Increased GABAergic inhibitory function against ischemic long-term potentiation in the CA1 region of the hippocampus

Potentiation of N-methyl-D-aspartate receptor (NMDAR)-mediated excitatory synaptic plasticity around 1 h after brief exposure to anoxia/aglycemia is called ischemic long-term potentiation (iLTP), which is considered a pathological form of synaptic response during the early phase of ischemic stroke. It is known that GABAergic inhibitory transmission is also an important molecular process involved in synaptic plasticity and learning memory. However, whether GABAergic transmission is involved in iLTP and early-phase plasticity in ischemic stroke remains unknown. In this study, iLTP was found to be induced in the hippocampal Schaffer-collateral pathway by exposure to oxygen glucose deprivation (OGD). Western blot analysis was conducted to analyze excitatory synaptic receptors and inhibitory synaptic receptors following OGD. The β3 subunit of the GABA_A receptor (GABA_AR) was markedly reduced, whereas the GluN2B subunit of the NMDAR was increased in the hippocampal area in the OGD group. Using extracellular recording, we demonstrated that application of GABA_AR agonist midazolam could abolish the hippocampal iLTP. Moreover, midazolam had no significant effect on the increase in NMDAR subunit GluN2B, but ameliorated the reduction in the β3 subunit of GABA_AR after OGD. In summary, our results indicated that hippocampal GABA_AR reduction promoted synaptic potentiation after OGD. Activation of GABAergic inhibitory transmission function could inhibit iLTP; thus, modulation of GABAergic function is a protective treatment method in the acute phase of synaptic plasticity in ischemic stroke.