Effects of deep pain of masticatory and neck/shoulder muscles to the tactile sensation from orofacial region and modification effect of autonomic nerve activation

目的：本研究调查是否体感皮层活动，诱发空气喷刺激的下唇区域，可以调制实验性咀嚼和/或颈/肩肌肉疼痛，并通过手浸泡在冷水中。方法：空气喷刺激，被施加到引起触觉从下唇表面。从C3、C4和Cz位置记录体感诱发电位（SBP）。分别向左咬肌和下颌肌注射等渗盐水（0.9%，0.5ml）和高渗盐水（5%，0.5ml）诱发咀嚼肌痛和颈肩肌痛。结果：冷加压试验中，左手浸入4℃冷水中。在咬肌和咬肌内注射等渗盐水后，N20和P30的振幅以及N20/P30的峰-峰振幅均无明显变化。另一方面，在咬肌注射高渗盐水后的第一阶段，N20和P30的峰值振幅和N20/P30的峰-峰振幅显著降低。然而，有没有显着的变化，在SBPs在高渗盐水注入肌内。这些结果提供了进一步的证据，咀嚼肌疼痛和调制同伦触觉输入的定量分析的基础上的基础上的病理功能的相互关系。我们还分析了手浸入冷水（4℃）对口面部触觉的影响，并阐明了冷加压试验显著增强了唇表面的触觉。结论：咀嚼肌疼痛可根据疼痛的严重程度减少来自同向口面区域的触觉，而交感神经激活可以增强口面部区域的触觉。

Aim : This study was investigated whether somatosensory cortex activity, evoked by air puff stimulation of the lower lip region, could be modulated by experimental masticatory and/or neck/shoulder muscles pain, and by hand immersion in cold water.Methods : Air puff stimulation, was applied to evoke tactile sensation from the lower lip surface. Somatosensory evoked potentials (SBPs) were recorded from C3, C4, and Cz positions. Masticatory muscle pain and neck/shoulder muscle pain was evoked by the injection of isotonic (0.9%, 0.5ml) and hypertonic saline (5%, 0.5ml) into the left masseter muscle and trapezius muscle, respectively. As cold pressor test, left hand was immersed into cold water (4℃).Results : SBPs were composed of two wave factors, N20 and P30. By injecting isotonic saline into the masseter and trapezius muscles, amplitudes of N20 and P30 and peak-to-peak amplitudes of N20/P30 were not significantly altered. On the other hand, peak amplitudes of N20 and P30 and peak-to-peak amplitude of N20/P30 were significantly decreased during the first phase of the post-injection period of hypertonic saline into masseter muscle. However, there were no significant alterations in SBPs during the injection of hypertonic saline into trapezius muscle. These results present further evidences for the pathofunctional interrelationship between masticatory muscle pain and modulation of homotopical tactile input on the bases of quantitative analyses of SEPs. We also analyzed the effect of the hand immersion into cold water (4℃) on the tactile sensation from the orofacial region and it was clarified that the tactile sensation from the lip surface was significantly enhanced by the cold pressor test.Conclusions : Masticatory muscle pain may diminish the tactile sensation from the homotopical orofacial region depending on the severity of pain, while the sympathetic nerve activation may enhance the tactile sensation of the orofacial region.