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Z. Jiang, W. Shen; Metabotropic Effect of Glycine on Bipolar Cell Synapse . Invest. Ophthalmol. Vis. Sci. 2006;47(13):393.
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© ARVO (1962-2015); The Authors (2016-present)
To study the effect of glycine on glutamate synapse between bipolar cells and the third–order neurons. Glycine is an inhibitory neurotransmitter in retina. The effect of glycine on regulation of glutamate release is thought to be activation of chloride permeable ion channels. However, we find glycine also has a metabotropic effect that enhances glutamate synapse in the inner retina.
Whole cell patch clamp recordings were obtained from ganglion cells in tiger salamander retinal slices prepared under room light conditions. The spontaneous excitatory post–synaptic currents (sEPSCs) were studied on these neurons clamped at –60mV, near a chloride reversal potential, in dark conditions. The specific receptor agonists and antagonists were applied through bath perfusion and controlled manually.
Application of 10µM glycine, both frequency and amplitude of sEPSCs increased in ganglion cells. This effect was observed on a group of On–Off ganglion cells. The effect was strychnine insensitive and also insensitive to 40µM AP–7, a NMDA receptors inhibitor. 100µM NEM, a G–protein inhibitor, had no significant effect on the frequency and amplitude of sEPSCs. However, it completely locked the effect of glycine on sEPSCs in RGCs. This suggests that a metabotropic effect of glycine is involved in the synapse between bipolar cells and ganglion cells. Compared to the light driven EPSCs in ganglion cells, neither the glycine, nor the glycine with NEM, had significant effect on the light response in the ganglion cells.
The effect of glycine on potentiation of sEPSCs in ganglion cells might be related to presynaptic metabotropic effect in bipolar cell terminals. It also suggests that the mechanisms driven the spontaneous EPSCs and the light stimulated EPSCs might be different. Glycine enhances sEPSCs through a G–protein sensitive pathway.
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