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Xuefeng Shi, Kanxing Zhao; Stimulus Timing-Dependent Synaptic Modification in Rat Visual Cortex Induced by Training Stimuli Paired with Postsynaptic Subthreshold Depolarizations. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5723.
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© ARVO (1962-2015); The Authors (2016-present)
The visual development is a process of synaptic modification in neural circuitry dependent on the visual experience in the critical period. A widely accepted rule is that the timing of postsynaptic backpropagating action potential relative to the presynaptic input can determine the sign of synaptic plasticity. However, there is still criticism on whether the suprathreshold Na+ spike is necessary for synaptic plasticity induction. Here we investigated the effect of the subthreshold neuronal activities on the synaptic plasticity in rat visual cortex.
We performed whole-cell patch recordings in visual cortical slices of rats at postnatal days 19-24. The following training paradigms were exerted on patched neurons, respectively, 1) pairing stimuli with postsynaptic subthreshold depolarization of membrane potential induced by current injection in different time intervals between pre- and postsynaptic stimuli, 2) pairing stimuli with postsynaptic depolarization of different levels, 3) pairing stimuli with postsynaptic depolarization of different durations, 4) pairing stimuli with postsynaptic depolarization in single form or burst form. pClamp10 and Matlab2008 were used for analysis and data processing. Origin8.0 was used for statistical analysis.
Subthreshold pairing stimuli induced asymmetric bidirectional synaptic plasticity, but with an additional long-term depression (LTD) window at longer positive time intervals. Low-level subthreshold depolarization significantly reversed the long-term potentiation (LTP) effect (t=2.43, P<0.05). Also, short-duration (5ms) subthreshold depolarization reversed the LTP effect elicited under long duration of 30ms (t=2.25, P<0.05). LTP was induced under duration exceeding 20ms and LTD was induced under duration shorter than 20ms. Burst-form depolarization reversed the LTD effect induced by single-form depolarization (t=2.46, P<0.05).
Subthreshold neuronal activity is one of crucial factors in rearrangement of neural circuitry of visual cortex during critical period. Different parameters of postsynaptic subthreshold depolarization, including level, duration, and burst form, act significantly on the synaptic plasticity in visual cortex. Low-level or short-duration depolarization inclines to induce LTD, while burst form depolarization facilitates induction of LTP.
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