Neurons acquire their distinct shapes the tectal neuropil through emission and retraction of after passing through many transitional stages in early many branches during a period of ΓΊ20 h (our longest development. To reveal the dynamics and spatiotempocontinuous time-lapse movie). The tectal territory ''exral sequence of process formation in situ, the growth of plored'' in this way is larger than the area finally covneurons in the optic tectum of live zebrafish embryos ered by the tree resulting from growth and loss of (54 to ΓΊ100 h old) was monitored using time-lapse vidbranches. The dynamics observed here directly are eorecordings. Neurons were labeled by injecting the fluprobably characteristic for dendrite formation in verteorescent vital dye DiO into the cell-rich layer of the brates. Moreover, consistent with the sequence of neudeveloping tectum in 50-to 70-h-old embryos. In phase ronal differentiation observed in vitro, the growth of 1, tectal neurons possess an apical ''primary process'' the axon precedes that of the dendrites, although both which reaches to the ventral aspect of the tectal neuropil.
emerge from a common primary process in this type of The primary process produces at its tip short transitory tectal neuron. α§ 1997 John Wiley & Sons, Inc. J Neurobiol 32: branches, some with growth cones, over a period of 627-639, 1997 roughly 6 h. One of the growth cones then elongates Keywords: tectal neurons; in vivo development; zebrarapidly and grows toward the caudal tectum via a route fish embryos; primary process; axogenesis; dendrite characteristic of efferent axons. After retraction of exformation; transitory branches; time-lapse videorecess branches and growth cones, branching activity recordings sumes at the tip of the primary process to form the