title: Pain and allodynia/hyperalgesia induced by intramuscular injection of serotonin in patients with fibromyalgia and healthy individuals.
abstract: The aim of this study was to investigate the effect of injection of serotonin (5-HT) into the masseter muscle on pain and allodynia/hyperalgesia. Twelve female patients with fibromyalgia (FM) and 12 age-matched female healthy individuals (HI) participated in the study. The current pain intensity (CPI) and the pressure pain threshold (PPT) of the superficial masseter muscles were assessed bilaterally. 5-HT in one of three randomized concentrations (10(-3), 10(-5), 10(-7) M) or isotonic saline was then injected into either of the two masseter muscles in a double-blind manner. After the injections the CPI and PPT were recorded ten times during 30 min. The injections were repeated twice with the other concentrations of 5-HT after 1 and 2 weeks, respectively. In the FM-group there was a non-significant increase of CPI after injection that lasted during the entire 30-min period irrespective of whether 5-HT or saline was injected. Neither did the PPT change significantly. In the HI-group pain developed significantly after injection irrespective of whether 5-HT or saline was injected, but significantly more so after 5-HT at 10(-3) M than saline injection. CPI decreased quickly and then remained on a very low level for most of the experiment. 5-HT at both 10(-5) M and 10(-3) M caused a significantly greater decrease of PPT than saline. In conclusion, our results show that 5-HT injected into the masseter muscle of healthy female subjects elicits pain and allodynia/hyperalgesia, while no such responses occur in patients with fibromyalgia.
authors.affiliation: Department of Clinical Oral Physiology, Institute of Odontology, Box 4064, S-141 04, Huddinge, Sweden. malin.ernberg@ofa.ki.se
authors.forename: M
authors.initials: M
authors.lastname: Ernberg
authors.forename: T
authors.initials: T
authors.lastname: Lundeberg
authors.forename: S
authors.initials: S
authors.lastname: Kopp
mesh_terms: D000328:Adult; D004311:Double-Blind Method; D005260:Female; D005356:Fibromyalgia / Q000503:physiopathology*; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced* / Q000503:physiopathology; D007273:Injections, Intramuscular; D008406:Masseter Muscle / Q000503:physiopathology; D008875:Middle Aged; D010146:Pain / Q000139:chemically induced* / Q000503:physiopathology; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D011312:Pressure; D012701:Serotonin / Q000008:administration & dosage / Q000097:blood
chemical_list: D012701:Serotonin