Effects of defeat experiences on dopamine metabolism in different brain areas of the mouse

Abstract

Immediately after a single defeat experience, mice presented significant changes in dopamine (DA) metabolism in frontal cortex (FC), nucleus accumbens septi (NAS), tuberculum olfactorium (TO), septum (SEP), hypothalamus (HYP), amygdala (AMY), and bulbus olfactorius (BO) but not in caudatus putamen (CP). In BO, NAS, and TO, where levels of 3-methoxytyramine (3-MT) were detectable with our analytical methods, the increase of this metabolite suggested an increased DA release. Repeatedly defeated mice (3 days) sacrificed 24 hr after the last defeat experience presented significant increase 3-4-dihydroxyphenylacetic acid (DOPAC) levels in the HYP and a significant decrease in DA levels in the FC, showing only minor effects on DA metabolism 24 hr after the last defeat experience. Finally, mice subjected to three daily defeats and then confronted with environmental cues related to their defeat experiences presented an increase of DOPAC, homovanillic acid (HVA), and 3-MT in the BO, NAS, and TO and an increase of DOPAC and HVA in the HYP. Other brain areas did not show significant changes in DA metabolism compared with undefeated mice exposed to the same environmental cues. Taken together these results strongly suggest that changes in DA metabolism produced by defeat in some brain areas are elicited by environmental cues previously paired with the experience of being defeated.