Changes in brain dopamine levels and aggressive behavior with aging in 2 mouse strains.

The genetic programming of brain monoamine changes with aging show remarkable differences in 2 mouse strains. A marked increase in dopamine occurred in 32-week-old grouped ICR mice and the males showed intense irritability and aggressive behavior. Brain amines changed only slightly in old C57BL6J mice and behavior remained benign. Old females showed similar amine changes but aggresive behavior did not occur in either strain.