帕金森氏症 (Parkinson’s disease)是一種神經退化性疾病，因大腦黑質區多巴胺神經細胞大量退化，進而使多巴胺分泌減少，而影響到和運動功能相關的基底神經核的調控，造成患者出現運動障礙。高頻深層腦刺激(deep brain stimulation, DBS)主要運用於治療重度帕金森氏患者，可以有效的抑制腦部初級運動皮質(primary motor cortex, M1)不正常的神經電生理活性 (beta oscillation)，同時也明顯的改善患者運動行為方面症狀。許多研究指出在STN-DBS是透過逆向方向經由超直接路徑 (hyperdirect pathway)傳遞電生理訊號到運動皮質，進而影響運動皮質的神經訊號。經由我們先前研究指出，帕金森氏模式鼠不管在受損側或完整側，經由STN-DBS刺激後會在M1的第5b層引發細胞大量表現c-fos(蛋白質訊號)，而在M1內給予dopamine受器的抑制劑則會抑制這些細胞中的c-fos蛋白表現。這些結果顯示出STN-DBS活化皮質運動區細胞的過程除了透過逆向路徑的方式外，可能還牽涉到其他的機制參與，例如活化dopamine受器等。
腹側背蓋區(ventral tegmental area, VTA)同樣也是重要的多巴胺神經來源，經由中腦皮質路徑 (mesocortical pathway)會投射到大腦皮質運動區。臨床發現在帕金森氏症患者腦部， VTA多巴胺神經會受到影響，再加上VTA與STN位置相近以及STN的投射，推測在STN-DBS時，可能間接影響VTA，使多巴胺敏感的運動皮質接收到多巴胺活化，進一步調控皮質功能。
因此本篇想探討VTA是否會藉由投射的中腦皮質路徑參與STN-DBS對運動皮質異常beta震盪的抑制。在實驗的第一個部分，我們首先對由6-OHDA建立的帕金森氏模式鼠是否在VTA同樣會出現多巴胺神經受損的情形進行初步分析。藉由tyrosine hydroxylase (TH)免疫組織染色標定VTA區域中的多巴胺神經，結果顯示以6-OHDA所建立的帕金森氏模式鼠VTA多巴胺神經確實受到破壞。進一步探討STN-DBS對M1第5b層異常beta震盪的抑制效果是否會間接透過VTA的中腦皮質路徑而產生影響。在本實驗第二個部分，我們藉由記錄LFP (local field potential)的方法，觀察VTA刺激對STN-DBS抑制M1第5b層異常beta震盪的影響。藉由FFT(fast Fourier transform)分析STN與VTA共同刺激以及VTA單獨刺激下beta震盪的能量強度，分析結果顯示搭配VTA的共同刺激與STN單獨刺激對beta的影響並沒有顯著的差異，在VTA的單獨刺激經分析後同樣沒有顯著的差異。經我們實驗結果發現，不管是與STN搭配的共同刺激以及VTA的單獨刺激皆對M1第5b層出現的異常beta震盪沒有顯著的影響。

Parkinson’s disease is one of the most common neurodegeneration. PD patients usually experience motor symptoms associated with pathological losses of the dopaminergic neurons in substantia nigra (SN). SNc dopaminergic neuron degeneration break the balance of basal ganglia system which plays important functions in controlling movements. High frequency deep brain stimulation (DBS) is mainly used in treating the movement abnormalities of severe Parkinson's patients. STN can also effectively inhibit the abnormal neurophysiological activity (beta oscillation) in primary motor cortex (M1) observed in PD patients and animal models of PD. Earlier studies have indicated that STN-DBS may send antidromic activities to the motor cortex via the hyperdirect pathway, thereby affecting the physiological signals in M1 neural circuits. In an earlier study of our laboratory, STN-DBS has been found to induce M1 layer 5b neurons to express intensely c-Fos protein (giant c-Fos) in hemi-Parkinsonian rats. The intense c-Fos expression is these motor cortex neurons could be blocked by local application of dopamine receptor antagonist in M1. This observation suggests that STN-DBS activates motor cortex not only through antidromic pathway, but DBS also induce dopamine receptor activation in the motor cortex.
In addition to substantial nigra pars compacta, ventral tegmental area (VTA) is also an important source of dopamine of motor cortex via the mesocortical pathway. Clinically, loses of dopaminergic neurons in VTA area have also been reported. The VTA resides near STN, and VTA receive STN projection. Therefore, we speculate that STN-DBS may stimulate VTA dopaminergic neurons and result in releave of dopamine in the motor cortex.
The aim of my thesis is to investigate whether VTA mesocortical pathway is involved in the inhibition M1 abnormal beta-oscillation by STN-DBS. First, I confirmed that the dompaminergic neurons in theVTA was depleted by 6-OHDA injection in hemi-Parkinsonian rats. My quantitative analyses by tyrosine hydroxylase (TH) staining indicated that in the VTA, DA neurons in the lesioned side were reduced to ~25% of that in the intact side. I further investigated whether the STN-DBS inducedinhibition of the abnormal beta-oscillation in M1 layer 5b by directly stimulating the VTA. The results indicate that direct sitmulation of VTA did not affect the beta-oscillations recorded in the motor cortex of hemi-Parkinsonian rats. Coupling VTA stimulation with STN-DBS did not affect the STN-DBS-induced inhibition of beta-oscillations recorded in the motor cortex, either. However, it remains unclear if direct stimulation of VTA affects the STN-DBS effects on the behavioral abnormalities associated with PD.

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