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Joanna Diane Crook, Orin S. Packer, Julian Vrieslander, Dennis M. Dacey; Excitatory conductances drive S-ON and LM-OFF opponency in small bistratified blue-ON ganglion cells . Journal of Vision 2009;9(14):34. doi: 10.1167/9.14.34.
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The primate small bistratified blue-ON ganglion cell responds to the onset of a short wavelength light and to the offset of a middle and long wavelength light. We hypothesize, based on the small bistratified cell's well described anatomy (Dacey, 1993), and extracellular recordings from blue-ON ganglion cells combined with pharmacology (Crook et al., 2009), that the blue-ON cell's basic wavelength opponent response is generated primarily by excitatory conductances originating from ON and OFF bipolar cell pathways. The blue-ON bipolar cell exclusively contacts short (S)-wavelength sensitive cone photoreceptors and relays to the small bistratified ganglion cell's inner dendrites; and OFF diffuse bipolar cells contact long (L)- and middle (M)-wavelength sensitive cone photoreceptors and synapse on the outer dendrites. Recording from macaque monkey blue-ON cells in vitro in whole-cell voltage-clamp, we show that light evoked ON and OFF responses, to S- and LM-cone modulation, respectively, are produced primarily by excitatory conductances. ON pathway block with the mGluR6 agonist, L-AP-4, knocks out the excitatory conductance to S-cone modulation, but spares the excitatory conductance to LM-cone modulation. Blocking inner retinal inhibitory pathways with the addition of GABAa/c receptor antagonists, TPMPA and GABAzine, and the glycine receptor antagonist strychnine, further isolates this conductance. These results are consistent with the blue-ON cells basic wavelength opponent response originating from ON and OFF bipolar pathways. Inhibition, from inner retinal amacrine cells, appears to shape the kinetics of the excitatory inputs.
CrookJD J Neurosci 29(
DaceyDM Vis Neurosci 10(
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