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Jay Neitz, Sara Patterson, Jolie Chang, Beatrice Q Giebel, Isabelle Rieke-Wey, Maureen Neitz; Another Blue-ON Ganglion Cell in the Primate Retina. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2338.
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© ARVO (1962-2015); The Authors (2016-present)
The primate retina's color-coding strategy is classically described as redundancy reduction, with the spectral tuning of the three most common retinal ganglion cells (RGCs) capturing most of the variance in natural spectra. These models propose midget RGCs encode red-green while “Blue-ON” small bistratified RGCs encode blue-yellow. However, the discoveries of two distinct Blue-OFF RGCs indicate that there is more redundancy in the retinal color code than previously appreciated. Here, we further explore the diversity of Blue/S-cone circuits in the primate.
We reconstructed the neurons and synapses of the S-cone connectome in a serial electron microscopy volume of macaque central retina.We reconstructed over 50 S-ON bipolar cell (BC) terminals, confirmed by contacts with small bistratified RGCs and/or input from previously identified S-cones (Patterson et al., 2019, Sci Rep 9, 11913). The small bistratified RGC’s “Blue-ON” responses are provided by excitatory input from S-ON BCs, so we focused on reconstructing the uncharacterized RGCs post-synaptic to S-ON BCs.
We identified a population of wide-field monostratified RGCs receiving excitatory input exclusively from S-ON BCs. These wide-field RGCs accounted for only a small fraction of each S-ON BC’s output (1-3 ribbon synapses), however, each received input from over 20 S-ON BCs. Except for small branches receiving input from nearby S-ON BCs, the wide-field RGCs had large dendrites that branched sparsely in sublamina 5. They received most of their inhibitory input from a single type of wide-field amacrine cell.
The small bistratified RGC was long thought to be the only pathway carrying S-cone signals from the retina, but here we identify an addtional RGC with the same "Blue-ON” input. This is a distinct Blue-ON channel from any previously described in the primate. Multiple channels carrying “duplicate” spectral signals in the primate argues for parallel pathways distributed to different brain areas as described for other mammalian retinas. Each Blue-ON RGC type likely uses its color tuning for distinct functions, which are not necessarily hue perception. Based on morphology and stratification, the new Blue-ON RGC likely corresponds to the M2 ipRGCs, which mediate non-image-forming visual functions. The strong S-cone input to these neurons could mediate some of the wide-ranging effects of short-wavelength light on human circadian rhythms, mood and health.
This is a 2020 ARVO Annual Meeting abstract.
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