Figure 2.

Dendrite labeling in LM and EM. A, SEM photomicrographs of three consecutive 70 nm ultrathin sections obtained at low magnification (12 nm/pixel) reveal punctate staining of the dendrite labeled with an Alexa Fluor-Nanogold-streptavidin triple-conjugate. The dendrite shaft, spine heads, and spine necks are clearly labeled, but a large mitochondrion remains unlabeled, implying that biotin did not penetrate this organelle during the neuron's filling. B, Single LM plane (equal in thickness to several consecutive ultrathin sections) that corresponds approximately to the same area of dendrite shown in A. Deconvolution permits distinction between the dendrite's biotin-filled cytoplasm and its unfilled mitochondrion. This photomicrograph is an x, y, z cropping of the dendrite shown in Figure 3A. C, High-magnification (2 nm/pixel) SEM photomicrograph showing a peroxidase-labeled VGluT2⁺ vesicle pool (green arrowhead, dark gray diffuse stain) apposed to a silver-enhanced Nanogold-labeled spine (black punctate stain) containing a PSD (red arrowhead); this contrasts with an unlabeled VGluT2⁻ vesicle pool (blue arrowhead) apposed to an unlabeled spine containing a PSD (yellow arrowhead). This photomicrograph shows a larger field of view surrounding the spine/vesicle pool shown in Figure 3F.