Protective effect of liquiritigenin on depressive-like behavior in mice after lipopolysaccharide administration

Liquiritigenin (Liq), the main active ingredient of traditional Chinese medicine licorice, possesses anti-inflammatory and neuroprotective properties. The current investigation was designed to explore whether liquiritigenin could relieve lipopolysaccharide (LPS)-induced depression-like behavior in mice and the underlying mechanism. Liquiritigenin (7.5mg/kg, 15mg/kg) and fluoxetine (20mg/kg) were pretreated intragastrically once daily for 7 consecutive days. LPS (0.5mg/kg) was injected subcutaneously to establish the depression model 30min after pretreatment on day 7. Interleukin (IL)-6 and tumor necrosis factor (TNF)-α levels in serum and hippocampus were detected by enzyme-linked immunosorbent assay (ELISA). Behavioral assessment was conduct 24h post LPS injection. The expressions of p65NF-κB, IκBα, brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B (TrkB) in hippocampus were determined by western blot. The obtained results showed that liquiritigenin effectively reduced the levels of pro-inflammatory cytokines and the expressions of p-p65NF-κB and p-IκBα. Furthermore, liquiritigenin preconditioning could down-regulate the immobility time in tail suspension test (TST), forced swimming test (FST) and up-regulate BDNF and TrkB contents in hippocampus. Thus, it is assumed that the antidepressant activity of liquiritigenin might be attributed to its anti-inflammatory property and BDNF/TrkB signaling pathway.