Husson T. Robert, Issa Naoum P.
While great strides have been made in the development of novel optical imaging techniques in the past two decades, these methods still either measure coarsely or require relatively invasive procedures. The ideal optical measure would faithfully represent local neural activity, both spiking and nonspiking, at subcellular resolution, with persistent, reliable responses without the use of exogenous agents. Practically, there are several opportunities to measure endogenous signals that could serve as indirect measures of neural activity: most commonly, metabolic processes which take advantage of the tight coupling between neural activity and ATP production. Unfortunately, the most robust metabolic signals (such as blood deoxygenation) are only weakly linked to neural activity, and can be spatially diffuse, putting strict limitations on the interpretation of these data. Recently, the endogenous fluorescence of mitochondrial flavoproteins (FA, flavoprotein autofluorescence) has been exploited for functional imaging in a variety of preparations, both in vivo and in vitro. These flavoproteins are oxidized during aerobic metabolism, which is closely coupled to neuronal signaling, and their fluorescence has been shown to follow neural activity in response to pharmacological, electrical, and sensory stimulation. They have been used to confirm functional maps in several cortical areas, and are supported by a growing body of in vitro work. As these signals (1) are highly spatially localized, (2) can be measured by a variety of optical techniques both in vitro and in vivo, and (3) require no exogenous dyes, they offer substantial improvement in our ability to map functional activity and trace neural circuits. Here, we describe the underlying biochemistry of the flavoprotein signal, the experimental details of using it for functional imaging in vivo, and outline example studies and future directions for this promising new approach to visualizing neural activity patterns.
在过去二十年中，新型光学成像技术取得了长足发展，但这些方法仍存在测量粗糙或需要相对侵入性操作的问题。理想的光学测量方法应能在亚细胞分辨率下忠实地呈现局部神经活动，包括动作电位发放和非动作电位发放，具有持续、可靠的响应，且无需使用外源性试剂。实际上，有多种测量内源性信号的机会，这些信号可作为神经活动的间接测量指标：最常见的是利用神经活动与ATP生成之间紧密耦合的代谢过程。不幸的是，最强烈的代谢信号（如血液脱氧）与神经活动的联系较弱，且可能在空间上扩散，这对这些数据的解释造成了严格限制。最近，线粒体黄素蛋白的内源性荧光（FA，黄素蛋白自发荧光）已被用于多种体内和体外制剂的功能成像。这些黄素蛋白在有氧代谢过程中被氧化，而有氧代谢与神经元信号传导密切相关，并且已证明它们的荧光会随着药理学、电刺激和感觉刺激而跟随神经活动。它们已被用于确认多个皮质区域的功能图谱，并得到了越来越多体外研究的支持。由于这些信号（1）在空间上高度局限，（2）可在体内和体外通过多种光学技术进行测量，（3）无需外源性染料，它们在我们绘制功能活动图谱和追踪神经回路的能力方面有了显著提升。在这里，我们描述了黄素蛋白信号的潜在生物化学原理、在体内用于功能成像的实验细节，并概述了示例研究以及这种用于可视化神经活动模式的有前景新方法的未来方向。
