Meeting Abstract

P2.107  Friday, Jan. 4  Developmental changes in neural corticosteroid receptor capacity in altricial nestlings WADA, H.*; BREUNER, C.W.; Virginia Polytechnic Institute and State University; University of Montana haruka@vt.edu

The hypothalamo-pituitary-adrenal (HPA) axis is continuously controlled by negative feedback via corticosteroid receptors in hypothalamus and hippocampus areas, maintaining baseline levels as well as regulating the magnitude and duration of the adrenocortical response. Recent studies suggest that altricial nestlings do not respond to handling stress at early ages. We hypothesized that this low corticosterone secretion early in development may be a result of higher corticosteroid receptor (mineralocorticoid and glucocorticoid receptors; MR and GR) densities in hypothalamus and hippocampus. Thus we predicted that either MR or GR levels would be elevated in early development, increasing negative feedback and keeping glucocorticoid levels low. Using free-living white-crowned sparrow nestlings (Zonotrichia leucophrys nuttalli), we investigated the ontogenetic patterns of MR and GR in whole brain as well as specific regions of the brain in three ages of nestlings (days 1-3, 4-6, and 7-9). Supporting our prediction, whole brain MR capacity decreased with age. However, this decline in MR levels was driven entirely by a decline in cerebellar MR; no age-related changes were observed in hippocampal or hypothalamic areas. Hence, the low glucocorticoid reactivity of early staged nestlings does not appear to be driven by greater hippocampal or hypothalamic receptor number.