Brain glutamate in anorexia nervosa: a magnetic resonance spectroscopy case control study at 7 Tesla

Abstract

Rationale: Anorexia nervosa (AN) is a serious psychiatric disorder with high morbidity and mortality. There are no established pharmacological treatments and the neurobiology of the condition is poorly understood. Previous studies using magnetic resonance spectroscopy (MRS) have shown that AN may be associated with reductions in indices of brain glutamate; however, at conventional field strengths (≤3 T), it is difficult to separate glutamate from its precursor and metabolite, glutamine.

Objectives: The objective of the present study was to use high field (7 T) MRS to measure concentrations of glutamate, in three separate brain voxels, in women with AN.

Methods: We studied 13 female participants with AN and 12 healthy female controls who underwent MRS scanning at 7 T with voxels placed in anterior cingulate cortex, occipital cortex and putamen. Neurometabolites were calculated using the unsuppressed water signal as a reference and corrected for individual cerebrospinal fluid concentration in the voxel.

Results: We found that participants with AN had significantly lower concentrations of glutamate in all three voxels (mean reduction 8%, p = 0.002) but glutamine levels were not altered. Concentrations of N-acetylaspartate, creatine, GABA and glutathione were also unchanged. However, inositol was lower in AN participants in anterior cingulate (p = 0.022) and occipital cortex (p = 0.002).

Conclusions: Women with AN apparently have widespread reductions in brain glutamate. Further work will be needed to assess if this change has pathophysiological relevance or whether it is a consequence of the many physical changes produced in AN by food restriction.

Keywords: Anorexia nervosa; Glutamate; Glutamine; Magnetic resonance spectroscopy.

Fig. 1

Voxel placement and representative spectra from the anterior cingulate cortex (ACC), occipital cortex (OCC) and putamen (PUT). Each acquired spectrum (64 averages) is overlaid with the metabolite fit from LCModel (red line) with major peaks labeled. The difference between the metabolite fit and underlying spectrum is shown below as a residual, which remains small and uniform indicating a high quality spectral fit. tCR total creatine, Ins myo-Inositol, Cho choline, Glu glutamate, NAA N-acetylaspartate

Fig. 2

Mean (SEM) glutamate levels in 11 female patients with anorexia nervosa (AN) and 10 female healthy controls (CON) in three brain regions, anterior cingulate cortex (ACC), occipital cortex (OCC) and putamen (PUT). There is a main effect of diagnosis on glutamate levels, independent of region (F = 13.7; df = 1.19; p = 0.002)