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. 2022 Mar 28;23(7):3707.
doi: 10.3390/ijms23073707.

GABAA Receptor Autoantibodies Decrease GABAergic Synaptic Transmission in the Hippocampal CA3 Network

Amélie F Menke  1 , Fatme Seval Ismail  2 , Klaus Dornmair  3   4 , Manuela Cerina  1 , Sven G Meuth  5 , Nico Melzer  5
Affiliations

GABAA Receptor Autoantibodies Decrease GABAergic Synaptic Transmission in the Hippocampal CA3 Network

Amélie F Menke et al. Int J Mol Sci. .

Abstract

Autoimmune encephalitis associated with antibodies (Abs) against α1, β3, and γ2 subunits of γ-aminobutyric acid receptor A (GABAAR) represents a severe form of encephalitis with refractory seizures and status epilepticus. Reduction in inhibitory GABAergic synaptic activity is linked to dysfunction of neuronal networks, hyperexcitability, and seizures. The aim in this study was to investigate the direct pathogenic effect of a recombinant GABAAR autoantibody (rAb-IP2), derived from the cerebrospinal fluid (CSF) of a patient with autoimmune GABAAR encephalitis, on hippocampal CA1 and CA3 networks. Acute brain slices from C57BL/6 mice were incubated with rAb-IP2. The spontaneous synaptic GABAergic transmission was measured using electrophysiological recordings in voltage-clamp mode. The GABAAR autoantibody rAb-IP2 reduced inhibitory postsynaptic signaling in the hippocampal CA1 pyramidal neurons with regard to the number of spontaneous inhibitory postsynaptic currents (sIPSCs) but did not affect their amplitude. In the hippocampal CA3 network, decreased number and amplitude of sIPSCs were detected, leading to decreased GABAergic synaptic transmission. Immunohistochemical staining confirmed the rAb-IP2 bound to hippocampal tissue. These findings suggest that GABAAR autoantibodies exert direct functional effects on both hippocampal CA1 and CA3 pyramidal neurons and play a crucial role in seizure generation in GABAAR autoimmune encephalitis.

Keywords: GABAA receptor autoantibody; electrophysiology; hippocampal CA1/CA3.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The recombinant GABAA receptor autoantibody rAb-IP2 reduced the number of spontaneous inhibitory postsynaptic currents (sIPSCs) generated in CA1 pyramidal neurons. (a) Exemplary traces depict the GABAergic synaptic transmission in rAb-IP2-incubated pyramidal neurons and controls. Notably, the exemplary traces are cropped at 600 pA to simplify illustration and do not represent the full high-amplitude currents with an amplitude > 1400 pA, which were very likely contaminated with Na+ currents and were not GABA-mediated. (b) Scatter plot showing that the number of sIPSCs recorded in 10 min decreased upon rAb-IP2 incubation in comparison with the control. (c) Bar graphs showing the amplitude of sIPSCs in rAb-IP2-incubated neurons and controls. The amplitude of sIPSCs ≤ 1400 pA was not altered by rAb-IP2 incubation. ** p < 0.01, ns: not significant.
Figure 2
Figure 2
Incubation with the recombinant GABAA receptor autoantibody rAb-IP2 led to both decreased number and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) in pyramidal CA3 neurons. (a) Exemplary traces show GABA-mediated synaptic currents in rAb-IP2-incubated pyramidal neurons and controls. For illustration purposes, the amplitude of the high-amplitude currents is cut at 800 pA. (b) rAb-IP2-incubated neurons showed a significantly reduced number of sIPSCs in comparison with controls. (c) rAb-IP2 led to a significant reduction in the amplitude of sIPSCs when sIPSCs ≤ 1400 pA were analyzed. * p < 0.05, ns: not significant.
Figure 3
Figure 3
Immunohistochemical staining of a formalin-fixed, paraffin-embedded murine hippocampus with the recombinant human GABAA receptor autoantibody rAb-IP2. Murine-fixed hippocampal tissue shows immunoreactivity to the recombinant human antibody rAb-IP2. (a) Representative coronal hippocampal slices with immunoreactivity to rAb-IP2 (red). The box marks the hippocampal region CA3, showing the area used for the in vitro electrophysiological recordings as shown in Figure 1 and Figure 2. For more visibility of CA1, we also referred to our previous study [13]. (b) DAPI (blue) was used as a marker for the cell nuclei. (c) Merged picture. Scale bars represent 100 μm.
See this image and copyright information in PMC

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Supplementary concepts