Chen Tianwen, Huang Jun, Yu Yue, Tang Xuehui, Zhang Chunming, Xu Youguo, Arteaga Alberto, Allison Jerome, Mustain William, Donald Matthew C, Rappai Tracy, Zhang Michael, Zhou Wu, Zhu Hong
Department of Otolaryngology-Head and Neck Surgery, University of Mississippi Medical Center, Jackson, MS, United States.
Department of Otolaryngology, First Affiliated Hospital, Shanxi Medical University, Taiyuan, China.
Front Neurosci. 2021 Oct 14;15:741571. doi: 10.3389/fnins.2021.741571. eCollection 2021.
Vestibular evoked myogenic potentials (VEMP) have been used to assess otolith function in clinics worldwide. However, there are accumulating evidence suggesting that the clinically used sound stimuli activate not only the otolith afferents, but also the canal afferents, indicating canal contributions to the VEMPs. To better understand the neural mechanisms underlying the VEMPs and develop discriminative VEMP protocols, we further examined sound-evoked responses of the vestibular nucleus neurons and the abducens neurons, which have the interneurons and motoneurons of the vestibulo-ocular reflex (VOR) pathways. Air-conducted clicks (50-80 dB SL re ABR threshold, 0.1 ms duration) or tone bursts (60-80 dB SL, 125-4,000 Hz, 8 ms plateau, 1 ms rise/fall) were delivered to the ears of Sprague-Dawley or Long-Evans rats. Among 425 vestibular nucleus neurons recorded in anesthetized rats and 18 abducens neurons recorded in awake rats, sound activated 35.9% of the vestibular neurons that increased discharge rates for ipsilateral head rotation (Type I neuron), 15.7% of the vestibular neurons that increased discharge rates for contralateral head rotation (Type II neuron), 57.2% of the vestibular neurons that did not change discharge rates during head rotation (non-canal neuron), and 38.9% of the abducens neurons. Sound sensitive vestibular nucleus neurons and abducens neurons exhibited characteristic tuning curves that reflected convergence of canal and otolith inputs in the VOR pathways. Tone bursts also evoked well-defined eye movements that increased with tone intensity and duration and exhibited peak frequency of ∼1,500 Hz. For the left eye, tone bursts evoked upward/rightward eye movements for ipsilateral stimulation, and downward/leftward eye movements for contralateral stimulation. These results demonstrate that sound stimulation results in activation of the canal and otolith VOR pathways that can be measured by eye tracking devices to develop discriminative tests of vestibular function in animal models and in humans.
前庭诱发肌源性电位（VEMP）已在全球范围内的临床中用于评估耳石功能。然而，越来越多的证据表明，临床使用的声音刺激不仅激活耳石传入神经，还激活半规管传入神经，这表明半规管对VEMP有贡献。为了更好地理解VEMP背后的神经机制并开发有鉴别力的VEMP方案，我们进一步研究了前庭核神经元和展神经神经元的声音诱发反应，这些神经元具有前庭眼反射（VOR）通路的中间神经元和运动神经元。将气导短声（相对于ABR阈值为50 - 80 dB SL，持续时间0.1 ms）或短纯音（60 - 80 dB SL，125 - 4000 Hz，8 ms平台期，1 ms上升/下降时间）施加到Sprague-Dawley或Long-Evans大鼠的耳朵。在麻醉大鼠中记录的425个前庭核神经元和清醒大鼠中记录的18个展神经神经元中，声音激活了35.9%的前庭神经元，这些神经元在同侧头部旋转时放电率增加（I型神经元），15.7%的前庭神经元在对侧头部旋转时放电率增加（II型神经元），57.2%的前庭神经元在头部旋转期间放电率不变（非半规管神经元），以及38.9%的展神经神经元。对声音敏感的前庭核神经元和展神经神经元表现出特征性的调谐曲线，反映了VOR通路中半规管和耳石输入的汇聚。短纯音还诱发了明确的眼球运动，这种运动随着声音强度和持续时间的增加而增加，并且表现出约1500 Hz的峰值频率。对于左眼，短纯音在同侧刺激时诱发向上/向右的眼球运动，在对侧刺激时诱发向下/向左的眼球运动。这些结果表明，声音刺激会导致半规管和耳石VOR通路的激活，这可以通过眼动追踪设备进行测量，以开发动物模型和人类前庭功能的鉴别测试。
