[Functional organization of escape circuits built in teleost hindbrain segments]

Abstract

Hindbrain reticulospinal (RS) neurons in goldfish and zebrafish consist of seven clusters spaced periodically along the rostrocaudal axis. Morphologically similar RS neurons, homologs, are arranged in adjacent segments. Electrophysiological examination in goldfish suggests that paired, large M-cells, in the fourth segment (r4) and their homologs, MiD 2 cm in r5 and MiD 3 cm in r6, receive auditory inputs similarly but show different firing pattern in response to depolarization. In addition, there is inhibitory connection from M-cell to its homologs but not in the reverse direction. Calcium imaging of these neurons during escape behavior in larval zebrafish reveals that the M-cell and its homologs fire in a complementary fashion. Thus, the segmentally homologous RS neurons may work as a functional unit to initiate and control escape behavior.