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Z. Q. Yin, C. Wang; EPSC Changes After CSPG Degradation in Rat Visual Cortex During Visual Critical Period. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4709.
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© ARVO (1962-2015); The Authors (2016-present)
For the treatment of amblyopia is closely related with critical period of visual plasticity which terminative mechanism was unknown. The relationship between chondroitin sulphate proteoglycan (CSPG) and synaptic events during the critical period of the visual cortex was studied. CSPG, an extracellular matrix component condenses around neurons to form perineuronal nets (PNNs) encapsulating the cell, and may be a mechanism that ends the critical period of visual plasticity.
Recordings from normal rat (Long Evens) visual cortex between postnatal week 3 (P3W) to P8W were compared with those from rats after chondroitinase ABC (chABC) injections to degrade CSPG. Whole-cell patch-clamping was used to record glutamatergic excitatory postsynaptic currents (Glu-EPSCs), and NMDA and AMPA receptor mediated EPSCs from layers II - IV in tissue slices of the visual cortex.
1: EPSCs were recorded from 33/58 neurons in the normal visual cortex. There were no significant changes in NMDA-EPSCs amplitude (pA) (P > 0.05) between P3W to P8W. AMPA-EPSC amplitude steadily increased between P3W and P7W (P6W-P8W vs P3W, P < 0.05) coinciding with the closure of the rat’s visual critical period. NMDA/Glu EPSC amplitude ratios gradually decreased between P3w - P6W, concomitant with an increase in AMPA/Glu EPSC amplitude ratios. 2: Neurons (31/51) were isolated and recorded after CSPG degradation following chABC injections 7 days before recording. There was a significant and steady increase in NMDA-EPSC amplitudes until P7W (P < 0.05 vs P3W). AMPA-EPSCs amplitudes similarly increased, albeit not as significantly. After chABC NMDA/Glu EPSC amplitude ratios were consistently higher than in normal animals, whereas the AMPA/Glu EPSC amplitude ratios were consistently lower.
The PNNs formed with CSPG appear to be correlated with a decrease in of NMDA-EPSC amplitudes in rat visual cortex between P4W - P8W. CSPG may preferentially inhibit of NMDA transmission and synaptic plasticity as development proceeds by shifting the balance towards more AMPA/Glu receptor sites, thus, ending the visual critical period.
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