Characterized by difficulty falling asleep, short sleep duration, and poor sleep quality (Buysse, 2013), insomnia has become a serious problem and is closely associated with an increased risk of dementia (Shi et al., 2018) disease, Alzheimer (Irwin and Vitiello, 2019) disease, depression (Riemann et al., 2020), cardiovascular (Tobaldini et al., 2017) and other diseases. Insomnia is also a common symptom of almost all mental disorders (Baglioni et al., 2016). The central parts related to sleep mainly include the hypothalamus and hippocampus. The preoptic area of the anterior hypothalamus is considered to be a key area in relation to the sleep center and the wake center (Bremer, 1975). The hippocampus is part of the limbic system of the brain and has complex connections to the neural structures that regulate sleep (Zhao et al., 2019). The hippocampus contains 5-hydroxytryptamine and other neurotransmitters related to sleep regulation, which can promote slow-wave sleep (Mork et al., 2012; Yohn et al., 2017). Currently, the clinical treatment of sleep disorders mainly includes cognitive behavioral therapy and pharmacotherapy (Morin and Benca, 2012). To find a safe and effective treatment remains a challenge due to the high cost of treatment and adverse side effects (Winkler et al., 2014).

Currently, plant extracts are becoming increasingly popular in the treatment of insomnia. Studies have shown that the ethanol extract of Passiflora incarnata L. has significant sleep-inducing effects on cells and animals (Kim et al., 2020). The extract of Ziziphi Spinosae Semen significantly inhibited the high-level expression of HTR1A, GABRA1 and GABRG2 in the hypothalamus of mice (Bian et al., 2021). Saponins have also been found to be effective in treating insomnia (Hu et al., 2014). Saponins from Rhodiola rosea L. improved insomnia by altering the serotonergic, GABAAergic, and immune systems (Hao et al., 2021). The sedative-hypnotic activity of two ginsenosides, protopanaxadiol-type ginsenosides and protopanaxatriol-type ginsenosides, may be mediated through serotonergic and GABAergic systems (Mou et al., 2019).

Polygala tenuifolia Willd., which also named Yuan Zhi, mainly contains saponins (Liu et al., 2007), terpenoids (Lacaille-Dubois et al., 2020), sugar esters (Li et al., 2000), xanthones (Yang et al., 2022) and other chemical components and is used to treat dementia (Hugel et al., 2012), neurasthenia, inflammation, cancer (Yoo et al., 2014) and other symptoms. Studies have shown that the chemical composition of P. tenuifolia have multiple effects. Tenuifolia, which isolated from the root of P. tenuifolia has potential in the treatment of learning and memory deficits in APP/PS1 transgenic AD mice (Wang et al., 2019). The anti-inflammatory effects of tenuifoliside A which separated from P. tenuifolia were mediated by the inhibition of the NF-κB and MAPK pathways (Kim et al., 2013). Polysaccharide from the roots of P. tenuifolia showed significant suppress ovarian tumor effect by studying SKOV3 xenograft tumor growth in BALB/c mice (Yao et al., 2018).

In this study, total saponins (YZ-I) were extracted by organic solvent extraction, and further purified with D-101 macroporous adsorption resin to obtain the fractions rich in saponins (YZ-II). Tail suspension test and sodium pentobarbital-induced sleep test were used to evaluate the effect of saponins separated from P. tenuifolia on sleep behavior in ICR mice. The levels of the neurotransmitters, hormones, and inflammation cytokines in the plasma of insomnia mice were detected by ELISA. RT-PCR and Western blotting. Finally, the expressions of 5-HT, GABA, DPR, PGD2 receptors and iNOS, TNF-α in the hypothalamus and hippocampus were detected.