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. 2015 Mar 12;9:65. doi: 10.3389/fnbeh.2015.00065

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Copyright © 2015 Costa, Sardone, Lacivita, Leopoldo and Ciranna.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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LP-211 reversed mGluR-LTD in the hippocampus of wild-type and Fmr1 KO mice. Excitatory post-synaptic currents (EPSCs) mediated by AMPA receptors were recorded under whole-cell patch clamp from CA1 pyramidal neurons after stimulation of Schaffer collaterals in the continuous presence of the NMDA receptor antagonist D-AP5 (50 μM). EPSC amplitude is represented as percent of control EPSC amplitude prior to any substance application. Pooled data of % EPSC values (mean ± SEM) were plotted vs. time; insets show individual EPSC traces from representative experiments. (A) Hippocampal slices (300 μm) were prepared from wild-type mice on a C57BL/6J background (PN 14-21). Bath application of DHPG (100 μM, 5 min), an agonist of group I metabotropic glutamate receptors, induced a long term depression of EPSC amplitude. In another group of recordings, LP-211 (10 nM, 5 min) was applied 5 min after LTD induction. Following application of LP-211, EPSC amplitude returned to control values (100%), indicating that mGluR-LTD was reversed. (B) Histograms show mean EPSC amplitude values (% of control) in control conditions (empty column, n = 9) and 45 min after application of DHPG alone (black column, n = 9) or application of DHPG followed by LP-211 (dark gray column, n = 5). Application of DHPG significantly reduced EPSC amplitude (^*P < 0.01), thus induced mGluR-LTD. Vice-versa, when DHPG application was followed by LP-211, EPSC values were not reduced with respect to control, indicating that mGluR-LTD was completely reversed. (C) Hippocampal slices were prepared from Fmr1 KO mice (C57BL6J strain; PN 14-21) Application of DHPG (100 μM, 5 min) induced a long-term depression (mGluR-LTD) of EPSC amplitude. When LP-211 (10 nM, 5 min) was applied after DHPG, mGluR-LTD was partially reversed. A complete reversal of mGluR-LTD was observed around 55 min after LTD induction. (D), upper panel: EPSC current amplitude in control conditions (100%) and 45 min after application of DHPG. In slices from Fmr1 KO mice, the amount of mGluR-LTD induced by DHPG alone was highly significant (black column; ^****P < 0.00001) and was larger than in wild-type (compare with panel B). When DHPG application was followed by application of LP-211, the amount of mGluR-LTD was still significant (^**P < 0.001) but was significantly reduced (^*P < 0.01) with respect to mGluR-LTD induced by DHPG alone, indicating that mGluR-LTD was partially reversed. (D) Lower panel: EPSC current amplitude in control conditions (100%) and 55 min after application of DHPG: mGluR-LTD was completely reversed by LP-211, indicating a slower time course of LP-211-mediated reversal in Fmr1 KO with respect to wild-type.