Fig. 1: Loss of GABA_B R-mediated tonic inhibition contributes to amygdala hyperexcitability after chronic stress.

A A scheme of the experimental protocol (top) and a graph illustrating body weight changes during the chronic restraint stress (CRS, n = 10, control n = 10; RM ANOVA F_{(1, 18)} = 10.54, **p = 0.0045). B Results of the open field (OF) test. The graphs show the total time spent in the center area of the open field (OF), the center time in 5 min bins (control, n = 10, CRS, n = 10, t-test t = 3.232, df = 18, **p = 0.0046; RM ANOVA F_{(1, 18)} = 10.45, **p = 0.0046) and total distance traveled during OF test (t-test, t = 4.546, df = 18, ***p = 0.0003). C Action potential (AP) firing rate of principal neurons (PN) in the lateral amygdala (LA) in response to depolarizing current steps, recorded from brain slices of control and CRS-exposed mice (control, n = 17 (8 mice), CRS, n = 19 (7 mice); RM ANOVA F _{(1, 29)} = 4.877, *p = 0.035). The example traces illustrate the response to 240 pA step current. D Representative traces and pooled data illustrating the effect of CRS on sIPSC frequency and amplitude in LA PNs. Recordings were done using high-Cl containing electrode filling solution and in the presence of antagonists for AMPA and NMDA receptors (control, n = 12 (4 mice), CRS, n = 15 (4 mice), frequency: t-test, t = 1.381, df = 25, p = 0.1796; amplitude: t-test, t = 1.276, df = 25, p = 0.2136). The decay time distribution of sIPSCs for the same data is shown below (multiple t-test, Holm-Sidak, 1 ms: t = 3.070 df = 390.0, *p = 0.027; 2 ms : t = 3.250 df = 390.0, *p = 0.016). E Tonic GABA_B receptor-mediated currents recorded from LA PNs in response to application of GABA_B antagonist CGP55845 (10 μM), in control and CRS-exposed mice as well as in the presence of GDP-β-S in control mice. All recordings were done in the presence of 50 μM of D-AP5, 200 μM picrotoxin, and 50 μM GYKI 53655 to block NMDA, GABA_A, and AMPA receptors, respectively. Pooled data on the maximal amplitude of the GABA_B current under control conditions and in the presence of GDP-β-S (750 µM) in the electrode filling solution (control, n = 8 (3 mice), GDP-β-S n = 5 (3 mice); t-test, t = 4.599, df = 11, ***p = 0.0008). Amplitudes of the tonic GABA_B current in control and CRS-exposed animals (control, n = 17 (7 mice), CRS, n = 14 (3 mice); t-test t = 3.786, df = 29, ***p = 0.0007). F Effect of GABA_B antagonism on firing frequency of LA PNs in control and CRS-exposed mice, as well as in the presence of GDP-β−S in control mice. Action potential frequencies in response to depolarizing current steps were recorded from brain slices under control conditions (in ACSF) and in the presence of CGP55845 (5 µM) (control, n = 10 (4 mice), control+CGP55845, n = 10 (4 mice); RM ANOVA, F_{(2, 26)} = 3.498, *p = 0.045; GDP-β−S n = 12 (3 mice), GDP-β−S+CGP55845 n = 10 (3 mice); RM ANOVA F_(1,20) = 0.8588, p = 0.365; CRS, n = 17 (6 mice), CRS+CGP55845, n = 9 (3 mice); RM ANOVA, F_{(1, 24)} = 1.824, p = 0.1894). Example traces show the response to 240 pA current step. All the data are presented as mean ± SEM.