properties of the masticatory muscle primary afferent neurons from rat trigeminal ganglion

咀嚼肌痛是颞下颌关节紊乱病的重要症状之一。本课题对大鼠三叉神经节咀嚼肌初级传入神经元的特性进行了研究。本研究旨在探讨三磷酸腺苷(ATP)在颅面神经感觉机制中的作用。与D-半乳糖结合的凝集素IB4在73%的P2X3阳性神经元中表达，而只有16%的IB4神经元表达P2X3。单独表达P2X3的神经元明显大于IB4或IB4/P2X3阳性神经元。靶向性研究表明，22%的三叉神经节肌肉传入神经元表达P2X3，16%的皮肤传入神经元表达P2X3。肌肉中的P2X3传入神经元明显少于整个肌肉传入神经元，而P2X3皮肤传入神经元则不明显。此外，还发现了可能的异构型肌肉传入神经元，占P2X_3肌肉传入神经元总数的77%。肌肉传入神经元与降钙素基因相关肽(15%)或P物质(4%)共表达。完全弗氏佐剂诱导咬肌炎症后1d和4d，P2X3阳性的肌肉传入神经元数量显著增加，12d后显著减少。这些结果表明，在三叉神经节内：1.P2X_3受体在中小型神经元中均有表达；2.P2X_3受体并非仅在IB4神经元中表达；3.P_2X_3与神经肽共表达；4.皮肤和肌肉中P_2X_3传入的比例无明显差异。因此，三叉神经节的P2X_3神经元与背根神经节的P2X_3传入神经元有明显的区别。这项研究还表明，深部组织炎症调节了P2X3受体的表达，因此有必要探索作为治疗干预的靶点。

Masticatory muscle pain is one of the important symptoms of the tempolomandibular disorders. In this project, properties of the masticatory muscle primary afferent neurons from the rat trigeminal ganglion were investigated. The distribution and modulation of the P2X_3 receptor was studied to provide insight into the role of ATP in craniofacial sensory mechanisms. Binding to the D-galactose specific lectin IB4 was found in 73% of P2X_3-positive neurons while only 16% of IB4 neurons expressed P2X_3. Neurons expressing P2X_3 alone were significantly larger than IB4-or IB4/P2X_3-positive neurons. Investigation of target-specificity revealed that 22% of trigeminal ganglion muscle afferent neurons were positive for P2X_3 versus 16% of cutaneous afferent neurons. Muscle P2X_3 afferents were significantly smaller than the overall muscle afferent population while P2X_3 cutaneous afferent neurons were not. Presumptive heteromeric (P2X_<2/3>) muscle afferent neurons were also identified and comprised 77% of the P2X_3 muscle afferent population. Muscle afferent neurons co-expressed P2X_3 with either calcitonin gene-related peptide (15%) or substance P (4%). The number of P2X_3-positive muscle afferent neurons significantly increased one and four days following complete Freund's adjuvant-induced masseter muscle inflammation, but significantly decreased after 12 days. These results indicate that within trigeminal ganglia : 1.the P2X_3 receptor is expressed in both small and medium-sized neurons ; 2.the P2X_3 receptor is not exclusively expressed in IB4 neurons ; 3.P2X_3 is co-expressed with neuropeptides ; 4.differences in the proportion of cutaneous versus muscle P2X_3 afferents are not apparent. Trigeminal P2X_3 neurons therefore differ markedly from dorsal root ganglion P2X_3 afferents. This study also shows that deep tissue inflammation modulates expression of the P2X_3 receptor and thus may warrant exploration as a target for therapeutic intervention.