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Muscle pain sensitivity after glutamate injection is not modified by systemic administration of monosodium glutamate
Akiko Shimada1, Eduardo Castrillon, Lene Baad-Hansen
1Section 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.
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.
Conclusion:
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.
Insights
Monosodium glutamate (MSG) intake did not alter pain intensity or sensitivity in jaw muscles after glutamate injections. However, MSG consumption did increase pain sensitivity in the trapezius muscle.
Area of Science:
- Pain research
- Neuroscience
- Muscle physiology
Background:
- Monosodium glutamate (MSG) is commonly linked to headaches and craniofacial pain, including temporomandibular disorders.
- This study investigated MSG's effect on muscle pain sensitivity following experimentally induced pain.
Purpose of the Study:
- To determine if MSG ingestion affects muscle pain sensitivity and intensity.
- To examine the impact of MSG on experimentally induced muscle pain in healthy adults.
Main Methods:
- A randomized, double-blinded, placebo-controlled study involving 16 healthy adults.
- Subjects received intramuscular injections of glutamate (Glu) or saline into masseter and temporalis muscles after consuming either MSG or a placebo.
- Measurements included pressure pain thresholds (PPT), pain intensity, and autonomic parameters before and after injections.
Main Results:
- MSG ingestion increased glutamate levels in saliva and systolic blood pressure.
- Glutamate injections were more painful than saline, but MSG did not alter pain intensity.
- MSG ingestion did not affect PPT in the masseter or temporalis muscles but increased PPT in the trapezius muscle.
Conclusions:
- Systemic intake of MSG does not influence pain intensity or pressure pain sensitivity in the masseter and temporalis muscles.
- MSG may have differential effects on pain sensitivity in different muscle groups, as evidenced by increased PPT in the trapezius.
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