Spines of various sizes show Ca2+ transients in response to 2pMAPG. (A-C) Three examples of 2pMAPG mapping and Ca2+ imaging. The top panels show grouped Ca2+ transient-evoking pixels (yellow pixels) and dendritic spines that exhibited Ca2+ transients induced by 2pMAPG (green dots indicate the position of these spines). Red boxes show 2pMAPG mapping areas. White broken lines indicate the pial surface. In the middle and bottom images, green arrows indicate the spines with Ca2+ transients. These images were taken from larger Ca2+ imaging regions. The middle and lower panels show Alexa Fluor 594 and Fluo-5F fluorescence, respectively. The images were taken immediately before and after 2pMAPG at the solid yellow pixels shown in the top panels. (D) The size distribution of spines showing Ca2+ transients in the first or second imaging frame after 2pMAPG (n = 34 in 18 cells). (E) The size distribution of all spines included in the imaging regions (n = 494 in 18 cells). (F) The mean amplitudes of Ca2+ transients are plotted against spine size. Bars, standard error of mean.