Summary
This study identifies Type 6 ON cone bipolar cells as the dominant synaptic input to ipRGCs for luminance encoding, with additional modest contributions from Types 7, 8, and 9, and reveals that temporal filtering of excitatory drive is largely governed by postsynaptic mechanisms rather than amacrine-cell feedback. These findings deepen understanding of how the retina constructs the irradiance signal that drives circadian rhythms and pupillary reflexes, with implications for designing light stimuli that effectively target melanopsin-based pathways.
Key Findings
- Type 6 ON cone bipolar cells are the dominant excitatory input to ipRGCs for luminance encoding; Types 7, 8, and 9 provide modest input; Types 5i, 5o, 5t and rod bipolar cells contribute virtually none.
- Conventional RGCs show stronger high-pass temporal filtering of bipolar cell excitatory drive compared to ipRGCs, with postsynaptic mechanisms (rather than amacrine-to-bipolar feedback) primarily responsible.
- M1 ipRGCs specifically avoid OFF bipolar input and receive only ectopic ribbon synapses from ON cone bipolar axonal shafts, which are unusual monad synapses bearing up to a dozen ribbons with a single postsynaptic process.
- Intensity-encoding capacity is widespread among cone bipolar types including OFF types, but the bipolar cells driving ipRGCs carry the strongest luminance signal.
Categories
The Science of Light: Investigates the synaptic circuits and bipolar cell types responsible for irradiance coding in ipRGCs, directly relevant to understanding how the retina encodes the luminance signals driving circadian and pupillary responses.
Sleep & Circadian Health: The luminance-encoding capacity of ipRGCs is foundational to circadian entrainment, and identifying the specific synaptic inputs shaping this signal informs understanding of how light drives circadian responses.
Author(s)
S Sabbah, C Papendorp, E Koplas, M Beltoja
Publication Year
2018
Number of Citations
7
Related Publications
The Science of Light
- Phototransduction by retinal ganglion cells that set the circadian clock
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- The mammalian circadian timing system: organization and coordination of central and peripheral clocks
- Diminished pupillary light reflex at high irradiances in melanopsin-knockout mice
- Melanopsin is required for non-image-forming photic responses in blind mice
Sleep & Circadian Health
- Phototransduction by retinal ganglion cells that set the circadian clock
- The mammalian circadian timing system: organization and coordination of central and peripheral clocks
- The twoāprocess model of sleep regulation: a reappraisal
- Melanopsin is required for non-image-forming photic responses in blind mice
- Strange vision: ganglion cells as circadian photoreceptors