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T. Ichinose, P. D. Lukasiewicz; Inner and Outer Retinal Contributions to Mouse Ganglion Cell Surround Inhibition. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3618.
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© ARVO (1962-2015); The Authors (2016-present)
Ganglion cell receptive fields are organized into antagonistic center and surround regions. Previous work suggests that surround inhibition in ganglion cells is mediated by lateral inhibition in both the outer (OPL) and inner plexiform layers (IPL). However, the relative roles of each plexiform layer remain unknown. Here we determined the relative contribution of each plexiform layer to surround inhibition in mouse ganglion cells (GCs), using HEPES and GABA receptor blockers as pharmacological tools to block outer and inner lateral inhibition, respectively.
Light-evoked excitatory postsynaptic currents (L-EPSCs) were recorded from GCs voltage clamped to ECl in light-adapted retinal slices. Light responses were elicited by bright full field illumination with a white LED. Lateral inhibition in the OPL was blocked by changing the bath from bicarbonate to a 20 mM HEPES containing solution. Lateral inhibition in the IPL was blocked by the subsequent addition of GABA receptor (R) antagonists, bicuculline and TPMPA, to the bath. Strychnine was present at all times to block glycine receptors. GCs were morphologically characterized by including sulforhodamine in the pipette.
HEPES reduced a component of surround inhibition and increased the cone-mediated L-EPSC charge transfer (Q). The subsequent blockade of GABAARs and GABACRs reduced a second surround component, producing an additional increase in L-EPSC Q. The relative contributions of OPL and IPL lateral inhibition were variable, but were correlated with GC type. Surround inhibition in ON and OFF GCs with dendritic processes at the margins of the IPL were several times more sensitive to GABAR blockade than HEPES. By contrast, for GCs with processes ramifying in mid IPL, GABAR blockade and HEPES were equally effective in reducing surround inhibition.
We found both OPL and IPL contributions to surround inhibition of mouse GCs. However, the relative contributions of each layer varied with GC type. GCs that ramified near the mid IPL were more influenced by the OPL compared to GCs that ramified at the IPL margins, suggesting that distinct surround circuits influence GC receptive fields in cell specific ways.
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