Effects of unilateral amygdala dopamine depletion on behaviour in the elevated plus maze: Role of sex, hemisphere and retesting

A growing body of literature suggests that sex differences exist in both rodents and humans in terms of the central processing of stress and emotion, and an important factor in this regard may involve differential hemispheric specialization. The amygdala has been shown to be functionally asymmetrical in both rats and humans and its involvement in stress and emotion processing is well documented. Given that amygdala function is importantly modulated by dopamine (DA), the present study examined the effects of left vs. right unilateral DAergic depletion targeting the basolateral amygdala in male and female rats. We examined behaviour in the elevated plus maze over two consecutive days, and plasma adrenocorticotropic hormone (ACTH) levels in response to a separate 30 min restraint stress.Overall, females showed significantly more exploration of open arms of the plus maze than males, while not differing in general activity reflected in closed arm entries. Significant Sex × Hemisphere interactions were observed for all measures related to open arm exploration, as right amygdala DA depletion produced an anxiolytic effect in males, increasing open arm exploration, but reduced this behaviour in females. Moreover, open arm exploration was greatly reduced on the second maze exposure in males, but unchanged in females. A Sex × Hemisphere interaction was also found for plasma ACTH levels. It is suggested that the role of amygdala DA on stress-related behaviour and physiology reflects inherent differences in amygdala function dependent on both sex and hemisphere.