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T. A. Munch, R. A. da Silveira, S. Siegert, B. Roska; A Functional Role of AII Amacrine Cells in Light-Adapted Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1415.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize an inhibitory pathway in the light adapted retina which is mediated by AII amacrine cells.
Light adapted retinas were isolated from transgenic mice in which specific subsets of ganglion cells are labeled with YFP. Those cells were identified with 2-photon fluorescent imaging. We recorded their synaptic currents in voltage clamp mode in response to stimulation by light or by depolarization of a simultaneously patched AII amacrine cell. The responses were further characterized with pharmacological agents.
Circuitry: In a subset of OFF ganglion cells we found a robust inhibitory current at light ON mediated by direct glycinergic input. This current survived the application of pharmacological blockers of ionotropic glutamate receptors (CPP and NBQX). This current was absent in Cx36KO mice. Dual-patch recordings from such an OFF ganglion cell and an AII amacrine cell demonstrated that depolarization of the AII cell elicits inhibitory currents in the ganglion cell. In these dual-patch experiments, the depolarization-elicited as well as light-evoked inhibitory currents in the ganglion cell, and the light evoked responses of the AII amacrine cell, survived the application of CPP and NBQX.Function: We showed that this local out-of-phase inhibition (ON inhibition in an OFF cell) can suppress the cell’s response when the receptive field experiences darkening and brightening simultaneously. The cell’s responses were suppressed at the onset of translational movement of a patterned scene, but not when a dark object in the scene approached the retina (looming motion). The suppression of the response was absent when the inhibitory ON currents were blocked with APB.
Taken together, these results indicate a novel role of AII amacrine cells, namely to supply robust inhibitory input to subsets of OFF ganglion cells in light adapted retina by virtue of their gap junction coupling to ON cone bipolar cells. AII amacrine cells therefore are not only a major neuron in the dark-adapted retinal circuitry, but also play an important role in the light adapted retina by supplying local fast ON inhibition. This inhibition can suppress the responses of the target OFF ganglion cells at the initiation of translational movement, thereby emphasizing other types of movement, such as axial or looming motion.
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