Pathogenic potential of antibodies to the GABA(B) receptor

GABA(B) receptor (GABA(B)R) autoantibodies have been detected in the serum of immunotherapy‐responsive patients with autoimmune encephalitis. This study aimed to investigate the effect of immunoglobulin G (IgG) from a patient with GABA(B)R antibodies on primary neuronal cultures and acute slices of entorhinal cortex. Primary hippocampal neuronal cultures were incubated with serum immunoglobulin from patients with GABA(B)R or AMPA receptor (AMPAR) antibodies for up to 72 h to investigate their effect on receptor surface expression. Whole‐cell patch‐clamp recordings from layer III pyramidal cells of the medial entorhinal cortex were used to examine the effect on neuronal activity. GABA(B)R surface expression was unaltered by incubation with GABA(B)R antibodies. By contrast, after 24 h application of AMPAR antibodies, AMPARs were undetectable. However, acute application of GABA(B)R IgG decreased both the duration of network UP states and the spike rate of pyramidal cells in the entorhinal cortex. GABA(B)R antibodies do not appear to affect GABA(B)Rs by internalization but rather reduce excitability on the medial temporal lobe networks. This unusual mechanism of action may be exploited in rational drug development strategies.