Figure 3

Distinct effects of polyribosomes and SER on synapse size. Serial electron micrographs and 3D reconstructions illustrate polyribosomes (blue arrows) in the heads of spines from the (A) control and (B) LTP conditions. (3Ds – spine and dendrite (yellow), PSD areas (red), SER (green), each ribosome in the polyribosome (blue 20 nm sphere)). (C) In the control condition (blue), 17.6% of spines contained polyribosomes (PR) while in the LTP condition (red) 12.3% of spines contained PR (χ² = 3.6, p = 0.059). (D) Of the PR+ spines, 19.2% also contained SER in control, and 13.3% also contained SER in the LTP condition (χ² = 0.6, p = 0.45).There was a strong positive correlation between log-normalized PSD areas and spine head diameters across spines with different sets of resources in the control and LTP conditions. Analysis of covariance accounting for head diameters revealed: (E) slightly larger PSD areas on PR− SER− spines in the LTP vs control conditions (F_(1,475) = 5.22, n = 478); (F) PR+ SER+ spines were rare and no statistically significant differences were detected in PSD areas between the LTP and control conditions (F_(1,12) = 0.16, n = 15); (G) PR+ SER− spines were significantly larger in PSD area in the LTP condition (F_(1,74) = 5.3, n = 77); and (H) PR− SER+ spines had the most enlargement of PSD area in the LTP vs control condition (F_(1,61) = 16.6, n = 64). Correlations for each condition, p values for the LTP vs control comparisons, and effect sizes (η²) of condition are presented in the lower corner of each graph.