Figure 2. Social defeat sensitized excitatory input and excitability of vmPFC-innervated DRN GABAergic neurons in SUS mice but not in RES mice. A, Schematic of DRN topography in recorded slices from GAD2-tdTomato mice. vlDR, ventrolateral DRN; Aq, aqueduct. Recorded neurons were purposely selected in ventrolateral subregions of the DRN that are rich in afferents from the vmPFC. Inset depicts a high-magnification confocal image of a biocytin-filled recorded GAD2-tdTomato neuron (red) in close contact with axon terminals from vmPFC neurons (green) anterogradely traced using AAV-CaMKIIa-ChR2-YFP. B, Raw data traces of membrane potential changes recorded from DRN GABA neurons in response to hyperpolarizing and depolarizing injection of current in control, RES, and SUS mice. Scale bar, 20 mV, 50 ms. C, Representative voltage-clamp traces of mEPSC synaptic activity in DRN GABA neurons from control, RES, and SUS mice. Scale bar, 20 pA, 500 ms. D, Frequency-intensity plots showed increased excitability of DRN GABA neurons in SUS mice [repeated-measures ANOVA, Fisher's post hoc; SUS vs CTRL, 20 pA *p = 0.030, 40 pA *p = 0.034, 60 pA **p = 0.008, 80 pA *p = 0.012, 100 pA *p = 0.025; N(n) = 7(29) for control, 4(20) for RES, 10(37) for SUS]. E, Cumulative probability plot shows a shift to shorter interstimulus intervals of mEPSC synaptic activity in DRN GABA neurons of SUS mice versus control or RES mice (Kolmogorov–Smirnov test, Z = 7.1402, p < 0.001). Inset displays summary histogram showing significantly higher average mEPSC frequency in SUS mice (one-way ANOVA, Fisher's post hoc; SUS vs CTRL **p = 0.006). F, Cumulative probability plot of mEPSC decay time shows the shift to faster decay times in DRN GABA neurons of SUS mice (Kolmogorov–Smirnov test, Z = 6.4021, p < 0.001). Inset shows summary histogram depicting the significantly lower average mEPSC decay times in SUS mice versus control and RES mice (one-way ANOVA, Fisher's post hoc; SUS vs CTRL *p = 0.014). G, Enlarged depiction of averaged individual EPSC synaptic events in GABA neurons for each group. Scale bar, 4 pA, 2 ms.