title: Muscle pain sensitivity after glutamate injection is not modified by systemic administration of monosodium glutamate.
abstract: BACKGROUND
  Monosodium glutamate (MSG) is often thought to be associated with headache and craniofacial pains like temporomandibular disorders. This randomized, double-blinded, placebo-controlled study was performed to investigate how ingestion of MSG affects muscle pain sensitivity before and after experimentally induced muscle pain.
  
  
  METHODS
  Sixteen healthy adult subjects participated in 2 sessions with at least 1-week interval between sessions. In each session, two injections of glutamate (Glu, 0.5 M, 0.2 ml) and two injections of saline (0.9%, 0.2 ml) into the masseter and temporalis muscles, respectively, were undertaken, with a 15 min interval between each injection. Injections of saline were made contralateral to Glu injections and done in a randomized order. Participants drank 400 mL of soda mixed with either MSG (150 mg/kg) or NaCl (24 mg/kg, placebo) 30 min before the intramuscular injections. Pressure pain thresholds (PPT), autonomic parameters and pain intensity were assessed prior to (baseline) and 30 min after ingestion of soda, as well as 5 min and 10 min after the intramuscular injections and at the end of the session. Whole saliva samples were collected prior to and 30, 45, 60, and 75 min after the ingestion of soda.
  
  
  RESULTS
  MSG administration resulted in a significantly higher Glu level in saliva than administration of NaCl and was associated with a significant increase in systolic blood pressure. Injections of Glu were significantly more painful than injections of NaCl. However, ingestion of MSG did not change the intensity of Glu-evoked pain. Glu injections also significantly increased systolic and diastolic blood pressure, but without an additional effect of MSG ingestion. Glu injections into the masseter muscle significantly reduced the PPT. However, pre-injection MSG ingestion did not significantly alter this effect. Interestingly, PPT was significantly increased in the trapezius after MSG ingestion and intramuscular injection of Glu in the jaw muscles.
  
  
  CONCLUSIONS
  The main finding in this study was that systemic intake of a substantial amount of MSG does not influence either pain intensity or pressure pain sensitivity in the masseter and temporalis muscles into which Glu injections were made.
authors.affiliation: Section of Orofacial Pain and Jaw Function, Department of Dentistry, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark, Vennelyst Boulevard 9, 8000, Aarhus C, Denmark, akiko.shimada@odont.au.dk.
authors.forename: Akiko
authors.initials: A
authors.lastname: Shimada
authors.forename: Eduardo
authors.initials: E
authors.lastname: Castrillon
authors.forename: Lene
authors.initials: L
authors.lastname: Baad-Hansen
authors.forename: Bijar
authors.initials: B
authors.lastname: Ghafouri
authors.forename: Björn
authors.initials: B
authors.lastname: Gerdle
authors.forename: Malin
authors.initials: M
authors.lastname: Ernberg
authors.forename: Brian
authors.initials: B
authors.lastname: Cairns
authors.forename: Peter
authors.initials: P
authors.lastname: Svensson
mesh_terms: D000328:Adult; D004311:Double-Blind Method; D005260:Female; D018698:Glutamic Acid / Q000008:administration & dosage* / Q000378:metabolism; D006801:Humans; D007273:Injections, Intramuscular; D008297:Male; D008406:Masseter Muscle / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D063806:Myalgia / Q000139:chemically induced / Q000175:diagnosis* / Q000378:metabolism; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects* / Q000502:physiology; D012463:Saliva / Q000187:drug effects / Q000378:metabolism; D012965:Sodium Chloride / Q000008:administration & dosage; D012970:Sodium Glutamate / Q000008:administration & dosage* / Q000633:toxicity; D055815:Young Adult
chemical_list: D018698:Glutamic Acid; D012965:Sodium Chloride; D012970:Sodium Glutamate