Chronic restraint stress-induced hyperalgesia is modulated by the periaqueductal gray neurons projecting to the rostral ventromedial medulla in mice

Stress-induced hyperalgesia (SIH) is induced by repeated or chronic exposure to stressful or uncomfortable environments. However, the neural mechanisms involved in the modulatory effects of the periaqueductal gray (PAG) and its associated loops on SIH development hav e not been elucidated. In the present study, we used chronic restraint stress (CRS)-induced hyperalgesia as a SIH model and manipulated neuronal activity via a pharmacogenetic approach to investigate the neural mechanism underlying the effects of descending pain-modulatory pathways on SIH. We found that activation of PAG neurons alleviates CRS-induced hyperalgesia; on the other hand, PAG neurons inhibition facilitates CRS-induced hyperalgesia. Moreover, this modulatory effect is achieved by the neurons which projecting to the rostral ventromedial medulla (RVM). Our data thus reveal the functional role of the PAG-RVM circuit in SIH and provide analgesic targets in the brain for clinical SIH treatment.