Figure 4. Cryo-immunogold EM of cell surface and vesicular PrP in stratum oriens.

Saf32 cryo-immunogold EM labeling of PrP on the cell surface (a–e, h) and vesicles (f, g) in stratum oriens (a-g), and alveus (h). (a) Sparse labeling of PrP^C (arrows) in neuropil of uninfected hippocampus. (b–h) Clusters of labeling indicate PrP^Sc at 65 dpi (b, c, h), 85 dpi (d), and 99 dpi (e, f, g). PrP^Sc can be seen on very small diameter processes in (b, e), and at cell-cell junctions (b and c arrowheads; d, e). (c) Cryo-section, 200 nm thick, grazing the surface of a process that runs horizontally across the image. Several other processes, which appear darker, are on top of this. The arrowhead indicates Saf32 labeling at a point of contact. In (d), the plasma membrane of one of the processes appears to be invaginating. Arrows in (h) indicate clusters of labeling. Abbreviations: Den, dendrite; Ax, axon; sv, synaptic vesicles; Li, lipid droplet. Bars, 200 nm.