Competition of mAb #113-115 Fab and #113-115 IgG for binding to murine brain tissue. (A) To confirm competitive binding to the identical target GABA_AR mAb #113-115 as Fab fragment was stained at serial dilutions as indicated in the presence of fluorophore-coupled #113-115 IgG (#113-115–CF488) at threshold concentration of 0.4 µg/ml (green). Binding of Fab was visualized using an anti-FLAG secondary antibody (red; nuclei in blue). The MFI was measured separately for Fab and IgG binding in identical ROIs within granule cells of the cerebellum. Representative scale bar indicates 100 µm. (B) MFI values from 18 ROIs of n = 2 independent experiments are shown as mean ± SEM. (C) Representative EEG recording from GABA_AR mAb–infused rat is shown with an example of a Racine stage 5 seizure with video-EEG and closeups of different EEG patterns during the recorded seizure. The corresponding video is included as Video 2. (D) Distribution of the detected ictal events over time as analyzed with Neuroarchiver seizure detection software in a subgroup of three animals that were recorded for a prolonged period of 21 d and that had received GABA_AR mAb infusion over 7 d (red bar). Data from 7-d recording period for all animals including controls is shown as Fig. 5 D. (E) From the same animals, the post seizure behavioral battery (PSBB) tests were performed and scored for 21 d. The dotted line represents the PSBB score of 10, above which the animals are likely to demonstrate aggresion and hyperexcitability on testing, which strongly correlates with the development of spontaneous recurrent seizures. Bars indicate mean ± SEM. cv-inf, cerebroventricular infusion.