经皮穴位电刺激镇痛脑阿片受体机制的药理学功能磁共振研究

Acupuncture, which has been used to treat highly diversified pain for thousands of years, has more recently been recognized in the West as a useful complementary medicinal approach. Electroacupuncture (EA), as well as transcutaneous electrical acupoint stimulation (TEAS), has often been used to enhance mechanical stimulation of manual acupuncture for the same purpose in safety way. Accumulated data show that the mechanisms of TEAS analgesia involve the activation of endogenous opioid antinociceptive systems and the opioid receptors in the central nervous system. Different frequencies of TEAS can induce analgesia by mobilizing the release of specific neuropeptides in the central nervous system. 2 Hz peripheral stimulation produces a significant increase in the content of endorphin and enkephalin but not in that of dynorphin, whereas 100 Hz peripheral stimulation increases dynorphin but not enkephalin. Although systematic studies have carried out to explore the central neurobiological mechanisms of TEAS analgesia, there are few real-time visualized evidences demonstrating the involvement of opioid system during acupuncture treatment in vivo, especially in human experiments. Our previously study investigated the effects of low and high frequency TEAS on the cerebral μ-opioid receptor (MOR) binding potential of using [11C]-carfentanil PET in rhesus monkeys. The results showed that the MOR binding potential increased in multiple pain and sensory processing brain regions, which may play a role in mediating the effect of low, but not high frequency TEAS,implying divergent opioid receptor mechanisms in low and high frequency TEAS. As the synthesis of [11C]-carfentanil is at its preliminary stage in China and not suitable for human trials presently, we select pharmacological functional magnetic resonance imaging (phMRI) instead to investigate central neurobiological mechanisms of TEAS analgesia. Futhermore, neither tracer PET nor fMRI alone can satisfy these two conditions, as tracer PET is not sensitive to increases or decreases in neural responses and standard fMRI cannot make inferences about neurochemical events. Pharmacological fMRI can be employed in two groups of subjects: one receiving the opioid antagonist naloxone and one receiving saline. This allowed us to compare both behavioral and blood-oxygen-level-dependent (BOLD) responses under a ''natural opioid state'' and a ''blocked opioid state.'' The phMRI experiment was performed before, during and after TEAS on healthy volunteers at two acupoint, Hegu and Laogong, which was previously implicated in a neural pathway for pain modulation. Functional connectivity change of brain networks involved in TEAS, which is derived from BOLD, can be calculated for these two state respectively. In this way, the real-time visualized evidence of cerebral opioid receptor mechanism of TEAS analgesia could be provided in human in vivo.

以往有关高低两种频率(2 Hz，100 Hz)经皮穴位电刺激(TEAS)镇痛频率特异性的阿片受体机制研究未能在人体获取直接的可视化证据。本课题组前期用[11C]-卡芬太尼为示踪剂的PET对恒河猴脑的研究结果表明：2 Hz TEAS可以使多个痛觉和感觉处理区的阿片受体可用度升高，而100 Hz TEAS则没有该效应。由于国内该示踪剂尚不适合应用于人体研究，故本课题拟选用药理学功能磁共振对人体在阿片受体正常和阻断两种情况下的TEAS镇痛机制进行研究。这种综合fMRI的时间及空间分辨率高和PET的受体特异性高两者优势的技术可用于探讨以下机制：TEAS通过激活或抑制哪些脑区的功能实现其镇痛效应；TEAS通过增强或减弱哪些脑区间的功能联系发挥镇痛作用；内源性阿片肽及阿片受体在脑区激活及脑功能网络调节中所起的作用及其作用的频率依赖性。本研究旨在发现人体TEAS镇痛脑阿片受体机制的在体实时可视性证据。

本课题选用药理学功能磁共振对人体在阿片受体正常和阻断两种情况下TEAS镇痛机制进行研究。这种综合fMRI的时间及空间分辨率高和PET的受体特异性高两者优势的技术可用于探讨以下机制：TEAS 通过激活或抑制哪些脑区的功能实现其镇痛效应；TEAS 通过增强或减弱哪些脑区间的功能联系发挥镇痛作用；内源性阿片肽及阿片受体在脑区激活及脑功能网络调节中所起的作用及其作用的频率依赖性。扫描在Simens 3.0 T磁共振机器上进行，所用线圈为标准8通道头部线圈。功能序列为BOLD信号。具体参数如下：重复时间（TR）= 2000 ms；扫描野（FOV）= 230×230；分辨率= 2.9×2.9；采集矩阵= 64×64；层厚= 8 mm；层间距= 2 mm；扫描层数= 12层，包括整个大脑皮层及大部分小脑。本实验中BOLD数据处理和分析主要应用基于Matlab平台的SPM5和Rest软件。BOLD数据与行为学数据的相关性分析应用软件为GraphPad Prism 5.0。.对两组被试的BOLD数据进行基于GLM的逐个体素点分析，具体将每组被试的TEAS或Minimal TEAS中的数据与基线水平进行t检验比较。发现2 Hz、100 Hz TEAS 均可不同程度的调节局部脑区的BOLD信号，其变化趋势相近，以早期激活、后期抑制为特征；抑制脑区包括：海马旁回、海马、后扣带回、运动前区、躯体感觉皮质、初级运动皮层，楔叶、楔前叶、中额前皮质、前扣带回、颞中回、小脑。Minimal TEAS组在上述比较中，阈限上激活、抑制脑区明显减少；仅在缘上回和岛叶有少量激活。给予纳洛酮可显著解除TEAS的抑制水平，且对2Hz的抑制水平大于100Hz。应用GIFT和REST软件，提取出针刺前后和刺激过程中与SMN和DMN相匹配的成分并计算各成分间的功能连接，Minimal TEAS的作用主要表现为对SMN网络内部功能联系的增强，而TEAS作用主要表现在对DMN、SMN网络内部功能联系的减弱。其中2 Hz TEAS特异性的减弱背侧前扣带回与SMN之间的关系，而100 Hz TEAS特异性的减弱DMN内部的功能连接度。给予纳洛酮可反转2Hz TEAS的作用，而对的100Hz作用不明显。数据进一步挖掘计划在痛觉相关通路上各核团的功能连接上进行，并对纳洛酮对脑静息态时的局部一致性和低频振辐的影响进行研究。