Dendritic Spines Participate in Synapse Formation
(A) PVI spines show stubby, thin, and mushroom morphologies. Top, example of a 3D-reconstructed segment. Bottom, thin spines were more abundant than stubby and mushroom spines (n = 5,700 spines, 57 cells, 6 mice).
(B) Electron micrograph showing a PV-immunogold-labeled spine (yellow) forming an asymmetrical synapse (asterisk).
(C) Single-plane confocal images showing immunoreactivity for GFP (green), PSD95 (red), and VGLUT1 (blue) in the ml. Examples of PSD95-positive puncta in shafts and spines apposed to VGLUT1 positive boutons (arrows and arrowheads, respectively) represent putative synapses.
(D) About 90% of all spines were positive for PSD95 and apposed to VGLUT1- or VGLUT2-positive terminals (n = 1,960 spines, 29 neurons, 3 mice).
(E) The percentages of VGLUT+/PSD95+ putative spine synapses over all synapses (shaft and spine) varied in individual spiny segments (n = 134 segments, 29 neurons, 3 mice) and (F) depended on the molecular sublayer when quantified for entire dendritic trees (n = 12 neurons, 3 mice); bars are means, and error bars show SD.