Glutamatergic neurons in the infralimbic cortex for motivational response of pain relief induced by electroacupuncture

Peripheral neuromodulation by electroacupuncture (EA) is a promising tool for both experimental and clinical applications. However, whether EA signals reflect a multidimensional composite and evoke affective and motivational processes remains largely elusive. Here, we demonstrated that EA at ST.36 acupuncture point considerably attenuated pain hypersensitivity at 24h and 48h postincision. In conditioned place preference (CPP) model, one chamber becomes associated with EA through three-day repeated pairings, whereas the other chamber is associated with no EA stimulation. EA stimulation resulted in strong preference for the chamber paired with EA in incisional injury (INP) rats. In contrast, EA at non-acupuncture points in INP rats did not relief pain and produce CPP. Notably, EA with the context in sham-operated animals did not induce CPP. Next, we identified neurons activation in brain associated with affective and motivational aspects of pain after EA stimulation using immediate early gene c-Fos expression in SNI rats. EA stimulation increased c-Fos positive neurons in the IL, but not cingulate (Cg1) and prelimbic (PL) subregion of the mPFC. Sham EA did not increase c-Fos expression in the IL in spared nerve injury (SNI) rats. Using reversible inactivation of IL in rats, inactivation of the IL significantly abolished CPP of pain relief induced by EA. Optogenetic activation of IL glutamatergic neurons mimicked EA-induced analgesia and CPP behaviors, and inhibition of glutamatergic neurons in the IL reversed the effects of EA. The study directly demonstrates a novel and important role for glutamatergic neurons in the infralimbic cortex in acupuncture-induced motivational response of pain relief and provides a new perspective for investigating acupuncture analgesia.