OBJECTIVE The preference for social novelty is crucial to the social life of humans and rodents.However,the neural mechanisms underlying social novelty preference are poorly understood.Dorsal hippocampal CA3(dCA3)is an important brain area that responds to social defeat stress,and the neural circuitry of dCA3→lat-eral septum(LS)participates in the context-associated memory.Meanwhile,the parvafox nucleus(PFN)Foxb1+ neurons regulate the defensive reaction to life-threaten-ing situations.Therefore,we investigate a cell-specific cir-cuit of dCA3CaMKⅡα+→dorsal LSGABA+→PFNFoxb1+ in social novelty preference.METHODS Chronic social defeat stress(CSDS)and three-chamber social interaction test were performed in adult male C57BL/6J mice to detect social behaviors.Optogenetic and chemical-genetic experiments were conducted to regulate the circuit.RESULTS CSDS reduced the preference for social nov-elty in mice and the response of dCA3CaMKⅡα+ neurons dur-ing approach to an unfamiliar mouse was impaired by CSDS.Optogenetic inhibition of dCA3CaMKⅡα+→dLS pro-jection reduced the preference for the unfamiliar mouse versus a familiar mouse.Meanwhile,optogenetic activa-tion of dCA3CaMKⅡα+→dLS projection rescued the prefer-ence for social novelty of CSDS-treated mice.Manipula-tions dLSGABA+→PFN projection activation regulated the preference for social novelty in mice.Optogenetic activa-tion of PFNFoxb1+→lPAG projection reduced the prefer-ence for a familiar C57BL/6J mouse versus a novel object in control mice.CSDS decreased the excitability of dCA3CaMKⅡα+ neurons by up-regulation of Kir2.4(Kcnj14)expression.CONCLUSION Our present study suggest-ed that activation of a cell-specific circuit of dCA3CaMKⅡα+→dLSGABA+→PFNFoxb1+→lPAG reverses the deficits of social novelty preference in defeated mice,and inhibition of this circuit reduces the preference for social novelty.The cir-cuit that regulates the preference for social novelty deficits may provide a new information for the potential therapeu-tic targets for neuropsychiatric diseases.