Christianson J A, McIlwrath S L, Koerber H R, Davis B M
Department of Medicine, University of Pittsburgh, 3550 Terrace Street, S843 Scaife Hall, Pittsburgh, PA 15261, USA.
Neuroscience. 2006 Jun 19;140(1):247-57. doi: 10.1016/j.neuroscience.2006.02.015. Epub 2006 Mar 29.
Previous studies in our laboratories found that isolectin B(4)(IB(4))-positive polymodal nociceptors in the mouse do not express transient receptor potential vanilloid 1 (TRPV1), nor does deletion of TRPV1 compromise the ability of these afferents to detect thermal stimuli. Considering that IB(4)-positive afferents account for over 70% of cutaneous nociceptors and that 30-50% of all mouse primary afferents express TRPV1, it is highly likely that many TRPV1-positive fibers project to non-cutaneous structures. To investigate this issue, Alexa Fluor-conjugated wheat germ agglutinin (WGA) or IB(4) was injected into the nerves innervating quadriceps muscle (femoral) or hindlimb skin (saphenous) of male C57Bl/6 mice. Similarly, Alexa Fluor-conjugated cholera toxin-beta was injected subserosally into the distal colon. Spinal ganglia at the appropriate level (L2-3 for saphenous and femoral nerves; L6 for colon) were processed for TRPV1, calcitonin gene-related peptide (CGRP), neurofilament heavy chain (NHF) and IB(4) visualization and examined on a confocal microscope. Colon afferents contained the highest percentage of both TRPV1- and CGRP-positive neurons, followed by femoral (WGA) and saphenous afferents (WGA and IB(4)). In contrast, NHF staining was more prevalent among femoral afferents, followed by saphenous (WGA) and colon afferents. IB(4) binding was observed in very few colon or saphenous (WGA) afferents, with no femoral afferents binding or transporting IB(4). Considering that the largest percentages of TRPV1-positive neurons observed in this study were within visceral and muscle afferent populations (neurons that typically are not subject to noxious temperatures), these results suggest that TRPV1 may not function primarily as a temperature sensor but rather as a detector of protons, vanilloid compounds or through interactions with other membrane proteins.
我们实验室之前的研究发现，小鼠体内的异凝集素B4（IB4）阳性多模式伤害感受器不表达瞬时受体电位香草酸受体1（TRPV1），而且TRPV1的缺失也不会损害这些传入神经检测热刺激的能力。鉴于IB4阳性传入神经占皮肤伤害感受器的70%以上，且所有小鼠初级传入神经中有30 - 50%表达TRPV1，很有可能许多TRPV1阳性纤维投射到非皮肤结构。为了研究这个问题，将Alexa Fluor偶联的小麦胚凝集素（WGA）或IB4注射到雄性C57Bl/6小鼠支配股四头肌（股神经）或后肢皮肤（隐神经）的神经中。同样，将Alexa Fluor偶联的霍乱毒素β亚基经浆膜下注射到远端结肠。对相应水平的脊髓神经节（隐神经和股神经为L2 - 3；结肠为L6）进行处理，以观察TRPV1、降钙素基因相关肽（CGRP）、神经丝重链（NHF）和IB4，并在共聚焦显微镜下检查。结肠传入神经中TRPV1和CGRP阳性神经元的比例最高，其次是股神经（WGA）和隐神经传入神经（WGA和IB4）。相比之下，NHF染色在股神经传入神经中更为普遍，其次是隐神经（WGA）和结肠传入神经。在极少数结肠或隐神经（WGA）传入神经中观察到IB4结合，股神经传入神经未结合或转运IB4。鉴于本研究中观察到的TRPV1阳性神经元的最大比例存在于内脏和肌肉传入神经群体中（这些神经元通常不会受到有害温度的影响），这些结果表明TRPV1可能主要不是作为温度传感器发挥作用，而是作为质子、香草酸类化合物的检测器，或者通过与其他膜蛋白的相互作用发挥作用。
