A Study On Tactile Stimulation Evoked Lone-term Plasticity In Mouse Cerebellar Cortical Granule Cell Layer

Objective:Information transferred into cerebellar cortex via mossy fiber or climbing fiber pathways,which is computated by cerebellar cortical neuronal circuits and output the command by cerebellar Purkinje cells to complete various phyaiological activities.The information coming form mossy-fiber and climing fiber could induce forms of long-term synaptic plasticity in cerebellar cortical neuronal circuitry,which has been proposed to provide the cellular mechanisms for motor learning.So far,the mechanisms of synaptic plasticity at mossy-fiber granule cells(MF-GC)synapses mainly been studied underin vitro conditions,however,the properties and mechanisms of facial tactile stimulation evoked synaptic plasticity at MF-GC synapses in cerebellar cortex in living animals are currently unclear.We here studied the properties and possible mechanisms of the long-term synaptic plasticity induced by the facial tactile stimulation at MF-GC synapses in urethane-anesthetized mice by field potential recording technique and pharmacological methods.To understand the long-term plasticity induced mechanism of MF-GC synaptic transmission in the cerebellar cortex.The study will provide a theoretical basis for further revealing the mechanism of motor learning in the cerebellar cortical circuitry.Methods:Adult(6-8 weeks old)ICR mice were anesthetized of urethane(1.3 g/kg)by intraperitoneal injection.After cut off thewhiskers,the mice were tracheotomized and the head of the mouse is fixed on the brain stereotaxic apparatus and placed under the microscope.A 1-1.5 mm-diameter circular hole was opened in the corresponding part of the skull.After exposing the corresponding site,the dura was opened with a needle,brain tissue was exposed,and the brain surface was continuously perfused with oxygenated artificial cerebrospinal fluid(ACSF)with a peristaltic pump.Sensory stimulation was performed by air puff stimulation(10 ms,60psi)on the ipsilateral whisker pad.The train stimula for induction of plasticity was performat 20 Hz,240 pulses.Sensory stimulation was synchronized with the electrophysiological recording.Field potential recording data were analyzed using Clampfit 10.4 software.All values are expressed as the mean ± SEM,and differences were evaluated by the Student's paired t-test or one-way ANOVA using SPSS(Version 21)software.One-way ANOVA was used to compare the means.P<0.05 was considered statistically significant.Results:1.Air-puff stimulation of mouse ipsilateral whisker pad can induce negative reaction of granular cell layer N1.After giving 20Hz and 240 consecutive facial sensory stimuli,the amplitude of of N1 was peaked at 30 minutes of the train stimualtion,and the will be continued fro longer than 50 minutes.The result indicates that facial sensory stimulation at 20Hz can induce long term potentiation ynaptic transmission at mossy fiber-granule cell synapses(MF-GC LTP).2.After 40-50 minutes of 20Hz tactile stimulation,the amplitude of N1 amplitude was significantly higher than that before the tetanus stimulation,and accompanied by a significant increase in the area under N1 waveform(AUC).3.In the presence of NMD A receptor blocker,D-APV,the facial sensory stimulation of 20Hz did not induce MF-GC LTP,but resulted in a significant decrease in the amplitude and AUC of N1 and the occurrence of long term inhibition(LTD)after stimulation,suggesting that the LTP of MF-GC induced by facial sensory stimulation depends on the activation of NMD A receptor.4.After perfusion of NMD A,the mean value of N1 amplitude and AUC was significantly higher than that before the tetanic stimulation,indicating that pharmacological activation of NMDA receptor can induce MF-GC LTP,and further confirmed that the LTP of MF-GC induced by facial sensation stimulation depends on the activation of the NMDA receptor.5.In the presence of mGluRl receptor blocker JNJ,the facial sensory stimulation of 20Hz still induces MF-GC LTP,and the mean values of N1 amplitude and AUC are significantly higher than that before the tetanic stimulation,suggesting that the LTP of MF-GC in the facial sensory stimulation is not dependent on the activation of mGluRl.Conclusion:The results of this study show that the facial sensory stimulation at 20Hz induces the LTP at MF-GC synaptic transmission.The MF-GC LTP induced by facial sensory stimulation depends on the activation of the NMDA receptor,but it does not depend on the activation of mGluR1,which is suggested that external information can induce long-term synaptic plasticity at MF-GC synaptic transmission in cerebellar cortex may involve in a motor learning mechanism of cerebellum.