Dynamics of process formation during differentiation of tectal neurons in embryonic zebrafish

Abstract

Neurons acquire their distinct shapes after passing through many transitional stages in early development. To reveal the dynamics and spatiotemporal sequence of process formation in situ, the growth of neurons in the optic tectum of live zebrafish embryos (54 to >100 h old) was monitored using time‐lapse videorecordings. Neurons were labeled by injecting the fluorescent vital dye DiO into the cell‐rich layer of the developing tectum in 50‐ to 70‐h‐old embryos. In phase 1, tectal neurons possess an apical “primary process” which reaches to the ventral aspect of the tectal neuropil. The primary process produces at its tip short transitory branches, some with growth cones, over a period of roughly 6 h. One of the growth cones then elongates rapidly and grows toward the caudal tectum via a route characteristic of efferent axons. After retraction of excess branches and growth cones, branching activity resumes at the tip of the primary process to form the dendritic tree (phase 2). The dendritic tree develops in the tectal neuropil through emission and retraction of many branches during a period of >20 h (our longest continuous time‐lapse movie). The tectal territory “explored” in this way is larger than the area finally covered by the tree resulting from growth and loss of branches. The dynamics observed here directly are probably characteristic for dendrite formation in vertebrates. Moreover, consistent with the sequence of neuronal differentiation observed in vitro, the growth of the axon precedes that of the dendrites, although both emerge from a common primary process in this type of tectal neuron. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 627–639, 1997

Characterization of Genetically Targeted Neuron Types in the Zebrafish Optic Tectum

“…Studies examining neuronal development in the tectum have typically utilized methods that label a broad cross-section of tectal neurons (Kaethner and Stuermer, 1997; Niell and Smith, 2005; Sato et al, 2007; Scott and Baier, 2009). Although these studies have revealed general mechanisms common to many different cell types, a complete understanding of tectal circuit function will only be attained when we understand the structure and connectivity of specific neuron types.…”

Nicotine effects on learning in zebrafish: the role of dopaminergic systems

“…In mammals, nicotinic receptors' density in the superior colliculus (optic tectum in the zebrafish) is very dense (Clarke et al 1985). The optic tectum, positioned much like the neocortex in mammals and constituting a considerable portion of the zebrafish brain (Wullimann et al 1996), is the major processing area for visual processing in zebrafish (Kaethner and Stuermer 1997). Zebrafish express functional β3, α2, and α7 nicotinic receptors and these receptors show a high degree of similarity with mammalian nicotinic receptors (Zirger et al 2003).…”

Timing of nicotine effects on learning in zebrafish

“…In mammals, nicotinic receptor density in the optic tectum (superior colliculus) is very high (Clarke et al 1985). The optic tectum is the major processing area for visual processing in zebrafish (Kaethner and Stuermer 1997) and constitutes a considerable portion of the zebrafish brain, positioned much like the neocortex in mammals (Wullimann et al 1996). Further research is necessary to determine the possible role of nicotinic receptors in the zebrafish optic tectum for cognitive function.…”