An integrated evaluation of costs and benefits of corticosterone secretion through development

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dc.contributor.advisorJansen, Roberten
dc.contributor.advisorBreuner, Creaghen
dc.creatorWada, Harukaen
dc.date.accessioned2008-08-28T23:25:19Zen
dc.date.available2008-08-28T23:25:19Zen
dc.date.issued2007en
dc.descriptiontexten
dc.description.abstractGlucocorticoids (GCs) play critical roles during development: transient increases in GCs facilitate anticipatory physiological changes and trigger ontogenetic transitions such as promoting fetal/embryonic organ maturation and initiating birth/hatching. In contrast, chronically elevated GCs can be detrimental to growth, cognition, and survival. Thus, animals going through substantial growth may have higher corticosteroid binding globulin (CBG) levels, or enhance negative feedback/tonic inhibition on the hypothalamic-pituitary-adrenal (HPA) axis to keep GCs levels low. Here I investigated these hypotheses using altricial white-crowned sparrow nestlings. I examined 1) the ontogeny of the corticosterone (CORT) response (both total and free hormone levels), 2) changes in corticosteroid receptor levels in brain with age, and 3) effects of acute and extended elevation of CORT on behavior and growth. In response to acute stress, nestlings showed a low HPA reactivity in total CORT during the first 1/3 of the nestling period. When free CORT is considered, this hyporesponsive period was extended to 2/3 of the nestling period, suggesting CBG is one of the mechanisms to keep free CORT low. These periods coincided with rapid mass gain and acquiring thermoregulatory ability. The low reactivity was partly due to a dampened sensitivity at pituitary level or higher as all stages of nestlings responded to adrenocorticotropic hormone challenges; however it was not due to an enhanced negative feedback/tonic inhibition on hypothalamus or hippocampus. When CORT levels were artificially elevated, I only observed detrimental effects on begging behavior and growth. These series of data elucidated the ontogeny of the HPA axis in altricial nestlings regarding CORT, binding globulin, and receptor levels. In addition, I found that measured effects of exogenous CORT are primarily costly and highly age-specific.
dc.description.departmentBiological Sciences, School ofen
dc.format.mediumelectronicen
dc.identifierb68671829en
dc.identifier.oclc166422211en
dc.identifier.urihttp://hdl.handle.net/2152/3067en
dc.language.isoengen
dc.rightsCopyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en
dc.subject.lcshCorticosteroneen
dc.subject.lcshGlucocorticoids--Receptorsen
dc.subject.lcshGrowth--Regulationen
dc.subject.lcshOntogenyen
dc.subject.lcshWhite-crowned sparrow--Growthen
dc.subject.lcshWhite-crowned sparrow--Behavioren
dc.titleAn integrated evaluation of costs and benefits of corticosterone secretion through developmenten
dc.type.genreThesisen

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