Effects Of Higher Visual Areas Activity To Primary Visualcortex On Synaptic Plasticity In Developing Rats

ObjectiveTo explore the influences of higher cortical areas activity to primary visual cortex on synaptic plasticity in developing rats.Methods1. To examine the spatiotemporal interactions between the WM inputs and LM inputs under clamp voltages at-70mv and-50mv respectively, the responses to concurrent activation at various interstimulus intervals (ISIs) of any two inputs were recorded. The ISIs used were0,±0.1,±0.2,±0.3,±0.4,±0.5,±1,±2ms and ISIs were analysised.2. Compare the LTP/LTD induction rates between stimulate wm alone,wm and LM with ISIs=±2ms, wm and LM with ISIs=0,±0.1ms in cortex brain slices of P14-16rats.3. A short-term (inter-stimuli interval of40ms) paired-pulse stimuli was delivered to the layer IV of slices to evoke postsynaptic currents of pyramidal neurons of layer Ⅱ/Ⅲ. Inhibitory postsynaptic currents (IPSCs) were recorded under different clamp voltages though whole-cell patch clamp technique. Inhibitory input conductance (gi) calculated from their current-voltage fitting curves were used for analysis of their developmental changes and effect of paired-pulse stimuli. The changes of coefficient of variance (CV) between the postsynaptic currents induced by paired-pulse stimuli in different groups were compared.Results1. At the resting membrane potential, when two inputs were driven simultaneously, the SI of the three groups were4.65±1.28;2.90±0.44;2.54±0.33. At the-50mv membrane potential,the SI were2.82±0.63;1.99±0.42;1.34±0.30respectively.The SI decreased with the growth.2. The changes of amplitude of EPSCs were29.59±26.28;22.93±17.05;67.28±44.94respectively when stimulate wm alone,wm and LM with ISIs=±2ms, win and LM with ISIs=0,±0.1ms in cortex brain slices of P14-16rats.The average amplitude of the wm and LM with ISIs=0,±0.1ms was significantly larger than that of the other groups(p<0.05),and the LTP/LTD induction rates was significantly larger than that of the other groups(p<0.05).3. The IPSCs showed that PPF decreased with ages2.41±0.72(A group),1.62±0.83(B group),0.19±0.79(C group); while the gi level increased ages1.48±0.78nS(A group),2.05±0.84nS(B group),5.67±2.22nS(C group).The CV value was reduced significantly with ages-2.09±0.46(A group),-1.90±0.58(B group),-0.29±0.18(C group).Conclusions1.When WM inputs and LM input were driven simultaneously on the rat slices around critical period, the evoked EPSCs were larger than the mathematical summation of the two individual EPSCs. The SI decreased with the growth and the positive changes of clamp voltage.2.Higher visual areas activity can affect Primary visual cortex on synaptic plasticity in developing rats,it can improve the LTP/LTD induction rates.3.In the postnatal early period of rat, the inhibitory synaptic circuitry was strengthened and matured with the visual cortex development, but its short-term plasticity decreased with the time. In the first several days after open eyes, the presynaptic mechanism of IPSCs-PPF is in the dominant status. The short-term plasticity reflected by PPF may participates in the experience dependent visual cortical development of rats.4. LTD induction maybe connected with the PPF of IPSCs during the postnatal early period.