Dynamic, adaptive changes in MAO-A binding after alterations in substrate availability an in vivo (11)C-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 (11)C-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.