GABA_AR mAbs caused spontaneous seizures in vivo and spontaneous epileptic activity ex vivo. (A) Representative EEG of an ictal event recorded from a CA3 depth electrode in a Wistar rat receiving GABA_AR mAb infusion. (B) Comparison of hourly averages of coastline length between GABA_AR mAb (#113-115, n = 3; #113-175, n = 3) and control (n = 6) infused animals, analyzed using Mann-Whitney (***, P ≤ 0.001; n = 900–905 average values per group). Horizontal lines indicate mean and quartiles. (C) Comparison of the hourly ictal event counts between animals during infusion with GABA_AR mAb or control as analyzed from Neuroarchiver seizure detection software and using Mann-Whitney (****, P ≤ 0.0001). Animal numbers as in B, n = 120 events per group. Bars indicate mean ± SEM. (D) Distribution of the detected ictal event over time. (E) Comparison of hourly EEG power averages throughout 7-d recordings during GABA_AR mAb or control infusion, analyzed using Mann-Whitney (**, P ≤ 0.01; ****, P ≤ 0.0001). Animal numbers as in B, n = 899–900 average values per group. Bars indicate mean + SEM. (F) Local field potential recording from the CA3 region in a sagittal brain slice from a rat after GABA_AR mAb infusion (upper trace) showing spontaneous ictal activity ex vivo, not seen in controls (lower trace). (G) Comparison of interevent intervals of spontaneous ictal activity from postmortem acute brain slice recordings from rats after cerebroventricular antibody infusion over 7 d. Recordings from GABA_AR mAb–exposed brains are from day 7/8 (#113-115, n = 3; #113-175, n = 3) or day 21 after beginning of infusion and from day 7 of control exposed brains (n = 6), analyzed using Mann-Whitney (****, P ≤ 0.0001; n = 44–10,302 intervals per group). Bars indicate geometric mean ± SD.