Functional Synaptic Activities And Spike-timing Dependent Plasticity Of Rats Visual Cortex During Development Stage

ObjectivesIntroduce the visual patch clamp whole-cell recording technique and investigatefunctional synaptic activities and spike-timing dependent plasticity of rats visualcortex during development stage.So as to account for aspects of experience-dependentvisual-cortical plasticity.To explore the role of visual experience when aging.And tounderstand the mechanism of amplyopia from functional aspects,through studyingthe changes of synaptic function status.Thus to find a reasonable and effectiveprevention methods and treatment of amblyopia.Methods1.By combining infrared differential interference contrast(IR-DIC)technique andCCD-Camera system with visual patch clamp whole-cell recording technique,spontaneous EPSCs of P2～7,P8～14,P15～21,P22～28 groups were oberved andanalyzed,simultaneously the neurons were stained by adding 0.3% luciferyellow tothe pipette solultion.Including the sEPSCs of P17 coronal slices of normal andabnormal visual experience group.2.Dual whole-cell voltage recording technique was used to stimulate in the cell atlow-frquency.To observe the long-lasting changed efficency of transmission betweentwo neurons in layer 2/3 of visual cortex under deferent stimulating protocols.At thesame time to observe the morphology of neurons and dendrites through addingluciferyellow to the pipette solution.3.Using dual whole-cell recording technique with STDP mode,control EPSP wasobtained from binocular deprived and control group respectively Then theeffectiveness of changes in synaptic transmission was compared.Observe the changeof test EPSP in the two groups after different pairing of individual postsynaptic APswith EPSPs precisely.And with the conventional LTP evoking protocol that onlyconsists of presynaptic stimulation,enhancing the frequency from lower to higher tilla theta-burst like stimulation,test EPSP was measured in sequence. Results1.Visual patch clamp technique can be used to make direct localization and healthscreening exactly.The amplitude and frequency of sEPSCs were all enhanced whenaging (One way ANOV,P＜0.01).But there was no significant difference betweenP2～7 group and P8～14 group(P＞0.05).The electrophysiology and dendrite of neuronbecame mature whilst development.The amplitude of sEPSCs in binocular deprivedgroup was significantly lower than that of the controled group(P＜0.05).Yet thediference of frequency between the two groups was not significant(P＞0.05)2.Depending on the precise control of timing of spike evoked in the pre/post neuron,after paring stimulating average test EPSP increased beyond 120%,LTP was evokedsucessfully.Yet when stimulation only applied to the pre-or postsynaptic neuron,testEPSP increased below 110%,LTP was not evoked sucessfully.3.The effectiveness of synaptic transmission decreased in binocular deprived group.The difference between binocular deprived and control groups was significant atP＜0.01 50 minutes after paring stimulation,it produced stable LTP in slices frombinocular deprived anmimals,but little potentiation in controls.Yet with theconventional LTP evoking protocol at lower frequency,no LTP was producedsuccessfully in 24 slices.Potentiation did not arrive at 110% even when the frequencywas near 100 Hz a theta-burst like stimulation.Conclusions1.Visual patch clamp technique,better than blind patch clamp technique,can improvethe success of sealing process.During the early postnatal days neurons wererelatively immature,and became mature during development.Visual experienceplayed an important role in this process.The results suggested that early AMPAreceptor-mediated functional activities existed in layer 2/3 pyramidal neurons,andsynapses were not completely silent,but had early spontaneous activities.2.The varing transmissional efficency of synapse was determined by paring pre-andpostsynaptic spike and the pre/post spike orders.There was an STDP timing windowin the layer 2/3.Spike-timing dependent plasticity may explain some experience-dependentmodifications in cortex.3.Abnormal visual experience during early postnatal days can decrease theeffectiveness of synaptic transmission,thus affecting the visual cortex neurons in presenting information.During developmental stages,visual-cortical plasticity inbinocular deprived group was not lower than the control group.