Nat Methods：科学家发现促进BOLD信号的相关细胞

近日，国际著名杂志《自然—方法学》Nature Methods报道了一种采用功能性磁共振成像（fMRI）作为记录手段的与信号促进有关的细胞鉴定方法。

磁共振成像（MRI）机器一般通过测量血液流动中的变化来监控大脑功能活动。基于对比度的血氧水平依赖性（BOLD）fMRI作为一种非侵入性工具，在检测健康或患病的动物模型和人体的脑功能方面已经获得广泛应用。但是，反映局部细胞活动的BOLD信号的变化范围仍是未知，这让fMRI相关研究的分析变得不确定。利用配备有荧光传感器的显微镜，科学家可以跟踪观察到动物脑部的个体细胞的活动情况，但是迄今为止该方法还未直接与fMRI相结合。

Fritjof Helmchen等人采用fMRI对经过荧光染色的大鼠个体细胞的活动信号进行记录。通过监视脑部神经细胞和神经胶质细胞的活动情况及其与BOLD信号的联系，他们发现在一定条件下神经胶质细胞的活动对BOLD信号有促进作用。

这项研究强调了fMRI中BOLD信号的复杂性，并为进一步了解fMRI研究提供了新思路。（生物谷Bioon.com）

doi:10.1038/nmeth.2013
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Simultaneous BOLD fMRI and fiber-optic calcium recording in rat neocortex

Kristina Schulz, Esther Sydekum, Roland Krueppel, Christoph J Engelbrecht, Felix Schlegel, Aileen Schröter, Markus Rudin & Fritjof Helmchen

Functional magnetic resonance imaging (fMRI) based on blood oxygen level–dependent (BOLD) contrast is widely used for probing brain activity, but its relationship to underlying neural activity remains elusive. Here, we combined fMRI with fiber-optic recordings of fluorescent calcium indicator signals to investigate this relationship in rat somatosensory cortex. Electrical forepaw stimulation (1–10 Hz) evoked fast calcium signals of neuronal origin that showed frequency-dependent adaptation. Additionally, slower calcium signals occurred in astrocyte networks, as verified by astrocyte-specific staining and two-photon microscopy. Without apparent glia activation, we could predict BOLD responses well from simultaneously recorded fiber-optic signals, assuming an impulse response function and taking into account neuronal adaptation. In cases with glia activation, we uncovered additional prolonged BOLD signal components. Our findings highlight the complexity of fMRI BOLD signals, involving both neuronal and glial activity. Combined fMRI and fiber-optic recordings should help to clarify cellular mechanisms underlying BOLD signals.