Fig. 2

Comparison on structural preservation upon different fixation conditions and subsequent treatments. Images show synaptic profiles from 3 week-old dissociated hippocampal cultures without (a, b) or with (c, d) immunogold labeling. Clusters of synaptic vesicles (SV in a) and the postsynaptic density (PSD, edges of which marked with arrows in a) are characteristics of glutamatergic asymmetric synapses. The fixation treatments were 4% PF in PBS for 45 min (a), 4% glutaraldehyde in 0.1 M cacodylate buffer at pH 7.4 for 30 min (b), 4% PF in PBS for 30 min and labeled for CaMKII (c), a cytosolic protein in neurons [6], and 2% PF in PBS for 15 min and labeled for IRSp53 (d), an actin-associated protein enriched at the PSD [20]. All fixations were carried out at room temperature. Membranes were poorly preserved in (d) due to the lower concentration of PF and the shorter fixation time. Scale bars = 100 nm