Electroacupuncture activates corticotrophin-releasing hormone-containing neurons in the paraventricular nucleus of the hypothalammus to alleviate edema in a rat model of inflammation

Background: Studies show that electroacupuncture (EA) has beneficial effects in patients with inflammatory diseases. This study investigated the mechanisms of EA anti-inflammation using a rat model of complete Freund's adjuvant (CFA)-induced hind paw inflammation and hyperalgesia. Design: Four experiments were conducted on male Sprague-Dawley rats (n = 6-7/per group). Inflammation was induced by injecting CFA into the plantar surface of one hind paw. Experiment I examined whether EA increases plasma adrenocorticotropic hormone (ACTH) levels. Experiments 2 and 3 studied the effects of the ACTH and corticotropin-releasing hormone (CRH) receptor antagonists ACTH((11-24)) and astressin on the EA anti-edema. Experiment 4 determined whether EA activates CRH neurons in the paraventricular nucleus of the hypothalammus. EA treatment 10 Hz at 3 mA and 0.1 ms pulse width was given twice for 20 min each once immediately post and again 2 hr post-CFA. Plasma ACTH levels paw thickness and paw withdrawal latency to a noxious thermal stimulus were measured 2 h and 5 h after the CFA. Results: EA significantly increased ACTH levels 5 h (2 folds) after CFA compared to sham EA control but EA alone in naive rats and CFA alone did not induce significant increases in ACTH. ACTH((11-24)) and astressin blocked EA anti-edema but not EA anti-hyperalgesia. EA induced phosphorylation of NRI, an essential subunit of the N-methyl-D-aspartic acid (NMDA) receptor in CRH-containing neurons of the paraventricular nucleus. Conclusion: The data demonstrate that EA activates CRH neurons to significantly increase plasma ACTH levels and suppress edema through CRH and ACTH receptors in a rat model of inflammation.