(A–C) Example dendrite segment imaged repeatedly over 6 weeks. Day 0 indicates the first day of imaging, subsequent imaging days indicated. White arrows, stable spines; cyan arrows, transient spines; orange arrows, filopodia. (D) Turnover ratios in WT (n = 3–5 animals per age group) and Gfap Smo CKO juvenile mice (n = 4 animals per age group) analyzed over 2 days. (E) Turnover ratios in WT (n = 8 animals) and Gfap Smo CKO (n = 8 animals) adult mice analyzed over 7 days. Statistical analysis by two-way ANOVA, Tukey’s post hoc test (D) and unpaired Student’s t-test (E). (F) Fraction of protrusions identified as filopodia in juvenile (WT, n = 7 animals; Gfap Smo CKO, n = 10 animals) and adult mice (WT, n = 16: Gfap Smo CKO, n = 7 animals). Statistics by two-way ANOVA, Tukey’s post hoc test. (G) Comparison of spine survival curves for WT and Gfap Smo CKO neurons. Each dashed curve represents the curve from an individual mouse (WT, n = 7 animals; Gfap Smo CKO, n = 5 animals). Solid curves represent best-fits to exponential decay models. (H) The fraction of spines belonging to the stable, recurrent, and transient populations. Statistical significance was assessed by Student’s t-test for each class (stable, recurrent, or transient; n = 7 and 8 animals, WT and Gfap Smo CKO, respectively). Stable, p=0.0485; Recurrent, p=0.1023; Transient, p=0.7709. (I) Breakdown of spine morphology in juvenile mice. Statistical analysis by unpaired Student’s t-test for each spine class. For graphs D-F and I, data points represent individual animals, bars represent mean ± SEM.