Article Figures & Data
Figures
- Figure 1.
Protein kinase A activation induces iLTP on hippocampal GCs. A, Top, Schematic of experimental procedure. Bottom, Representative example of a biocytin-filled GC (green) recorded during the experiments. The boxed region is magnified in the right part of the panel and shows a dendritic spine covered dendritic segment. Scale bars: bottom panel, left, 20 μm; bottom panel, right, 5 μm. B, Representative traces of electrically eIPSCs before (Bsl) and after FSK (10 μm) bath application in the absence or presence of PKA inhibitor H89 (+H89, 10 μm). Calibration: 50 ms, 50 pA. The time course of FSK effects on normalized eIPSC amplitude in the absence (FSK) or presence of PKA inhibitors H89 (+H89, 10 μm) and PKI14-22 (+PKI, 1 μm) is shown in the right graph. C, Parts of whole graphs represent the proportion of recorded GCs showing significant increase of eIPSC amplitude after FSK application in the absence (FSK) or presence of PKA inhibitors H89 (+H89, 10 μm) and PKI14-22 (+PKI, 1 μm). Two-sided Fisher’s exact test; FSK versus FSK+H89, p = 0.002; FSK versus FSK+PKI, p = 0.002; FSK, n = 24 GCs; FSK+H89, n = 8 GCs; and FSK + PKI, n = 5 GCs. D, Population data of FSK effects on normalized eIPSC amplitude before (Bsl) and 20 after FSK application in the presence and absence of PKA inhibitors H89 and PKI14-22. Two-way ANOVA; Treatment (FSK, FSK+H89, FSK+PKI): F(2,34) = 13.86, p = 0.0001; Bonferroni’s multiple-comparisons test; Bsl versus FSK, p < 0.0001; Bsl versus FSK+H89, p = 0.27; Bsl versus FSK+PKI, p > 0.99; FSK, n = 24 GCs; FSK+H89, n = 8 GCs; FSK+PKI, n = 5 GCs. E, Representative traces of eIPSC before (Bsl) and after FSK (10 μm) bath application recorded with a low-chloride internal solution. The time course of FSK effects is shown in the right graph. F, Proportion of GCs recorded with low chloride showing a significant increase of eIPSC amplitude after FSK application. G, Population data of FSK effects on normalized eIPSC amplitude before (Bsl) and after FSK application in the low-chloride condition. Two-sided t test; t(12) = 2.772, p = 0.02; n = 7 GCs. *p < 0.05; n.s., nonsignificant. Dots and vertical bars in B and E, and horizontal and vertical bars in D and G represent the mean ± SEM. Dots in D and G represent individual measurements.
- Figure 2.
PKA-induced iLTP is observed in GABA synapses originated in SST but not in PV INs. A, Schematic of experimental procedure. B, Representative traces of normalized oeIPSCs recorded in GCs from PV-Cre and SST-Cre mice infected with AAV-DIO-ChETA-EYFP. The blue light (490 nm) pulse used to elicit oeIPSCs is represented with a vertical blue bar. Scale bar, 10 ms. C, Representative images of Cre-dependent ChETA expression (cyan) and biocytin-filled GC (green) in the DG of slices prepared from PV-Cre and SST-Cre mice. Scale bar, 25 μm. D, Representative traces of oeIPSCs before (Bsl) and after FSK bath application in GCs from PV-Cre (PVGC) and SST-Cre (SSTGC) mice. Calibration: 50 ms; 30 pA (SST-Cre) and 50 pA (PV-Cre). The time course of FSK effects on normalized oeIPSC amplitude in both conditions is shown in the right graph. Open symbols correspond to FSK application in the presence of PKA inhibitor H89 in experiments performed in SST-Cre mice (SSTGC+H89). E, Parts of whole graphs represent the proportion of recorded GCs showing significant increase of eIPSC amplitude after FSK application in PV-Cre and SST-Cre mice in the absence and presence of PKA inhibitor H89. Two-sided Fisher’s exact test; SSTGC versus PVGC, p = 0.002; SSTGC versus SSTGC+H89, p = 0.0007; PV-Cre, n = 12 GCs; SST-Cre, n = 10 GCs; SST-Cre + H89, n = 8 GCs. F, Population data of FSK effects on normalized oeIPSC amplitude before (Bsl) and after FSK application in GCs from PV-Cre and SST-Cre mice. Two-way ANOVA; treatment/genotype: F(2,27) = 20.64, p < 0.0001; Bonferroni’s multiple-comparisons test; PV-Cre Bsl versus FSK, p = 0.99; SST-Cre Bsl versus FSK, p < 0.0001; SST-Cre+H89 Bsl versus FSK, p = 0.71; PV-Cre mice, n = 12 GCs; SST-Cre mice, n = 10; SST-Cre+H89, n = 8 GCs. *p < 0.05; n.s., nonsignificant. Dots and vertical bars in D, and horizontal and vertical bars in F represent the mean ± SEM. Dots in F represent individual measurements.
- Figure 3.
PKA-induced iLTP is accompanied by changes in PPR. A, Schematic of the method used to calculate PPR for eIPSCs and oeIPSCs. ISI, Interstimulus interval. B, Population data for eIPSCs PPR calculated before (Bsl) and after FSK application in the presence and absence of PKA inhibitor H89. Two-way ANOVA; FSK versus FSK+H89: F(1,24) = 2.57, p = 0.12; Bonferroni’s multiple-comparisons test; Bsl versus FSK, p = 0.003; Bsl versus FSK+H89, p = 0.99; FSK, n = 18 GCs; FSK + H89, n = 8 GCs. C, Population data for oeIPSC PPR calculated before (Bsl) and after FSK application in PVGC and SSTGC synapses. Two-way ANOVA; PVGC versus SSTGC: F(1,20) = 4.71, p = 0.04; Bonferroni’s multiple-comparisons test; PVGC Bsl versus FSK, p = 0.29; SSTGC Bsl versus FSK, p = 0.03; PV-Cre mice, n = 12 GCs; SST-Cre mice, n = 10 GCs. *p < 0.05; n.s., nonsignificant. Dots in B and C represent individual measurements.
- Figure 4.
Synaptic properties and PKA-dependent plasticity of DG SST IN distal synapses on medial septal neurons (SSTMS). A, Schematic of experimental procedure. B, Representative images of AAV-dependent ChETA expression in SST-Cre mice injected in the DG. Top, The injection site of AAV in the DG. Scale bar, 200 μm. Bottom, Low-magnification (scale bar: left, 500 μm) and high-magnification (scale bar: right, 200 μm) of DG SST IN long-range projections in the MS. Anatomical diagrams approximately corresponding to the images shown are adapted from Paxinos and Franklin (2012). C, Representative image of medial septum slice showing a biocytin-filled MS neuron (green). Long-range axonal projections from hilar ChETA expressing SST IN are shown in cyan. Scale bar, 50 μm. D, Connectivity and rise slope comparison between distal SSTMS and local SSTGC synapses. Connectivity: two-sided Fisher’s exact test, p < 0,001; rise slope: two-sided Mann–Whitney test: U = 89.5, p = 0.04; SSTGC, n = 36 synapses; SSTMS, n = 9 synapses. E, The GABAA receptor blocker gabazine (GBZ) blocks oeIPSC responses in MS neurons to SSTMS synapses optogenetic stimulation. Two-sided Mann–Whitney test: U = 0, p < 0.0001. Calibration: 100 pA, 50 ms. F, The PPR of SSTMS and SSTGC oeIPSCs did not differ. Two-sided Mann–Whitney test: U = 71, p = 0.97; SSTGC, n = 16 synapses; SSTMS, n = 9 synapses. G, Representative traces of SSTMS oeIPSCs before (Bsl) and after FSK bath application. Calibration: 50 pA, 50 ms. The time course of FSK effect on normalized SSTMS oeIPSC amplitude is shown in the right graph. H, Proportion of recorded MS neurons showing a significant increase of eIPSC amplitude after FSK application. I, Population data of FSK effects on normalized SSTMS oeIPSC amplitude before (Bsl) and after FSK application. Two-sided t test: t(16) = 0.93, p = 0.37; MS neurons, n = 9. *p < 0.05; n.s., nonsignificant. Dots in D, E, F, and I represent individual measurements. Horizontal and vertical bars in D and I, and circles and vertical bars in G represent the mean ± SEM.
- Figure 5.
Kainic acid-induced increases in synaptic activity prevent the induction of iLTP in GCs. A, Schematic of experimental procedure. B, Representative example of c-Fos (green) expression in the DGs of vehicle- and KA-injected mice. Boxed regions in top panels are shown in bottom panels. Scale bars: top, 500 μm; bottom, 50 μm. C, Representative traces of eIPSCs before (Bsl) and after FSK bath application recorded from GCs in vehicle- and KA-treated mice. Calibration: 25 ms, 50 pA. D, Time course of FSK effects on normalized eIPSC amplitude in GCs from vehicle- and KA-treated mice. Vehicle-injected mice, n = 8 GCs; KA-injected mice, n = 11 GCs. E, Proportion of recorded GCs showing a significant increase of eIPSC amplitude after FSK application in the vehicle- and KA-treated mice. Two-sided Fisher’s exact test, p = 0.001; vehicle-treated mice, n = 8 GCs; KA-injected mice, n = 11 GCs. F, Population data of FSK effects on normalized eIPSC amplitude before (Bsl) and after FSK application in GCs from vehicle- and KA-injected mice. Two-way ANOVA; Vehicle versus KA: F(1,17) = 15.85, p = 0.001; Bonferroni’s multiple-comparisons test; Vehicle Bsl versus FSK, p = 0.004; KA Bsl versus FSK, p = 0.19; vehicle-treated mice, n = 8 GCs; KA-injected mice, n = 11 GCs. G, Population data for eIPSC PPR calculated before (Bsl) and after FSK application in GCs from vehicle- and KA-injected mice. Two-way ANOVA; Vehicle versus KA: F(1,17) = 2.43, p = 0.14; Bonferroni’s multiple-comparisons test; vehicle Bsl versus FSK, p = 0.02; KA Bsl versus FSK, p = 0.99; Bsl Vehicle versus KA, p = 0.02; vehicle-treated mice, n = 8; KA-injected mice, n = 11 GCs. *p < 0.05; n.s., nonsignificant. Dots and vertical bars in D and horizontal and vertical bars in F represent the mean ± SEM. Dots in F and G represent individual measurements.
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