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S. Lee, Z.J. Zhou; Directionally Asymmetric Synaptic Inputs to Starburst Amacrine Cell Dendrites During Light Stimulation . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2337.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It has been reported that the starburst amacrine cell (SAC) shows directionally selective Ca2+ responses at its distal dendrites. However, the mechanisms underlying the direction–selective Ca2+ responses are largely unclear. This study sought to determine whether synaptic inputs to SAC are asymmetric and, if they are so, which circuits are responsible for the asymmetry. Methods: Using specific patterns of light stimulation and pharmacological agents, we isolated the excitatory and inhibitory synaptic inputs to SAC in whole–mount retinae of rabbits aged P15 to P28. Dual and single patch–clamp techniques were used to further dissect the underlying presynaptic circuits. Results: Dual patch–clamp recording from neighboring SAC pairs revealed Ca2+–dependent GABA release at the distal dendrites. GABA–A receptor mediated synaptic transmission was detected between two overlapping SACs, regardless of the relative distance between the two cells, although the amplitude of peak GABA–A currents decreased with the cell–cell distance. Under stationary light stimulation, the excitatory input to a SAC was localized within the dendritic field of the cell, while the inhibitory inputs were evoked both within and beyond the dendritic field. The extent of the inhibitory surround reached a distance equivalent to the radius of a SAC (∼150 micron). Remarkably, the GABA–mediated inhibitory input was asymmetric and appeared ahead of the excitatory input when the light stimulus moved centripetally. The spatiotemperal properties of this inhibitory input were characterized and compared with those of the excitatory input, which also showed radial asymmetry. Conclusions: SACs make GABA–A synapses onto neighboring SACs, forming an inhibitory GABAergic network. This network creates an asymmetric inhibitory receptive field and a direct leading inhibition of starburst distal dendrites during centripetal motion stimulation.
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