Introduction:
Licorice could exhibit beneficial effect in the management of insomnia by regulating key modulators such as GABA and serotonin, we therefore aimed to study the potentail hypnotic effect of licorice extract, glycyrrhizin (GCZ), on insomnia and the underlying mechanisms.

Material and methods:
Mice were randomly grouped as a Control group, a GCZ (low) group, a GCZ (high) group and a DZP group with 8 mice in each group. Sleep latency, sleep duration and locomotor activities were recorded. ELISA assays were performed to evaluate the level of GABA, glutamate (Glu) and GABA/Glu ratio in mice tissues. Real-time PCR and IHC were performed to study the expression of GABAA-R.

Results:
Oral GCZ treatment at 300mg/kg and 100mg/kg dose-dependently shortened the sleep latency and increased the sleep duration of mice. Locomotor activity was also inhibited by GCZ, while GABA binding affinity was higher in mice treated with GCZ. Moreover, GCZ treatment in mice also increased the GABA level and GALA/Glu ratio in mice plasma, brain, hippocampus and cerebrospinal fluid. Moreover, the level of GABAA receptor (GABAA-R) was also increased by GCZ treatment in a dose-dependent manner.

Conclusions:
Our study validated that the glycyrrhizin, content of licorice, could alleviate insomnia by upregulating the level of GABA and its receptor.