DENVER, Robert/J; Univ. of Michigan, Ann Arbor: The Vertebrate Neuroendocrine Stress System and its Role in Orchestrating Life History Transitions

Animals make critical decisions at all stages of their life cycles. For example, the timing of metamorphosis, hatching or birth depends on the tradeoffs between growth opportunity and mortality risk in the developmental habitat. Physiological sensors compute these tradeoffs as a function of energy balance and environmental stress, and effectors initiate physiological, developmental and behavioral responses to these determinations. The neuroendocrine stress axis provides a means for animals to integrate information from multiple sources and to respond accordingly. We have focused on the role of stress hormones in life history transitions in animals with complex life cycles. The secretion of hormones critical to development (corticosteroid [CS] and thyroid hormones [TH]) may be controlled by a common neuroendocrine stress pathway involving corticotropin-releasing hormone (CRH). Hypothalamic CRH stimulates the production of both CS and TH, leading to accelerated metamorphosis. Similarly, in mammals, CRH of fetal or placental origin has been shown to influence the timing of birth. In amphibians, TH and CS synergize at the level of target tissues to promote metamorphosis. Thus, environmental stress results in changes in hormone secretion and hormone action at both central and peripheral sites, with the result that the timing of development is altered. The basic endocrine signaling components are evolutionarily conserved among vertebrates, and thus the integrated neuroendocrine response to stress, and its role in timing critical life history transitions, likely arose early in the evolution of vertebrates (supported by NSF grant IBN9974672).