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Z. Jiang, W. Shen; Excitatory Currents in Ganglion Cells Generated by Glycine Input in the Distal Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3620.
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© ARVO (1962-2015); The Authors (2016-present)
Glycinergic interplexiform cells are a group of centrifugal neurons that provide a feedback of glycine to the distal retinas. However, the role of the glycine feedback remains obscured. This study was performed to determine the effect of glycine feedback in central glutamate transduction in the output neurons.
Whole cell and perforated patch recordings were made in isolated cells and slices of tiger salamander retinas. Glyince was locally puffed on the OPL and the responses were recorded on photoreceptors, bipolar cells (BCs) and ganglion cells (GCs).
Local application of 100µM glycine in the OPL could generate a CNQX-sensitive excitatory current in GCs. This effect was further studied in photoreceptors and BC’s dendrites. The glycine increased Ca2+ channel currents in isolated photoreceptors. This might serve as a mechanism for enhancing glutamate release in photoreceptors. Meanwhile, in the presence of Cd, puff glycine on the OPL depolarized the dark membrane potential in some On-BCs to around the Cl- reversal potential at -40mV, which counteracted the glutamate response in the On-BCs. Puff glycine on the dendrites of Off-BC’s had a less significant effect on the dark membrane potential since the Cl- reversal was close to dark membrane potential in Off-BCs. We also found that NKCC1, a Cl- cotransporter uptaking Cl-, was present in the On-BC dendrites through immunocytochemistry. This would cause the Cl- reversal positive to the dark membrane potential in the local regions.
Our results indicate that a glycine input in the distal retina provide a positives control on glutamate transduction. The effect was confined to photoreceptor terminals by increasing Ca2+ dependent glutamate release, and BC dendrites by exciting some On-BCs. A positive control of Off-BCs by glycine happens most likely through an enhancement of glutamate input. The function of the glycine centrifugal feedback pathway potentiates glutamate signal in the retinal output neurons.
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