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

脊椎动物的后脑是分段的结构。斑马鱼和金鱼后脑的7个网状脊髓神经元(RSNs)沿神经轴周期性排列。在相邻片段中具有共同形态的RSN称为片段同源基因。在本研究中，我们通过检测它们在逃避行为中的活动以及它们之间的相互联系，研究了一系列片段同源物，即第四片段(R4)中的Mauthner(M)细胞及其在R5和R6中的同源物的功能组织。对斑马鱼RSNs在快速逃逸行为中对头部水脉冲刺激的共聚焦钙成像显示，M细胞启动了听觉诱发的快速逃逸，其同系物更多地参与了触觉诱发的逃逸。M细胞及其同系物在快速逃逸过程中呈现互补激活。这种活性关系是由M细胞的抑制性中间神经元与…上的同源物介导的抑制性连接所支持的更多的是通过配对记录它们在金鱼身上的表现。听觉诱发的逃逸行为比触觉诱发的逃逸行为出现得晚。我们研究了M细胞获得听觉反应性的潜在机制。斑马鱼胚胎和仔鱼M细胞的全细胞记录、内耳毛细胞(HC)活动的胞外记录以及从HC到M细胞的听觉传入的形态研究表明，内耳HC在形成听觉传入回路后的功能成熟是M细胞获得听觉输入的关键过程。有趣的是，在获得听觉反应后，M细胞会改变它们的放电模式，以响应逐步去极化，从其他RSN表现出的爆发到成熟M细胞的典型单次放电。总之，获得特定感觉输入所引起的功能分化和同源物之间的相互联系可能是节段性同源物在不同环境中产生适应性逃避行为的功能组织的基础。较少

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