Capra N F, Ro J Y
Department of Oral and Craniofacial Biological Sciences, University of Maryland Baltimore, School of Dentistry, Baltimore, MD 21201, USA.
Pain. 2000 May;86(1-2):151-62. doi: 10.1016/s0304-3959(00)00231-1.
The aim of the present study was to investigate the effects of intramuscular injection with hypertonic saline, a well-established experimental model for muscle pain, on central processing of proprioceptive input from jaw muscle spindle afferents. Fifty-seven cells were recorded from the medial edge of the subnucleus interpolaris (Vi) and the adjacent parvicellular reticular formation from 11 adult cats. These cells were characterized as central units receiving jaw muscle spindle input based on their responses to electrical stimulation of the masseter nerve, muscle palpation and jaw stretch. Forty-five cells, which were successfully tested with 5% hypertonic saline, were categorized as either dynamic-static (DS) (n=25) or static (S) (n=20) neurons based on their responses to different speeds and amplitudes of jaw movement. Seventy-six percent of the cells tested with an ipsilateral injection of hypertonic saline showed a significant modulation of mean firing rates (MFRs) during opening and/or holding phases. The most remarkable saline-induced change was a significant reduction of MFR during the hold phase in S units (100%, 18/18 modulated). Sixty-nine percent of the DS units (11/16 modulated) also showed significant changes in MFRs limited to the hold phase. However, in the DS neurons, the MFRs increased in seven units and decreased in four units. Finally, five DS neurons showed significant changes of MFRs during both opening and holding phases. Injections of isotonic saline into the ipsilateral masseter muscle had little effect, but hypertonic saline injections made into the contralateral masseter muscle produced similar results to ipsilateral injections with hypertonic saline. These results unequivocally demonstrate that intramuscular injection with an algesic substance, sufficient to produce muscle pain, produces significant changes in the proprioceptive properties of the jaw movement-related neurons. Potential mechanisms involved in saline-induced changes in the proprioceptive signals and functional implications of the changes are discussed.
本研究的目的是调查肌肉注射高渗盐水（一种成熟的肌肉疼痛实验模型）对来自下颌肌肉梭传入纤维的本体感觉输入的中枢处理的影响。从11只成年猫的极间亚核（Vi）内侧边缘和相邻的小细胞网状结构记录了57个细胞。根据这些细胞对咬肌神经电刺激、肌肉触诊和下颌伸展的反应，将其表征为接受下颌肌肉梭输入的中枢单元。45个成功用5%高渗盐水测试的细胞，根据其对不同速度和幅度的下颌运动的反应，被分类为动态 - 静态（DS）（n = 25）或静态（S）（n = 20）神经元。同侧注射高渗盐水测试的细胞中，76%在开口和/或保持阶段显示平均放电率（MFRs）有显著调制。最显著的盐水诱导变化是S单位在保持阶段MFR显著降低（100%，18/18个被调制）。69%的DS单位（11/16个被调制）在保持阶段也显示MFR有显著变化。然而，在DS神经元中，7个单位的MFR增加，4个单位的MFR降低。最后，5个DS神经元在开口和保持阶段都显示MFR有显著变化。向同侧咬肌注射等渗盐水几乎没有影响，但向对侧咬肌注射高渗盐水产生了与同侧注射高渗盐水相似的结果。这些结果明确表明，肌肉注射足以产生肌肉疼痛的镇痛物质会使与下颌运动相关的神经元的本体感觉特性发生显著变化。讨论了盐水诱导的本体感觉信号变化所涉及的潜在机制以及这些变化的功能意义。
