Figure 3.

Developmental maturation of spine density occurs rapidly at dendrites receiving LOT input. A₁, Two-photon image of a representative pyramidal cell (P34). Dashed lines indicate boundaries from which distal apical, proximal apical, and basal dendritic spines were measured. The solid line represents pial surface. Scale bar, 20 μm. A₂, Distal apical (red), proximal apical (white), and basal dendritic (blue) regions from three cells at age P5, P12, and P34. Scale bar, 5 μm. B, Developmental time course for increases in spine density at distal apical, proximal apical, and basal dendritic compartments. Each symbol represents values averages pooled over 2 d intervals. Distal apical spine density data for the nine age groups starting from P5–P6 to P34–P35 are as follows: 21 ± 0.9, 33 ± 1.5, 35 ± 3.3, 42 ± 1.6, 41 ± 0.8, 38 ± 1.0, 46 ± 1.5, 41 ± 4.6, and 45 ± 3.1 spines/100 μm; n = ∼12 cells for each age. Basal spine density data for the nine age groups starting from P5–P6 to P34–P35 are as follows: 19 ± 1.3, 32 ± 2.7, 31 ± 1.7, 43 ± 1.7, 65 ± 1.8, 61 ± 2.3, 80 ± 4.0, 75 ± 6.6, and 76 ± 3.8 spines/100 μm; n = ∼12 cells for each age. Proximal apical spine density data for the seven age groups starting from P5–P6 to P34–P35 are as follows: 22 ± 1.9, 38 ± 2.2, 41 ± 2.7, 77 ± 3.5, 76 ± 6.3, 86 ± 8.6, and 94 ± 12.3 spines/100 μm; n = ∼5 cells for each time point. Lines are exponential fits with time constants of 3, 12, and 16 d for distal apical, basal, and proximal apical dendrites, respectively.