Subregion-specific dendritic spine abnormalities in the hippocampus of Fmr1 KO mice

► Adult Fmr1 knockout mice show an immature spine phenotype in the hippocampus. ► Immature spine phenotype present in CA1 region but not in CA3 region of hippocampus. ► Spine phenotype in the hippocampus of Fmr1 knockout mice is region = specific.