Astragaloside IV enhances memory and modulates hippocampal synaptic plasticity by decreasing GABAergic inhibition through EGR-1 mediated BDNF/TrkB signaling pathway in mice

Abstract

Background Astragaloside IV (ASIV) is one of the saponins isolated from Astragalus membranaceus, a widely used traditional Chinese medicine and a health product sold all over the world. However, so far, the effect of ASIV on GABAergic synaptic transmission has not been elucidated yet. In the present study, the effect of ASIV on memory and hippocampal synaptic plasticity was investigated in mice and down-regulated early growth response protein 1 (EGR-1) knockout mice. Methods Behavior tests including radial-arm maze test and shuttle-box test, liquid chromatography-tandem mass spectrometry, western blotting analysis, quantitative PCR, electrophysiological recording, and electron microscopy were used in this study. The difference of data was detected by unpaired student t-test or two-factor analysis of variance (ANOVA) or Mann-Whitney U test. Results ASIV was shown to enhance the learning and memory of mice in behavior tests, such as radial-arm maze test and shuttle-box test, as well as the synaptic plasticity in electrophysiological experiments. Moreover, it significantly reduced the concentration of gamma-aminobutyric acid (GABA) and the expression of glutamate decarboxylase 2 (GAD65) in mouse hippocampus, which was accompanied with decreased ratio of inhibitory synapses, and EGR-1, brain-derived neurotrophic factor (BDNF) and tyrosine receptor kinase B (TrkB). When EGR-1 was knocked out, the promotive effects of ASIV on memory and synaptic plasticity, as well as the inhibitory effects on GAD65, BDNF and TrkB, were abolished. In addition, ASIV was found to down-regulate the pre-existing EGR-1 baseline to better adapt to the learning stimuli. Conclusions Together, these results demonstrated a novel role of ASIV in enhancing memory and modulating hippocampal synaptic plasticity by decreasing GABAergic inhibition through EGR-1 mediated BDNF/TrkB signaling pathway in mice.