Fig. 4.

Dynamics of long-lived, spiny protrusions on differentiating dendrites (7 d in vitro). These extended time-lapse sequences show changes in length and shape of spiny protrusions (arrowheads) over a period of up to 18.6 hr. All images are composites of two adjacent focal planes selected from a five-image stack to ensure that the full lengths of the structures were captured. Images were selected from an original data set collected at 5 min intervals. Elapsed time is shown in hours. A, Two of the spiny protrusions (1 and 2) were highly dynamic but persisted for the entire observation period. Length plots for these protrusions are shown in C (traces 1 and2). B, De novo appearance of a spiny protrusion (arrowhead) that persisted after being formed. Length plot for this protrusion is shown in C (trace3). C, Plots of length versus time for spiny protrusions shown above. Measurements of protrusion length were made at each time point (5 min intervals). Traces 1 and2 correspond to the protrusions indicated in A. Note that transient length excursions (arrows), which can effectively double or triple the length of the protrusion, are made from relatively stable bases (arrowheads). Reduction in the transient length excursions of protrusions 1 and3 near the end of the sequences suggests a further stabilization of these protrusions. In contrast, the transient length excursions persist in trace 2.