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Xiwu Zhao, Ben K. Stafford, Kwoon Y. Wong; Functional diversity among intrinsically photosensitive retinal ganglion cells. Journal of Vision 2013;13(15):T8. doi: 10.1167/13.15.8.
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© ARVO (1962-2015); The Authors (2016-present)
Melanopsin-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate non-image-forming visual responses, including pupillary constriction, circadian photoentrainment and suppression of pineal melatonin secretion. Five morphological types of ipRGCs, named M1 – M5, have been identified in mice. To better understand their functions, we studied the resting properties and light-evoked responses of all five cell types, by whole-cell-recording from ipRGCs genetically labeled with green fluorescent protein. In darkness, the five ipRGC types had different resting membrane potentials and generated action potentials at different rates, suggesting that they send different information to the brain even in the absence of light. All five cell types generated melanopsin-based (“intrinsic”) as well as synaptically driven (“extrinsic”) light responses. The intrinsic light responses of M1 cells were more sensitive and larger than those of M2 – M5 cells, and response peak latencies varied substantially among the cell types. In response to uniform full-field lights, the peak amplitudes of extrinsic light responses differed somewhat among the ipRGC types, although all cell types' responses had comparable thresholds, kinetics and waveforms. The receptive fields of M2 – M5 cells exhibited antagonistic center and surround regions, implicating a capacity to detect spatial contrast. On the other hand, M1 cells' receptive fields lacked surround antagonism, consistent with their primary role in non-image-forming vision. All ipRGCs responded robustly to a wide range of motion speeds and different cell types appeared to prefer different speeds, suggesting they might participate in motion analysis.
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