title: Elevated monoamine oxidase a levels in the brain: an explanation for the monoamine imbalance of major depression.
abstract: BACKGROUND
  The monoamine theory of depression proposes that monoamine levels are lowered, but there is no explanation for how monoamine loss occurs. Monoamine oxidase A (MAO-A) is an enzyme that metabolizes monoamines, such as serotonin, norepinephrine, and dopamine.
  
  
  OBJECTIVE
  To determine whether MAO-A levels in the brain are elevated during untreated depression.
  
  
  METHODS
  Tertiary care psychiatric hospital.
  
  
  METHODS
  Seventeen healthy and 17 depressed individuals with major depressive disorder that met entry criteria were recruited from the care of general practitioners and psychiatrists. All study participants were otherwise healthy and nonsmoking. Depressed individuals had been medication free for at least 5 months.
  
  
  METHODS
  Harmine labeled with carbon 11, a radioligand selective for MAO-A and positron emission tomography, was used to measure MAO-A DVS (specific distribution volume), an index of MAO-A density, in different brain regions (prefrontal cortex, anterior cingulate cortex, posterior cingulate cortex, caudate, putamen, thalamus, anterior temporal cortex, midbrain, hippocampus, and parahippocampus).
  
  
  RESULTS
  The MAO-A DVS was highly significantly elevated in every brain region assessed (t test; P=.001 to 3x10(-7)). The MAO-A DVS was elevated on average by 34% (2 SDs) throughout the brain during major depression.
  
  
  CONCLUSIONS
  The sizable magnitude of this finding and the absence of other compelling explanations for monoamine loss during major depressive episodes led to the conclusion that elevated MAO-A density is the primary monoamine-lowering process during major depression.
authors.affiliation: Vivian M. Rakoff PET Imaging Centre and Mood and Anxiety Disorders Division, Clarke Division, Centre for Addiction and Mental Health and Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada. jeff.meyer@camhpet.ca
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Meyer
authors.forename: Nathalie
authors.initials: N
authors.lastname: Ginovart
authors.forename: Anahita
authors.initials: A
authors.lastname: Boovariwala
authors.forename: Sandra
authors.initials: S
authors.lastname: Sagrati
authors.forename: Doug
authors.initials: D
authors.lastname: Hussey
authors.forename: Armando
authors.initials: A
authors.lastname: Garcia
authors.forename: Trevor
authors.initials: T
authors.lastname: Young
authors.forename: Nicole
authors.initials: N
authors.lastname: Praschak-Rieder
authors.forename: Alan A
authors.initials: AA
authors.lastname: Wilson
authors.forename: Sylvain
authors.initials: S
authors.lastname: Houle
mesh_terms: D000328:Adult; D000367:Age Factors; D015306:Biogenic Monoamines / Q000032:analysis / Q000378:metabolism*; D001921:Brain / Q000000981:diagnostic imaging / Q000201:enzymology* / Q000378:metabolism; D002250:Carbon Radioisotopes / Q000378:metabolism; D002395:Catecholamines / Q000032:analysis / Q000378:metabolism; D003865:Major Depressive Disorder / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000378:metabolism*; D005260:Female; D006247:Harmine / Q000378:metabolism; D006801:Humans; D008297:Male; D008995:Monoamine Oxidase / Q000032:analysis / Q000378:metabolism*; D049268:Positron-Emission Tomography; D012737:Sex Factors; D014018:Tissue Distribution
chemical_list: D015306:Biogenic Monoamines; D002250:Carbon Radioisotopes; D002395:Catecholamines; D006247:Harmine; D008995:Monoamine Oxidase