| ObjectivesTo study the change rules of passive membrane properties of cone neurons of primary visual cortex layer Ⅱ/Ⅲ in rats in different visual development periods, and investigate the influence of visual experience in two rising way on passive membrane properties parameters.MethodsWistar rats at14-60days were separately raised by normal way (12hours day/night alternate environment) and completely darkness way, then each group was further divided into five groups:before visual development critical period (P13-15);early stage of visual development critical period (P16-20); rush hour stage of visual development critical period (P25-27); late stage of visual development critical period (P30-35); after visual development critical period (P55-60).This experiment performed whole-cell recordings with Axon700B by combining infrared differential interference contrast (IR-DIC) technique and CCD-Camera system. First, in the current clamp mode, time constant (τ) was calculated according to the change of induced hyperpolarized voltage. Second, in voltage clamp mode, recording current change in different potential from-50mv to-100mv or from-100mv to-50mv which was-5mv for steps order, so different change trend of membrane resistance(Rm) can be calculated.Result1.With the visual development, the change trend of time constant in two rising way: in normal rising group, time constant of p13-15group (28.79±6.68ms) was significantly greater than p25-27group (21.51±4.64ms)(P<0.05, t=4.000) meanwhile in dark rising group, time constant of p13-15group (38.71±6.04ms) was also significantly greater than p25-27group(19.13±7.35ms)(P<0.05, t=9.202) In conclusion, the time constant performanced the trend of decline with visual development. At the same time, in p13-15group, time constant in dark rising group (38.71±6.04ms) was greater than which in normal rising group (28.79±6.68ms) (P<0.05, t=4.92); but in rush hour stage of visual development critical period (p25-27group), there was no obvious statistical differences between dark rising group (19.13±7.35ms) and normal rising group (21.51±4.64ms)2.With the visual development, the change trend of membrane resistance in two rising way:in normal rising group, membrane resistance of p13-15group (131.03±40.78MΩ)was significantly greater than p16-20group(100.47±22.94MΩ)(P<0.05, t=2.59), as well as membrane resistance of p30-35group (82.38±20.43MΩ) was greater than p55-60group (66.25±18.93MΩ)(P<0.05, t=2.13), even if there was no statistical differences between other group, the overall trend performance declined with the visual development. There had same situation in dark rising.3. The change trend of membrane resistance in different voltage potential:membrane resistance performed the change trend from low to high when voltage potential was from-50MV to-100MV, and at the meantime, membrane resistance performed the change trend from high to low when voltage potential was from-100MV to-50MV.4.The correlation coefficient of all time constants and membrane resistances was0.275(P=0.033), which mean two related variables had positive correlation:the greater the membrane resistances, the greater time constants.Conclusionl.In both two rising ways, time constant and membrane resistances were performed similar change trend that gradually declined with visual development.2.1n the same visual development stage, the parameters of passive membrane properties in dark rising way were slightly higher than that in normal way, but the difference was no statistical significance which suggested that age was the key factor in the change of passive membrane properties.3. The membrane resistance of cone neurons of primary visual cortex layer2in rats had reduced in polarization state and increased in hyper-polarization state.4. The time constants and membrane resistances in every visual development had positive correlation:the greater the membrane resistances, the greater time constants. |
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