Figure 2. Molecular pathway to MLI_dep-LTP.

MLI_dep-LTP was effectively prevented by the broad spectrum low threshold voltage-gated T-type calcium channels specific antagonist TTA-P2 (a, mean ± SEM, N = 5, RM ANOVA P < 0.001). To identify the Ca_V3 isoform required for the GABA-dependent potentiation, long-term plasticity experiments were performed in Ca_V3.1 KO mice. MLI_dep-LTP is absent in Ca_V3.1 KO mice (b, mean ± SEM, N = 5, RM ANOVA P < 0.001) under the same experimental condition that leads to GABA_A receptor-dependent potentiation of PF to PN transmission in WT mice and traces from a representative experiment are shown in the middle inset. PF-induced inhibitory responses were recorded in PNs from WT and Ca_V3.1 KO mice (c, inset) and input/output curves obtained (c: WT, black circle: N = 8; KO, white diamond: N = 10, mean ± SEM). No statistically significant difference was detected among the two curves (P > 0.05, t-test at all stimulus intensities). MLI_dep-LTP also depends on mGluR1 and intracellular calcium stores; high frequency PFs stimulation failed to induce MLI_dep-LTP when activation of the metabotropic glutamate receptor mGluR1was prevented by bath application of the specific antagonist JNJ16259685 (d, mean ± SEM, N = 5, RM ANOVA P < 0.001). Inclusion of the non-hydrolysable GDP analog GDPβS (e, mean ± SEM, N = 3) or heparin (f, mean ± SEM, N = 6, RM ANOVA P = 0.006) in the intracellular recording solution also impaired MLI_dep-LTP. PPRs value (mean ± SEM) for the baseline (t = 10 min) and the post induction phase (t = 45 min) under each condition are shown in the left insets in panel a,b,d.