Distribution of Extrasynaptic NMDA Receptors on Neurons

Figure 3

Extrasynaptic NMDARs (NR1 antibody; arrowheads) in the CA1 stratum radiatum of the adult hippocampus (A–H) using immunogold (AB,G,H) or EM immunoperoxidase/DAB (C–F: E and F were processed further with silver/gold toning), and immunofluorescence colocalization of NR2B/VGLUT1/PSD-95/93 (I) or NR2A/VGLUT1/SAP102 (J) in cultured hippocampal neurons. For A–H, extrasynaptic NMDARs can be seen on postsynaptic spines (A–F, H) or dendrites (G; d) adjacent to other processes, including glia (g) and various neuronal processes (see text for details). a: axon terminal; p: presynaptic terminal; asterisk: postsynaptic density. In I, NR2B labeling (red) forms in a perisynaptic ring (**) around synaptic PSD-95/93 (green) and the terminal (labeled with the presynaptic marker, VGLUT1 [blue]) and forms a ring of three puncta around an extrasynaptic punctum of PSD-95/93 (*). In J, this is an enlarged region found along a thin, distal dendrite. Note how NR2A labeling (red) is spread in the perisynaptic regions surrounding two synapses (*): SAP102 (green) forms around the enlargement in conjunction with both the synaptic and extrasynaptic (**) NR2A; the bottom image is a high contrast version of the top one. Scale bars are 100 nm for A–H and 500 nm for I, J. Reprinted from parts of Figures 2, 5, and 6 from Petralia et al. [8].