Age-related increases in brain monoamine oxidase B in living healthy human subjects

Several studies of human brain postmortem report that monoamine oxidase B (MAO B) increases with age and it has been proposed that this increase reflects age-associated increases in glial cells. We measured brain MAO B in a group of normal healthy human subjects (n = 21; age range 23-86; 9 females and 12 males; nonsmokers) using [¹¹C]L-deprenyl-D2 and positron emission tomography. Brain glucose metabolism was also measured with ¹⁸FDG in 15 of the subjects. MAO B increased (p < 0.004) in all brain regions examined except the cingulate gyrus. In contrast, subjects showed the expected regional age related decreases in blood flow and metabolism. In the 15 subjects in whom both MAO B and LCMRglu was measured, there was a trend (p < 0.03) toward an inverse association between brain glucose metabolism and MAO B activity in the frontal and parietal cortices. Although the age-related increase in brain MAO B in living subjects is consistent with postmortem reports, the degree of increase is generally lower.