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Peter B Detwiler, Orin S Packer, Felix Viana, Dennis M. Dacey; Cone type specific dendritic calcium signaling in the blue-yellow color opponent ganglion cells of the primate retina . Invest. Ophthalmol. Vis. Sci. 2018;59(9):2587.
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© ARVO (1962-2015); The Authors (2016-present)
The small bistratified ganglion cell of the primate retina shows ‘blue-ON/yellowOFF’ color opponency. Densely branched inner dendrites receive excitatory ON-input from bipolar cells connected to short (S) wavelength sensitive cones and sparsely branched outer dendrites receive excitatory-OFF input from bipolar cells connected to long (L) and middle (M) wavelength sensitive cones. The role that inner and outer dendrites play in processing color information was investigated using 2-photon Ca imaging to determine whether S-ON and LM-OFF evoked dendritic Ca responses were restricted to inner and outer dendrites and to assess the degree to which somatic spike back-propagation vs dendritic Na channels are required for dendritic Ca responses.
Ganglion cells in the in vitro macaque monkey retina were targeted for patch recordings of light evoked spike discharge to S and LM cone selective stimuli sinusoidally modulated about a photopic mean level (~105 isomerizations/cone/sec) at 0. 2 to 2 Hz. Calcium-dependent fluorescence, excited by 2-photon absorption of 935 nm light, was recorded from cells filled with Oregon Green 488 BAPTA during whole-cell recording.
Inner and outer dendrites displayed large S-ON and LM-OFF evoked calcium responses with no evidence that light evoked Ca responses were segregated in dendritic compartments related to S-ON and LM-OFF synaptic inputs. Dendritic Ca signals persisted after elimination of somatic action potentials by bath application of TTX (0.1 µM) and thus not dependent on back-propagated spikes. The effect of TTX on the Ca response varied at different dendritic recording sites from no change to about a 30% reduction. TTX insensitive recording sites were more commonly observed in distal than proximal dendrite, but not exclusively so.
Both S-ON and LM-OFF evoked calcium signals were recorded in inner and outer tiers of the bistratified dendritic tree in the absence and presence of TTX, which indcates they are not produced by somatic spike back-propagation. TTX did however reduce the amplitude of Ca responses at some but not all dendritic recording recording sites, suggesting that dendritic calcium signals are result of localized synaptic input and that TTX-sensitive Na channels may participate in dendritic intergration by amplifing excitatory synaptic potentials.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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