Figure 1.

Chronic two-photon in vivo imaging of dendritic branch tip dynamics in superficial L2/3 cortical interneurons. A, Left, A maximum z-projection (MZP) of chronically imaged interneuron (black arrow) superimposed over blood vessel map with primary visual cortex (VC) outlined. Right, The experimental timeline. B, MZP (top row) along with two-dimensional projections of three-dimensional skeletal reconstructions (middle row) of a superficial L2/3 interneuron acquired over 2 weeks in a 6-month-old animal. Green boxes indicate a dynamic branch tip shown at high-magnification in bottom. Green arrow marks the approximate distal end of the branch tip on the first day of imaging (d0). C, MZP (top row) and two-dimensional projections of three-dimensional skeletal reconstructions (middle row) of a superficial L2/3 interneuron acquired over 2 weeks in an 18-month-old animal. Red boxes indicate a stable branch tip shown at high-magnification in bottom. Red arrow shows no change in the distal branch tip over 2 weeks of imaging. D, Average cell FF (dynamic index) at different ages. Each circle represents an individual cell. Dashed line marks the experimentally determined threshold for a dynamic cell. The 3 month group has a significantly higher average FF than the 6 month group (**p = 0.0012, by bootstrap using Holm–Sidak's test with α = 0.05 to correct for multiple comparisons, n = 16 for 3 and 14 for 6 months). The 6 month group is significantly different from the 18 month time point (*p = 0.0229, by bootstrap using Holm–Sidak's test with α = 0.05 to correct for multiple comparisons, n = 14 for 6 and 11 for 18 months), but does not differ from the later ages (p = 0.0607 for 6 vs 9 months, p = 0.0607 for 6 vs 12 months, by bootstrap using Holm–Sidak's test with α = 0.05 to correct for multiple comparisons, n = 14 for 6 months, 10 for 9 months, and 8 for 12 months,). Error bars represent SD of the bootstrapped population. Scale bars: A, 200 μm; B, C (on cells), 20 μm; B, C (on tips), 5 μm.