Fig 2: Itgb3 haplo-insufficiency limits synaptic activation of mGluR5(A) Timeline for bicuculline application (10 µM) in the presence or absence of mGluR1 (Bay; 10 µM) or mGluR5 (MPEP; 5 µM) inverse agonists. Bay and MPEP application started 30 min before Bicuculline. (B) Representative raster plots of network activity from WT and Het cultures for the indicated conditions. (C–F) Quantification for experiments as in (A) and (B). Values are normalized to baseline for each recording. If only mGluR5 can be activated (Bay condition; yellow background), bicuculline is less effective in elevating firing rate in Het cultures (**p < 0.01, two-way ANOVA followed by Bonferroni post-test; n = 4–6 for each condition from 3 independent cultures). Data are presented as mean ± SEM; dots represent individual values. (G) Scheme showing that synaptically released glutamate (Glu) activates only synaptic mGluR5 in the presence of the mGluR1 antagonist Bay. (H) Representative confocal images of primary cortical neurons from WT and Het cultures stained for mGluR5 and the presynaptic marker vGlut1. (I) Line profiles of mGluR5 intensity for WT (left, black) and Het (right, gray) from the green dotted lines in H (S, dendritic spine; D, dendritic shaft). (J) Quantification of the distribution of mGluR5 between vGlut1-positive dendritic spines and adjacent dendritic shafts for experiments as in (H). Left, cumulative distribution of the relative difference ((S-D)/(S+D); S, synaptic signal; D, dendritic signal) for each spine/dendritic shaft pair (n = 44–48 pairs). Right, same data expressed as mean ± SEM (***p < 0.001, unpaired two-tailed Student’s t test). mGluR5 signal is weaker in dendritic spines of Itgb3 Het neurons. (K) Co-immunoprecipitation experiments from brain cortical extracts, showing that ß3 integrin co-precipitates mGluR5 (left) and mGluR5 co-precipitates ß3 integrin (right).

Fig 3: Chronic blockade of mGluR5 rescues impaired network activity of Itgb3 Het neurons(A) Experimental timeline of MEA experiments with mGluR1 (Bay; 10 µM) and mGluR5 (MPEP; 5 µM) inverse agonists. (B) Representative raster plots of network activity from WT and Itgb3 Het cultures for the indicated conditions. (C–F) Quantification of experiments as in (A) and (B) after 10, 30, 60, 120, and 240 min long applications of the indicated drugs. Values are normalized to baseline (B) for each recording. Chronic blockade of mGluR5 with MPEP increases firing and burst rate selectively in Itgb3 Het cultures (*p < 0.05, **p < 0.01, ***p < 0.001, two-way ANOVA followed by Dunnett post-test; n = 4–8 per condition; 3 independent cultures). Data are presented as mean ± SEM. Lines through points are sigmoid fits. (G) Scheme depicting the action of the mGluR5 inverse agonist MPEP on Itgb3 Het neurons. (H) Representative heatmaps of Pearson’s correlation coefficients (r) for burst activity from wells containing 9 electrodes (E1–E9). (I) Quantification of experiment as in (H). All electrode pairs exhibited a positive r. The graph shows the percentage of r with a p <0.05 (positively correlated) and a p >0.05 (non-correlated; *p < 0.05, chi-square test; n = 128–280 pairs). Chronic blockade of mGluR5 with MPEP rescues burst synchrony in Itgb3 Het cultures.