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Sources of variation in HPG axis reactivity and individually consistent elevation of sex steroids in a female songbird.

ABSTRACT: Understanding sources of individual differences in steroid hormone production has important implications for the evolution of reproductive and social behaviors. In females in particular, little is known about the mechanistic sources of these individual differences, despite established linkages between sex steroids and a variety of fitness-related traits. Using captive female dark-eyed juncos (Junco hyemalis) from two subspecies, we asked how variation in different components of the hypothalamo-pituitary-gonadal (HPG) axis related to variation in testosterone production among females, and we compared females to males in multiple components of the HPG axis. We demonstrated consistent individual differences in testosterone elevation in response to challenges with luteinizing hormone (LH) and gonadotropin-releasing hormone (GnRH). These hormone challenges led to more LH production but less testosterone production in females than males, and the sexes differed in some but not all measures of sensitivity to hormones along the HPG axis. Similar to findings in males, variation in testosterone production among females was not related to variation in LH production, gonadal LH-receptor mRNA abundance, or hypothalamic abundance of androgen receptor mRNA or aromatase mRNA. Rather, the primary source of individual variation in circulating steroids appears to the gonad, a conclusion further supported by positive correlations between testosterone and estradiol production. Unlike males, females did not differ by subspecies in any of the endocrine parameters that we assessed, suggesting some degree of independent evolution between the two sexes. Our results highlight the sources of physiological variation that may underlie the evolution of hormone-mediated phenotypes in females.

SUBMITTER: Rosvall KA

PROVIDER: S-EPMC3852689 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature

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Sources of variation in HPG axis reactivity and individually consistent elevation of sex steroids in a female songbird.

Rosvall Kimberly A KA Bergeon Burns Christine M CM Hahn Thomas P TP Ketterson Ellen D ED

General and comparative endocrinology 20131001

Understanding sources of individual differences in steroid hormone production has important implications for the evolution of reproductive and social behaviors. In females in particular, little is known about the mechanistic sources of these individual differences, despite established linkages between sex steroids and a variety of fitness-related traits. Using captive female dark-eyed juncos (Junco hyemalis) from two subspecies, we asked how variation in different components of the hypothalamo-p ...[more]

PMID: 24090613

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Project description:Affective disorders show sex-specific differences in prevalence, symptoms, and complications. One hypothesis for this discrepancy is the interaction between the hypothalamic-pituitary-adrenal (HPA) axis and hypothalamic-pituitary-gonadal (HPG) axis. The present study investigates the influence of androgen on the behavioral phenotype and explores how it interacts with HPA axis genes. Gonadectomized (GDX) and GDX rats treated with testosterone propionate (T) were tested for learned helplessness (LH) behavior and compared with tested controls (TC). Prefrontal cortex was used for analyses of HPG- axis-related genes (androgen receptor, (Ar); estrogen receptor-? (Er-?)) and HPA axis-related genes (corticotropin-releasing hormone, (Crh); glucocorticoid receptor, (Nr3c1); corticotropin-releasing hormone receptor 1, (Crhr1); corticotropin-releasing hormone receptor 2, (Crhr2); FK506 binding protein 5, (Fkbp5)). Promoter-specific CpG methylation in the Crh gene was determined by bisulfite sequencing. Chromatin immunoprecipitation (ChIP) assay was used for determining ER-? binding on the proximal promoter region of Crh gene. Serum testosterone levels confirmed a testosterone-depleted GDX group, a group with supraphysiological levels of testosterone (T) and another group with physiological levels of testosterone (control (C)). Unlike GDX rats, T group exhibited significantly higher LH score when compared with any other group. Crh and Fkbp5 genes were significantly upregulated in GDX group compared with controls, whereas Er-? showed a significant downregulation in the same group. Methylation analysis showed no significant differences in-between groups. ChIP assay was unable to determine a significant change in ER-? binding but revealed a notable contrast in Crh promoter occupancy between T and GDX groups. Altogether, the present study reveals an increased susceptibility to depression-like behavior due to chronic supraphysiological level of androgen via HPA axis inhibition.

Dataset Information

Sources of variation in HPG axis reactivity and individually consistent elevation of sex steroids in a female songbird.

Publications

Sources of variation in HPG axis reactivity and individually consistent elevation of sex steroids in a female songbird.

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