Animal Models of Social Stress: Implications for the Study of Stress Related Pathologies in Humans

Many of the challenges and threats human beings face in life are directly or indirectly related to the way they interact with each other, the relationships between people, and the “positions” individuals occupy in the society. It is probably not far off the truth to say that social interactions are one of the most important sources of stress in a human life. This may vary from mild stress induced by quarrels in the family or interactions at the work place, to more serious forms of stress associated with aggression, rape, conflicts and war. Although primarily stress is a functional response of the body that allows an individual to deal with a challenge, it is well known that especially uncontrollable stressors may ultimately result in disease. Our current understanding of the mechanisms underlying stress-related disorders in humans owes a lot to the experimental data obtained in a wide variety of animal models. Notwithstanding, laboratory stress models often suffer from scarce resemblance to the challenges encountered by animals and human beings in real life. For this reason, increasing our knowledge about stress and stress-related disorders may be linked to the use of more naturalistic experimental paradigms. Accordingly, recent years have shown a growing interest in models based on social interactions as an approach to learn about stress pathology, a development that was reflected in two focused symposia in 2001. The first was held in Parma, Italy, and resulted in a special issue of the international journal Physiology and Behavior (Vol. 73(3), June 2001), containing a thorough description of the acute and longterm effects of social stress on various physiological and behavioural parameters. The second symposium, “Animal models of social stress: implications for the study of stress related pathologies in humans”, was held in September during the Third World Congress on Stress in Dublin, Ireland, and resulted in this themed issue of Stress. The present series of articles is meant to give the reader an understanding of the widespread and serious consequences of stressful social interactions, effects that range from changes in neuronal activity to alterations in behaviour. Also, the papers deal with social stress in different animal species (from rodents to tree shrews and primates) and different social stress regimens (acute, intermittent, and chronic exposure to social stimuli). The first paper by Manuela Martinez and colleagues reviews the effects of social defeat on neuronal activity in the rat brain, particularly by measuring the expression of the immediate early gene c-fos. The review not only discusses neuronal activation in response to an acute social challenge but also deals with adaptational processes in the brain when animals are exposed to social stress repeatedly. Although further research is necessary to understand the meaning of the changes in the brain activity, studies such as these may ultimately provide important insights in the cognitive and behavioural consequences of social stress. In addition, the data may provide insights into the changes and adaptation of peripheral stress responses observed after repeated social defeat and subordination. The second article by Peter Meerlo and colleagues reviews the effects of social defeat stress on the expression of circadian rhythms in rats, and compares such effects with those produced by other, non-social challenges. One important implication of the data presented is that even a single short-lasting social stressor can produce physiological and behavioural changes that last for several days up to weeks. Although social defeat and other stressors do not seem to disturb the biological clock in the suprachiasmatic nucleus of the hypothalamus directly,