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E. D. Vickers, H. von Gersdorff; Light-Evoked Short-Term Synaptic Plasticity in the Inner Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5179.
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Synapses in the inner-plexiform layer (IPL) of the retina can undergo short-term plasticity (STP) over timescales ranging from hundreds of milliseconds to seconds. We have combined in vitro, whole-cell recordings from goldfish isolated (axon-cut) Mb (ON, mixed-input) bipolar cell presynaptic terminals with full-field, paired-pulse light stimulation. This combination of techniques has allowed us to quantify STP of ON and OFF lateral inhibitory synaptic inputs from amacrine cells onto the Mb terminal.
Retinal slices were prepared from goldfish (Carassius Auratus). Slice preparation was done at room temperature under dim red light following 1-2 hr dark adaptation. Whole-cell patch-clamp recordings were performed with an EPC-9 amplifier and Pulse Software. Full-field illumination of the recording chamber was provided by a white (broad-spectrum) LED positioned 3 cm from the sample and controlled through the EPC-9. Light-evoked IPSCs were quantified as peak amplitude and total charge transfer, and paired-pulse ratio (PPR) was computed as the ratio of the responses to each of the paired light pulses.
Preliminary studies found STP in response to paired, 100ms duration light pulses over intervals ranging from 200ms to 2000ms. Depression of light-evoked lateral inhibition was observed for intervals <500ms, and facilitation was observed for intervals >500ms. In order to separate the ON and OFF components of the light-response, we then tested longer, 400ms duration light pulses. The ON and OFF components of light-evoked lateral inhibition both showed depression at short intervals (300ms) and facilitation at long intervals (1900ms). The OFF component also showed facilitation at intermediate intervals (700, 1100, 1500ms).
Light-evoked lateral inhibition arriving at the Mb terminal can be separated into ON and OFF components. The ON and OFF components exhibit both depression and facilitation over distinct timescales. These STP in light-evoked inhibition arriving at the Mb terminal will exert direct, dynamic control of glutamate release from the Mb ribbon synapse onto post-synaptic, ON ganglion cells. This rapid modulation of synaptic transmission is a novel mechanism for dynamic, spatiotemporal filtering of visual stimuli in the IPL.
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