Quercitrin (Qc) is a well-known flavonoid compound that exerts anti-inflammation effects on various diseases. The present study aimed to investigate the antidepressant-like response of Qc and its underlying mechanisms concerning neuroinflammation and neuroplasticity in mice with lipopolysaccharide (LPS)-induced depression-like behaviors. The results showed a single dose of Qc (10 mg/kg) produced an antidepressant-like effect at 2 h postadministration and lasted for at least 3 days. The expressions of neuroplasticity signaling molecules of pCREB/BDNF/PSD95/Synapsin1 were upregulated at 2 h, and ERK signaling was upregulated for 3 days in the hippocampus after a single administration of Oc or ketamine. A 5-day treatment of LPS led to depression-like behaviors, including reduced sucrose preference and increased immobility in the tail suspension test or forced swim test, which were all reversed by a single dose of Qc. In LPS-treated mice, Qc reduced the levels of inflammation-related factors including IL-10, IL-1β, and TNF-α in serum, as well as the activations of PI3K/AKT/NF-κB and MEK/ERK pathways in the hippocampus. Moreover, Qc restored the expressions of pCREB/BDNF/PSD95/Synapsin1 signaling in the hippocampus that were impaired by LPS. LY294002, a PI3K inhibitor, but not PD98059, a MEK inhibitor, produced effects similar to Qc. LY294002 also restored the expressions of pCREB/BDNF/PSD95/Synapsin1 signaling in the hippocampus impaired by LPS. Additionally, subeffective doses of Qc and LY294002 induced behavioral and molecular synergism. Together, the depression-like behaviors in LPS-treated mice were alleviated by a single dose of Qc likely via inhibition of the activations PI3K/AKT/NF-κB inflammation signaling and subsequent improvement of neuroplasticity.

Previous studies have demonstrated that Yueju-Ganmaidazao (YG) decoction induces rapid antidepressant-like effects, and the antidepressant response is mostly dependent on the suppression of nitric oxide-cyclic guanosine monophosphate signaling in male mice. This study aimed to investigate the sex difference mediated by calcium/calmodulin-dependent protein kinase II (CaMKII)-neuronal nitric oxide synthase (nNOS) signaling involved in the antidepressant-like effect of YG in mice. We found that the immobility times in the tail suspension test (TST) were found to be decreased after the single injection of YG in male and female mice with the same dosage. Additionally, chronic administration for 4 days of subthreshold dosage of YG and escitalopram (ES) also significantly decreased the immobility time in mice of both sexes. Chronic subthreshold dosage of YG and ES in LPS-treated mice and in chronic unpredictable stress (CUS) mice both decreased the immobility time, which was increased by stress. Meanwhile, in CUS-treated mice, sucrose preference test, forced swimming test, and open field test were applied to further confirm the antidepressant-like effects of YG and ES. Moreover, CUS significantly decreased the expression of nNOS and CaMKII, and both YG and ES could enhance the expression in the hippocampus of female mice, which was opposite to that in male mice, while endothelial nitric oxide synthase expression was not affected by stress or drug treatment neither in male mice nor in female mice. Finally, subthreshold dosage of YG combined with 7-nitroindazole (nNOS inhibitor) induced the antidepressant-like effects both in female and in male mice, while the single use of YG or 7-NI did not display any effect. However, pretreatment with KN-93 (CaMKII inhibitor) only blocked the antidepressant-like effect of high-dosage YG in female mice. Meanwhile, in CUS mice, chronic stress caused NR1 overexpression and inhibited cAMP response element binding protein action, which were both reversed by YG and ES in male and female mice, implying that YG and ES produced the same antidepressant-like effect in mice of both sexes. The study revealed that chronic treatment with a subthreshold dose of YG also produced antidepressant-like effects in female mice, and these effects depended on the regulation of the CaMKII-nNOS signaling pathway.