An intact perineural network is necessary for GluA recruitment to the postsynaptic membrane.Figure 3A) Low and high magnification images of control and PTX3-treated neurons stained for the PNN main component, aggrecan (red), the synaptic proteins PSD95 (green) and Bsn (blue). Scale bar: 5µm B-D) PTX3 application induces a remodeling of the PNN in culture, as assessed by the increase mean intensity and integrated density value of the synapse-co-localizing aggrecan signal whereas no difference in the total area of aggrecan is evident (integrated density: Ctr=1±0.103, PTX3=1.874±0.197; mean intensity: Ctr=1.000±0.088, PTX3=1.556±0.107; total area: Ctr=1±0.179, PTX3=0.982±0.149. Number of fields examined: 26 Ctr, 22 PTX3; Mann-Whitney test; 3 independent experiments, data are presented as normalized mean values±SEM) E) Overnight treatment with hyaluronidase destroys PNN as shown by immunofluorescence for aggrecan (red), DAPI (cyan) and βIII-tubulin (green) and confocal analysis. Scale bar: 20µm F) Representative images showing 14DIV neurons stained for surface AMPARs (GluA, green), the presynaptic protein Bassoon (blue) and tubulin (red) in the different tested conditions. Arrowheads point to postsynaptic GluA clusters. Scale bar: 5µm G) HAse treatment blocks PTX3-induced synaptic surface AMPA receptors clustering (Ctr=1.000±0.075, PTX3=1.425±0.088, PTX3+HAse=0.961±0.053, HAse=1.080±0.087. Number of fields examined: 37, 23, 53, 28 respectively; Kruskall-Wallis test, p=0.0004 followed by post hoc Tukey test as indicated in figure; 3 independent experiments, data are presented as normalized mean value±SEM) H) Representative images showing 14DIV WT and TSG6 KO neurons stained for surface AMPARs (GluA, green), the presynaptic protein Bassoon (blue) and tubulin (red) in the different tested conditions. Arrowheads point to postsynaptic GluA clusters. Scale bar: 5µm I) Synaptic surface GluA quantitation showing no effect of PTX3 treatment in TSG6 KO cultures. On the contrary WT cultures (from littermates) display increased surface GluA&Bsn/Bsn upon PTX3 treatment. A significant enhancement of surface GluA receptors was induced by TTX in both TSG6 KO and WT cultures (WT=1±0.06; WT+PTX3=1.389±0.113; WT+TTX=1.698±0.109; Number of fields examined: 40, 39, 32 respectively; Kruskall-Wallis test p<0.0001 followed by post hoc Dunn"s test. TSG6 KO=1.000±0.047; TSG6 KO+PTX3=0.979±0.048; TSG6 KO+TTX=1.363±0.077. Number of fields examined: 54, 57, 29 respectively; one-way ANOVA analysis of variance, p<0.0001 followed by post hoc Tukey test as indicated in figure. n=3 independent experiments, data are presented as normalized mean values J) Representative mEPSC traces recorded from WT and TSG6 KO littermates cultures treated or not with PTX3 (1μg/ml for 48hrs). K) On the contrary of WT cultures, mEPSC frequency quantitation shows no increase in frequency in TSG6 KO cultures when treated with PTX3(Normalized Frequency, WT Ctr: 1.000±0.074; Wt+PTX3=1.912±0.289; TSG6 KO Ctr=1±0.079; TSG6 KO+PTX3=1.226±0.096; 22, 20, 30, 24 cells respectively, 6 TSG6 KO mice and 4 WT littermates. One way ANOVA test p=0.002 followed by post hoc Dunn's test, data are presented as normalized mean±SEM plus the distribution). L) Cumulative probability plot of mEPSC amplitude and average mEPSC amplitude quantitation (inset) showing no difference in amplitude (WT Ctr: 1.000±0.034, Wt+PTX3=1.069±0.046, TSG6 KO Ctr =1.000±0.028; TSG6 KO+PTX3=1.074±0.67; 22, 20, 30, 24 cells respectively, 6 TSG6 KO mice and 4 WT littermates. One way ANOVA test p=0.817 followed by post hoc Dunn's test, data are presented as normalized mean±SEM plus the distribution. Cumulative distribution is analyzed by Kolmogorov-Smirnov test).