Defeat is a major stressor in males while social instability is stressful mainly in females: Towards the development of a social stress model in female rats

Social stress models appear useful in elucidating the interrelationship bet ween stress, mood disorders, and drug efficacy. However, reliable social st ress models for females are virtually lacking. The aim of this study was to determine stress-related consequences of (a) defeat in aggressive encounte rs and (b) social instability, in male and female rats. Defeat in male and female subjects was induced by aggressive male residents and female residen ts made aggressive by surgery (mediobasal hypothalamic lesion [MBHL]), resp ectively. Aggressiveness of resident males and resident MBHL females was re markably similar. Alternating isolation and mixed-sex crowding phases with membership rotation were used to induce social instability. Aggression was kept low in the latter paradigm by manipulating crowding group composition. Defeat stress reduced weight gain, and increased both adrenals and plasma corticosterone in males. Only adrenal weight was affected in females. Socia l instability reduced weight gain, and induced thymus involution, adrenal h ypertrophy and elevated plasma corticosterone levels in females. Only weigh t gain and thymus weights were affected in males. It is concluded that defe at stresses males more than females, while social instability is more stres sful for females than for males, if aggressive contacts are low. It is sugg ested that the social instability model is a good model of social stress in females. (C) 1999 Elsevier Science Inc.