Editorial: Stressors in animals and humans - Practical issues and limitations

Stress e the physiological response to an environmental challenge is now a fundamental scientific, clinical and societal concept, which serves as testimony to the importance of its initial description by Hans Selye some 80 years ago (Fink, 2016; Selye, 1936). Whilst the stress response (and related states such as emotionality and arousal) is typically the focus of attention, in the present special issue of Neurobiology of Stress emphasis is placed on the environmental stimuli e the so-called stressors e that induce stress, emotionality and arousal. Stressors can be neurogenic (e.g. painful stimuli) or psychogenic (e.g. social stimuli) or a combination of the two; this issue comprises contributions that focus on psychogenic stressors. Stressors can already impact on mammals at the prenatal stage of development, and the first paper (M. Weinstock: Prenatal stressors in rodents: effects on behavior) presents a review of recent studies of maternal-gestational stressors and their longterm effects on offspring brain and behavior in mice and rats. Postnatally, environmental stressors can impact on the lactatingmother who in turn acts as a stressor on her dependent offspring. One majormaternal stressor is atypical maternal care andH. J. Krugers, J. M. Arp, H. Xiong, S. Kanatsou, S. L. Lesuis, A. Korosi, M. Joels and P. J. Lucassen review the evidence for this (Early life adversity: lasting consequences for emotional learning). They describe some of the various manipulations of maternal care that have been applied in controlled experiments in rodents, as well as the descriptive evidence for correlates of postnatal stress in humans, with emotional learning being the major dependent variable of interest across species. Another, complementary approach to the study of postnatal stressors is to increase levels of maternal corticosteroids (corticosterone in rodents). In his contribution, S. Macri (Neonatal corticosterone administration in rodents as a tool to investigate the maternal programming of emotional and immune domains) proposes that “this mother-offspring transfer mechanism can be leveraged to devise experimental protocols based on the exogenous administration of corticosterone during lactation”. He describes studies of neonatal corticosterone administration in rats and mice that have demonstrated programming of phenotypes with respect to emotionality and immune status. Of course, as emphasized by Selye, the organism's own hypothalamic-pituitary-adrenal (HPA) system is one of the major components of its stress response, and the final developmental contribution considers the major stressors that are used to investigate HPA stress responses and their consequences in adolescence and at puberty in rats. This topic is discussed in the contribution “Translational relevance of rodent models of hypothalamic-pituitary-adrenal function and stressors