光基因刺激法是一新興的神經科學研究技術，藉由光照射來控制基因改造的神經元。將光敏感性通道視紫蛋白表現於神經細胞膜上，再以特定波長的光線照射，便可活化通道視紫蛋白造成帶電離子的運輸，改變細胞膜電位進而調控神經細胞的電生理活性。藉由搭配組織特異性的遺傳工程技術，可以將通道視紫蛋白表現於特定的腦區、神經細胞種類，或是細胞的局部區域中，達成細胞選擇性與特異性的活化或是抑制。光基因刺激法已經有效地被應用於離體細胞模式或是活體動物模式中，產生空間上局部的、時間上精準的神經活性操控，以研究特定的神經迴路功能，或是探討各種神經疾病治病機轉。傳統的活體光基因刺激實驗，是使用光纖將來自於雷射或是發光二極體的光線，導入神經組織中進行光基因刺激。然而，光纖的連接限制了實驗動物的行為與運動型態，對於清醒動物模式的神經行為學研究有諸多不便。因此，研究者發展了許多可植入式的無線光基因刺激系統，以滿足這方面的實驗需求。然而，許多無線光基因刺激系統體積龐大、造價昂貴，還無法整合無線電生理量測。為了探討清醒自由運動的動物模式，其腦皮質電生理的活性受到光基因刺激的影響，在本研究中，我們開發一套利用紅外線傳輸的無線光基因系統，來自LabVIEW使用者介面的刺激紅外線訊號，經由紅外線感測與放大電路接收後，驅動植入式光電極內的微小發光二極體。刺激光源藉由光纖導入深層組織中，所引發的神經組織電位反應，則由包覆於光纖外的不鏽鋼管收集量測，最後神經電生理訊號藉由整合的無線射頻傳輸模組，同步記錄於LabVIEW程式中。本系統造價低廉，光電極模組與控制電路分開，控制電路只有在進行實驗時才需要裝設在動物的頭部，不僅可以縮小植入體積與節省製造成本，還可以降低植入物對動物日常生活的干擾，更有利於長期的動物實驗。紅外線傳輸原理簡單，體積小兼省電，紅外線放大電路作用於飽和區間，可以達成快速同步且穩定的高頻光基因刺激。本系統可以幫助神經科學家，採用光基因刺激法在清醒活動的小動物模式中，探究各種神經迴路機制與神經疾病治病機轉，如帕金森氏症。

Optogenetics is an emerging neuro-engineering technique that using light to control cellular function in genetic modified neurons. Optogenetics takes advantage of opsins found in retinal photoreceptor cells, which can be activated by light at specific wavelengths. By molecule-specific expression of opsins and light stimulation pulses, optogenetics allows investigator to activate or inhibit specific neurons with spatiotemporal precision. These features make optogenetics an ideal tool to investigate neural network underlying motor dysfunction in animal models of neural disorders. Although optical stimulation promises new exciting possibilities for neuroscience research, there is still an unmet need for reliable and implantable devices to precisely deliver light to the targeted neural pathways and to simultaneously record the electrical signals from the individual pathways. In conventional in vivo optogenetic study, the light from laser or photo-diode will be coupled into optical fiber then stimulate the specific neuron. However, the tethered optical fiber will restrict the animals’ behavior, which cause many limitations in awake and freely moving animals. Therefore, many implantable wireless optogenetic systems were proposed to solve the problems. However, many implantable wireless optogenetic systems are huge, high-cost and without wireless electrophysiological signals recording. In this study, we have developed a wireless optogenetic neural interface with one channel of optical stimulation and up to five channels of neural recording for freely moving animal experiments. The wireless optical stimulation was achieved by Infrared (IR) remote control. When the highly sensitive IR receiver was triggered, micro blue LED mounted on the rat’s head can be activated to emit blue light. The blue light was guided into brain tissue through a short segment of optical fiber, which was enclosed with a stainless steel cannula. The stainless steel cannula also functions as neural electrode to pick up neural response evoked by optogenetic stimulation. The recorded neural signals are amplified and transmitted through a commercially available radio-frequency (RF) head-stage. This simple designed neural interface is separated from IR-receiver head-stage, which minimizes the size of the implant and causes less interference to freely moving rats. The electrophysiology, which is filtered and amplified, was recorded from 4-weeks ChR2-expressed rats. The recording of neural readouts: local field potentials (LFPs) and multi-unit activities (MUAs), can be synchronized with optical stimulation and behavioral events, which provide benefits in studies of awake and freely moving animal models. Photoelectric artifacts less than 4 ms of pulse width was confined during LFPs recording induced by optical stimuli. The artifact can be easily distinguished with LFPs by lengths of latency. The implantable wireless device allows highly precise optogenetic controlling of specific neuronal populations in freely moving animal models. The designed experiments allow clearer elucidation of the mechanisms of motor control in neural system. These features of wireless optogeentic stimulation and recording system will be very helpful in the understanding of brain functions and for the study of neural disorder with motor dysfunction such as Parkinson’s disease.

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