OBJECTIVE: Social stressors modulate the hypothalamic-pituitary-adrenal axis in rodents. However, reports on the association between corticosterone level and behavioural responses to the stressor are ambivalent. This may depend on the experimental paradigm, species- and strain-differences, duration of exposure to the stressor, but also on using either the social state (dominant or subordinate) or the coping style (proactive or passive) of an animal to correlate the corticosterone level with.
DESIGN AND SETTING: We used male Balb-C mice in a resident-intruder paradigm. Adolescent intruders (aged five to eight weeks) were transferred into the cage of an adult resident (aged about four month) for five minutes. The interactions were video-taped for behavioural analysis. Ten minutes after the encounters, intruders were sacrificed and blood samples were collected.
RESULTS: Dominant intruders showed offensive behaviours (attack, chase, tail tracking) and won most of the fights, whereas subordinate intrudes showed mainly submissive behaviours (flight, freezing) and were further classified into active and passive subordinates. Active subordinates displayed significantly more flight-behaviour than passive subordinates. Dominant intruders showed significantly higher post-stress levels of corticosterone than subordinates, which did not differ from control mice, which experienced five minutes of novel-cage exposure. Comparing all three behavioural phenotypes we found the lowest corticosterone levels in active subordinates.
CONCLUSION: Social state significantly affects the HPA-axis response to acute social stressors.