title: Stress responses of testosterone and corticosterone-binding globulin in a multi-brooded species, Eurasian Tree Sparrows (Passer montanus): Does CBG function as a mediator?
abstract: In avian plasma, testosterone (T) and corticosterone (CORT) compete to bind with corticosterone-binding globulin (CBG). Elevation of CBG may function to "buffer" the tissues against high circulating levels of T and stress-induced levels of CORT. To demonstrate the effects of acute stress on CBG and T levels and their biological functions, we investigated seasonal changes of baseline and stress-induced T and CBG levels in Eurasian Tree Sparrows (Passer montanus) during different life stages using the capture-handling-restraint stress method. Our results show that (1) male sparrows had significantly higher baseline T levels and CBG capacities during the nest building, the first egg-laying, and the first nestling stages, and significantly decreased stress-induced T levels only during the nest building and the first egg-laying stages. They also expressed significantly increased stress-induced CBG capacities during the second nestling stage. (2) Females showed significantly higher baseline CBG capacities but significantly decreased stress-induced CBG capacities during the nest building stage, and females also showed significantly increased stress-induced CBG capacities during the second egg-laying and the second nestling stages. Therefore, the seasonal fluctuations of baseline CBG in both sexes and baseline T in males reflect their adaptive strategies for optimizing their physiological and behavioral states to the life history cycle. The different patterns of stress-induced CBG in females suggest CBG functions as an essential mediator in regulating stress response to unpredictable perturbations. Our results highlight the need for future studies of stress-induced CBG and T levels on a wide range of vertebrate species that vary in different life history stages to gain a full understanding of the mechanisms that underlie biological functions of CBG and T for unpredictable stressors.
authors.affiliation: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, PR China. lidngmng@gmail.com
authors.forename: Dongming
authors.initials: D
authors.lastname: Li
authors.forename: Xiaorui
authors.initials: X
authors.lastname: Zhang
authors.forename: Yaqing
authors.initials: Y
authors.lastname: Li
authors.forename: Chenyang
authors.initials: C
authors.lastname: Hao
authors.forename: Ji
authors.initials: J
authors.lastname: Zhang
authors.forename: Yuefeng
authors.initials: Y
authors.lastname: Wu
mesh_terms: D000818:Animals; D003345:Corticosterone / Q000097:blood* / Q000502:physiology; D003627:Data Interpretation, Statistical; D005260:Female; D008297:Male; D009425:Nesting Behavior; D017711:Nonlinear Dynamics; D010809:Physical Fitness; D012149:Restraint, Physical; D012621:Seasons; D046370:Sparrows / Q000502:physiology*; D013315:Stress, Psychological / Q000097:blood*; D013737:Testis / Q000033:anatomy & histology / Q000254:growth & development; D013739:Testosterone / Q000097:blood* / Q000502:physiology; D014156:Transcortin / Q000502:physiology*
chemical_list: D013739:Testosterone; D014156:Transcortin; D003345:Corticosterone