Evaluating a genetically encoded optical sensor of neural activity using electrophysiology in intact adult fruit flies.
Evaluating a genetically encoded optical sensor of neural activity using electrophysiology in intact adult fruit flies.
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DOI：
10.3389/neuro.04.003.2007
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发表时间：
2007
影响因子：
3.5
通讯作者：
Laurent G
中科院分区：
文献类型：
--
作者：
Jayaraman V;Laurent G
基因编码的光学指示器有望实现对行为生物体中已识别神经元活动的非侵入性监测。然而，这种传感器产生的大脑活动图像的解释并不是直截了当的。最近的几项感官编码研究使用G-CaMP 1.3（一种钙传感器）作为神经活动的指标；其中一些研究的特征是成像神经元具有狭窄的调谐曲线，这一结论并不总是得到平行电生理学研究的支持。为了更好地理解这些相互矛盾的结果的可能原因，我们对完整果蝇触角叶（AL）中表达G-CaMP 1.3的神经元进行了体内双光子成像和电生理记录。我们发现G-CaMP有一个相对较高的阈值，它的信号经常不能捕捉到尖峰反应动力学，如果这些反应不能持续下去，它甚至会错过高的瞬时活动速率。虽然G-CaMP可能会误导人，但它对于识别有希望的神经目标显然是有用的：当电活动远高于传感器的检测阈值时，其信号与平均放电率相当好地相关，并且G-CaMP似乎不会显著改变表达它的神经元的反应。我们提出的方法应该能够在果蝇体内完整的神经回路中评估任何基因编码的传感器、激活器或沉默器。
Genetically encoded optical indicators hold the promise of enabling non-invasive monitoring of activity in identified neurons in behaving organisms. However, the interpretation of images of brain activity produced using such sensors is not straightforward. Several recent studies of sensory coding used G-CaMP 1.3—a calcium sensor—as an indicator of neural activity; some of these studies characterized the imaged neurons as having narrow tuning curves, a conclusion not always supported by parallel electrophysiological studies. To better understand the possible cause of these conflicting results, we performed simultaneous in vivo 2-photon imaging and electrophysiological recording of G-CaMP 1.3 expressing neurons in the antennal lobe (AL) of intact fruitflies. We find that G-CaMP has a relatively high threshold, that its signal often fails to capture spiking response kinetics, and that it can miss even high instantaneous rates of activity if those are not sustained. While G-CaMP can be misleading, it is clearly useful for the identification of promising neural targets: when electrical activity is well above the sensor's detection threshold, its signal is fairly well correlated with mean firing rate and G-CaMP does not appear to alter significantly the responses of neurons that express it. The methods we present should enable any genetically encoded sensor, activator, or silencer to be evaluated in an intact neural circuit in vivo in Drosophila.
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