Histamine H1 Receptor Antagonists Facilitate Electroacupuncture Analgesia

This study investigated the influence of the histamine H1 receptor antagonists, chlorpheniramine (CHL) and pyrilamine, on the analgesic effects of acupuncture in mice. Nociceptive response was evaluated by the acetic acid-induced abdominal writhe test. Electroacupuncture (EA) at bilateral ST36 reduced the manifestations of acetic acid-induced abdominal writhing, whereas needle insertion without electrostimulation had no such effect. Notably, EA treatment was not associated with any analgesic effects in mice pretreated with naloxone. Low doses of CHL (0.6mg/kg; p.o.) or pyrilamine (2.5mg/kg; i.p.) as monotherapy did not affect acetic acid-induced abdominal writhing. However, when each agent was combined with EA, acetic acid-induced abdominal writhing was reduced by a greater extent when compared with EA alone. Interestingly, the effects of CHL on acupuncture analgesia were not completely reversed by naloxone treatment. Acetic acid induced increases of phospho-p38 expression in spinal cord, as determined by...