Modulation of Threat Response in Larval Zebrafish.

High-throughput, whole-organism phenotypic drug screening is made possible using live zebrafish larvae. Many human drugs have now been shown to affect zebrafish larvae in similar ways, through homologous molecular mechanisms. At this stage in life, zebrafish are small enough to fit in multi-well, microliter plates, yet developed enough to exhibit complex phenotypes, such as hunting behaviors and avoidance of predators. Importantly, zebrafish larvae can be easily dosed via automated pipetting of chemical compounds directly into their liquid medium, without injection. Only microgram amounts of small molecules are required, making animal husbandry and dosing regimens cost effective. This chapter describes how the stereotyped zebrafish larval responses to darkness and strobe light-which cause hyperactivity and freezing behavior, respectively-can be used to efficiently screen small molecules for brain and behavior-modulating activity.