title: Interaction of morphine and selective serotonin receptor inhibitors in rats experiencing inflammatory pain.
abstract: Citalopram and paroxetine are selective serotonin reuptake inhibitors and also have antinociceptive effects. We investigated the antiallodynic and antihyperalgesic effects of intrathecally administered morphine, citalopram, paroxetine, and combinations thereof, in a rat model in which peripheral inflammation was induced by complete Freund's adjuvant (CFA). Drugs were intrathecally administered via direct lumbar puncture. Mechanical allodynia was measured using a Dynamic Plantar Aesthesiometer. Thermal hyperalgesia and cold allodynia were determined by measuring latency of paw withdrawal in response to radiant heat and cold water. Behavioral tests were run before and 15, 30, 45, and 60 min after intrathecal injection. Intraplantar injection of CFA produced mechanical allodynia, thermal hyperalgesia, and cold allodynia. Intrathecally administered morphine (0.3 or 1 µg) had antiallodynic or antihyperalgesic effects (24.0%-71.9% elevation). The effects of morphine were significantly increased when a combination of citalopram (100 µg) and paroxetine (100 µg) was added (35.2%-95.1% elevation). This rise was reversed by naloxone and methysergide. The effects of citalopram and paroxetine were also reversed by naloxone and methysergide. We suggest that the mu opioid receptor and serotonin receptors play major roles in production of the antiallodynic and antihyperalgesic effects of morphine, citalopram, paroxetine, and combinations thereof, in animals experiencing inflammatory pain.
authors.affiliation: Department of Anesthesiology and Pain Medicine, CHA Medical Center, CHA University, Gumi, Korea.
authors.forename: Byung-Sang
authors.initials: BS
authors.lastname: Lee
authors.forename: In-Gu
authors.initials: IG
authors.lastname: Jun
authors.forename: Sung-Hoon
authors.initials: SH
authors.lastname: Kim
authors.forename: Jong Yeon
authors.initials: JY
authors.lastname: Park
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D015283:Citalopram / Q000008:administration & dosage / Q000494:pharmacology; D004195:Disease Models, Animal; D006930:Hyperalgesia / Q000209:etiology; D007249:Inflammation / Q000139:chemically induced* / Q000473:pathology; D007278:Injections, Spinal; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D010146:Pain / Q000517:prevention & control*; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D017374:Paroxetine / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000737:chemistry* / Q000378:metabolism; D017367:Selective Serotonin Reuptake Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D013696:Temperature; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D015283:Citalopram; D009020:Morphine; D017374:Paroxetine; D011985:Receptors, Serotonin; D017367:Selective Serotonin Reuptake Inhibitors