Functional organization of morphologically homologous neurons repeated in the adjacent segments of vertebrate hindbrain

脊椎动物后脑是分节结构。斑马鱼和金鱼后脑沿神经轴周期性地排列着7个网状脊髓神经元簇。在相邻片段中具有共同形态的rsn被称为片段同源物。在本研究中，我们研究了一系列同源片段的功能组织，第四片段（r4）中的Mauthner (M)细胞及其同源片段r5和r6中的Mauthner (M)细胞，通过研究它们在逃逸行为中的活性和它们之间的相互联系。对斑马鱼头部水脉冲刺激下快速逃逸行为的共聚焦钙成像显示，m细胞启动声诱发的快速逃逸，其同系物更多地参与触觉诱发的快速逃逸。m细胞和同源物在快速逃逸过程中表现出互补激活。m细胞与同系物之间的抑制性连接是其活性关系的支持机制。听觉诱发的逃逸行为出现晚于触觉诱发的逃逸。我们研究了M细胞听觉反应性获得的机制。对斑马鱼胚胎和幼体中M细胞的全细胞记录、内耳毛细胞（HC）活性的细胞外记录以及从HC到M细胞的听觉传入的形态学研究表明，听觉传入回路形成后内耳毛细胞的功能成熟是M细胞获取听觉输入的关键过程。有趣的是，在获得听觉反应性后，m细胞改变了它们的放电模式，以响应逐步去极化，从其他rsn表现出的爆发到成熟m细胞典型的单次放电。通过对特定感觉输入的获取所引起的功能分化和同源物之间的相互联系，可能是同源物在不同环境下产生适应性逃避行为的功能组织的基础。少

Vertebrate hindbrains are segmented structure. Seven clusters of reticulospinal neurons (RSNs) are periodically arranged along the neuraxis in the hindbrain of zebrafish and goldfish. RSNs sharing a common morphology in adjacent segments are referred to as segmental homologs. In the present study we have investigated the functional organization of a series of segmental homologs, Mauthner (M) cells in the fourth segment (r4) and its homologs in r5 and r6, by examining their activities during escape behavior and mutual connections between them. Confocal calcium imaging of zebrafish RSNs during fast escape behavior in response to water pulse stimulus to head revealed that M-cell initiates acoustically evoked fast escape and its homologs are more involved in tactile evoked escape. M-cell and the homologs show complementary activation during fast escape. The activity relationship is supported by inhibitory connection mediated by inhibitory interneurons from M-cell to the homologs demonstrat … More ed by paired recording of them in goldfish. Acoustically evoked escape behavior appears later than tactile induced escape. We investigated mechanisms underlying acquisition of auditory responsiveness of M cell. Whole-cell recordings from M-cells, exracellular recording of inner ear hair cell (HC) activity and morphological investigations of the auditory afferents from HC to M cells in zebrafish embryos and larvae suggested that functional maturation of inner ear HCs after formation of the auditory afferent circuits is a critical process in the acquisition of auditory inputs by M-cell. Interestingly after acquisition of auditory responsiveness, the M-cell changes their firing pattern in response to stepwise depolarization, from burst as other RSNs exhibit to typical single firing of matured M-cell. Together, the functional differentiation elicited by acquisition of specific sensory input and the interconnection among the homologs may underlie functional organization of segmental homologs to produce adaptive escape behaviors during various environments. Less