Fig. 3.

Preservation of punctate staining for proteins of the postsynaptic density. Cultured hippocampal neurons were incubated in the absence (A, C, E,G) or presence (B, D,F, H) of 50 μm NMDA for 5 min before double-labeling for PSD-95 (A,B) or for the NR1 subunit of NMDA receptors (C, D). In other experiments cells were double-labeled for PSD-95 (E, F) and the presynaptic marker synapsin-1 (G,H) to identify synaptic versus extrasynaptic clusters of PSD-95. Extrasynaptic clusters of PSD-95 (arrowheads in E, G) were rare in control cultures. Similarly, cultures incubated with NMDA for 5 min exhibited mainly synaptic clusters of PSD-95 (F,H).