Differential age-related changes of MAO-A and MAO-B in mouse brain and peripheral organs.

Distribution and age-related changes of MAO in BL/C57 mouse were studied by quantitative enzyme radioautography with [3H]Ro41-1049 and [3H]Ro19-6327. In the brain, MAO-A was highest in locus coeruleus and interpeduncular nucleus, and MAO-B in raphe nuclei, paraventricular thalamic nucleus, and ependyma of ventricles. Extremely high MAO-B levels were also measured in the choroid plexus in contrast to the very low MAO-B levels in rat choroid plexus. With aging, brain MAO-A showed a clear decrease between 4 and 9 weeks, followed by no change between 9 weeks and 19 months, and a slight increase between 19 and 25 months. On the other hand, all brain structures showed age-related increases in MAO-B. Peripheral organs showed different patterns of MAO age-related changes. Particularly interesting was the marked MAO-B increase in heart, parallel to the MAO-A increase in rat heart. Also of interest is the decrease of liver MAO-B in old animals, which, together with the increase of MAO-B in the brain, might underlie the high sensitivity of old BL/C57 mice to MPTP.