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Όλ¬Έ (λ°μ¬)-- μμΈλνκ΅ λνμ : μκ³Όλν μκ³Όνκ³Ό, 2019. 2. κΉμμ .Learning rule has been thought to be implemented by activity-dependent modifications of synaptic function and neuronal excitability which contributing to maximization the information flow in the neural network. Since the sensory information is conveyed by forms of action potential (AP) firing, the plasticity of the intrinsic excitability (intrinsic plasticity) has been highlighted the computational feature of the brain. Given the cerebellar Purkinje cells (PCs) is the sole output neurons in the cerebellar cortex, coordination of the synaptic plasticity at the parallel fiber (PF) to PC synapses including long-term depression (LTD) and long-term potentiation (LTP) but also the intrinsic plasticity may play a essential role in information processing in the cerebellum. In this Dissertation, I have investigated several features of intrinsic plasticity in the cerebellar PCs in an activity-dependent manner and their cellular mechanism. Furthermore, the functional implications of the intrinsic plasticity in the cerebellum-dependent behavioral output are discussed. Firstly, I first cover the ion channels regulating the spiking activity of the cerebellar PCs and the cellular mechanisms of the plastic changes in excitability. Various ion channels indeed harmonize the cellular activity and shaping the optimal ranges of the neuronal excitability. Among the ion channels expressed in the cerebellar PCs, hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contribute to the non-Hebbian homeostatic intrinsic plasticity in the cerebellar PCs. Chronic activity-deprivation of PC activity caused the upregulation of agonist-independent activity of type 1 metabotropic glutamate receptor (mGluR1). The increased mGluR1 activity consequently enhanced the HCN channel current density through protein kinase A (PKA) pathway thereby downregulation of intrinsic excitability in PCs. In addition, the intrinsic excitability of PCs is found to be modulated by synaptic activity. Of interest, I investigated that the PF-PC LTD is accompanied by LTD of intrinsic excitability (LTD-IE). The LTD-IE indeed shared intracellular signal cascade for governing the synaptic LTD such as large amount of Ca2+ influx, mGluR1, protein kinase C (PKC) and Ca2+-calmodulin-dependent protein kinase II (CaMKII) activation. Interestingly, the LTD-IE reduced PC spike output without changes in patterns of synaptic integration and spike generation, suggesting that the intrinsic plasticity alters the quantity of information rather than the quality of information processing. In consistent, the LTD-IE was shown in the floccular PCs when the PF-PC LTD occurs. Notably, not only the synaptic LTD but also LTD-IE was found to be formed at the conditioned dendritic branch. Thus, synaptic plasticity could significantly affect to the neuronal net output through the synergistic coordination of synaptic and intrinsic plasticity in the dendrosomatic axis of the cerebellar PCs. In conclusion, the activity-dependent modulation of intrinsic excitability may contribute to dynamic tuning of the cerebellar PC output for appropriate signal transduction into the downstream neurons of the cerebellar PCs.μλͺ
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Abstract
General introduction
Chapter 1. Summary of the previous literatures and further implication for physiological significance of the intrinsic plasticity in the cerebellar Purkinje cells
Summary.
1.1 Ion channels and spiking activity of the cerebellar Purkinje cells
1.1.1 Voltage-gated Na+ channels
1.1.2 Voltage-gated K+ channels and Ca2+-activated K+ channels
1.2 Activity-dependent plasticity of intrinsic excitability through ion channel modulation
1.2.1 Activity-dependent plasticity of intrinsic. excitability through ion channel
1.2.2 Possible mechanisms for LTD-IE.
1.2.3 Upside down: to what extent does bidirectional intrinsic plasticity in. the cerebellar dependent-motor learning do?
1.3 The further implication of intrinsic plasticity in the memory circuits.
Chapter 2. Type 1 metabotropic glutamate receptor mediates homeostatic control of intrinsic excitability through hyperpolarization-activated current in cerebellar Purkinje cells
Introduction
Material and Method
Results
2.1 Chronic activity-deprivation reduces intrinsic excitability of the
cerebellar. Purkinje cells 35
2.2 Homeostatic intrinsic plasticity of the cerebellar Purkinje cells is mediated activity-dependent modulation of Ih
2.3 Homeostatic intrinsic plasticity of the cerebellar Purkinje cells requires agonist-independent action of mGluR1
2.4 Homeostatic intrinsic plasticity of the cerebellar Purkinje cells is mediated. PKA activity
Discussion
Chapter 3. Long-Term Depression of Intrinsic Excitability Accompanied by Synaptic Depression in Cerebellar Purkinje Cells
Introduction
Material and Method
Results
3.1 LTD of intrinsic excitability of PC accompanied by PF-PC LTD
3.2 LTD-IE has different developing kinetics from synaptic LTD
3.3 LTD-IE was not reversed by subsequent LTP-IE induction
3.4 The number of recruited synapses were not correlated to the magnitude of the neuronal
3.5 Information processing after LTD induction LTD-IE was not. reversed by subsequent LTP-IE induction
3.6 LTD-IE required the Ca2+-signal but not depended on the Ca2+-activated K+ channels
Discussion
Chapter 4. Synergies between synaptic depression and intrinsic plasticity of the cerebellar Purkinje cells determining the Purkinje cell output
Introduction
Material and Method
Restuls
4.1 Timing rules of intrinsic plasticity of floccular PCs 87
4.2 Intrinsic plasticity shares intracellular signaling for PF-PC LTD
4.3 Conditioned PF branches contributing to robust reduction of spike output of the PCs
4.4 Sufficient changes in spiking output require both of plasticity, synaptic and. intrinsic plasticity
4.5 Supralinearity of spiking output coordination after induction of PC plasticity
Discussion
Bibliography
Abstract in Korean
AcknowledgementDocto