Fig. 3.

SERT^PyramidΔ impairs postnatal development of CA1 pyramidal neuron dendritic spines, secondarily resulting in increased mushroom type mature spine density on adult CA1 pyramidal neurons. (A,B) Thy1-GFP/M-expressing neurons develop postnatally in the hippocampus. (A) Representative images of Thy1-GFP/M-expressing neurons in hippocampal coronal sections from SERT^fl/fl mice at various postnatal stages. (B) Number of GFP⁺ neurons in the CA1 pyramidal layer in serial coronal sections throughout the hippocampus in SERT^PyramidΔ mice and SERT^fl/fl littermates at indicated ages. n=3 mice/age/genotype. Data are mean±s.e.m. two-tailed t-test. (C) 3D dendritic tree reconstruction analyses of Thy1-GFP/M-expressing CA1 pyramidal neurons showed no difference in the number of branching points or the total length of the dendrites of the entire apical dendritic trees and 3rd order branch segments in SERT^PyramidΔ mice versus SERT^fl/fl littermates age P16. Fifteen neurons from three SERT^fl/fl mice and 15 neurons from three SERT^PyramidΔ mice. Data are mean±s.e.m, two-tailed t-test. (D) Representative images of 3rd order apical dendritic segments of Thy1-GFP/M-expressing CA1 pyramidal neurons in SERT^PyramidΔ mice and SERT^fl/fl littermates age P16. Dendritic segments in collapsed z-stack confocal images (white) and corresponding 3D rendering of the segments (red) were subjected to semi-automatic spine morphometric analyses using Imaris. Areas outlined by white boxes are shown at a higher magnification in the bottom panels. (E,F) Spine morphometric analyses of 50 µm long, 3rd order Thy1-GFP/M-expressing apical dendritic segments located in the stratum radiatum in SERT^PyramidΔ mice and SERT^fl/fl littermates age P16. Females, 26 segments from three mice/genotype; males, 21 segments for SERT^PyramidΔ and 20 segments for SERT^fl/fl from four mice/genotype. Data are mean±s.e.m. two-tailed t-test. (G,H) Spine morphometric analyses of 50 µm long, 3rd order Thy1-GFP/M-expressing apical dendritic segments located in the stratum radiatum in SERT^PyramidΔ mice and SERT^fl/fl littermates age 12±2 weeks old. Females, 20 segments from four SERT^PyramidΔ mice and 21 segments from three SERT^fl/fl littermates. Males, 30 segments from five SERT^PyramidΔ mice and 32 segments from four SERT^fl/fl littermates. Data are mean±s.e.m. two-tailed t-test.