IMAGING THE FUNCTIONAL-ORGANIZATION OF ZEBRAFISH HINDBRAIN SEGMENTS DURING ESCAPE BEHAVIORS

Although vertebrate hindbrains are segmented structures, the functiona l significance of the segmentation is unknown. In zebrafish, the hindb rain segments contain serially repeated classes of individually identi fiable neurons. We took advantage of the transparency of larval zebraf ish and used confocal calcium imaging in the intact fish to study the activity of one set of individually identified, serially homologous re ticulospinal cells (the Mauthner cell, MiD2cm, and MiD3cm) during beha vior. Behavioral studies predicted that differential activity in this set of serially homologous neurons might serve to control the directio nality of the escape behavior that fish use to avoid predators. We fou nd that the serially homologous cells are indeed activated during esca pes and that the combination of cells activated depends upon the locat ion of the sensory stimulus used to elicit the escape. The patterns of activation we observed were exactly those predicted by behavioral stu dies. The data suggest that duplication of ancestral hindbrain segment s, and subsequent functional diversification, resulted in sets of rela ted neurons whose activity patterns create behavioral variability.