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Deepayan Kar, Ramya Singireddy, Jeff W Lichtman, Dennis M Dacey, Christine A Curcio; Morphology of a human central bouquet Müller cell explored using 3-dimensional volume reconstruction via connectomics. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4400.
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© ARVO (1962-2015); The Authors (2016-present)
Foveal Müller glia (MG) play vital roles in normal physiology, participate in macular disease, and are visualizable through optical coherence tomography and autofluorescence, interpretation of which could be informed by the morphology and distribution of MG. We reconstructed one central bouquet MG in its entirety via connectomics.
Globes from a preterm-born 21-year old male were opened anteriorly, placed into oxygenated Ames medium for 2 hours, and preserved in 4% glutaraldehyde. A fovea-centered 3.5-mm2 tissue block underwent automated tape-collecting ultramicrotomy. Horizontal 65-nm thick serial sections were imaged by electron microscopy at 6-nm resolution. Foveal cells were investigated with 3-dimensional reconstructions using TrakEM2.
Tissue was reconstructed from the outer fibers of cones to the internal limiting membrane. Across the center of the foveal depression, ganglion cell and inner nuclear layers were continuous, possibly related to either pre-term birth or to normal variation. The avascular zone diameter was 89.2 µm. The Henle fiber layer was thin, due to short and vertically oriented cone inner fibers.The reconstructed MG was vertically organized with numerous intermediate filaments, a cell body in the INL, and cytoplasm with electron-density that contrasted with surrounding cells. It ensheathed the vertical extent (13.1 µm) of 2 central bouquet cone outer fibers (1, 8). In the ONL, a ‘pericellular basket’ wrapped cone 8’s cell body (1.5×1.8 µm). Four concavities on the surface of MG suggested interaction with more cones. A glial sheath wrapped around cone 1’s 4.5 µm-long-inner fiber. Here, it molded fluidly around cone 1’s pedicle, contacting 3 bipolar cells (2 diffuse ON, 1 diffuse OFF). In the INL, the MG opposed several bipolar cell bodies. It passed through a dense network of ganglion and bipolar cell synaptic terminals in the IPL. Near the foveal floor, MG ensheathed an ON ganglion cell associated with an ON midget bipolar, in turn related to cone 1.
For the first time, the unique morphology and neural-glial relationships of one central bouquet Müller cell was visualized in near-entirety. Spatial distribution of MG differed markedly between retinal layers. Individual MG may also ensheath post-receptoral neurons in a cone-driven circuit. How MG contribute to a “MG cone” in the foveal floor remain to be determined.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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