Longinterval Imaging Of Dendritic Arbor Growth

In vivo time-lapse imaging of developing tectal neurons reveals that dendritic arbor growth involves more that than straightforward extension to presynaptic targets25. Rather, there is a highly dynamic process involving considerable remodeling. Imaging the same developing neuron over multiple days within the intact brain reveals that neurons pass through distinct growth phases. Neurons are initially round cells devoid of processes. Short neurites extend, and axons differentiate and extend toward targets. During this initial axonal extension phase, the dendritic arbor is in a quiescent state with few dendritic branches or length added. Dendritic growth then switches to a period of rapid arbor elaboration. In Xenopus tectal neurons, a dynamic period of growth lasting 4 days ensues (Figure 20.1). New branches are added both by extension of dendritic growth cones and addition of interstitial branches, with the majority of growth associated with extension of interstitial branches. New branch length then supports the emergence of further new interstitial branches, thereby continuously increasing arbor complexity. Comparing dendrites from the same neuron from one day to the next reveals that even relatively large portions of the arbor can be partially or completely retracted. After 4 days, growth rates plateau and no further net increase in arbor length or branch number occurs.

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