Developmental changes in neural corticosteroid receptor binding capacity in altricial nestlings

Abstract

Altricial nestlings typically do not show an adrenocortical response during the early post-hatch period. This may be a result of an immature hypothalamic-pituitary-adrenal axis, or an enhanced control of the axis by negative feedback. To examine whether the dampened adrenocortical response is due to higher receptor densities in hypothalamus and hippocampus, the major sites for negative feedback and tonic inhibition, we explored the ontogenetic changes in glucocorticoid (GR) and mineralocorticoid receptor (MR) binding capacities in the brain of white-crowned sparrow nestlings. During the 10-day nestling period, MR binding capacity decreased with age, whereas GR capacity was not affected. In addition, this overall decline in MR levels was driven entirely by a decline in cerebellar MR. No age-related changes were observed in hippocampal or hypothalamic areas. Our findings suggest that enhanced negative feedback does not play a major role in the attenuated adrenocortical responses seen in white-crowned sparrow nestlings.

Chronic stress alters concentrations of corticosterone receptors in a tissue-specific manner in wild house sparrows (Passer domesticus)

“…Two intracellular receptors for CORT have been characterized in both mammals and birds -the high-affinity, low-capacity mineralocorticoid receptor (MR), found in relatively high The Journal of Experimental Biology 2602 concentrations in brain, kidney, liver and testes and in lower concentrations in other tissues (Breuner et al, 2003; Funder, 2005;Lattin et al, 2012b), and the low-affinity, high-capacity glucocorticoid receptor (GR), which appears practically ubiquitous, occurring in metabolic and immune tissues and throughout the brain (Ballard et al, 1974;Lattin et al, 2012b;Schmidt et al, 2010;Wada and Breuner, 2010). In mammals, MR seems primarily responsible for mediating baseline effects of CORT, whereas GR and MR work together to mediate the response to acute stress (De Kloet et al, 1998).…”

“…CORT receptors are ubiquitous throughout the body in both mammals (Ballard et al, 1974) and birds (Lattin et al, 2012b), and although CORT receptor dysregulation during chronic stress has only been examined in a few tissues, those studies suggest that receptors may provide insight into the transition from helpful to harmful CORT-mediated effects that occurs with chronic stress. For example, CORT receptor changes in brain areas such as the hippocampus may contribute to the attenuation of the negative feedback response in chronically stressed rats (Mizoguchi et al, 2003), and increased access of CORT to receptors in rat spleen may be part of the mechanism for chronic-stress-induced immunosuppression (Spencer et al, 1996).Two intracellular receptors for CORT have been characterized in both mammals and birds -the high-affinity, low-capacity mineralocorticoid receptor (MR), found in relatively high The Journal of Experimental Biology 2602 concentrations in brain, kidney, liver and testes and in lower concentrations in other tissues (Breuner et al, 2003; Funder, 2005;Lattin et al, 2012b), and the low-affinity, high-capacity glucocorticoid receptor (GR), which appears practically ubiquitous, occurring in metabolic and immune tissues and throughout the brain (Ballard et al, 1974;Lattin et al, 2012b;Schmidt et al, 2010;Wada and Breuner, 2010). In mammals, MR seems primarily responsible for mediating baseline effects of CORT, whereas GR and MR work together to mediate the response to acute stress (De Kloet et al, 1998).…”

Pharmacological characterization of intracellular glucocorticoid receptors in nine tissues from house sparrow (Passer domesticus)

“…MR-and GR-like receptors have also been characterized in several avian tissues, including brain [5,7,52], immune tissues [21,47], kidney [3,12] and intestine [19]. However, there are many peripheral tissues where CORT receptors have yet to be identified in birds.…”

“…It is not known if MR distribution in birds is similarly limited or if MR may play a different role in avian systems. Neural MR has very different distributions between mammalian and avian systems examined [52], hence there is precedent for non-homology in localization or function.…”

Dexamethasone treatment supports age‐related maturation of the stress response in altricial nestling birds

“…modifying factors; Wingfield ) may cause an energy imbalance mediated through an over‐activation of the HPA axis (i.e. allostatic overload type 2; McEwen and Wingfield ), resulting in chronic Cort elevations that potentially exert deleterious effects on critical traits such as growth, reproduction and neuronal function (Müllner et al , Angelier et al , Müller et al , Newman et al ).…”