SK2 immunoparticles repopulate the PSD after LTP. a – c , Electron micrographs of the stratum radiatum of the CA1 region of mouse hippocampus showing immunoparticles for SK2 at 5 min ( a ), 60 min ( b ), and 5 h ( c ) after chemical LTP induction as detected using postembedding immunogold methods. At 5 and 60 min after LTP, SK2 immunoparticles were localized to intracellular sites (arrowheads) associated with intracellular membranes in dendritic spines (s) of pyramidal cells establishing synapses with axon terminals (b), presumably Schaffer collaterals, but by 5 h they were mostly associated with the PSD (arrow). d , Time course of the recovery of SK2 channels to within 15 nm of the PSD as determined by the distribution of immunoparticles. e , The localization of PSD95 immunoparticles to the PSD did not change after LTP. Scale bar, 0.2 μm.