Cingulate metabolites during pain and morphine treatment as assessed by magnetic resonance spectroscopy

Background: Experimental investigation of cerebral mechanisms underlying pain and analgesia are important in the development of methods for diagnosis and treatment of pain. The aim of the current study was to explore brain metabolites in response to pain and treatment with morphine. Methods: Proton magnetic resonance spectroscopy of the anterior cingulate cortex was performed in 20 healthy volunteers (13 males and seven females, aged 24.9 +/- 2.6 years) during rest and acute pain before and during treatment with 30 mg of oral morphine or placebo in a randomized, double-blinded, cross-over study design. Pain was evoked by skin stimulation applied to the right upper leg using a contact heat-evoked potential stimulator. Results: Data from 12 subjects were valid for analysis. Painful stimulation induced an increase in N-acetylaspartate/creatine compared with rest (F=5.5, P=0.04). During treatment with morphine, painful stimulation induced decreased glutamate/creatine (F=7.3, P=0.02), myo-inositol/creatine (F=8.38, P=0.02), and N-acetylaspartate/creatine (F=13.8, P=0.004) concentrations, whereas an increase in the pain-evoked N-acetylaspartate/creatine concentration (F=6.1, P=0.04) was seen during treatment with placebo. Conclusion: This explorative study indicates that neuronal metabolites in the anterior cingulate cortex, such as N-acetylaspartate, glutamate, and myo-inositol, could be related to the physiology of pain and treatment with morphine. This experimental method has the potential to enable the study of brain metabolites involved in pain and its treatment, and may in the future be used to provide further insight into these mechanisms.