My cover Image has been selected for the cover of Neuron for the December 9th 2020 and its legend:
On the cover: The first synaptic step in the human visual process begins at the foveal cone photoreceptor where many parallel circuitries emerge to compute form, color, and motion. One connection of critical importance is the so-called midget pathway, where a foveal cone makes a unique, nearly private line synaptic connection with downstream neurons serving to preserve the spatial resolution afforded by the array of cones that densely sample the visual image. How this highly specialized foveal microcircuitry is achieved in retinal development is unknown. In this issue of Neuron, Zhang et al. (pages 905–918) use volume electron microscopy to identify and reconstruct the midget circuit in the fetal fovea, reporting that the non-divergent synaptic connections that characterize the human midget circuit arise in stages, by extensive synaptic remodeling. The cover, inspired by Chagallian fantastic symbolism and the complex ultrastructure of the outer retina in the background, provides a metaphorical montage of the intricate morphology at the bell-shaped cone synaptic pedicle, represented by the hanging fuchsia flower and the feeding swallowtail, reflecting the distinctive butterfly-shaped synaptic triad (see Figure 1E) at the start of the visual process. Original artwork by Yeon Jin Kim.
Midget circuit in the adult human retina
A video reveals serial block face reconstruction of 3 neighboring OFF midget circuits at ~500micronmeters from the foveal center that I reconstructed. I generated this video using Dragonfly (Object Research Systems).
Note: A small retinal cube extending from the border of the inner nuclear layer (top of cube) through the inner plexiform layer (bottom of cube) contains these three circuits. The glomerulus-like complex of the midget bipolar axon terminals enveloped by the ganglion cell dendritic trees is revealed as the surrounding tissue is peeled away. Bipolar cell axon terminals from a closely spaced mosaic but do not overlap. The ribbon synapse locations are then shown by the red balls in the each bipolar terminal. Nearly all of the ribbons in each bipolar cell are targeted to its single ganglion cell partner (Published in Neuron as a supplemental video S1: Zhang, C., Kim, Y.J., Silverstein, A., Hoshino, A., Reh, T., Dacey, D.M., & Wong, R.O. (2020). Circuit reorganization shapes the developing human foveal midget connectome towards single-cone resolution. Neuron, 108, 1-14. https://doi.org/10.1016/j.neuron.2020.09.014 PDF)
Distinctive dendritic morphology of starburst amacrine cells in the macaque monkey retina Four examples of ON-center starburst cells filled with Alex Fluor 568 and OGB. Retinal location relative to fovea and distance from the foveal center is indicated. Macaque starbursts show the characteristic circular field, extremely thin and radiate proximal branches, and varicosity-bearing terminal dendrites characterized previously in mouse and rabbit. At peri-foveal eccentricities (right-most panel) starburst cells are greatly reduced in field diameter (scale bar applied to all panels).
