Li Jia-Ni, Ren Jia-Hao, Zhao Liu-Jie, Wu Xue-Mei, Li Hui, Dong Yu-Lin, Li Yun-Qing
Department of Anatomy, Histology and Embryology & K. K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, 710032, China.
Department of Anatomy, Basic Medical College, Zhengzhou University, Zhengzhou, 450001, China.
Brain Res Bull. 2021 Apr;169:184-195. doi: 10.1016/j.brainresbull.2021.01.012. Epub 2021 Jan 27.
Itch is an annoying sensation that always triggers scratching behavior, yet little is known about its transmission pathway in the central nervous system. Parabrachial nucleus (PBN), an essential transmission nucleus in the brainstem, has been proved to be the first relay station in itch sensation. Meanwhile, dorsal midline/intralaminar thalamic complex (dMITC) is proved to be activated with nociceptive stimuli. However, whether the PBN-projecting neurons in spinal dorsal horn (SDH) send collateral projections to dMITC, and whether these projections involve in itch remain unknown. In the present study, a double retrograde tracing method was applied when the tetramethylrhodamine-dextran (TMR) was injected into the dMITC and Fluoro-gold (FG) was injected into the PBN, respectively. Immunofluorescent staining for NeuN, substance P receptor (SPR), substance P (SP), or FOS induced by itch or pain stimulations with TMR and FG were conducted to provide morphological evidence. The results revealed that TMR/FG double-labeled neurons could be predominately observed in superficial laminae and lateral spinal nucleus (LSN) of SDH; Meanwhile, most of the collateral projection neurons expressed SPR and some of them expressed FOS in acute itch model induced by histamine. The present results implicated that some of the SPR-expressing neurons in SDH send collateral projections to the dMITC and PBN in itch transmission, which might be involved in itch related complex affective/emotional processing to the higher brain centers.
瘙痒是一种令人烦恼的感觉，总是引发搔抓行为，但我们对其在中枢神经系统中的传导途径知之甚少。臂旁核（PBN）是脑干中的一个重要传导核，已被证明是瘙痒感觉的第一中继站。同时，背中线/丘脑板内核复合体（dMITC）被证明在受到伤害性刺激时会被激活。然而，脊髓背角（SDH）中投射到PBN的神经元是否向dMITC发出侧支投射，以及这些投射是否与瘙痒有关，目前尚不清楚。在本研究中，当分别将四甲基罗丹明-葡聚糖（TMR）注入dMITC和荧光金（FG）注入PBN时，应用了双重逆行追踪方法。对由瘙痒或疼痛刺激诱导的NeuN、P物质受体（SPR）、P物质（SP）或FOS进行免疫荧光染色，以提供形态学证据。结果显示，在SDH的浅层和外侧脊髓核（LSN）中可主要观察到TMR/FG双标记神经元；同时，在组胺诱导的急性瘙痒模型中，大多数侧支投射神经元表达SPR，其中一些表达FOS。目前的结果表明，SDH中一些表达SPR的神经元在瘙痒传递过程中向dMITC和PBN发出侧支投射，这可能参与了向高级脑中枢的与瘙痒相关的复杂情感/情绪处理。
