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Seunghoon Lee, minggang chen, yi Zhang, Lujing Chen, Z Jimmy Zhou; Synaptic properties of vGluT3 amacrine cells in the mouse retina. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4377.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate synaptic transmission and postsynaptic targets of vGluT3 amacrine cells (GACs) in the mammalian retina.
Optogenetic stimulation was applied to GACs in the whole-mount retina of vGluT3/ChR2-YFP mouse, while postsynaptic responses from retinal ganglion cell (RGC) types were recorded with patch clamp under pharmacological blockade of endogenous light responses. Direct synaptic transmission was further confirmed by dual patch clamp recording between GACs and identified target RGC types. Morphologic, synaptic, and receptive field properties of GACs and their postsynaptic RGCs were characterized with electrophysiology and two-photon imaging.
Optogenetic stimulation of channel rhodopsin 2 (ChR2)-expressing GACs evoked direct postsynaptic responses from several RGC types, including ON-OFF DSGC, ON DSGC, W3 GC, and an OFF GC type. Among these GC types, the OFF GC received significantly bigger glutamatergic inputs than other GC types, suggesting that GACs form glutamatergic connections with multiple, but specific, RGC types, with the OFF RGC being a primary target. In addition to GC types, GACs also provided glutamatergic inputs to amacrine cells type that form feedback GABAergic synapses onto GACs. The postsynaptic glutamate response to optogenetic activation of GACs contained a fast and transient current component, followed by a slow and sustained component in most target GC types. Similar results were also obtained by dual patch clamp between GACs and their target GC types. Both the fast and the slow postsynaptic currents were mediated mainly by AMPA and NMDA receptors. Application of TTX (1 µM) dramatically reduced the fast/transient component and moderately altered slow/sustained component, suggesting an important role of Na+ channels in glutamate release from GACs. Under current clamp, the target GCs responded to optogenetic activation of GACs with a depolarization and dendritic or somatic spikes. Glycinergic response was not clearly detected from the RGCs that gave glutamatergic responses to GAC activation, but the possibility of glycine release from GACs is still under investigation.
The study demonstrates that a subset of amacrine cells contribute to glutamatergic signaling in the mammalian retina. The synaptic and receptive field properties of GACs suggest that GACs convey a distinct form of excitatory signal in visual transmission.
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