Acute restraint stress does not alter corticosteroid receptors or 11β-hydroxysteroid dehydrogenase gene expression at hypothalamic-pituitary-adrenal axis regulatory sites in captive male white-crowned sparrows (Zonotrichia leucophrys gambelii)

Abstract

Capture-restraint is often used to investigate the acute hypothalamic-pituitary-adrenal axis (HPA) response to stress in wild and captive animals through the production of glucocorticoids. Although this approach is useful for understanding changes in glucocorticoids, it overlooks potential changes in the complex regulatory systems associated with the glucocorticoid response, including genomic receptors, steroid metabolizing enzymes, carrier proteins, and downstream target proteins (e.g. gonadotropin-inhibitory hormone; GnIH). The present study in captive male white-crowned sparrows (Zonotrichia leucophrys) tests the hypothesis that corticosteroid receptors (mineralocorticoid - MR and glucocorticoid - GR), 11β-hydroxysteroid dehydrogenase 1 (11βHSD1) and 2 (11βHSD2), corticosteroid binding globulin (CBG), and GnIH undergo rapid changes in expression to mediate the glucocorticoid response to acute stress. To determine dynamic changes in gene mRNA expression in the hippocampus, hypothalamus, pituitary gland, and liver, birds were sampled within 3 min of entering the room and after 10, 30, and 60 min of capture restraint stress in a cloth bag. Restraint stress handling increased CBG and decreased GnIH mRNA expression in the liver and hypothalamus, respectively. MR, GR, 11βHSD1, and 11βHSD2 mRNA expression in the brain, pituitary gland, and liver did not change. No correlations were found between gene expression and baseline or stress-induced plasma corticosterone levels. No rapid changes of MR, GR, 11βHSD1, and 11βHSD2 mRNA expression during a standardized acute restraint protocol suggests that tissue level sensitivity may remain constant during acute stressors. However, the observed rise in CBG mRNA expression could act to facilitate transport to target tissues or buffer the rise in circulating glucocorticoids. Further studies on tissue specific sensitivity are warranted.

Keywords: 11β Hydroxysteroid dehydrogenase (11βHSD1, 11βHSD2); Acute stress; Bird; Corticosteroid; Corticosterone; Corticosterone binding globulin (CBG); Glucocorticoid receptor; Gonadotropin-inhibitory hormone (GnIH); Hypothalamic-pituitary-adrenal (HPA) axis; Mineralocorticoid receptor.