April 2010
Volume 51, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2010
Excitatory Synaptic Conductances Mediate ‘Blue-Yellow’ and ‘Red-Green’ Opponency in Macaque Monkey Retinal Ganglion Cells
Author Affiliations & Notes
  • J. D. Crook
    Biological Structure, University of Washington, Seattle, Washington
  • M. Manookin
    Biological Structure, University of Washington, Seattle, Washington
  • O. S. Packer
    Biological Structure, University of Washington, Seattle, Washington
  • D. M. Dacey
    Biological Structure, University of Washington, Seattle, Washington
  • Footnotes
    Commercial Relationships  J.D. Crook, None; M. Manookin, None; O.S. Packer, None; D.M. Dacey, None.
  • Footnotes
    Support  EY006678, RR00166, T32 EY07031
Investigative Ophthalmology & Visual Science April 2010, Vol.51, 5178. doi:
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      J. D. Crook, M. Manookin, O. S. Packer, D. M. Dacey; Excitatory Synaptic Conductances Mediate ‘Blue-Yellow’ and ‘Red-Green’ Opponency in Macaque Monkey Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5178.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: : Our goal was to determine the synaptic interactions underlying cone opponent receptive field structure in the trichromatic primate retina.

Methods: : We recorded from identified midget (long (L) vs middle (M) wavelength cone opponent) and small bistratified (short wavelength (S)-ON vs L+M-OFF cone opponent) ganglion cells in whole cell voltage clamp and measured the synaptic conductances evoked by selective modulation of the S, L or M cones.

Results: : For the bistratified S-ON ganglion cells our main goal was to directly determine whether the L+M-OFF response originates presynaptically via surround inhibition or postsynaptically by excitatory OFF-bipolar input. S cone increments elicited sustained ON-excitatory and ON-feedforward inhibitory conductances. No evidence was found for ‘crossover’ inhibition at S decrement consistent with the absence of S-OFF bipolar circuitry. L+M cone stimuli elicited sustained OFF-excitation and both feedforward and crossover inhibition. Bath application of L-AP4, the mGluR6 receptor agonist and GABAa/c (GABAzine/TPMPA) and glycine (strychnine) receptor antagonists abolished ON excitatory and all inhibitory currents but spared a clear L+M OFF-excitatory conductance presumably arising from known OFF bipolar synaptic inputs. Similarly for midget cells our goal was to determine whether L vs M cone antagonism arises pre- or postsynaptically or by some combination of both synaptic mechanisms. L and M cone selective stimuli modulated sustained excitatory L and M conductances in counterphase. Block of all inner retinal feedforward inhibition evoked by L and M cone stimuli spared and amplified clear L vs M opponent excitatory conductances.

Conclusions: : For the blue-ON cell the S vs L+M receptive field arises postsynaptically by converging excitatory S-ON and L+M-OFF bipolar inputs to the bistratified tree. By contrast L vs M cone opponency arises presynaptically for the midget ganlgion cell presumably from the unequal distribution of randomly arranged L and M cones to the centers vs surrounds of midget bipolar receptive fields. Inner retinal inhibitory pathways appear to play little, if any, role in constructing either blue-yellow or red-green cone opponency.

Keywords: ganglion cells • color vision • synapse 
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