Meeting Abstract
Despite considerable empirical and theoretical work on stress physiology in free-living animals, the relationships between stress hormone receptor densities in the brain and concentrations of circulating hormones in the blood are underexplored empirically. Testing these associations is important because the use of established field assays including dexamethasone- and ACTH-challenge are often assumed to provide a proxy estimate for the neural expression of the two types of hormone receptors: mineralocoritcoid (MR) and glucocorticoid receptors (GR). Here we tested these assumptions and quantitatively examined the relationships among the density and distribution of MR and GR and plasma concentrations of corticosterone (CORT). To do this we used a population of great tits (Parus major) housed individually in semi-natural outdoor enclosures that were characterized for individual differences in stress physiology and behavior. We measured initial and stress-induced CORT, as well as negative feedback (dexamethasone challenge) and adrenal sensitivity (ACTH challenge). Receptors were quantified using radioactive in situ hybridization. We explored these links in two regions of interest, the hippocampus and paraventricular nucleus, areas known to be involved in HPA regulation. Furthermore, we developed the first MR/GR distribution map for P. major based on sampling of multiple regions of the brain. By analyzing this blood-brain dataset, we were able to test a set of hypotheses about the relationships between the physiological dynamics of the HPA axis and patterns of neuroendocrine receptor expression.
