title: Amino acid neurotransmitters assessed by proton magnetic resonance spectroscopy: relationship to treatment resistance in major depressive disorder.
abstract: BACKGROUND
  Significant alterations in gamma-aminobutyric acid (GABA) and glutamate levels have been previously reported in major depressive disorder (MDD); however, no studies to date have investigated associations between these amino acid neurotransmitters and treatment resistance.
  
  
  METHODS
  The objective of this study was to compare occipital cortex (OCC) and anterior cingulate cortex (ACC) GABA and glutamate+glutamine (Glx) levels measured by proton magnetic resonance spectroscopy ((1)H MRS) in 15 medication-free treatment-resistant depression (TRD) patients with those in 18 nontreatment-resistant MDD (nTRD) patients and 24 healthy volunteers (HVs).
  
  
  RESULTS
  Levels of OCC GABA relative to voxel tissue water (W) were decreased in TRD patients compared with both HV (20.2% mean reduction; p = .001; Cohen's d = 1.3) and nTRD subjects (16.4% mean reduction; p = .007; Cohen's d = 1.4). There was a similar main effect of diagnosis for ACC GABA/W levels (p = .047; Cohen's d = .76) with TRD patients exhibiting reduced GABA in comparison with the other two groups (22.4% to 24.5% mean reductions). Group differences in Glx/W were not significant in either brain region. Only GABA results in OCC survived correction for multiple comparisons.
  
  
  CONCLUSIONS
  Our findings corroborate previous reports of decreased GABA in MDD and provide initial evidence for a distinct neuronal amino acid profile in patients who have failed to respond to several standard antidepressants, possibly indicative of abnormal glutamate/glutamine/GABA cycling. Given interest in novel antidepressant mechanisms in TRD that selectively target amino acid neurotransmitter function, the translational relevance of these findings awaits further study.
authors.affiliation: Department of Psychiatry, Mount Sinai School of Medicine, New York, New York 10029-6574, USA.
authors.forename: Rebecca B
authors.initials: RB
authors.lastname: Price
authors.forename: Dikoma C
authors.initials: DC
authors.lastname: Shungu
authors.forename: Xiangling
authors.initials: X
authors.lastname: Mao
authors.forename: Paul
authors.initials: P
authors.lastname: Nestadt
authors.forename: Chris
authors.initials: C
authors.lastname: Kelly
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Collins
authors.forename: James W
authors.initials: JW
authors.lastname: Murrough
authors.forename: Dennis S
authors.initials: DS
authors.lastname: Charney
authors.forename: Sanjay J
authors.initials: SJ
authors.lastname: Mathew
mesh_terms: D000328:Adult; D001921:Brain / Q000378:metabolism*; D016022:Case-Control Studies; D003865:Major Depressive Disorder / Q000378:metabolism*; D004351:Drug Resistance; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism*; D006179:Gyrus Cinguli / Q000378:metabolism; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009778:Occipital Lobe / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D018377:Neurotransmitter Agents; D005973:Glutamine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid