Lam David K, Sessle Barry J, Hu James W
Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
Brain Res. 2009 Feb 9;1253:48-59. doi: 10.1016/j.brainres.2008.11.056. Epub 2008 Nov 28.
We examined the effect of the peripheral application of glutamate and capsaicin to the temporomandibular joint (TMJ) in influencing the activation and central sensitization of TMJ-responsive nociceptive neurons in the trigeminal subnucleus caudalis/upper cervical cord (Vc/UCC). The activity of single neurons activated by noxious mechanical stimulation of the TMJ was recorded in the Vc/UCC of 49 halothane-anesthetized male rats. Cutaneous mechanoreceptive field (RF), cutaneous mechanical activation threshold (MAT), and TMJ MAT of each neuron were assessed before and after injection of 0.5 M glutamate (or vehicle) and 1% capsaicin (or vehicle) into the TMJ. A total of 49 nociceptive neurons (37 nociceptive-specific, 12 wide-dynamic-range) that could be activated by blunt noxious mechanical stimulation of the TMJ were studied. When injected alone, glutamate and capsaicin activated and induced central sensitization (reflected in cutaneous RF expansion and cutaneous and/or TMJ MAT reduction) in most Vc/UCC neurons. Following glutamate injection, capsaicin evoked greater activity and less cutaneous/TMJ MAT reduction compared with capsaicin alone, whereas capsaicin abolished all subsequent glutamate-evoked activity and depressed cutaneous RF expansion in most neurons. Glutamate effects on deep afferents and Vc/UCC neurons were analogous since glutamate sensitized afferent and neuronal responses to capsaicin but the desensitizing effects of capsaicin on glutamate-evoked excitability of Vc/UCC neurons contrast with the lack of capsaicin-induced modulation of glutamate-evoked afferent excitability [Lam, D.K., Sessle, B.J., Hu, J.W., 2008a. Glutamate and capsaicin effects on trigeminal nociception I: activation and peripheral sensitization of deep craniofacial nociceptive afferents. Brain Res. doi:10.1016/j.brainres.2008.11.029], suggesting that peripheral and central sensitization may be differentially involved in the nociceptive effects of glutamate and capsaicin applied to deep craniofacial tissues.
我们研究了向颞下颌关节（TMJ）外周应用谷氨酸和辣椒素对三叉神经尾侧亚核/颈髓上部（Vc/UCC）中TMJ反应性伤害性神经元激活和中枢敏化的影响。在49只接受氟烷麻醉的雄性大鼠的Vc/UCC中记录了由TMJ有害机械刺激激活的单个神经元的活动。在向TMJ注射0.5 M谷氨酸（或赋形剂）和1%辣椒素（或赋形剂）之前和之后，评估每个神经元的皮肤机械感受野（RF）、皮肤机械激活阈值（MAT）和TMJ MAT。共研究了49个可被TMJ钝性有害机械刺激激活的伤害性神经元（37个伤害性特异性神经元，12个广动力范围神经元）。单独注射时，谷氨酸和辣椒素激活并诱导大多数Vc/UCC神经元的中枢敏化（表现为皮肤RF扩大和皮肤和/或TMJ MAT降低）。注射谷氨酸后，与单独注射辣椒素相比，辣椒素诱发的活动更强，皮肤/TMJ MAT降低更少，而辣椒素消除了所有随后谷氨酸诱发的活动，并在大多数神经元中抑制了皮肤RF扩大。谷氨酸对深部传入神经和Vc/UCC神经元的作用类似，因为谷氨酸使传入神经和神经元对辣椒素的反应敏感，但辣椒素对Vc/UCC神经元谷氨酸诱发的兴奋性的脱敏作用与辣椒素对谷氨酸诱发的传入神经兴奋性缺乏调节形成对比[Lam, D.K., Sessle, B.J., Hu, J.W., 2008a. Glutamate and capsaicin effects on trigeminal nociception I: activation and peripheral sensitization of deep craniofacial nociceptive afferents. Brain Res. doi:10.1016/j.brainres.2008.11.029]，表明外周和中枢敏化可能在应用于深部颅面组织的谷氨酸和辣椒素的伤害性作用中发挥不同作用。
