多巴胺（DA）是一種重要的神經傳導物質，主要負責運動控制，學習和認知等功能。 多巴胺系統參與在許多人類疾病當中，包括帕金森氏症（PD）。然而，帕金森氏症的致病機制仍不清楚。為了確定細胞中多巴胺濃度的不平衡是否涉及帕金森氏症的發病機制，有必要建立一個適合的探針，以直接檢測活體細胞內的多巴胺。我們利用單胺氧化酶（MAO）其獨特的光譜特徵與綠色螢光蛋白結合，作為探針的設計。單胺氧化酶在氧化態時，可以吸收400-500nm的綠色螢光蛋白激發光，氧化多巴胺之後，這種特性便會消失，與單胺氧化酶結合的螢光蛋白便得以發光。因此，引發的螢光蛋白訊號可以作為多巴胺濃度的讀數。我們的實驗結果顯示，間接增加細胞內多巴胺濃度可以激發探針中的綠色螢光蛋白發光，表示該探針可以有效的偵測多巴胺變化。運用多巴胺探針，未來將能確定帕金森氏症和其他多巴胺系統相關疾病中多巴胺濃度變化所扮演的角色。

Dopamine (DA) is an essential neurotransmitter that mainly involved in motor control, learning and cognitive association. The dysfunction of DA system links to several human diseases, including Parkinson’s disease (PD). However, the pathogenic mechanism of this disease is still unclear. To determine whether the imbalance of cellular DA level is involved in PD pathogenesis, it is essential to develop a genetically amenable probe that can directly detect intracellular DA in vivo. Here we utilize the unique spectrum feature of MAO B to design a MAO B-split GFP fusion protein as a DA probe. MAO B is a redox enzyme that catalyses catecholamine oxidation. In the absence of substrate, MAO B is at oxidized form that can absorb 400-500nm spectrums. Upon DA binding to MAO B, MAO B is reduced and losses this absorption property. Therefore, the elicit of GFP signal can serve as a readout of DA. We show that indirect modulations of cellular DA can trigger GFP fluorescence emission of the probe, suggesting this probe is feasible for DA detection. By applying this probe to PD models, we may be able to determine whether cellular DA imbalance is responsible for regional vulnerability of PD and other DA system related psychiatric disorders.

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