Park S J, Chiang C Y, Hu J W, Sessle B J
Faculty of Dentistry, University of Toronto, Toronto, Ontario M5G 1G6, Canada.
J Neurophysiol. 2001 May;85(5):1836-46. doi: 10.1152/jn.2001.85.5.1836.
We have recently demonstrated that application of the mustard oil (MO), a small-fiber excitant and inflammatory irritant, to the rat maxillary molar tooth pulp induces significant increases in jaw muscle electromyographic (EMG) activity and neuroplastic changes in trigeminal (V) subnucleus caudalis. Since subnucleus oralis (Vo) as well as caudalis receives projections from molar pulp afferents and is also an integral brain stem relay of afferent input from orofacial structures, we tested whether MO application to the exposed pulp induces neuroplastic changes in oralis neurons and whether microinjection of MK-801, a noncompetitive NMDA antagonist, into the Vo influences the pulp/MO-induced neuroplastic changes in chloralose/urethan-anesthetized rats. Single neuronal activity was recorded in Vo, and neurons classified as low-threshold mechanoreceptive (LTM), wide dynamic range (WDR), nociceptive-specific (NS), deep (D), or skin/mucosa and deep (S + D). The spontaneous activity, mechanoreceptive field (RF) size, mechanical threshold, and response to suprathreshold mechanical stimuli applied to the neuronal RF were assessed prior to and throughout a 40- to 60-min period after MO application to the maxillary molar pulp. In animals pretreated with saline microinjection (0.3 microl) into the Vo, MO application to the pulp produced a significant increase in spontaneous activity, expansion of the pinch or deep RF, decrease in the mechanical threshold, and increase in response to suprathreshold mechanical stimuli of the nociceptive (WDR, NS, and S + D) neurons except for those nociceptive neurons having their RF only in the intraoral region. The pulpal application of MO did not produce any significant neuroplastic changes in LTM neurons. Furthermore, in animals pretreated with MK-801 microinjection (3 microg/0.3 microl) into the Vo, MO application to the pulp did not produce any significant changes in the RF and response properties of nociceptive neurons. In other animals pretreated with saline (0.3 microl) or MK-801 (3 microg/0.3 microl) microinjected into the Vo, mineral oil application to the pulp did not produce any significant changes in RF and response properties of nociceptive neurons. These findings indicate that the application of MO to the tooth pulp can induce significant neuroplastic changes in oralis nociceptive neurons and that central NMDA receptor mechanisms may be involved in these neuroplastic changes.
我们最近证明，将芥子油（MO）（一种小纤维刺激剂和炎性刺激物）应用于大鼠上颌磨牙牙髓，会导致颌面部肌肉肌电图（EMG）活动显著增加以及三叉神经（V）尾侧亚核发生神经可塑性变化。由于口侧亚核（Vo）以及尾侧亚核都接受来自磨牙牙髓传入纤维的投射，并且也是来自口面部结构的传入输入的一个完整脑干中继站，我们测试了将MO应用于暴露的牙髓是否会诱导口侧神经元发生神经可塑性变化，以及向Vo微量注射非竞争性NMDA拮抗剂MK-801是否会影响在水合氯醛/乌拉坦麻醉的大鼠中牙髓/MO诱导的神经可塑性变化。在Vo记录单个神经元活动，并将神经元分类为低阈值机械感受性（LTM）、广动力范围（WDR）、伤害性特异性（NS）、深部（D）或皮肤/黏膜和深部（S + D）。在将MO应用于上颌磨牙牙髓之前以及在应用后的40至60分钟内，评估自发活动、机械感受野（RF）大小、机械阈值以及对施加到神经元RF的阈上机械刺激的反应。在向Vo微量注射生理盐水（0.3微升）预处理的动物中，将MO应用于牙髓会使自发活动显著增加、捏或深部RF扩大、机械阈值降低，并且除了那些RF仅在口腔内区域的伤害性神经元外，伤害性（WDR、NS和S + D）神经元对阈上机械刺激的反应增加。将MO应用于牙髓对LTM神经元未产生任何显著的神经可塑性变化。此外，在向Vo微量注射MK-801（3微克/0.3微升）预处理的动物中，将MO应用于牙髓对伤害性神经元的RF和反应特性未产生任何显著变化。在其他向Vo微量注射生理盐水（0.3微升）或MK-801（3微克/0.3微升）预处理的动物中，将矿物油应用于牙髓对伤害性神经元的RF和反应特性未产生任何显著变化。这些发现表明，将MO应用于牙髓可诱导口侧伤害性神经元发生显著的神经可塑性变化，并且中枢NMDA受体机制可能参与了这些神经可塑性变化。
