Abstract
Individuals exposed to social stress in childhood are more predisposed to developing psychoemotional disorders in adulthood. Here we use an animal model to determine the influence of hostile social environment in adolescence on behavior during adult life. One-month-old adolescent male mice were placed for 2 weeks in a common cage with an adult aggressive male. Animals were separated by a transparent perforated partition, but the adolescent male was exposed daily to short attacks from the adult male. After exposure to social stress, some of the adolescent mice were placed for 3 weeks in comfortable conditions. Following this rest period, stressed young males and adult males were studied in a range of behavioral tests to evaluate the levels of anxiety, depressiveness, and communicativeness with an unfamiliar partner. In addition, adult mice exposed to social stress in adolescence were engaged in agonistic interactions. We found that 2 weeks of social stress result in a decrease of communicativeness in the home cage and diminished social interactions on the novel territory. Stressed adolescents demonstrated a high level of anxiety in the elevated plus-maze test and helplessness in the Porsolt test. Furthermore, the number of dividing (BrdU-positive) cells in the subgranular zone of the dentate gyrus was significantly lower in stressed adolescents. After 3 weeks of rest, most behavioral characteristics in different tests, as well as the number of BrdU-positive cells in the hippocampus, did not differ from those of the respective control mice. However, the level of anxiety remained high in adult males exposed to chronic social stress in childhood. Furthermore, these males were more aggressive in the agonistic interactions. Thus, hostile social environment in adolescence disturbs psychoemotional state and social behaviors of animals in adult life.
Highlights
Upon exposure to social stress, adolescents are at a greater risk than individuals of other age groups to develop psychoemotional disorders, such as heightened anxiety or depression [1,2,3]
Our results demonstrate that hostile social environment in adolescence compromises the psychoemotional state and social behavior of the animals in adulthood
Considering the psychogenic factors acting on the SDS and PS adolescents in our experimental paradigms, we found that for SDS adolescents, daily agonistic interactions with adult aggressive males resulted in social defeat stress; in other words, hostile social environment was revealed as a critical factor in our experiments
Summary
Upon exposure to social stress, adolescents are at a greater risk than individuals of other age groups to develop psychoemotional disorders, such as heightened anxiety or depression [1,2,3]. In male rats, social instability stress alters cell proliferation in the hippocampal dentate gyrus in adolescence and produces deficits in spatial location memory in adulthood [8]; it results in persistent alterations of hypothalamus-pituitary-adrenal axis function and increased anxiety [9]. Chronic restraint stress during adolescence affects basal corticosterone levels and decreases neurogenesis in the dentate gyrus of adult female rats [10], suggesting that stress during adolescence has long-term consequences for hypothalamicpituitary-adrenal axis function and hippocampal plasticity in adulthood. Chronic mixed-modality stressor (consisting of isolation, restraint and social defeat stress) during adolescence has been shown to result in different and sustained changes leading to depressive-like behavior in rats: stressed animals display decreased sucrose consumption, hyperactivity in the elevated plus-maze, and decreased activity in the forced swim test during both adolescence and adulthood [12]. It has been shown that effects of early stress and its consequences may depend on species, sex and strain of animals [10,11,13,16,17]
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