Ruis M A, te Brake J H, Buwalda B, De Boer S F, Meerlo P, Korte S M, Blokhuis H J, Koolhaas J M
DLO-Institute for Animal Science and Health (ID-DLO), Department of Behaviour, Stress Physiology and Management, Lelystad, The Netherlands.
Psychoneuroendocrinology. 1999 Apr;24(3):285-300. doi: 10.1016/s0306-4530(98)00050-x.
Social stress in rats is known to induce long-lasting, adverse changes in behaviour and physiology, which seem to resemble certain human psychopathologies, such as depression and anxiety. The present experiment was designed to assess the influence of individual or group housing on the vulnerability of male Wildtype rats to long-term effects of inescapable social defeat. Group-housed rats were individually exposed to an aggressive, unfamiliar male conspecific, resulting in a social defeat. Defeated rats were then either individually housed or returned to their group. The changes in their behaviour and physiology were then studied for 3 weeks. Results showed that individually housed rats developed long-lasting, adverse behavioural and physiological changes after social defeat. Their body growth was significantly retarded (p < .05) between 7 and 14 days after defeat. When individually and group-housed rats were exposed to a mild stressor (sudden silence) 2 days after defeat, both groups became highly immobile. However, when exposure was repeated at day 21, individually housed rats were still highly immobile compared to group-housed rats which regained their normal mobility after only 7 days. In an open field test, also regularly repeated, individually housed rats took significantly longer to leave their home base and were also significantly less mobile than group-housed rats over the entire 3-week test period as well as at specific timepoints. When the rats were placed in an elevated plus-maze 14 days after defeat, those that were individually housed were significantly more anxious than those that were group-housed. When tested at 21 days after defeat in a combined dexamethasone (DEX)/corticotrophin-releasing factor (CRF) test, results showed that the hypothalamic-pituitary-adrenocortical (HPA) activity in individually housed rats was higher. This was evidenced in the latter animals by the fact that DEX was significantly less able to suppress the secretion of ACTH and corticosterone, and by a significantly higher release of ACTH after administration of CRF. Although the weights of the spleen and testes of the two groups did not differ, the adrenals of individually housed rats were larger and the thymus and seminal vesicles were smaller. We conclude that when rats are isolated after defeat, they show long-lasting, adverse behavioural and physiological changes that resemble symptoms of stress-related disorders. In contrast, when familiar rats are housed together these effects of a social defeat are greatly reduced. These findings show that housing conditions importantly influence the probability of long-term adverse behavioural and physiological effects of social defeat in male Wildtype rats.
已知大鼠的社会压力会引发行为和生理上持久的不良变化，这些变化似乎类似于某些人类精神病理学症状，如抑郁和焦虑。本实验旨在评估单独饲养或群居对雄性野生型大鼠遭受不可避免的社会挫败长期影响的易感性。将群居的大鼠单独暴露于一只具有攻击性、不熟悉的雄性同种大鼠面前，导致其遭受社会挫败。然后，将遭受挫败的大鼠要么单独饲养，要么放回其群体中。随后对它们的行为和生理变化进行了3周的研究。结果表明，单独饲养的大鼠在遭受社会挫败后出现了持久的不良行为和生理变化。在挫败后的7至14天内，它们的身体生长明显迟缓（p <.05）。在挫败后2天，当将单独饲养和群居的大鼠暴露于轻度应激源（突然安静）时，两组大鼠都变得高度不动。然而，在第21天重复暴露时，与群居大鼠相比，单独饲养的大鼠仍然高度不动，群居大鼠在仅7天后就恢复了正常活动能力。在同样定期重复进行的旷场试验中，在整个3周的试验期以及特定时间点，单独饲养的大鼠离开其巢穴的时间明显更长，活动能力也明显低于群居大鼠。在挫败后14天将大鼠置于高架十字迷宫中时，单独饲养的大鼠比群居大鼠明显更焦虑。在挫败后21天进行的联合地塞米松（DEX）/促肾上腺皮质激素释放因子（CRF）试验中，结果表明单独饲养的大鼠下丘脑-垂体-肾上腺皮质（HPA）活性更高。这在后者动物中表现为DEX显著降低抑制促肾上腺皮质激素（ACTH）和皮质酮分泌的能力，以及在给予CRF后ACTH的释放显著更高。尽管两组大鼠的脾脏和睾丸重量没有差异，但单独饲养的大鼠肾上腺更大，胸腺和精囊更小。我们得出结论，当大鼠在遭受挫败后被隔离时，它们会表现出持久的不良行为和生理变化，类似于与压力相关障碍的症状。相比之下，当熟悉的大鼠一起饲养时，社会挫败的这些影响会大大降低。这些发现表明，饲养条件对雄性野生型大鼠社会挫败长期不良行为和生理影响的可能性有重要影响。
