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Ya-Chien Chan, Seunghoon Lee, Chuan-Chin Chiao, Z Jimmy Zhou; Contextual Phase Tuning of Synaptic Inputs to Direction-selective Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3395.
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© ARVO (1962-2015); The Authors (2016-present)
The response of On-Off direction-selective ganglion cells (DSGCs) to light stimulation in the classical receptive field center is known to be tuned by the context of the silent, nonclassical receptive field surround, but the underlying mechanism is unknown. This study was to identify the key components of the contextual phase tuning of DSGCs.
DSGCs were recorded studied in the whole-mount rabbit retina under loose on-cell and whole-cell patch clamp. To study contextual phase tuning, the receptive field center of a DSGC was first mapped by flashes of stationary light spots. A drifting square-wave grating (composed of white and black bars) was then presented either in the receptive center alone, or in both the receptive field center and the surround. Effects of the phase difference between of the center and surround gratings on the responses of the DSGC were investigated.
Spike responses of DSGCs to the center drifting grating were strongly suppressed by the surround grating when the two gratings were moving in-phase, but were only minimally suppressed the grating were moving out-of-phase. Similarly, whole-cell recordings showed that the excitatory inputs to a DSGC (recorded at ECl) were contextually tuned: they were strongly suppressed when the surround grating moved in-phase with the center grating, but only weakly suppressed when the surround grating was moving out-of-phase, regardless whether the gratings moved in the preferred or the null direction. When hexamethonium was applied to block nicotinic cholinergic input, the same contextual phase tuning of the excitatory current input remained, suggesting that the glutamatergic input from bipolar cells was contextually tuned. This phase tuning of the glutamatergic input could be completely abolished by SR95531 plus TPMPA, but was only partially reduced by SR95531 or TPMPA alone, suggesting that the contextual phase tuning was mediated by GABAergic inputs through the activation of both GABAA and GABAC receptors. We found that the nicotinic input to DSGCs was contextually tuned in the same manner as well, and that the inhibitory inputs to DSGCs were also contextually tuned, albeit at a much weaker level.
The results suggest that contextual phase tuning of DSGCs was mediated predominantly by the tuning of the excitatory inputs from bipolar cells via GABAergic lateral inhibition from the receptive surround.
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