Fig. 7.

Stage-dependent differences in the dynamics of spiny protrusions. Representative plots of length versus time for spiny dendritic protrusions at 1 d (traces 1–4), 7 d (traces 5–8), and 12 d (traces 9–12) in vitro. The traces illustrate a range of behaviors, including transient protrusion (1, 2, 4, 5, 9), resorption of preexisting structures (6, 10), de novo formation and persistence (3, 7, 11), and persistence of preexisting structures (8, 12). Transient filopodia-like protrusions (1, 2, 5, 9) were observed at all times in vitrobut were most prominent at early stages (i.e., 1 d in vitro). At 7 d in vitro, persisting spiny protrusions often showed transient length excursions (arrows) from short, stable bases (arrowheads) (compare trace 8 and Fig. 4C). Most persisting spines at 12 d in vitro showed little change in length (e.g., trace 12), although there was some turnover of spines (e.g., traces 10, 11). (Note different time base of Figs. 4C and7.)