Investigations Of Molecular Mechanisms Involved In Long-term Synaptic Plasticity Of Cerebellar Purkinje Cell

As the major contact point and communication place between neurons,the synapse is regarded as the location where learning and memory happen.Synaptic transmission is modulatable by a phenomenon called synaptic plasticity,which could persist for hours even days.Extensive studies indicated that synaptic plasticity,such as long-term potentiation or long-term depression,is the cellular basis for learning and memory.Purkinje cells(PCs) receive inputs from both climbing fibers(CFs) and parallel fibers(PFs) and inhibit the major cerebellar output neurons,deep cerebellar nuclei.It is demonstrated that PC is regarded as the major location where cerebellar synaptic plasticities happen and involved into many physiologic processes.In this dissertation,we investigated some molecules that could affect synaptic plasticities on PC.It was shown that excitatory amino acid transporter 4(EAAT4) is expressed abundantly in PC and subsequently modulates the glutamate concentration in synaptic cleft,with detailed mechanisms unclear.In CF-PC synapse,EAAT4 and metabotropic glutamate receptor(mGluR) are located very closely in post-synaptic region, suggesting that EAAT4 may modulate the activation of mGluR1.We applied the inhibitors of EAAT4,DL-TBOA and D-Aspartate and observed the function of EAAT4 on mGluR1.Our results indicated that EAAT4 inhibition significantly prolonged AMAP-mediated EPSC activated by CF stimulation and enhanced mGluR1-dependent CF-PC synaptic LTD.LTD could not be induced at CF-PC synapse with lower frequency tetanus stimuli,however,blockade of EAAT4 could rescue expression of LTD under this condition.Thus,we were first to demonstrate that EAAT4 significantly affected mGluR1 -dependent cerebellar LTD.Recently,researchers showed that AMPA receptors trafficking(arriving to or away from membrane) is the key molecular event in neuronal plasticity.Our collaborator found that ICA69 is an important component of PICK1 complex.AMPA receptor trafficking is a subject to the interaction between PICK1 and ICA69 through BAR domain.Thus,we prepared fusion protein of ICA69 that would directly enhance the combining between ICA69 and PICK1.In experiments,we added MBP-ICA69 and MBP into pipette saline as the experimental and control groups respectively to observe influence of MBP-ICA69 interaction on PF-PC synaptic plasticity.Our results firstly showed that PF-PC synaptic plasticity was blocked after the effective formation of PICK1-ICA69.Niemann-Pick type C(NPC) is a chromosome mutation caused by progressive neuronal degeneration.Death typically occurs in the teenage subjects.It is generally accepted that glial ATP secretion is affected in NPC mouse model.We observed the synaptic plasticity in three-week-old mice and found synaptic plasticity on PF-PC was blocked.Our results suggested that synaptic adenosine 1 receptor was inhibited and thus LTD expression was affected in NPC transgenic mouse model.Alcohol has huge effects on human motor function.Previous studies showed that cerebellar function is affected but detailed mechanism is unclear.In this dissertation, our preliminary data showed that alcohol could affect expression of PF-PC synaptic LTD when measuring the influence of alcohol on cerebellar plasticities.In summary,our studies basically analyzed functions of several molecular signals on synaptic plasticities in cerebellar PC.We think that these results will help international neuroscientific researchers to understand better of molecular and cellular functions of cerebellar PCs.