Androgen Biosynthesis and Secretion in Developing Xenopus laevis

Kang, Lydia; Marin, Melanie L.; Kelly, Darcy

doi:10.1006/gcen.1995.1160

Cited by 46 publications

(25 citation statements)

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“…Hayes et al (2002) argued that changes in circulating or whole body testosterone reflect an alteration in aromatase activity in atrazine-exposed Xenopus laevis . However, this cannot be taken as evidence that atrazine is altering aromatase expression because plasma hormone levels change dynamically from moment to moment and are subject to a host of variables (age, sex, season, time of day, and stress level) that are uncontrolled in environmental studies (Kang et al , 1995). Other studies have failed to observe a relationship between triazine exposure and testosterone levels in wild-caught Xenopus laevis (Hecker et al , 2004).…”

Section: Resultsmentioning

confidence: 99%

Atrazine and Breast Cancer: A Framework Assessment of the Toxicological and Epidemiological Evidence

Simpkins¹,

Swenberg

Weiss

et al. 2011

Toxicological Sciences

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The causal relationship between atrazine exposure and the occurrence of breast cancer in women was evaluated using the framework developed by Adami et al. (2011) wherein biological plausibility and epidemiological evidence were combined to conclude that a causal relationship between atrazine exposure and breast cancer is “unlikely”. Carcinogenicity studies in female Sprague-Dawley (SD) but not Fischer-344 rats indicate that high doses of atrazine caused a decreased latency and an increased incidence of combined adenocarcinoma and fibroadenoma mammary tumors. There were no effects of atrazine on any other tumor type in male or female SD or Fischer-344 rats or in three strains of mice. Seven key events that precede tumor expression in female SD rats were identified. Atrazine induces mammary tumors in aging female SD rats by suppressing the luteinizing hormone surge, thereby supporting a state of persistent estrus and prolonged exposure to endogenous estrogen and prolactin. This endocrine mode of action has low biological plausibility for women because women who undergo reproductive senescence have low rather than elevated levels of estrogen and prolactin. Four alternative modes of action (genotoxicity, estrogenicity, upregulation of aromatase gene expression or delayed mammary gland development) were considered and none could account for the tumor response in SD rats. Epidemiological studies provide no support for a causal relationship between atrazine exposure and breast cancer. This conclusion is consistent with International Agency for Research on Cancer’s classification of atrazine as “unclassifiable as to carcinogenicity” and the United States Environmental Protection Agency's classification of atrazine as “not likely to be carcinogenic.”

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Section: Resultsmentioning

confidence: 99%

Atrazine and Breast Cancer: A Framework Assessment of the Toxicological and Epidemiological Evidence

Simpkins¹,

Swenberg

Weiss

et al. 2011

Toxicological Sciences

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“…LM is weakly expressed in the larynx until after metamorphosis is complete, although androgen and androgen receptor are present from much earlier stages (Kang et al, 1995;Cohen and Kelley, 1996). In addition, expression of LM is largely unaffected by androgen when administered at stage 63, but increases twofold when DHT is administered at stage 66.…”

Section: Discussion Prolactin Secretion Opens Sensitive Period For Anmentioning

confidence: 92%

Prolactin opens the sensitive period for androgen regulation of a larynx-specific myosin heavy chain gene

et al. 1999

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The larynx of Xenopus laevis is a sexually differentiated vocal organ in which male muscle is entirely fast twitch and expresses high levels of a fast twitch myosin heavy chain gene, LM. Female muscle, however, is mostly slow twitch and expresses little LM. Androgen is unable to induce expression of LM until after metamorphosis is complete. The expression of LM during metamorphic and early postmetamorphic development parallels secretion and expression of the pituitary hormone prolactin. Here, we show that exposure to prolactin is neccessary to allow androgen‐induced LM expression in postmetamorphic froglets. In prolactin‐deprived animals, androgen‐induced changes in the contactile properties of laryngeal muscle are blocked, which prevents the rapid rates of muscle contraction required for males to produce courtship songs. Thus, prolactin opens the sensitive period for androgen‐induced LM expression in the larynx and controls the ability of male sex hormones to masculinize the vocal system both at the level of gene expression and vocal organ physiology. © 1999 John Wiley & Sons, Inc. J Neurobiol 41: 443–451, 1999

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“…Immediately after ovary removal, T-filled (4-androsten-17␤-ol-3-one, Sigma Aldrich T-1500) silastic tubes (2.16 OD ϫ 1.02 ID; 0.5 mg/g body weight) were implanted into the ventral lymph sacs of 30 females. This treatment is known to elevate plasma levels of T from female-typical levels (1.1 ϳ 2.3 ng/ml) (Kang et al 1995) to very high levels (44 ng/ml) (Watson and Kelley 1992), about 70% higher than those of reproductively receptive males (26 ng/ml) (Kang et al 1995) for Ͼ1 yr (Watson and Kelley 1992). The remaining seven ovariectomized females were implanted with empty silastic tubes (2 cm long, ends sealed with silicone elastomer) as controls.…”

Section: Gonadectomy and T Implantsmentioning

confidence: 99%

Androgen-Induced Vocal Transformation in Adult Female African Clawed Frogs

Potter

Bose

Yamaguchi

2005

Journal of Neurophysiology

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. Sex-specific behaviors of some vertebrates are reversible by androgen administered in adulthood. Such behavioral transformations in adulthood provide opportunities to identify how neural systems reconfigure to produce sex-specific behavior. In this study, we focused on the vocalizations of the African clawed frog, Xenopus laevis. Male and female adult Xenopus produce sexually distinct vocalizations; males produce series of rapid clicks, whereas females produce slow trains of clicks. The differences in click rate can be reduced to differences in the firing rate of laryngeal motoneurons in vivo. This behavioral dimorphism is accompanied by various sex-specific characteristics throughout the vocal pathways, including functionally distinct laryngeal muscles and motoneurons in the sexes. In this study, we first determined whether and how testosterone (T) modifies the vocalizations of adult females and then examined changes underlying the behavioral modification at the laryngeal muscle and motoneuron levels. Our results show that, in response to T, the vocalizations of females were transformed within 13 wk. Vocal transformation was preceded by complete masculinization of muscle contractile properties and motoneuron soma size by the fourth week of T treatment, which suggests that the vocal pathways' peripheral components masculinize earlier than the behavior. Therefore the rate of transformation of vocal behavior must reflect a functional transformation of neurons in the central vocal pathways, which leads to the generation of male-like motor rhythms.

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Androgen Biosynthesis and Secretion in Developing Xenopus laevis

Cited by 46 publications

References 0 publications

Atrazine and Breast Cancer: A Framework Assessment of the Toxicological and Epidemiological Evidence

Atrazine and Breast Cancer: A Framework Assessment of the Toxicological and Epidemiological Evidence

Prolactin opens the sensitive period for androgen regulation of a larynx-specific myosin heavy chain gene

Androgen-Induced Vocal Transformation in Adult Female African Clawed Frogs

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