小腦皮質層神經元的震盪放電降低其資訊含量

Attenuation of Information by Oscillatory Firing of Cerebellar Cortical Neurons

黃建嘉(Jina-Jia Huang)

指導教授 ： 曹恆偉

共同指導教授 ： 嚴震東

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.02866

摘要

震盪放電(oscillatory firing)在大腦訊息處理上被認為在遠距離腦區間的訊息溝通上扮演重要的角色，然而其功能在小腦(cerebellum)中仍不清楚。小腦皮質(cerebellar cortex) 為小腦結構中重要之訊息中心且分佈著多種的神經細胞，其中Golgi細胞與Purkinje細胞則是兩個重要神經元。Purkinje 細胞是小腦皮質中唯一的輸出神經元，而Golgi細胞則與小腦皮質輸入級的信息調節有關。此兩類神經細胞皆具有較大的細胞本體 (soma) 與樹突結構 (dendrite) 可產生較大的影響也具有震盪放電的表現。基於探討此二類小腦神經元的震盪放電行為，本論文主要使用Long-Evans大鼠 (rat) 作為實驗的模式動物，以電生理記錄方式記錄小腦皮質中的Purkinje 與Golgi細胞之放電型態，使用自相關分析 (auto-correlogram) 與快速傅立葉轉換 (Fast-Fourier Transform, FFT) 處理所記錄到之神經元放電信號。另一方面也估算其震盪程度並以訊息熵 (Shannon Information Entropy)估計此兩類神經元在動物清醒與麻醉下之信息含量。本論文開始先探討其相關背景，而後分成三個部分實驗探討：首先，以比較於此二類神經元在清醒及以urethane深層麻醉下的差異，以對其神經元基本放電特性作探討；第二部分將使用酒精誘發之運動失調症 (ataxia) 做為動物模式於實驗中，研究小腦神經元在行為功能異常下之表現。因為酒精在世界各國都被廣泛飲用，小腦也是酒精影響的一個主要區域，然而其詳細的作用機制與對中樞神經系統的影響仍尚待研究。此外酒精亦可類比作一個較淺層麻醉效果，可與深層的urethane麻醉作比較，探討在不同程度麻醉下其神經元之放電特性。最後以自然生理的表現下之非清醒行為 (即睡眠) 作為動物模式比較藥物作用下的Purkinje細胞放電表現。實驗結果顯示此二類神經元的震盪性放電多發生於深層的麻醉狀態，且在震盪放電的表現下，其信息含量較低。在清醒動物的酒精實驗方面，酒精會提高小腦中的GABAergic中間神經元 (Golgi cell)，但會降低Purkinje細胞的放電頻率，此外也發現酒精會誘發Golgi細胞與Purkinje細胞產生震盪放電的行為。由於Golgi 細胞會抑制mossy fiber-granule cell系統的活性，給予酒精所造成之Golgi 細胞的放電頻率上升可能會增強抑制小腦皮質的訊息輸入，進而影響Purkinje細胞內的信息量。因此，由以上的實驗結果顯示，麻醉與酒精處理之大鼠，其小腦皮質內之Golgi與Purkinje 細胞會產生震盪性放電，且於震盪性放電下由Shannon Information Entropy所估計的信息含量較低。進一步比較在睡眠下的Purkinje 細胞的活性亦顯示類似的結果，其放電率有下降的趨勢且同樣表現震盪性放電。藉由比較不同狀態下的神經元放電模式得到，震盪的程度在非清醒狀態顯著高於清醒狀態，且訊息量亦隨震盪程度下降而增加。故小腦皮質神經元震盪性放電下，有較少的處理信息量。

關鍵字

神經元震盪性放電 ； Purkinje細胞 ； Golgi 細胞 ； 信息熵 ； 小腦皮質

並列摘要

Neuronal oscillations have been shown to contribute to the cerebral cortical functions by coordinating the neuronal activities of distant cortical regions via a temporal synchronization of neuronal discharge patterns. This can occur regardless whether these regions are linked by cortico-cortical pathways or not. Less is known concerning the role of neuronal oscillations in the cerebellum. Literatures showed that Golgi and Purkinje cells are both principle cell types in the cerebellum. The Purkinje cell is the sole output cell of the cerebellar cortex while the Golgi cell contributes to information processing at the input stage of the cerebellar cortex. Both cell types have large cell bodies, as well as dendritic structures, that can generate large currents. The discharge patterns of both cell types also exhibit oscillations. In view of the massive afferent information conveyed by the mossy-fiber-granule-cell system to different and distant areas of the cerebellar cortex, it is relevant to inquire the role of cerebellar neuronal oscillations in information processing. In this thesis, we firstly compared the discharge patterns of Golgi cells and Purkinje cells in conscious rats and in rats anesthetized with urethane. We assessed neuronal oscillations by analyzing the regularity in the timing of individual spikes within a spike train by using auto-correlograms and FFT (Fast-Fourier transform) in different levels of consciousness (urethane-anesthetized, EtOH-treated, and sleeping states). The differences of neuronal oscillations and the amount of information content in a spike train (defined by Shannon entropy processed per unit time) were measured from Long-Evans rats in anesthetized and conscious states. Next, alcohol-treated rats were used as animal model with a lower unconscious level comparing to the anesthetized state due to the cerebellum is one of the EtOH action targets and the precise mechanisms underlying ethanol (EtOH)’s actions in the central nervous system (CNS) remain elusive. Finally, we tested the oscillatory Purkinje cell’s activity using the natural unconsciousness behavior (sleeping). we studied the cerebellar cortical neuronal oscillation using EtOH induced ataxia in the rat as an animal model. We also compared the neuronal oscillation under different states, which were sleeping, urethane anesthetizing, and conscious resting. Our results showed that: 1) in the input stage of cerebellar cortex, the EtOH increases the firing frequency in the Golgi cells and induces a neuronal oscillation; 2) in the output stage of the cerebellar cortex, EtOH significantly decreased and regulated the simple spike firing patterns in the Purkinje cells and induced a weaker neuronal oscillation in conscious unconstrained freely moving rats; 3) the neuronal oscillation in the cerebellar cortex was induced in the urethane anesthetized state in both Purkinje cells and Golgi cells, however in the conscious state the neuronal oscillations were weak; 4) the Purkinje cells firing frequency in the conscious state was higher than in the urethane anesthetized state, but in the Golgi cells, there was no significant difference in both states; 5) in the Purkinje cells during the neuronal oscillation period, the firing rate was slower than under weak oscillation states; 6) Using information entropy, the information count during the neuronal oscillation period is lower than weak oscillations. In conclusion, we examined the neuronal oscillatory activity of cerebellar Golgi cell and Purkinje cell in different states that may attenuate the capability of information processing. Our data support those in the previous studies made in the anesthesia experiment and provide additional experimental data for understanding the neuronal oscillation in the cerebellar cortex participating in a more natural conditions.

並列關鍵字

Purkinje cell ； Golgi cell ； neuronal oscillation ； information entropy

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