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Modular Organization of Axial Microcircuits in Zebrafish

Science  10 Jan 2014:
Vol. 343, Issue 6167, pp. 197-200
DOI: 10.1126/science.1245629

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Spinal Circuit Complexity in Fish

Rapid coordination of opposing muscle groups helps zebrafish zip through water. Bagnall and McLean (p. 197) now describe the neuronal circuits that stabilize swimming fish in their three-dimensional environment. By studying the self-righting behavior of larval zebrafish immobilized in agar, the authors identified parallel excitatory and inhibitory circuits driving dorsal and ventral hemisegments that could be activated independently.

Abstract

Locomotion requires precise control of spinal networks. In tetrapods and bipeds, dynamic regulation of locomotion is simplified by the modular organization of spinal limb circuits, but it is not known whether their predecessors, fish axial circuits, are similarly organized. Here, we demonstrate that the larval zebrafish spinal cord contains distinct, parallel microcircuits for independent control of dorsal and ventral musculature on each side of the body. During normal swimming, dorsal and ventral microcircuits are equally active, but, during postural correction, fish differentially engage these microcircuits to generate torque for self-righting. These findings reveal greater complexity in the axial spinal networks responsible for swimming than previously recognized and suggest an early template of modular organization for more-complex locomotor circuits in later vertebrates.

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