Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, Minnesota.
Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, Minnesota
J Neurophysiol. 2015 Jan 1;113(1):14-22. doi: 10.1152/jn.00125.2014. Epub 2014 Sep 3.
The rostral ventromedial medulla (RVM) projects to the medullary and spinal dorsal horns and is a major source of descending modulation of nociceptive transmission. Traditionally, neurons in the RVM are classified functionally as on, off, and neutral cells on the basis of responses to noxious cutaneous stimulation of the tail or hind paw. On cells facilitate nociceptive transmission, off cells are inhibitory, whereas neutral cells are unresponsive to noxious stimuli and their role in pain modulation is unclear. Classification of RVM neurons with respect to stimulation of craniofacial tissues is not well defined. In isoflurane-anesthetized male rats, RVM neurons first were classified as on (25.5%), off (25.5%), or neutral (49%) cells by noxious pinch applied to the hind paw. Pinching the skin overlying the temporomandibular joint (TMJ) altered the proportions of on (39.2%), off (42.2%), and neutral (19.6%) cells. To assess the response of RVM cells to specialized craniofacial inputs, adenosine triphosphate (ATP; 0.01-1 mM) was injected into the TMJ and capsaicin (0.1%) was applied to the ocular surface. TMJ and ocular surface stimulation also resulted in a reduced proportion of neutral cells compared with hind paw pinch. Dose-effect analyses revealed that on and off cells encoded the intra-TMJ concentration of ATP. These results suggest that somatotopy plays a significant role in the functional classification of RVM cells and support the notion that neutral cells likely are subgroups of on and off cells. It is suggested that a portion of RVM neurons serve different functions in modulating craniofacial and spinal pain conditions.
延髓头端腹内侧区（RVM）投射到脊髓背角和髓质，是伤害性传入传递下行调制的主要来源。传统上，根据对尾巴或后脚的有害皮肤刺激的反应，RVM 中的神经元在功能上被分类为兴奋、抑制和中性细胞。兴奋细胞促进伤害性传递，抑制细胞是抑制性的，而中性细胞对有害刺激无反应，其在疼痛调制中的作用尚不清楚。关于颅面组织刺激的 RVM 神经元分类尚未明确界定。在异氟烷麻醉的雄性大鼠中，首先通过对后脚施加有害夹捏来将 RVM 神经元分类为兴奋（25.5%）、抑制（25.5%）或中性（49%）细胞。夹捏颞下颌关节（TMJ）上方的皮肤会改变兴奋（39.2%）、抑制（42.2%）和中性（19.6%）细胞的比例。为了评估 RVM 细胞对专门的颅面输入的反应，三磷酸腺苷（ATP；0.01-1mM）被注射到 TMJ 中，辣椒素（0.1%）被应用于眼表面。TMJ 和眼表面刺激也导致与后脚夹捏相比，中性细胞的比例降低。剂量-效应分析表明，兴奋和抑制细胞编码 TMJ 内的 ATP 浓度。这些结果表明，躯体定位在 RVM 细胞的功能分类中起着重要作用，并支持中性细胞可能是兴奋和抑制细胞的亚群的观点。有人提出，一部分 RVM 神经元在调节颅面和脊髓疼痛状况方面具有不同的功能。
