Corticotropin‐releasing factor is involved in acute stress‐induced analgesia and antipruritus

BACKGROUND: Under the condition of stress, the hypothalamic–pituitary–adrenal axis (HPA axis) is activated and causes the secretion of corticotropin‐releasing factor (CRF). Previous studies have demonstrated that CRF is involved in the regulation of pain and itch. Thus, it remains worthy to explore whether the desensitization of pain and itch under high‐intensity acute stress (such as high fear and tension) is related to the sharp increase of CRF. METHODS: Forced swimming was used to simulate acute stress. ELISA and pharmacological methods were conducted to observe the effects of forced swimming on acute pain or itch and the relationship between blood CRF content and itch or pain behavior. Intracerebroventricular (ICV) administration of CRF was conducted to examine the effects of CRF on acute pain or itch. Intrathecal administration of CRF receptor agonist or antagonist was conducted to examine the receptor mechanisms of the regulatory role of CRF in pain and itch. RESULTS: ELISA experiment showed that the serum CRF in mice reached its peak within 5–10 min after acute stress (forced swimming). Behavioral data showed that the scratching behavior induced by itch agents decreased after acute swimming, while the mechanical pain threshold increased significantly. The inhibitory effect of acute stress on pain and itch is mediated by CRF receptor2 (CRFR2). Then, ICV injection of CRF was used to simulate the massive release of CRF under acute stress, and we observed that the scratching behavior induced by histamine or chloroquine was significantly inhibited after ICV injection of CRF. The above effects of CRF are mainly mediated by CRFR2. These results suggest that 5–10 min after acute stress, a large amount of CRF is released into the blood from the hypothalamus, which significantly inhibits acute pain and itch by acting on CRFR2. ICV injection of CRF can replicate the antipruritus effects of acute stress. CONCLUSIONS: The present study investigated the mechanism of acute stress‐induced analgesia and antipruritus and provided theoretical support for the treatment of pain and itch.