PMC

a, fgf22 and fgf7 mRNAs are highly expressed in CA3 pyramidal neurons (arrowheads), but not in CA1 pyramidal neurons. Bottom panels are negative controls using FGFKO sections. b, fgfr2 mRNA is widely expressed throughout the hippocampus. c, FGF22 and FGF7 proteins are localized in CA3 synapse-rich areas. Pictured areas correspond to the boxed area in a. Scale bars, 500 μm (a, b) and 50 μm (c). SR: stratum radiatum, SL: stratum lucidum.

a–d, Representative whole-cell recordings of mEPSCs (a) and mIPSCs (c) from WT and FGFKO hippocampal neurons; frequency and amplitude of mEPSCs (b) and mIPSCs (d) in the indicated groups (18–24 neurons/group). e, Representative time-course of seizure development during kindling experiments. f, Percentage of mice kindled when about half of the control mice are kindled (~21 PTZ injections) from four independent experiments (4–6 mice/experiment). Error bars are s.e.m. Significant difference from control at *P < 0.05 and ***P < 0.001, ANOVA followed by Tukey test. g, Summary model. FGF22 and FGF7 from CA3 pyramidal neurons promote the differentiation of excitatory and inhibitory presynaptic terminals, respectively. FGF22 and FGF7 are localized at corresponding synapses and activate differential signaling pathways for specific presynaptic differentiation.

a, SV2 staining in CA1 and CA3 from P14 WT, FGF22KO and FGF7KO mice demonstrates decreased synaptic vesicle (SV) clustering in CA3 of FGFKO mice. b, Normal active zone formation (bassoon clustering) in CA3 of FGFKO mice. c, d, Staining in CA3 for VGLUT1 (c) and VGAT (d), showing impaired glutamatergic and GABAergic SV clustering in CA3 of FGF22KO and FGF7KO mice, respectively. e, Normal PSD95 and gephyrin clustering in CA3 of FGFKO mice. f–k, Electron microscopic (EM) analysis of asymmetric (excitatory, f–h) and symmetric (inhibitory, i–k) synapses in CA3. Synaptic density (x1,000/mm², f, i), representative synapses (g, j), and analysis of SVs within 400 nm from the active zone (AZ; h, k) show specific presynaptic defects in FGFKO mice. l, Western blotting of CA3 lysates, indicating no overall change in synaptic protein expression in FGFKO mice. Error bars are s.e.m. Staining data are from 15–126 fields from 5–14 mice. EM data are from 5–20 synapses. Significant difference from control at *P < 0.05; **P < 0.01; ***P < 0.001, ANOVA followed by Tukey test. Scale bars, 20 μm (c, d) and 200 nm (g, j).

a, VGLUT1 and VGAT clustering on FGF-transfected WT hippocampal neurons (labeled with GFP; 7 DIV). b, Defects in the clustering of VGLUT1 and VGAT on the dendrites of FGF22KO or FGF7KO CA3 pyramidal neurons (Py-positive; 14 DIV). The number (puncta/mm neurite) and size of puncta were quantified. c, The number (x1,000 puncta/mm²) and size of VGLUT1 and VGAT puncta on non-CA3 pyramidal neurons (Py-negative). d, The presynaptic defects in FGFKO cultures are rescued by expression of the corresponding FGF in postsynaptic CA3 pyramidal neurons. Data are normalized to WT. e, f, FGF22-EGFP localizes to glutamatergic, and FGF7-DsRed to GABAergic synapses (arrowheads). g, Endogenous FGF22 and FGF7 are colocalized with PSD95 or VGAT. h, FGF22-EGFP and FGF7-DsRed exhibit differential dendritic localization. i, j, The number (x1,000 puncta/mm²) and size of VGLUT1 (i) or VGAT (j) puncta after FGF bath application to WT cultures. k, VGLUT1 and VGAT staining intensity of control and FGFR2KO CA3 sections (P8). l, Normalized staining intensity of FGFR2KO sections. Error bars are s.e.m. Data are from 50–290 neurites or 8–66 fields from at least three experiments. Significant difference from control at *P < 0.05; **P < 0.01; ***P < 0.001, t-test (d, k, l) or ANOVA followed by Tukey test; #P=0.073 (i). Scale bars, 10 μm.