Takanami Keiko, Sakamoto Hirotaka, Matsuda Ken Ichi, Satoh Keita, Tanida Takashi, Yamada Shunji, Inoue Kaihei, Oti Takumi, Sakamoto Tatsuya, Kawata Mitsuhiro
Department of Anatomy and Neurobiology, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto, 602-8566, Japan.
J Comp Neurol. 2014 Jun 1;522(8):1858-73. doi: 10.1002/cne.23506.
Gastrin-releasing peptide (GRP) has recently been identified as an itch-specific neuropeptide in the spinal sensory system in mice, but there are no reports of the expression and distribution of GRP in the trigeminal sensory system in mammals. We characterized and compared GRP-immunoreactive (ir) neurons in the trigeminal ganglion (TG) with those in the rat spinal dorsal root ganglion (DRG). GRP immunoreactivity was expressed in 12% of TG and 6% of DRG neurons and was restricted to the small- and medium-sized type cells. In both the TG and DRG, many GRP-ir neurons also expressed substance P and calcitonin gene-related peptide, but not isolectin B4 . The different proportions of GRP and transient receptor potential vanilloid 1 double-positive neurons in the TG and DRG imply that itch sensations via the TG and DRG pathways are transmitted through distinct mechanisms. The distribution of the axon terminals of GRP-ir primary afferents and their synaptic connectivity with the rat trigeminal sensory nuclei and spinal dorsal horn were investigated by using light and electron microscopic histochemistry. Although GRP-ir fibers were rarely observed in the trigeminal sensory nucleus principalis, oralis, and interpolaris, they were predominant in the superficial layers of the trigeminal sensory nucleus caudalis (Vc), similar to the spinal dorsal horn. Ultrastructural analysis revealed that GRP-ir terminals contained clear microvesicles and large dense-cored vesicles, and formed asymmetric synaptic contacts with a few dendrites in the Vc and spinal dorsal horn. These results suggest that GRP-dependent orofacial and spinal pruriceptive inputs are processed mainly in the superficial laminae of the Vc and spinal dorsal horn.
胃泌素释放肽（GRP）最近被确定为小鼠脊髓感觉系统中一种特异性的瘙痒神经肽，但尚无关于GRP在哺乳动物三叉神经感觉系统中表达和分布的报道。我们对三叉神经节（TG）中的GRP免疫反应性（ir）神经元与大鼠脊髓背根神经节（DRG）中的GRP免疫反应性神经元进行了特征描述和比较。GRP免疫反应性在12%的TG神经元和6%的DRG神经元中表达，且仅限于中小型细胞类型。在TG和DRG中，许多GRP-ir神经元也表达P物质和降钙素基因相关肽，但不表达异凝集素B4。TG和DRG中GRP与瞬时受体电位香草酸亚型1双阳性神经元的比例不同，这意味着通过TG和DRG途径的瘙痒感觉是通过不同机制传递的。通过光镜和电镜组织化学研究了GRP-ir初级传入纤维的轴突终末分布及其与大鼠三叉神经感觉核和脊髓背角的突触连接。虽然在三叉神经感觉主核、口核和极间核中很少观察到GRP-ir纤维，但它们在三叉神经感觉尾核（Vc）的浅层中占主导地位，类似于脊髓背角。超微结构分析显示，GRP-ir终末含有清亮小泡和大的致密核心小泡，并在Vc和脊髓背角与少数树突形成不对称突触联系。这些结果表明，依赖GRP的口面部和脊髓瘙痒传入主要在Vc和脊髓背角的浅层进行处理。
