Laser ablations reveal functional relationships of segmental hindbrain neurons in zebrafish

Segmentation of the vertebrate brain is most obvious in the hindbrain, wher e successive segments contain repeated neuronal types. One such set of thre e repeated reticulospinal neurons - the Mauthner cell, MiD2cm, and MiD3cm - is thought to produce different forms of the escape response that fish use to avoid predators. We used laser ablations in larval zebrafish to test th e hypothesis that these segmental hindbrain cells form a functional group. Killing all three cells eliminated short-latency, high-performance escape r esponses to both head- and tail-directed stimuli. Killing just the Mauthner cell affected escapes from tail-directed but not from head-directed stimul i. These results reveal the contributions of one set of reticulospinal neur ons to behavior and support the idea that serially repeated hindbrain neuro ns form functional groups.