Fig. 8.

Stage-dependent differences in the lifetime and fate of spiny protrusions. A, The lifetimes of spiny protrusions increased progressively with time in vitro. Distribution of lifetimes of 146 spiny protrusions from apical dendrites of eight pyramidal cells in six tissue slices. B, Fate of spiny protrusions in tissue slices. All spiny structures observed during the first 3 hr of imaging were classified asTRANSIENT (came and went during the 3 hr observation period), DISAPPEARED (evident at the beginning but were resorbed during the 3 hr observation), APPEARED (formedde novo and persisted), or STABLE (evident throughout the 3 hr observation period). Note that a greater fraction of spines were stable on more mature (i.e., 12 d in vitro) dendrites, but there remained a low level of spine turnover.