Quantification of protein expression from cultured neurons treated with GABA_AR mAbs. (A–C) Representative Western blots of total protein (TP) and biotinylated surface protein (SP) samples from neocortical rat neurons after preincubation with indicated GABA_AR or control mAb #mGO53. Blots were stained with commercial antibodies against the α1-subunit of GABA_AR (A), the GluR1-subunit of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (B), and N-Cadherin (C). Quantifications of protein levels are shown in Fig. 4, G–J. (D) Quantification of human IgG from neocortical rat neuron culture media used for Western blotting experiments (Fig. S4, A–C; and Fig. 3, G–J). The reduction of IgG was measured as the relative difference between post-treatment medium and matched source medium samples, which have not been applied to the culture [relative reduction = (concentration_{source medium} − concentration_{post-treatment medium})/concentration_{source medium}]. Bars indicate mean ± SEM; n = 6 experiments from two separate cultures. (E) Representative immunofluorescence staining of post-treatment neuronal culture medium containing mAb #113-115 on an unfixed murine brain section confirmed GABA_AR reactivity of the antibody by typical staining pattern, as shown here in hippocampus. Scale bar indicates 500 µm. (F) Quantifications of GABA_AR surface levels from reader-based immunohistochemistry recordings from neocortical rat neurons after preincubation with indicated human GABA_AR or control mAbs. Representative recording is shown on top from neurons after live staining with a commercial antibody against the α1-subunit of GABA_AR. Quantifications revealed no difference. Bars indicate mean ± SEM; n = 6 experiments from three separate cultures.