A) Example images of coronal sections from a WT naïve and (H) Fmr1 KO naïve mice. (B), with panels to the right depicting CA1 (B; I) and dentate gyrus (E; L). Panels below CA1 and DG show the PV (C; F; J; M) and PNN (D; G; K; N) channels separately. In CA1 both WT and Fmr1 KO mice have similar levels of PV (O; R) and PNN (P; S). Both genotypes had increased PNN density in naïve and fear conditioned mice (P). These PNNs were located both around PV cells (Q) and non-PV cells (S). In the DG, there were more PV cells in Fmr1 KO mice than WT mice (T), both PV cells surrounded by PNN (V) and PV cells without PNNs (W). Similar to CA1 there was increased PNN density in naïve and fear conditioned mice (U), but unlike CA1 the increased PNN seem to be around PV cells (V) and not around non-PV cells (X). Conditioning effect #, ##, ###; paired comparison *, **, *** (p = 0.05, 0.01, 0.001). N per group: WT Nv = 5; WT FrC = 6; WT C = 6, Fmr1 KO Nv = 6, Fmr1 KO FrC = 6, Fmr1 KO C = 5. Image # per group: WT Nv = 16, WT FrC = 17, WT C = 28, Fmr1 KO Nv = 18, Fmr1 KO FrC = 16, Fmr1 KO C = 27.