A Nociceptive Neuronal Ensemble In Dorsomedial Prefrontal Cortex Underlies Pain Chronicity

Although acute pain evokes protective behavioral responses from tissue injury,chronic pain that affects about 20% of the human population worldwide,is excruciating in perceptual,affective and cognitive dimensions.However,the mechanism underlying pain chronicity in brain remain indistinct.Although present study indicates that m PFC(Medial prefrontal cortex)undergoes functional and structural changes during pain chronicity,the cellular mechanism in m PFC is poorly clarified.Thus,observation and manipulation of m PFC under cellular level is required to better understand its role in pain chronicity.In this study we firstly identified a nociceptive ensemble in the dorsomedial prefrontal cortex(dm PFC)via c-fos screening and in vivo fiber photometry recording.Meanwhile,with fluorescent immunostaining,we confirmed that over 90% neurons in this ensemble are glutamatergic.Further,using FHIRM-TPM(Fast high-resolution miniaturized two-photon microscope)in vivo recording,we affirmed a nociceptive ensemble in dm PFC and found increased proportion and activity of dm PFC nociceptive ensemble to noxious stimuli during CFA(complete Freund’s adjuvant)inflammatory pain.It’s worth noting that more activation of dm PFC nociceptive ensemble was predictive of increased nociceptive behaviors,suggesting that dm PFC nociceptive processing influences the magnitude of pain behavior.By using Tet-off(Tetracycline off)selectively labeling and chemogenetic manipulation,we showed that silencing this dm PFC nociceptive ensemble relieved chronic inflammatory pain,while prolonged activation induced chronic pain-like behaviors in both sensory and emotional dimensions.By contrast,pan activation of glutamatergic neurons in dm PFC did not induce chronic pain-like behaviors.Fluorescence activated cell sorting followed by RNA sequencing exhibited that Htr1F(5-hydroxytryptamine receptor 1F),Oprl1(opioid related nociceptin receptor 1)and Cdk3(cyclin dependent kinase 3)were highly expressed in dm PFC nociceptive ensemble,markablely.Combined with virus tracing and in vivo fiber photometry recording,we revealed that the basolateral amygdala(BLA)and lateral parabranchial nuclei(LPB)are downstream of the ensemble modulating response towards noxious stimuli during pain chronicity.Taken together,our present study demonstrates that a nociceptive ensemble in dm PFC plays an important role in pain chronicity,via modulating activity of BLA and LPB,as the dm PFC downstream brain targets,towards peripheral nociceptive stimulus.Our results reveal that a novel mechanism of pain chronicity in brain and raised potentials of dm PFC nociceptive neuronal ensemble in chronic pain prevention and treatment in clinic.