 mM cobalt to synaptically isolate the cells. Sulforhodamine B was included in the recording pipettes to label the cells during the whole-cell recordings in order to correlate the cell’s morphology with its physiology. The off-cone bipolar cells were identified based on the distinct stratification of their axon terminals within sublamina-a. GABA and glycine were applied by pressure through a glass pipette positioned above the IPL near the cell. Specific antagonists were applied in the Ringer’s solution as it bathed the retina. Results: In all cone bipolar cells examined, the application of GABA or glycine activated chloride currents that hyperpolarized the cells. Certain subtypes of off-cone bipolar cells had larger glycine-activated currents than GABA-activated currents and visa versa. Furthermore, it did not matter whether GABA mediated the major or minor chloride current, some fraction of this total current involved the activation of GABAa and GABAc receptors. Conclusion: Based on the present knowledge of the rod and cone pathways in the mammalian retina, the major inhibitory synaptic input to off-cone bipolar cell axon terminals is mediated by glycine from the AII amacrine cell. This synaptic input opens channels for chloride ions to hyperpolarize the cell during scotopic light stimulation in order to transfer the rod signals in a way that mimics the photopic action of the cell. Off-cone bipolar cells that are the major receivers of synaptic input from a population of AII amacrine cells possess more glycine receptors and hence display a larger glycine-activated current. The GABAa- and GABAc-activated currents most likely confer inhibitory modulation on the off-cone bipolar cell response.
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