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SI Fried, TA Münch, FS Werblin; Directionally Selective Ganglion Cells Receive Directionally Selective Excitatory and Inhibitory Input . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2979.
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Purpose:Our goal was to characterize the synaptic inputs to directionally selective (DS) ganglion cells and to determine how these inputs are integrated to form the final DS output. Methods:By patch clamping at the appropriate reversal potentials for synaptic inputs in the flat mount rabbit retina, we were able to isolate both the excitatory and inhibitory inputs to DS cells. Moving stimuli, in either the preferred or null directions were presented to DS cells. The stimuli were either contained within the dendritic field of the DS cell or limited to areas outside the dendritic field on either the preferred or null sides. Pharmacological blockers were used to further separate and identify the different synaptic components. Results:Asymmetries in Magnitude. The magnitude of excitation was always stronger for movement in the preferred direction; the magnitude of inhibition was always stronger for movement in the null direction. SR-95531, a GABA-A antagonist, eliminated inhibitory input to the cell but did not affect excitatory input. Asymmetries in Space. The spatial profiles of excitatory and inhibitory inputs extended beyond the dendritic field of the DS cell: the excitatory profile was shifted towards the preferred side and the inhibitory profile was shifted towards the null side. Stimuli completely outside the dendritic field on the preferred side generated primarily excitatory input that was stronger for preferred direction movements. Stimuli outside the dendritic field on the null side generated primarily inhibitory input that was stronger for null direction movements. Conclusion:DS cells receive excitatory and inhibitory inputs that are asymmetrical in magnitude and are oriented along the same preferred and null directions as the spiking output. The directional asymmetry extends beyond the dendritic field of the DS cell, excitation predominating on the preferred side, inhibition predominating on the null side. This suggests that directional selectivity is generated in neural elements presynaptic to, and having similar directional orientation as the DS cells that they drive.
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