Colocalization of α-actinin-2 with NR1 (A) and GKAP (B–D). A, Postembedding immunogold labeling (18 nm) for NR1 is on synapse stained also for α-actinin-2 with pre-embedding immunoperoxidase (thestar marks postsynaptic electron-dense diaminobenzidine reaction product). B, Immunogold labeling for GKAP (12 nm gold particles) over postsynaptic density of α-actinin-2-positive profile is shown. C, D, Serial thin sections were mounted on different grids and processed with silver-intensified immunogold for α-actinin-2 (C) or GKAP (D). One synapse is positive for both antigens (double arrows); the other is positive for only GKAP (arrowheads onright). Scale bars, 250 nm; C andD are to the same scale.