Objective To explore the improving effect and mechanism of saikosaponin A on insomnia rats based on cAMP/PKA/CREB pathway.Methods Seventy-five SD rats were randomly divided into blank group,model group,low-dose saikosaponin A group(0.625 mg·kg-1),high-dose saikosaponin A group(2.500 mg·kg-1)and Estazolam group(0.1 mg·kg-1),with 15 rats in each group.Insomnia rat model was established by intraperitoneal injection of Phenylalanine(PCPA,0.1 mg·kg-1).The general condition and circadian rhythm of rats were observed;the sleep latency and sleep duration of rats were measured by pentobarbital sodium righting experiment.The sleep phase of rats was observed,and the duration of slow wave sleep phase 1(SWS1),slow wave sleep phase 2(SWS2),rapid eye movement sleep phase(REMS)and total sleep time(TST)were recorded.The mRNA expression levels of hypothalamic circadian genes Clock,Bmal1 and clock-controlled genes Rev-erbα and Rorα were determined by qRT-PCR.The expression level of NeuN in hippocampus was determined by immunofluorescence.The level of cAMP in brain tissue was determined by ELISA.The expression levels of Clock,Bmal1,Rev-erbα,Rorα and cAMP/PKA/CREB pathway-related proteins in brain tissue were determined by Western Blot.Results Compared with the blank group,the rats in the model group had disordered circadian rhythms,extreme excitement,irritability,and reduced sleep;the sleep latency was significantly prolonged(P＜0.05),and the sleep duration and SWS1,SWS2,REMS and TST were significantly shortened(P＜0.05).The arrangement of neurons was disordered,and the IOD value of NeuN positive neurons was significantly decreased(P＜0.05).The mRNA and protein expression levels of Clock,Bmal1,Rev-erbα and Rorα in brain tissue were significantly decreased(P＜0.05).The expression levels of cAMP,p-PKA/PKA and p-CREB/CREB in brain tissue were significantly decreased(P＜0.05).Compared with the model group,the aggressiveness of the rats in the administration group was significantly weakened,the circadian rhythm was rhythmic,the activity was reduced,and the sleep was increased.The sleep latency was significantly shortened(P＜0.05),and the sleep duration and SWS1,SWS2,REMS and TST were significantly prolonged(P＜0.05).The disorder of neuronal arrangement was restored,and the IOD value of NeuN positive neurons was significantly increased(P＜0.05).The mRNA and protein expression levels of Clock,Bmal1,Rev-erbα and Rorα in brain tissue were significantly increased(P＜0.05).The protein expression levels of cAMP,p-PKA/PKA and p-CREB/CREB in brain tissue were significantly increased(P＜0.05).Conclusion Saikosaponin A may improve the circadian rhythm of insomnia rats by activating cAMP/PKA/CREB pathway.