Lee Hyun Joon, White Jason M, Chung Jumi, Tansey Keith E
Departments of Neurology and Physiology, Emory University School of Medicine, Atlanta, Georgia.
Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, Georgia.
J Comp Neurol. 2017 Jun 15;525(9):2216-2234. doi: 10.1002/cne.24201. Epub 2017 Mar 29.
Stimulation of rat segmental dorsal cutaneous nerves (DCNs) evokes the nociceptive intersegmental cutaneus trunci muscle (CTM) reflex. The reflex consists of early and late responses, mediated by Aδ and C fibers, respectively, based on required stimulation strengths, and shows segmental differences in terms of amplitude and duration. We have now investigated whether the peripheral or central anatomy of nociceptive afferent subtypes in different DCNs also vary in a segmental manner. The numbers of different axon subtypes, determined by axon diameter, were analyzed across peripheral DCNs from T6 to L1. The central projections of T7 and T13 DCN afferents were traced using DCN injections of cholera toxin subunit B (CTB) for myelinated A fibers and isolectin B4 (IB4) for unmyelinated C fibers and both labels were quantified in the dorsal horns. Peripheral axon subtype numbers did not differ significantly across DCNs. Centrally, IB4 , but not CTB , projection areas were different between T7 and T13, consistent with different segmental CTM neurogram responses. At both levels, A fibers projected to deeper layers of the dorsal horn than did C fibers. These termination sites are consistent with both mono- and polysynaptic connections between these afferents and the ascending propriospinal interneurons of the reflex. Also analyzed were the spatial distribution, the synaptic termination, and the glutamatergic transporter profiles of DCN A and C fibers and their relationship to calcitonin gene-related peptide (CGRP) staining in the dorsal horn.
刺激大鼠节段性背侧皮神经（DCNs）可诱发伤害性节段间躯干皮肌（CTM）反射。该反射由早期和晚期反应组成，根据所需刺激强度，分别由Aδ纤维和C纤维介导，并且在幅度和持续时间方面表现出节段差异。我们现在研究了不同DCNs中伤害性传入亚型的外周或中枢解剖结构是否也存在节段性差异。通过轴突直径确定的不同轴突亚型的数量，在从T6到L1的外周DCNs中进行了分析。使用霍乱毒素B亚基（CTB）注射到DCNs中来追踪T7和T13 DCN传入纤维的中枢投射，用于有髓鞘的A纤维，使用异凝集素B4（IB4）用于无髓鞘的C纤维，并且在背角中对这两种标记物进行了定量。外周轴突亚型数量在不同的DCNs之间没有显著差异。在中枢，T7和T13之间IB4而非CTB的投射区域不同，这与不同的节段性CTM神经图反应一致。在这两个水平上，A纤维比C纤维投射到背角更深的层。这些终末位点与这些传入纤维和反射的上行脊髓固有中间神经元之间的单突触和多突触连接一致。还分析了DCN A和C纤维的空间分布、突触终末和谷氨酸能转运体谱及其与背角中降钙素基因相关肽（CGRP）染色的关系。
