Brain monoamine oxidase in mice after exposure to aggression and defeat.

Effects on the monoamine Oxidase activity of the hypothalamus, amygdala, and frontal cortex of untrained mice exposed to repeated defeat by trained fighters for two 5-minute periods a day for 0, 1, 2, 4, 8, 14, or 20 days were studied. Activity in the hypothalamus increased significantly during the first 2 days of fighting, while the activity in the amygdala and frontal cortex remained essentially unchanged. After 8 days, activity in all three brain areas declined. After 14 days of fighting the monoamine Oxidase activity returned to normal, but another decrease was observed in the three areas after 20 days of fighting.