The structural plasticity of dendritic spines is considered to be an important basis of synaptic plasticity, learning, and memory. Here, we induced input-specific structural LTP (sLTP) in single dendritic spines in organotypic hippocampal slices from mice of either sex and performed ultrastructural analyses of the spines using efficient correlative light and electron microscopy. We observed reorganization of the PSD nanostructure, such as perforation and segmentation, at 2–3, 20, and 120 min after sLTP induction. In addition, PSD and nonsynaptic axon–spine interface (nsASI) membrane expanded unevenly during sLTP. Specifically, the PSD area showed a transient increase at 2–3 min after sLTP induction. The PSD growth was to a degree less than spine volume growth at 2–3 min and 20 min after sLTP induction but became similar at 120 min. On the other hand, the nsASI area showed a profound and lasting expansion, to a degree similar to spine volume growth throughout the process. These rapid ultrastructural changes in PSD and surrounding membrane may contribute to rapid electrophysiological plasticity during sLTP.
Rapid Ultrastructural Changes in the PSD and Surrounding Membrane after Induction of Structural LTP in Single Dendritic Spines
sLTP induction disrupts the correlation between PSD and spine head volume. A, B, Serial images of an example spine (A) and 3D reconstruction of the example spine (B), with spine head shown in yellow and PSD shown in red. Scale bar, 200 nm. C, PSD size at early, intermediate, and late phases of sLTP. Welch's t test on log-transformed data. D, Correlation between spine head volume and PSD size for control spines (Ctrl) and sLTP spines at early, intermediate, and late phases of sLTP. Regression line forced through origin. Black line and open circles represent control spines, and red line and solid dots represent sLTP spines at each phase of sLTP. The p value was calculated by comparing the two regression lines with an extra sum-of-squares F test. E, Ratio of PSD area to spine volume at early, intermediate, and late phases of sLTP. Two-way ANOVA followed by Bonferroni's post hoc test was used for comparison between control and sLTP spines, and Tukey's post hoc test was used for comparison among different sLTP phases. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.
Max Planck Florida Institute for Neuroscience
