There are clear sex differences in incidence and onset of stress-related and other psychiatric disorders in humans. Yet, rodent models for psychiatric disorders are predominantly based on male... Show moreThere are clear sex differences in incidence and onset of stress-related and other psychiatric disorders in humans. Yet, rodent models for psychiatric disorders are predominantly based on male animals. The strongest argument for not using female rodents is their estrous cycle and the fluctuating sex hormones per phase which multiplies the number of animals to be tested. Here, we will discuss studies focused on sex differences in emotionality and cognitive abilities in experimental conditions with and without stress. First, female sex hormones such as estrogens and progesterone affect emotions and cognition, contributing to sex differences in behavior. Second, females respond differently to stress than males which might be related to the phase of the estrous cycle. For example, female rats and mice express less anxiety than males in a novel environment. Proestrus females are less anxious than females in the other estrous phases. Third, males perform in spatial tasks superior to females. However, while stress impairs spatial memory in males, females improve their spatial abilities, depending on the task and kind of stressor. We conclude that the differences in emotion, cognition and responses to stress between males and females over the different phases of the estrous cycle should be used in animal models for stress-related psychiatric disorders. Show less
Claessens, S.E.F.; Daskalakis, N.P.; Veen, R. van der; Oitzl, M.S.; Kloet, E.R. de; Champagne, D.L. 2011
Human epidemiology and animal studies have convincingly shown the long-lasting impact of early life experiences on the development of individual differences in stress responsiveness in later life.... Show moreHuman epidemiology and animal studies have convincingly shown the long-lasting impact of early life experiences on the development of individual differences in stress responsiveness in later life. The interplay between genes and environment underlies this phenomenon.We provide an overview of studies investigating the impact of early life experiences on the development of individual differences in neuroendocrine stress responsiveness in adulthood and address (1) impact of environment on later stress phenotypes, (2) role of genetic factors in modulating the outcome of environment, and (3) role of nonshared environmental experience in the outcome of gene x environment interplays. We present original findings where we investigated the influence of nonshared experiences in terms of individual differences in maternal care received, on the development of stress phenotype in later life in rats.Environmental influences in early life exert powerful effects on later stress phenotypes, but they do not always lead to expression of diseases. Heterogeneity in response is explained by the role of particular genetic factors in modulating the influence of environment. Nonshared experiences are important in the outcome of gene x environment interplays in humans. We show that nonshared experiences acquired through within-litter variation in maternal care in rats predict the stress phenotype of the offspring.The outcome of early experience is not deterministic and depends on several environmental and genetic factors interacting in an intricate manner to support stress adaptation. The degree of "match" and "mismatch" between early and later life environments predicts resilience and vulnerability to stress-related diseases, respectively. Show less
