Department of Physiology and Pathophysiology, Xi'an Jiaotong University, Medical School, Xi'an, Shaanxi 710061, PR China.
Faculty of Dentistry, University of Toronto, Toronto, Ontario M5G 1G6, Canada.
Brain Res. 2021 Sep 15;1767:147539. doi: 10.1016/j.brainres.2021.147539. Epub 2021 May 28.
The rostral ventromedial medulla (RVM) plays a key role in the endogenous modulation of nociceptive transmission in the central nervous system (CNS). The primary aim of this study was to examine whether the activities of RVM neurons were related to craniofacial nociceptive behaviour (jaw-motor response, JMR) as well as the tail-flick response (TF). The activities of RVM neurons and TF and JMR evoked by noxious heating of the tail or perioral skin were recorded simultaneously in lightly anaesthetized rats. Tail or perioral heating evoked the TF and JMR, and the latency of the JMR was significantly shorter (P < 0.001) than that of the TF. Of 89 neurons recorded in RVM, 40 were classified as ON-cells, 27 as OFF-cells, and 22 as NEUTRAL-cells based on their responsiveness to heating of the tail. Heating at either site caused an increase in ON-cell and decrease in OFF-cell activity before the occurrence of the TF and JMR, but did not alter the activity of NEUTRAL cells. Likewise, noxious stimulation of the temporomandibular joint had similar effects on RVM neurons. These findings reveal that the JMR is a measure of the excitability of trigeminal and spinal nociceptive circuits in the CNS, and that the JMR as well as TF can be used for studying processes related to descending modulation of pain. The findings also support the view that RVM ON- and OFF-cells play an important role in the elaboration of diverse nociceptive behaviours evoked by noxious stimulation of widely separated regions of the body.
延髓头端腹内侧区（RVM）在中枢神经系统（CNS）内源性调节伤害性传入中起着关键作用。本研究的主要目的是检验 RVM 神经元的活动是否与头面部伤害性感受行为（颌运动反应，JMR）以及尾部回缩反应（TF）有关。在轻度麻醉的大鼠中，同时记录 RVM 神经元的活动以及 TF 和 JMR，这些神经元的活动是由尾部或口周皮肤的伤害性加热所诱发的。尾部或口周加热可诱发 TF 和 JMR，且 JMR 的潜伏期明显短于 TF（P<0.001）。在记录的 89 个 RVM 神经元中，根据其对尾部加热的反应，有 40 个被分类为 ON 细胞，27 个为 OFF 细胞，22 个为 NEUTRAL 细胞。在这两个部位加热，在 TF 和 JMR 发生之前，会引起 ON 细胞活性增加和 OFF 细胞活性减少，但不会改变 NEUTRAL 细胞的活性。同样，对颞下颌关节的伤害性刺激对 RVM 神经元也有类似的影响。这些发现表明，JMR 是 CNS 中三叉神经和脊髓伤害性传入回路兴奋性的一种测量方法，并且 JMR 和 TF 都可用于研究与疼痛下行调节相关的过程。这些发现还支持了 RVM ON 和 OFF 细胞在由身体广泛分离区域的伤害性刺激引起的各种伤害性行为的产生中发挥重要作用的观点。
