Development of the dopamine systems in zebrafish.

Dopaminergic neurons develop in several distinct regions of the vertebrate brain and project locally or send long axonal projections to distant parts of the CNS to modulate the activity of a variety of circuits, controlling aspects of physiology, behavior and movement. The molecular control of dopaminergic differentiation and the evolution of the various dopaminergic systems are not well understood, as research has mostly focused on ascending mammalian dopaminergic systems of the substantia nigra and ventral tegmental area. Zebrafish have evolved as an excellent genetic and experimental embryological model to study specification and axonal projectivity of dopaminergic neurons. The large evolutionary distance between fish and mammals provides the opportunity to identify conserved core regulatory mechanisms that control differentiation and projection behavior of the various dopaminergic groups in vertebrates. Here, we present an overview of the formation of dopaminergic groups and their projections in zebrafish. We will further review the results from genetic analyses, which have revealed insights on signals as well as transcription factors contributing to dopaminergic differentiation. Together with recently established paradigms for behavioral analysis, dopaminergic systems are studied at all levels in zebrafish, from molecular and cellular to systems and behavioral.