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Xuefeng Shi, Li Yao, Yang Gao, Kanxing Zhao; Synaptic Modifications In Neurons Of Rat Visual Cortex Induced By Correlated Subthreshold Pre- And Postsynaptic Signals. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6102.
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© ARVO (1962-2015); The Authors (2016-present)
Experience-dependent plasticity of visual cortex during development involves synaptic modifications in the underlying neural circuits. It is widely accepted that temporal correlations between the suprathreshold signals of pre- and postsynaptic neurons contribute to the development and refinement of neuronal circuits, which is known as spike-timing dependent plasticity (STDP). However, the form of neuronal activity is not always suprathreshold, especially during the early time of visual development. Here we sought to examine whether the correlated subthreshold pre- and postsynaptic signals also lead to synaptic modifications in visual cortex.
We performed whole-cell patch recordings in visual cortical slices of rats at postnatal days 13-17. Excitatory postsynaptic potentials were recorded from pyramidal neurons in layer IV under voltage clamp. A brief postsynaptic subthreshold current injection into the cell paired with a presynaptic subthrehold electric stimulus to white matter in different time orders (pre-post or post-pre) and intervals (-200 to +200ms), were conducted for 100 times in a frequency of 1Hz as the conditioning training. The synaptic strength at 10min before and 60min after conditioning was compared and calculated to determine the directions and amplitudes of synaptic modifications.
The subthreshold paired stimuli induced bi-directional long-term changes of synaptic strength in a broad time window (-110 to +110ms). However, unlike the asymmetric profile of STDP, the directions of synaptic modifications was not dependent on the time order of the paired stimuli. We observed no significant difference of the induction rates of long-term synaptic potentiation (LTP) and depression (LTD) between the two time orders (p=0.88).
These findings indicate that correlated subthrethold pre- and postsynaptic signals could lead to synaptic modifications in visual cortex, but with a profile different from STDP, suggesting a different mechanism of synaptic plasticity induced by subthreshold neuronal activities.
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