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A. V. Dmitriev, K. E. Gavrikov, S. C. Mangel; Spatial Relationship Between the Receptive Field and Dendritic Tree of Starburst Amacrine Cells. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1028.
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Starburst amacrine cells (SAC) have receptive fields (RF) that are about 4-5 times larger in diameter than their dendritic trees (DTs). Light stimulation of the RF center strongly depolarizes displaced SACs due to glutamate input from ON-bipolar cells. The SAC RF surround maps onto the DT with GABA inputs from neighboring SACs, and possibly other ACs. Stationary light stimulation of the RF surround hyperpolarizes SACs, but the polarity of SAC responses to stimuli that move through the surround depends on the direction of motion: centrifugal motion depolarizes SACs, but centripetal motion hyperpolarizes them. This robust direction selective (DS) SAC light response is mediated in part by the Cl- cotransporter NKCC2-containing, proximal DT and KCC2-containing, distal DT, which GABA depolarizes and hyperpolarizes, respectively (Gavrikov et al., 2006). We examined the RF structure of SACs to investigate how SAC DS is generated.
We obtained whole-cell patch-clamp recordings of displaced rabbit SAC responses evoked by computer-generated stationary and moving light stimuli. Computational modeling of the RF-DT relationship was performed.
Voltage clamp analysis of SAC responses to stationary and moving light stimuli and computational analysis suggest that the SAC RF can be divided into at least 4 distinct zones: 1) the center which is similar in size to the DT, 2) the near surround, which is just outside the RF center, extending 1 to 2 DT radii from the soma, 3) the intermediate surround, which extends 2 to 3 DT radii from the soma, and 4) the far surround, which is located more than 3 DT radii from the soma. The near and intermediate surrounds are the two RF zones primarily responsible for SAC DS, because sequential stimulation of these zones in the centrifugal and centripetal directions depolarizes and hyperpolarizes SACs, respectively. Each SAC receives only hyperpolarizing GABA input from other SACs whose DTs are located in its intermediate surround, because these SACs provide GABA input only to the KCC2-containing distal DT. Each SAC receives both hyper- and depolarizing GABA input from SACs whose DTs are located mostly in its near surround, because these SACs provide GABA input to the distal and proximal DT.
These results suggest that the near and intermediate surrounds preferentially map onto the NKCC2-containing, proximal and KCC2-containing, distal compartments, respectively, of SAC dendrites. The ability of SACs to distinguish between different directions of stimulus motion is achieved in part because GABA input from the near and intermediate surrounds differentially modulates the effect of the glutamate input from the RF center.
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