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Ben Stafford, Jonathan B. Demb; Microstructure Of Glutamate-mediated Receptive Field Properties Of Mammalian Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1168.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal ganglion cells encode excitatory glutamatergic inputs using AMPA and NMDA receptors. These receptors are apparently distributed uniformly across the ganglion cell dendritic tree, based on anatomical studies, but neurons in other regions of the CNS can show discrete localization of receptors on their dendrites. Here, we tested for discrete functional localization of AMPA and NMDA receptors across ganglion cell receptive field centers.
We recorded whole-cell responses to visual stimuli from ganglion cells in the whole-mount guinea pig retina. The spatial distribution of different postsynaptic receptors was probed by stimulating either central or peripheral regions of the receptive field center with brief flashes. Stimuli were 100% contrast spots and annuli (200 ms duration, 100-2500 µm diameter). We analyzed two well-characterized cell types: OFF Alpha and OFF Delta. We decomposed the light-evoked response into three underlying ligand-gated receptor components: an inhibitory GABA/Glycine conductance, an excitatory AMPA conductance, and an excitatory NMDA conductance. The weighted sum of these three conductance ‘basis functions’ was then used to describe light-evoked I-V plots and quantify the contribution of each receptor conductance to the light response.
OFF Alpha and Delta cells used NMDA receptors to encode responses to small stimuli at the central region of the receptive field center but not to stimuli in the peripheral region of the receptive field center. OFF Alpha cells used NMDA receptors to encode responses to large stimuli, while the NMDA contribution in OFF Delta cells was suppressed by large stimuli. Both cell types used AMPA receptors to encode stimuli of all sizes and at all locations.
Our findings indicate that AMPARs are uniformly distributed across the dendritic tree, whereas NMDARs are restricted to a small, central region of the tree. For both OFF Alpha and Delta cells, the receptive field apparently combines two overlapping excitatory center components: a narrow NMDA-mediated component and a broader AMPA-mediated component.
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