Summary

Recent studies employing time-lapse imaging of growing neurons within intact brains, brain slices and retinal explants have discovered a remarkable amount of morphological remodeling as dendritic arbors grow. Most of this dynamic growth involves rapid turnover of dendritic filopodia, a small fraction of which stabilize and grow to become persistent branches. Why do growing neurons expend such extensive resources extending processes that are mostly retracted, and what influences or confers stabilization on the few filopodia that persist? One hypothesis is that filopodia sample their environment for appropriate presynaptic contacts. This 'synaptotropic' model is supported by findings that afferent input and synaptogenesis are significant contributors to filopodial stabilization and dendrite growth. Remarkably, increased dendrite growth in response to brief periods of enhanced sensory stimuli, mediated by glutamatergic transmission, has been directly observed in the intact brain of developing animals. In vivo imaging of PSD-95 puncta in growing dendrites demonstrates that synapses occur on filopodia and that the presence of synapses confers morphologic stabilization. Further in vitro studies have identified components of activity-regulated molecular cascades including Ca2+ influx, and the activation of CaMKII, CaMKIV, CREB, CREST, and small GTPases that may translate afferent input into both synaptogenesis and cytoskeletal plasticity. Innervation that triggers both synapse

'Brain Research Centre, University of British Columbia, Vancouver, BC, Canada V6T2B5; [email protected]

formation and local dendrite growth promotes arborization in regions with appropriate afferent input.

Brain Blaster

Brain Blaster

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