Figure 7.

Labeling compared for NMDA vs. AMPA glutamate receptors in PSDs of probable interneurons. (A) Low magnification overview of three glutamate receptor-containing PSDs (white circles and white box). The circled PSDs are conventionally shadowed with platinum and have a low (but typical) LE of ca. 1:50–1:100, whereas the boxed PSD, within a large spine, is shadowed by platinum on only about half its surface, revealing a much higher LE (ca. 1:6) of the glutamate receptors in the unshadowed half. (B) A higher magnification stereoscopic view of the PSD within the large spine had its upper half shadowed by Pt/C and its lower half coated only with carbon (double-ended arrow). Interestingly, the Pt-shadowed half has only one 12-nm gold bead on >190 IMPs, whereas the carbon-replicated half is labeled by 32 12-nm gold beads on ca. 200 IMPs that are weakly delineated by carbon, for a 30-fold higher LE of glutamate receptors beneath carbon as compared with those beneath Pt/C. Two additional gold beads are at the margin between unshadowed and Pt-shadowed IMPs. This image also shows that it is possible to visualize glutamate receptor PSDs even where the Pt replica is not present. (C,D) In an adult rat hippocampal interneuron, FRIL reveals that NMDA receptors (10-nm gold beads, arrowheads) are concentrated at PSDs, but that few clusters of glutamate receptor IMPs are present in the E-face. Scale bars are 0.1 μm, unless otherwise indicated.