Journal: Proceedings of the National Academy of Sciences of the United States of America

Article Title: Synaptic plasticity at the dentate gyrus granule cell to somatostatin-expressing interneuron synapses supports object location memory

doi: 10.1073/pnas.2312752120

Figure Lengend Snippet: Induction of LTP at MF-SOMIs synapse requires activation of mGluR1α, triggering G-protein-associated molecular cascades. ( A ) Schematic illustration of the proposed molecular mechanism mediating LTP at MF-SOMI synapses. Glutamate is released from MF terminals and binds to mGluR1α and NMDAR at the post-synaptic membrane of a SOMI, inducing an increased intracellular concentration of Ca 2+ via several pathways. MGluR1α-mediated phosphorylation of G-proteins ultimately triggers activation of several kinases including PKC and ERK1/ERK2 MAP kinases. Intracellular Ca 2+ rise is supported not only by an influx of Ca 2+ via NMDAR, but also by interaction of ERK1/2 with TRP channels and Ca 2+ release from internal stores. ( B ) LTP at MF-SOMI synapses was completely abolished by the application of the selective mGluR1α antagonist LY 367385 (100 μM, 8 SOMIs, red circles), while a blockade of mGluR5 by the selective antagonist MPEP (10 μM, 7 SOMIs, white circles) had no effect on LTP induction or expression. Note that hippocampal slices were incubated with antagonist for 30 min prior to transfer into the recording chamber. The horizontal black bar indicates the time of application of the antagonist during recording. ( C and D ) Summary plots demonstrating the importance of G-protein-activated pathways for MF-LTP. Intracellular dialysis of the G-protein inhibitor GDP-β-S (0.5 mM, 6 SOMIs, white circles) and the PKC pseudosubstrate inhibitor PKC 19 to 36 (10 µM, 5 SOMIs, black circles), as well as inhibition of ERK1/2 kinases by bath-application of FR 180204 (20 μM, 6 SOMIs, gray circles), led to a significant reduction of aBFS-induced PTP and LTP of MF-SOMI synapses. Interestingly, inhibition of ERK1/2 kinases unmasked a depression of transmission. The MF-mediated nature of eEPSCs was confirmed by a further decrease in eEPSC amplitudes in response to the application of DCG IV (1 μM, 4 SOMIs). In ( B–D ), LTP was induced by applying the aBFS protocol (time-point indicated by arrows on all plots). Gray panels indicate intervals used to measure PTP and LTP. Insets show representative recorded eEPSC traces (individuals in gray, average as an overlay in green) before ( Left , baseline) and after PTP ( Middle ) and LTP ( Right ). (Scale bars, 5 ms, 100 pA.) ( E and F ) Bar-graphs summarizing changes in peak amplitudes compared to baseline of recorded eEPSCs immediately after aBFS (PTP, E ) and after 15 to 20 min of recording (LTP, F ) in controls (same as in Fig. 1 E and F ) or following pharmacological manipulations. * P < 0.05; ** P < 0.01; ns, not significant; one-way ANOVA test. Bars denote mean, error bars indicate SEM, and circles show individual cells.

Article Snippet: To dissect the cellular mechanism of potentiation at MF-SOMI synapse, we either incubated slices in or bath-applied the following agents: the group II mGluR agonist DCG IV ((2 S ,2′ R ,3′ R )-2-(2′,3′-Dicarboxycyclopropyl) glycine; 1 μM, Tocris); the GABA A R antagonist SR 95531 (6-Imino-3-(4-methoxyphenyl)-1(6 H )-pyridazinebutanoic acid hydrobromide; 5 μM, Tocris); the selective mGlu1α antagonist LY 367385 [( S )-(+)-α-Amino-4-carboxy-2-methyl benzeneacetic acid; 100 μM, Tocris]; the potent mGlu5 antagonist MPEP [2-Methyl-6-(phenylethynyl)pyridine hydrochloride; 10 μM, Tocris]; the ERK inhibitor FR 180204 (5-(2-Phenyl-pyrazolo[1,5- a ]pyridin-3-yl)-1 H -pyrazolo[3,4- c ]pyridazin-3-ylamine; 20 μM, Tocris); the TRPC inhibitor that also inhibits store-operated Ca 2+ entry SKF 96365 (1-[2-(4-Methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl-1 H -imidazole hydrochloride; 30 μM, Tocris); the L - and R -type VGCC blockers Nimodipine [1,4-Dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic acid 2-methyloxyethyl 1-methylethyl ester; 50 μM] with Ni 2+ (10 μM, Tocris); the NMDAR antagonist D-APV (also termed D-AP-5; 100 μM, Tocris); the inhibitor of the SERCA ATPase α-CPA (100 μM, Tocris).

Techniques: Activation Assay, Membrane, Concentration Assay, Phospho-proteomics, Expressing, Incubation, Inhibition, Transmission Assay

Journal: Proceedings of the National Academy of Sciences of the United States of America

Article Title: Synaptic plasticity at the dentate gyrus granule cell to somatostatin-expressing interneuron synapses supports object location memory

doi: 10.1073/pnas.2312752120

Figure Lengend Snippet: Contribution of different Ca 2+ sources to LTP of MF-SOMI synapse in DG. ( A ) Reducing the concentration of intracellular Ca 2+ by chelating cytoplasmic Ca 2+ by intracellularly dialyzing with BAPTA (30 μM, 5 SOMIs, black circles) or by depleting internal Ca 2+ stores with bath-applied CPA (7 SOMIs, white circles) led to striking reductions in both PTP and LTP. ( B ) Pharmacological block of NMDAR by application APV (100 μM, 5 SOMIs) for 15 min prior to aBFS protocol application failed to induce either PTP or LTP at MF-SOMI synapses. ( C ) Bath application of the TRP channel and T-type VGCC blocker SKF 96365 (30 μM, 6 SOMIs, black bordered circles) for 15 min strongly affected both PTP and LTP at MF-SOMIs. The inhibition of L - and R -type VGCCs by co-application of the corresponding blockers Nimodipine (50 μM) and Ni 2+ (10 μM) significantly reduced PTP and led to a non-significant decrease in the magnitude of LTP (6 SOMIs, gray bordered circles). ( A–C ) aBFS delivery is indicated by arrows, gray panels indicate the intervals used to measure PTP and LTP. Insets show representative recorded eEPSC traces (individuals in gray, average as an overlay in green) before ( Left , baseline) and immediately after aBFS ( Middle , PTP) and 20 mins later ( Right , LTP). (Scale bars, 5 ms, 100 pA.) ( D ) Comparison of changes in peak amplitudes of recorded eEPSCs immediately following aBFS ( Left , PTP) and after 20 to 25 min of recording ( Right , LTP) in control conditions (same as in Fig. 1 E and F ) or following pharmacological manipulations. * P < 0.05; ** P < 0.01; ns, not significant; one-way ANOVA test. Bars with lines denote mean ± SEM, circles represent individual data points.

Article Snippet: To dissect the cellular mechanism of potentiation at MF-SOMI synapse, we either incubated slices in or bath-applied the following agents: the group II mGluR agonist DCG IV ((2 S ,2′ R ,3′ R )-2-(2′,3′-Dicarboxycyclopropyl) glycine; 1 μM, Tocris); the GABA A R antagonist SR 95531 (6-Imino-3-(4-methoxyphenyl)-1(6 H )-pyridazinebutanoic acid hydrobromide; 5 μM, Tocris); the selective mGlu1α antagonist LY 367385 [( S )-(+)-α-Amino-4-carboxy-2-methyl benzeneacetic acid; 100 μM, Tocris]; the potent mGlu5 antagonist MPEP [2-Methyl-6-(phenylethynyl)pyridine hydrochloride; 10 μM, Tocris]; the ERK inhibitor FR 180204 (5-(2-Phenyl-pyrazolo[1,5- a ]pyridin-3-yl)-1 H -pyrazolo[3,4- c ]pyridazin-3-ylamine; 20 μM, Tocris); the TRPC inhibitor that also inhibits store-operated Ca 2+ entry SKF 96365 (1-[2-(4-Methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl-1 H -imidazole hydrochloride; 30 μM, Tocris); the L - and R -type VGCC blockers Nimodipine [1,4-Dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic acid 2-methyloxyethyl 1-methylethyl ester; 50 μM] with Ni 2+ (10 μM, Tocris); the NMDAR antagonist D-APV (also termed D-AP-5; 100 μM, Tocris); the inhibitor of the SERCA ATPase α-CPA (100 μM, Tocris).

Techniques: Concentration Assay, Blocking Assay, Inhibition, Comparison, Control