2007 Fiscal Year Final Research Report Summary
Functional organization of morphologically homologous neurons repeated in the adjacent segments of vertebrate hindbrain
| Project/Area Number |
18300134
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Neurophysiology and muscle physiology
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| Research Institution | Nagoya University |
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Principal Investigator |
ODA Yoichi Nagoya University, Graduate School of Science, Professor (00144444)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAGI Shin Nagoya University, 大学院・理学研究科, Associate Professor (90171420)
HIRATA Hiromi Nagoya University, 大学院・理学研究科, Assistant Professor (60402450)
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| Project Period (FY) |
2006 – 2007
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| Keywords | Mauthner cell / zebrafish / hindbrain / escape behavior / imaging / auditory / tactile / segments |
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| Research Abstract |
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
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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
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