Faculty of Biological Sciences, School of Biomedical Sciences, University of Leeds, United Kingdom; Drug and Herbal Research Centre, Faculty of Pharmacy, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia.
Faculty of Biological Sciences, School of Biomedical Sciences, University of Leeds, United Kingdom.
Brain Stimul. 2019 Sep-Oct;12(5):1151-1158. doi: 10.1016/j.brs.2019.05.002. Epub 2019 May 6.
Electrical stimulation on select areas of the external auricular dermatome influences the autonomic nervous system. It has been postulated that activation of the Auricular Branch of the Vagus Nerve (ABVN) mediates such autonomic changes. However, the underlying neural pathways mediating these effects are unknown and, further, our understanding of the anatomical distribution of the ABVN in the auricle has now been questioned.
To investigate the effects of electrical stimulation of the tragus on autonomic outputs in the rat and probe the underlying neural pathways.
Central neuronal projections from nerves innervating the external auricle were investigated by injections of the transganglionic tracer cholera toxin B chain (CTB) into the right tragus of Wistar rats. Physiological recordings of heart rate, perfusion pressure, respiratory rate and sympathetic nerve activity were made in an anaesthetic free Working Heart Brainstem Preparation (WHBP) of the rat and changes in response to electrical stimulation of the tragus analysed.
Neuronal tracing from the tragus revealed that the densest CTB labelling was within laminae III-IV of the dorsal horn of the upper cervical spinal cord, ipsilateral to the injection sites. In the medulla oblongata, CTB labelled afferents were observed in the paratrigeminal nucleus, spinal trigeminal tract and cuneate nucleus. Surprisingly, only sparse labelling was observed in the vagal afferent termination site, the nucleus tractus solitarius. Recordings made from rats at night time revealed more robust sympathetic activity in comparison to day time rats, thus subsequent experiments were conducted in rats at night time. Electrical stimulation was delivered across the tragus for 5 min. Direct recording from the sympathetic chain revealed a central sympathoinhibition by up to 36% following tragus stimulation. Sympathoinhibition remained following sectioning of the cervical vagus nerve ipsilateral to the stimulation site, but was attenuated by sectioning of the upper cervical afferent nerve roots.
Inhibition of the sympathetic nervous system activity upon electrical stimulation of the tragus in the rat is mediated at least in part through sensory afferent projections to the upper cervical spinal cord. This challenges the notion that tragal stimulation is mediated by the auricular branch of the vagus nerve and suggests that alternative mechanisms may be involved.
对耳廓外部皮区的特定区域进行电刺激会影响自主神经系统。有人假设，迷走神经耳支（ABVN）的激活介导了这种自主变化。然而，介导这些效应的潜在神经通路尚不清楚，此外，我们对耳廓中 ABVN 的解剖分布的理解现在也受到了质疑。
研究电刺激耳屏对大鼠自主输出的影响，并探讨其潜在的神经通路。
通过将跨神经节示踪剂霍乱毒素 B 链（CTB）注入 Wistar 大鼠右侧耳屏，研究支配外耳廓的神经的中枢神经元投射。在大鼠麻醉自由的工作心脏脑桥制备（WHBP）中进行心率、灌注压、呼吸率和交感神经活动的生理记录，并分析对耳屏电刺激的反应变化。
从耳屏进行的神经元追踪显示，最密集的 CTB 标记位于注射部位同侧上颈脊髓背角的 III-IV 层。在延髓中，观察到 CTB 标记的传入纤维位于三叉神经旁核、三叉神经脊髓束和楔束核。令人惊讶的是，仅在迷走神经传入终末部位——孤束核中观察到稀疏的标记。在夜间进行的大鼠记录显示，与白天相比，交感神经活动更为活跃，因此后续实验在夜间进行。电刺激持续 5 分钟。直接从交感神经链记录显示，耳屏刺激后，交感神经兴奋抑制高达 36%。在刺激部位同侧颈迷走神经切断后，交感神经抑制仍然存在，但在上颈传入神经根切断后，抑制作用减弱。
在大鼠中，电刺激耳屏抑制交感神经系统活动至少部分是通过感觉传入纤维投射到上颈脊髓介导的。这挑战了耳屏刺激是由迷走神经耳支介导的观点，并表明可能涉及替代机制。
