Golgi‐Cox staining and neuronal dendrite and spine morphology analysis

Golgi‐Cox staining was performed on freshly dissected adult mouse brain using the FD Rapid GolgiStain™ Kit (FD NeuroTechonologies) according to manufacturer's instruction. Stained brain tissue was embedded in 3% low‐melt agarose, and vibratome sections were cut at 100 µm. Sections were mounted with Mowiol and imaged using a Zeiss Spinning Disc inverted microscope. Pyramidal neurons in layers II + III of the somatosensory cortex of the rostral neocortex were selected for further analysis. Dendritic tracings of upper‐layer neurons were quantified by Sholl analysis to estimate total dendritic length and dendritic arborization using the Sholl analysis Fiji plug‐in. The dendritic spine density was measured as previously reported (Parent et al, 2016). Briefly, secondary dendrites that were at least 10 μm long were traced, the exact length of the dendritic segment was calculated, and the number of spines along the dendrite was counted (to yield spines/10 µm). Also, dendritic spines were classified as previously reported (Parent et al, 2016; Laguesse et al, 2017) into filopodia, thin, stubby and mushroom.