Dynamic, adaptive changes in MAO-A binding after alterations in substrate availability: an in vivo [11C]-harmine positron emission tomography study

Monoamine oxidase A (MAO-A) is an important target in the pathophysiology and therapeutics of major depressive disorder, aggression, and neurodegenerative conditions. We measured the effect of changes in MAO-A substrate on MAO-A binding in regions implicated in affective and neurodegenerative disease with [C-11]-harmine positron emission tomography in healthy volunteers. Monoamine oxidase A V-T, an index of MAO-A density, was decreased (mean: 14%+/- 9%) following tryptophan depletion in prefrontal cortex (P < 0.031), and elevated (mean: 17%+/- 11%) in striatum following carbidopa-levodopa administration (P < 0.007). These findings suggest an adaptive role for MAO-A in maintaining monoamine neurotransmitter homeostasis by rapidly compensating fluctuating monoamine levels. Journal of Cerebral Blood Flow & Metabolism (2012) 32, 443-446; doi: 10.1038/jcbfm.2011.184; published online 21 December 2011