Stability Meets Plasticity in the Drosophila Olfactory System

Neural activity influences ongoing remodeling of axonal arbors, a phenomenon that is particularly evident in the development of the retinotectal system of fish and tadpoles. Two papers this week give us a multicolor view of these systems at work. Ruthazer et al. watched the growth of retinal ganglion cells (RGCs) in albino tadpoles, whereas Meyer and Smith used zebrafish. Both authors expressed cytosolic dsRED (discosoma red fluorescent protein) and GFP (green fluorescent protein)-tagged synaptophysin (SYP) in selected RGCs, allowing them to visualize punctate presynaptic vesicles in developing axons. Using time-lapse imaging, Ruthazer et al. report that new branches emerged from SYP-labeled puncta, and more intensely labeled axons were longer-lived. Moreover, branches with mature synapses were more stable, whereas those containing more faintly labeled synapses were more likely to retract. Patterned visual stimulation both stabilized branches containing more vesicles and destabilized branches with fewer. Meyer and Smith also found that new branches formed at SYP puncta and stabilized nascent branches invariably had SYP puncta.