Tsai C M, Chiang C Y, Yu X M, Sessle B J
Faculty of Dentistry, University of Toronto, Ontario, Canada.
Pain. 1999 May;81(1-2):115-28. doi: 10.1016/s0304-3959(99)00009-3.
We have previously shown that an increase in electromyographic (EMG) activity of digastric (DIG) and masseter (MASS) muscles can be reflexly evoked by injection into the rat's temporomandibular joint (TMJ) region of the small-fibre excitant and inflammatory irritant mustard oil (MO). Since the trigeminal (V) subnucleus caudalis (Vc, i.e. medullary dorsal horn) has traditionally been viewed as an essential brainstem relay site of nociceptive information from craniofacial tissues, an EMG study was carried out in 45 anaesthetized rats to determine if Vc is involved in the MO-evoked increases in jaw muscle EMG activity. The effects of histologically confirmed surgical or chemical lesions of Vc on this evoked EMG activity were tested in different groups of rats. MO injection into the left TMJ region of intact rats evoked bilateral increases in EMG activity of DIG and MASS which could be significantly reduced by surgical transection of the left caudal brainstem at the obex level; MO injection into the right TMJ region in these same rats still readily evoked increases in EMG activity. A sagittal section medial to Vc or transection at the level of the second cervical spinal segment did not produce any significant reduction in the reflexly evoked EMG activity. Neurones in Vc, as opposed to fibres of passage, appear to be important for the MO-evoked EMG activity, since injection into Vc of the neurotoxic chemical ibotenic acid significantly reduced the mustard oil-evoked EMG activity. The Vc also appears to play a role in the activation of contralateral V motoneurons, as evidenced by the activation of the contralateral DIG and MASS muscles by the injection of MO into the left TMJ region of intact rats and by the reduction of this evoked EMG activity in the contralateral DIG and MASS of rats with a surgical transection or ibotenic acid lesion of the left Vc. These findings suggest that Vc may be a critical element in the neural pathways underlying the reflex responses evoked bilaterally in DIG and MASS muscles by noxious stimulation of the TMJ region.
我们之前已经表明，通过向大鼠颞下颌关节（TMJ）区域注射小纤维兴奋性和炎性刺激物芥子油（MO），可反射性诱发二腹肌（DIG）和咬肌（MASS）的肌电图（EMG）活动增加。由于三叉神经（V）尾侧亚核（Vc，即延髓背角）传统上被视为来自颅面组织的伤害性信息的重要脑干中继位点，因此对45只麻醉大鼠进行了一项EMG研究，以确定Vc是否参与MO诱发的颌肌EMG活动增加。在不同组的大鼠中测试了经组织学证实的Vc手术或化学损伤对这种诱发的EMG活动的影响。向完整大鼠的左侧TMJ区域注射MO可诱发DIG和MASS的EMG活动双侧增加，在闩部水平对左侧脑干尾端进行手术横断可显著降低这种增加；在这些相同的大鼠中，向右侧TMJ区域注射MO仍很容易诱发EMG活动增加。在Vc内侧进行矢状切片或在第二颈髓节段水平进行横断，并未使反射诱发的EMG活动产生任何显著降低。与过路纤维相反，Vc中的神经元似乎对MO诱发的EMG活动很重要，因为向Vc注射神经毒性化学物质鹅膏蕈氨酸可显著降低芥子油诱发的EMG活动。Vc似乎也在对侧V运动神经元的激活中起作用，向完整大鼠的左侧TMJ区域注射MO可激活对侧的DIG和MASS肌肉，以及在左侧Vc进行手术横断或鹅膏蕈氨酸损伤的大鼠中，对侧DIG和MASS的这种诱发EMG活动降低，都证明了这一点。这些发现表明，Vc可能是TMJ区域有害刺激在DIG和MASS肌肉中双侧诱发的反射反应的神经通路中的关键要素。
