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Z. Jiang, W. Shen; Excitatory and Inhibitory Synaptic Input in Interplexiform Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1514. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Interplexiform Cells (IPC) are a group of centrifugal feedback neurons that receive an input in the inner retina and send a feedback to outer retina. Although the anatomic structure of the neurons is well defined, the physiological properties of IPCs are poorly understood in retinal circuits. This study investigated excitatory and inhibitory synaptic inputs in IPCs.
Whole-cell patch clamp recordings were made in IPCs in dark-adapted tiger salamander retinal slides. IPCs were identified by their morphology using Lucifer Yellow intracellular dialysis methods. Light responses in IPCs were evoked by a full field white LED. The intensity and duration of the light stimulus were controlled by an EPC-10 amplifier.
We found that IPCs possessed a large sodium current, which differs with amacrine cells. IPCs received major excitatory input from On- and Off-bipolar cells and excited at the onset and offset of a light stimulus. Cyclothiazide blocking AMPA receptor desensitization enhanced light-evoked excitatory responses, suggesting that AMPA receptors are expressed in IPCs. The excitatory input was regulated by inhibitory inputs, mainly from glycinergic amacrine cells. 1 microM strychnine, a glycine receptor inhibitor, blocked most of light-evoked inhibitory current in IPCs. The remaining current was sensitive to 10 microM I4AA, a GABAc receptor inhibitor, but not bicuculline, a GABAa inhibitor, suggesting that GABAc receptors might be involved in the inhibition. This was further identified by local puff 500 microM I4AA that activated GABAc receptors in the IPCs. Local puff a high concentration of glycine also evoked a current in IPCs. Also Glycine input to IPCs was enhanced by bicuculline and picrotoxin that blocked GABAa and GABAc receptors in network. Our results also suggested that the onset and offset of light responses in IPCs were suppressed by GABAc and glycine input respectively.
IPC feedback may depend on sodium-activated action potentials, initially triggered by On- and Off-excitatory input from bipolar cells. Meanwhile, inhibitory input modulates the excitatory signals through activation of glycine and GABAc receptors in IPCs. That shapes light responses of IPCs.
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