References of "Soma, Kiran K"
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See detailMultiple measures elucidate glucocorticoid responses to environmental variation in predation threat
Clinchy, Michael; Zanette, Liana; Charlier, Thierry ULg et al

in Oecologia (2011), 166

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See detailRapid effects of aggressive interactions on aromatase activity and oestradiol in discrete brain regions of wild male white-crowned sparrows
Charlier, Thierry ULg; Newman, Amy EM; Heimovics, Sarah A et al

in Journal of Neuroendocrinology (2011), 23

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See detail17β-estradiol levels in male zebra finch brain: combining Palkovits punch and an ultrasensitive radioimmunoassay
Charlier, Thierry ULg; Po, Kevin WL; Newman, Amy EM et al

in General and Comparative Endocrinology (2010), 167

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See detailEffects of aggressive encounters on plasma corticosteroid-binding globulin and its ligands in white-crowned sparrows.
Charlier, Thierry ULg; Underhill, Caroline; Hammond, Geoffrey L. et al

in Hormones & Behavior (2009), 56(3), 339-47

In birds, corticosteroid-binding globulin (CBG) binds corticosterone, progesterone and testosterone. The concentration of each ligand can alter the binding of the other ligands through competitive ... [more ▼]

In birds, corticosteroid-binding globulin (CBG) binds corticosterone, progesterone and testosterone. The concentration of each ligand can alter the binding of the other ligands through competitive interactions. Thus, an increase in corticosterone or progesterone may displace testosterone bound to CBG, leading to an increase in bioactive free testosterone levels without affecting total testosterone levels in the circulation. Aggressive interactions increase plasma total testosterone levels in some birds but not in others. Here, we tested the hypothesis that aggressive encounters in the late breeding season would not increase total testosterone levels in plasma, but would alter CBG, total corticosterone or total progesterone levels in such a way as to modify the number of available binding sites and therefore occupancy by testosterone. A marked decrease in CBG occupancy by testosterone would indirectly suggest an increase in free testosterone levels in plasma. Wild male white-crowned sparrows were exposed to a simulated territorial intrusion (STI) or control for 30 min. Subjects were then caught and bled. We measured CBG using a ligand-binding assay and corticosterone, progesterone and testosterone using highly sensitive radioimmunoassays. STI significantly increased aggressive behaviors but did not affect plasma total testosterone levels. STI significantly increased plasma CBG and total corticosterone levels and decreased plasma total progesterone levels. We predict that CBG occupancy by corticosterone will increase slightly following an aggressive encounter. However, this small change is unlikely to increase free testosterone levels, because of the large number of seemingly unoccupied CBG binding sites in these subjects. [less ▲]

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See detailNeurosteroids, immunosteroids, and the Balkanization of endocrinology.
Schmidt, Kim L; Pradhan, Devaleena S; Shah, Amit H et al

in General and Comparative Endocrinology (2008), 157(3), 266-74

Traditionally, the production and regulation of steroid hormones has been viewed as a multi-organ process involving the hypothalamic-pituitary-gonadal (HPG) axis for sex steroids and the hypothalamic ... [more ▼]

Traditionally, the production and regulation of steroid hormones has been viewed as a multi-organ process involving the hypothalamic-pituitary-gonadal (HPG) axis for sex steroids and the hypothalamic-pituitary-adrenal (HPA) axis for glucocorticoids. However, active steroids can also be synthesized locally in target tissues, either from circulating inactive precursors or de novo from cholesterol. Here, we review recent work demonstrating local steroid synthesis, with an emphasis on steroids synthesized in the brain (neurosteroids) and steroids synthesized in the immune system (immunosteroids). Furthermore, recent evidence suggests that other components of the HPG axis (luteinizing hormone and gonadotropin-releasing hormone) and HPA axis (adrenocorticotropic hormone and corticotropin-releasing hormone) are expressed locally in target tissues, potentially providing a mechanism for local regulation of neurosteroid and immunosteroid synthesis. The balance between systemic and local steroid signals depends critically on life history stage, species adaptations, and the costs of systemic signals. During particular life history stages, there can be a shift from systemic to local steroid signals. We propose that the shift to local synthesis and regulation of steroids within target tissues represents a "Balkanization" of the endocrine system, whereby individual tissues and organs may become capable of autonomously synthesizing and modulating local steroid signals, perhaps independently of the HPG and HPA axes. [less ▲]

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See detailDevelopment of a technique to measure 17β-estradiol in discrete brain regions in zebra finch
Charlier, Thierry ULg; Po, Kelvin WL; Shah, Amit H et al

Poster (2008)

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See detailEffect of aggressive interactions on aromatase activity in discrete brain regions in wild male white-crowned sparrows
Charlier, Thierry ULg; Newman, Amy EM; Soma, Kiran K

Poster (2008)

Testosterone (T) is a critical endocrine factor involved in the activation of aggressive behaviors. In many vertebrate species, circulating T levels rapidly increase after aggressive encounters during the ... [more ▼]

Testosterone (T) is a critical endocrine factor involved in the activation of aggressive behaviors. In many vertebrate species, circulating T levels rapidly increase after aggressive encounters during the breeding season. In contrast, we recently showed that circulating T concentrations did not change in white-crowned sparrows in the late breeding season after simulated territorial intrusions. We suggested that changes in local metabolism of T might be more important than changes in systemic T levels. Neural aromatization of T into 17􀀁-estradiol (E2) often mediates the physiological and behavioral actions of T. In vertebrates, aromatase is expressed in several discrete brain regions. We hypothesized that in the late breeding season, brain aromatase is rapidly modulated after aggressive interaction, leading to changes in local concentrations of E2. Wild male white-crowned sparrows were exposed to simulated territorial intrusion with song playback and decoy (STI) or control (CON) for 30 min. STI significantly increased aggressive behaviors. Birds were then caught, rapidly bled and sacrificed. Brains were collected and rapidly frozen on dry ice. We used 0.9 mm diameter punches from 300 μm coronal sections to isolate 13 different brain nuclei. Aromatase activity was analyzed in punches from the left side of the brain, while E2 was analyzed in punches from the right side of the brain. Aromatase activity was quantified by measuring the release of tritiated water during aromatization of [1􀀁-3H]-androstenedione. As expected, aromatase activity was high in the medial preoptic area, ventromedial nucleus of the hypothalamus, hippocampus, bed nucleus of the stria terminalis, nucleus taeniae of the amygdala, and caudomedial nidopallium. Aromatase activity was low in the medial magnocellular nucleus of anterior nidopallium, HVC, Area X, nucleus robustus of the arcopallium, optic lobes, periaqueductal gray and cerebellum. Aromatase activity was not different between the STI and CON groups in any region. There were no significant correlations between aromatase activity and aggressive behaviors or endocrine measures (plasma T, progesterone, corticosterone and corticosteroid binding globulin). These data provide no evidence for rapid modulation of brain aromatase activity following aggressive interactions. It is however possible that aromatase activity is more rapidly modulated (e.g. within 5 min) and these changes were not observed in our 30 min paradigm. We are currently investigating whether local E2 is affected by aggressive interactions. [less ▲]

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See detailNovel mechanisms for neuroendocrine regulation of aggression.
Soma, Kiran K; Scotti, Melissa-Ann L; Newman, Amy E M et al

in Frontiers in Neuroendocrinology (2008), 29(4), 476-89

In 1849, Berthold demonstrated that testicular secretions are necessary for aggressive behavior in roosters. Since then, research on the neuroendocrinology of aggression has been dominated by the paradigm ... [more ▼]

In 1849, Berthold demonstrated that testicular secretions are necessary for aggressive behavior in roosters. Since then, research on the neuroendocrinology of aggression has been dominated by the paradigm that the brain receives gonadal hormones, primarily testosterone, which modulate relevant neural circuits. While this paradigm has been extremely useful, recent studies reveal important alternatives. For example, most vertebrate species are seasonal breeders, and many species show aggression outside of the breeding season, when gonads are regressed and circulating testosterone levels are typically low. Studies in birds and mammals suggest that an adrenal androgen precursor-dehydroepiandrosterone (DHEA)-may be important for the expression of aggression when gonadal testosterone synthesis is low. Circulating DHEA can be metabolized into active sex steroids within the brain. Another possibility is that the brain can autonomously synthesize sex steroids de novo from cholesterol, thereby uncoupling brain steroid levels from circulating steroid levels. These alternative neuroendocrine mechanisms to provide sex steroids to specific neural circuits may have evolved to avoid the "costs" of high circulating testosterone during particular seasons. Physiological indicators of season (e.g., melatonin) may allow animals to switch from one neuroendocrine mechanism to another across the year. Such mechanisms may be important for the control of aggression in many vertebrate species, including humans. [less ▲]

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See detailEffect of aggressive encounters on plasma progesterone, corticosterone and corticosteroid binding capacity
Charlier, Thierry ULg; Hammond, Geoffrey L; Soma, Kiran K

Poster (2007)

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