No change in N-acetyl aspartate in first episode of moderate depression after antidepressant treatment: (1)H magnetic spectroscopy study of left amygdala and left dorsolateral prefrontal cortex

Choline elevation in amygdala region at recovery indicates longer survival without depressive episode: a magnetic resonance spectroscopy study

RATIONALE

Depression, with variable longitudinal patterns, recurs in one third of patients. We lack useful predictors of its course/outcome, and proton magnetic resonance spectroscopy (1H-MRS) of brain metabolites is an underused research modality in finding outcome correlates.

OBJECTIVES

To determine if brain metabolite levels/changes in the amygdala region observed early in the recovery phase indicate depression recurrence risk in patients receiving maintenance therapy.

METHODS

Forty-eight patients on stable-dose antidepressant (AD) maintenance therapy were analyzed from recovery onset until (i) recurrence of depression or (ii) start of AD discontinuation. Two 1H-MRS scans (6 months apart) were performed with a focus on amygdala at the beginning of recovery. N-acetylaspartate (NAA), choline-containing metabolites (Cho), and Glx (glutamine/glutamate and GABA) were evaluated with regard to time without recurrence, and risks were assessed by Cox proportional hazard modeling.

RESULTS

Twenty patients had depression recurrence, and 23 patients reached AD discontinuation. General linear model repeated measures analysis displayed three-way interaction of measurement time, metabolite level, and recurrence on maintenance therapy, in a multivariate test, Wilks' lambda = 0.857, F(2,40) = 3.348, p = 0.045. Cho levels at the beginning of recovery and subsequent changes convey the highest risk for earlier recurrence. Patients experiencing higher amygdala Cho after recovery are at a significantly lower risk for depression recurrence (hazard ratio = 0.32; 95% confidence interval 0.13-0.77).

CONCLUSION

Cho levels/changes in the amygdala early in the recovery phase correlate with clinical outcome. In the absence of major NAA fluctuations, changes in Cho and Glx may suggest a shift towards reduction in (previously increased) glutamatergic neurotransmission. Investigation of a larger sample with greater sampling frequency is needed to confirm the possible predictive role of metabolite changes in the amygdala region early in the recovery phase.

Promising Neuroimaging Biomarkers in Depression

The neuroimaging has been applied in the study of pathophysiology in major depressive disorder (MDD). In this review article, several kinds of methodologies of neuroimaging would be discussed to summarize the promising biomarkers in MDD. For the magnetic resonance imaging (MRI) and magnetoencephalography field, the literature review showed the potentially promising roles of frontal lobes, such as anterior cingulate cortex (ACC), dorsolateral prefrontal cortex (DLPFC) and orbitofrontal cortex (OFC). In addition, the limbic regions, such as hippocampus and amygdala, might be the potentially promising biomarkers for MDD. The structures and functions of ACC, DLPFC, OFC, amygdala and hippocampus might be confirmed as the biomarkers for the prediction of antidepressant treatment responses and for the pathophysiology of MDD. The functions of cognitive control and emotion regulation of these regions might be crucial for the establishment of biomarkers. The near-infrared spectroscopy studies demonstrated that blood flow in the frontal lobe, such as the DLPFC and OFC, might be the biomarkers for the field of near-infrared spectroscopy. The electroencephalography also supported the promising role of frontal regions, such as the ACC, DLPFC and OFC in the biomarker exploration, especially for the sleep electroencephalogram to detect biomarkers in MDD. The positron emission tomography (PET) and single-photon emission computed tomography (SPECT) in MDD demonstrated the promising biomarkers for the frontal and limbic regions, such as ACC, DLPFC and amygdala. However, additional findings in brainstem and midbrain were also found in PET and SPECT. The promising neuroimaging biomarkers of MDD seemed focused in the fronto-limbic regions.

Towards a neurochemical profile of the amygdala using short-TE 1 H magnetic resonance spectroscopy at 3 T

The amygdala plays a key role in emotional learning and in the processing of emotions. As disturbed amygdala function has been linked to several psychiatric conditions, a knowledge of its biochemistry, especially neurotransmitter levels, is highly desirable. The spin echo full intensity acquired localized (SPECIAL) sequence, together with a transmit/receive coil, was used to perform very short-TE magnetic resonance spectroscopy at 3 T to determine the neurochemical profile in a spectroscopic voxel containing the amygdala in 21 healthy adult subjects. For spectral analysis, advanced data processing was applied in combination with a macromolecule baseline measured in the anterior cingulate for spectral fitting. The concentrations of total N-acetylaspartate, total creatine, total choline, myo-inositol and, for the first time, glutamate were quantified with high reliability (uncertainties far below 10%). For these metabolites, the inter-individual variability, reflected by the relative standard deviations for the cohort studied, varied between 12% (glutamate) and 22% (myo-inositol). Glutamine and glutathione could also be determined, albeit with lower precision. Retest on four subjects showed good reproducibility. The devised method allows the determination of metabolite concentrations in the amygdala voxel, including glutamate, provides an estimation of glutamine and glutathione, and may help in the study of disturbed amygdala metabolism in pathologies such as anxiety disorder, autism and major depression.