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Macaque retina contains an S-cone OFF midget pathway
Karl Klug1, Steve Herr, Ivy Tran Ngo
1Brain Research Institute, University of California, Los Angeles, Los Angeles, California 90095-1563, USA.
Summary
Short-wavelength-sensitive (S) cones in primate retinas contact OFF midget bipolar cells, challenging previous assumptions about visual processing pathways. This finding clarifies how the visual system processes light onset and offset signals.
Area of Science:
- Neuroscience
- Vision Science
- Retinal Physiology
Background:
- Psychophysical studies indicate primate visual system sensitivity to both short-wavelength light onset and offset via separate pathways.
- Physiological studies reveal fewer OFF-center than ON-center cells driven by S cones in retina and lateral geniculate nucleus.
Purpose of the Study:
- To investigate whether S cones connect to ON and OFF midget bipolar cells, and ON "blue-cone" bipolar cells.
- To clarify the cellular pathways for short-wavelength light processing in the primate retina.
Main Methods:
- Electron microscopy of serial sections from macaque foveal retina.
- Analysis of 118 contiguous cone terminals and their associated bipolar cells.
- Identification of S cone terminals based on their synaptic contacts and morphology.
Main Results:
- Five S cone terminals were identified, distinguished by smaller size and more synaptic ribbons.
- These S cones contacted "blue-cone" bipolar cells, not ON midget bipolar cells.
- Each S cone also contacted its own OFF midget bipolar cell, which synapses with an OFF midget ganglion cell.
Conclusions:
- S cones directly contact OFF midget bipolar cells, providing a pathway for OFF signals.
- This study resolves discrepancies between psychophysical and physiological data on short-wavelength vision.
- Confirms a distinct cellular substrate for processing S cone-mediated visual information.