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J. Pang, F. Gao, D.E. Bramblett, D.L. Paul, S.M. Wu; Bipolar Cell Inputs to AII Amacrine Cells in Wild–Type Mice and in Mice Lacking Either Connexin36 or Rod Bipolar Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2279.
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© ARVO (1962-2015); The Authors (2016-present)
The objective is to determine the relative rod /cone bipolar cell synaptic inputs mediating the excitatory light–evoked currents in mammalian AII amacrine cells.
AII amacrine cells were recorded in living retinal slices from wild–type, connexin36 knockout (Cx36–/–), or Bhlhb4 knockout (Bhlhb4–/–, lacking rod bipolar cells) mice with the whole–cell voltage clamp technique and the cell morphology was revealed by Lucifer yellow fluorescence.
In the wild–type mouse retina, application of 5 µM L–AP4 suppressed light–evoked currents (ΔI) at all holding voltages, suggesting most light–elicited synaptic inputs are mediated by ON bipolar cells. In the presence of 40 µM DNQX, which blocks ionotropic glutamate receptors in the photoreceptor–Off bipolar cell and bipolar cell output synapses, AII amacrine cells exhibited robust light–evoked currents (ΔIDNQX), consistent with the idea that a substantial portion of the AII amacrine cell light response results from cone ON bipolar cell input through electrical synapses. We also studied the sensitivity of AII amacrine cell responses to 500nm light steps in Cx36–/– and Bhlhb4–/– retinas, and found that AII light sensitivity in the Bhlhb4–/– retina resembles that of the ΔIDNQX in the wild–type and that AII sensitivity in the Cx36–/– retina resembles that of the ΔIControl – ΔIDNQX in the wild–type. Light sensitivity of rod bipolar cells in Cx36–/– retinas and of cone ON bipolar cells in Bhlhb4–/– retina was similar to wild–type controls.
AII amacrine cell light responses in the mouse retina are mediated by a DNQX–sensitive, rod bipolar cell–output chemical synapse and a Cx36–mediated electrical synapse, and the two inputs sum linearly in AII amacrine cells. Cx36–/– and Bhlhb4–/– mice are useful animal models for dissecting functional circuitry in the mammalian retina.
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