Thalakoti Srikanth, Patil Vinit V, Damodaram Srikanth, Vause Carrie V, Langford Lauren E, Freeman Stacy E, Durham Paul L
Department of Biology, Missouri State University, Springfield, MO 65897, USA.
Headache. 2007 Jul-Aug;47(7):1008-23; discussion 24-5. doi: 10.1111/j.1526-4610.2007.00854.x.
The goal of this study was to investigate neuronal-glial cell signaling in trigeminal ganglia under basal and inflammatory conditions using an in vivo model of trigeminal nerve activation.
Activation of trigeminal ganglion nerves and release of calcitonin gene-related peptide (CGRP) are implicated in the pathology of migraine. Cell bodies of trigeminal neurons reside in the ganglion in close association with glial cells. Neuron-glia interactions are involved in all stages of inflammation and pain associated with several central nervous system (CNS) diseases. However, the role of neuron-glia interactions within the trigeminal ganglion under normal and inflammatory conditions is not known.
Sprague-Dawley rats were utilized to study neuron-glia signaling in the trigeminal ganglion. Initially, True Blue was used as a retrograde tracer to localize neuronal cell bodies in the ganglion by fluorescent microscopy and multiple image alignment. Dye-coupling studies were conducted under basal conditions and in response to capsaicin injection into the TMJ capsule. S100B and p38 expression in neurons and glia were determined by immunohistochemistry following chemical stimulation. CGRP levels in the ganglion were measured by radioimmunoassay in response to capsaicin. In addition, the effect of CGRP on the release of 19 different cytokines from cultured glial cells was investigated by protein microarray analysis.
In unstimulated control animals, True Blue was detected primarily in neuronal cell bodies localized in clusters within the ganglion corresponding to the V3 region (TMJ capsule), V2 region (whisker pad), or V1 region (eyebrow and eye). However, True Blue was detected in both neuronal cell bodies and adjacent glia in the V3 region of the ganglion obtained from animals injected with capsaicin. Dye movement into the surrounding glia correlated with the time after capsaicin injection. Chemical stimulation of V3 trigeminal nerves was found to increase the expression of the inflammatory proteins S100B and p38 in both neurons and glia within the V3 region. Unexpectedly, increased levels of these proteins were also observed in the V2 and V1 regions of the ganglion. CGRP and the vesicle docking protein SNAP-25 were colocalized in many neuronal cell bodies and processes. Decreased CGRP levels in the ganglion were observed 2 hours following capsaicin stimulation. Using protein microarray analysis, CGRP was shown to differentially regulate cytokine secretion from cultured trigeminal ganglion glia.
We demonstrated that activation of trigeminal neurons leads to changes in adjacent glia that involve communication through gap junctions and paracrine signaling. This is the first evidence, to our knowledge, of neuron-glia signaling via gap junctions within the trigeminal ganglion. Based on our findings, it is likely that neuronal-glial communication via gap junctions and paracrine signaling are involved in the development of peripheral sensitization within the trigeminal ganglion and, thus, are likely to play an important role in the initiation of migraine. Furthermore, we propose that propagation of inflammatory signals within the ganglion may help to explain commonly reported symptoms of comorbid conditions associated with migraine.
本研究的目的是使用三叉神经激活的体内模型，研究基础条件和炎症条件下三叉神经节中的神经元 - 胶质细胞信号传导。
三叉神经节神经的激活和降钙素基因相关肽（CGRP）的释放与偏头痛的病理过程有关。三叉神经元的细胞体位于神经节中，与胶质细胞紧密相连。神经元 - 胶质细胞相互作用参与了与几种中枢神经系统（CNS）疾病相关的炎症和疼痛的各个阶段。然而，在正常和炎症条件下三叉神经节内神经元 - 胶质细胞相互作用的作用尚不清楚。
使用Sprague-Dawley大鼠研究三叉神经节中的神经元 - 胶质细胞信号传导。最初，用真蓝作为逆行示踪剂，通过荧光显微镜和多重图像对齐来定位神经节中的神经元细胞体。在基础条件下以及响应向颞下颌关节囊内注射辣椒素进行染料偶联研究。化学刺激后，通过免疫组织化学测定神经元和胶质细胞中S100B和p38的表达。通过放射免疫测定法测量神经节中辣椒素刺激后CGRP水平。此外，通过蛋白质微阵列分析研究CGRP对培养的胶质细胞释放19种不同细胞因子的影响。
在未刺激的对照动物中，主要在对应于V3区域（颞下颌关节囊）、V2区域（触须垫）或V1区域（眉毛和眼睛）的神经节内成簇的神经元细胞体中检测到真蓝。然而，在注射辣椒素的动物获得的神经节的V3区域的神经元细胞体和相邻胶质细胞中均检测到真蓝。染料向周围胶质细胞的移动与辣椒素注射后的时间相关。发现化学刺激V3三叉神经会增加V3区域内神经元和胶质细胞中炎症蛋白S100B和p38的表达。出乎意料的是，在神经节的V2和V1区域也观察到这些蛋白质水平的增加。CGRP和囊泡对接蛋白SNAP-25在许多神经元细胞体和突起中共定位。辣椒素刺激2小时后，观察到神经节中CGRP水平降低。使用蛋白质微阵列分析，显示CGRP可差异调节培养的三叉神经节胶质细胞的细胞因子分泌。
我们证明三叉神经元的激活导致相邻胶质细胞的变化，这涉及通过缝隙连接和旁分泌信号传导的通信。据我们所知，这是三叉神经节内通过缝隙连接进行神经元 - 胶质细胞信号传导的首个证据。基于我们的发现，通过缝隙连接和旁分泌信号传导的神经元 - 胶质细胞通信可能参与三叉神经节内的外周敏化的发展，因此可能在偏头痛的发作中起重要作用。此外，我们提出神经节内炎症信号的传播可能有助于解释与偏头痛相关的共病状况中常见的症状。
