[show abstract][hide abstract] ABSTRACT: In the frog, Xenopus laevis, castration or anti-androgen treatment during late tadpole or early juvenile stages blocks masculinization of vocal neuroeffectors in males while exogenous androgen or a testicular transplant masculinizes vocal neuroeffectors in females. To elucidate the relation between androgen secretion and the process of masculinization, we measured androgens by radioimmunoassay in adults, juveniles, and tadpoles. In adult females, values for both testosterone (T) and dihydrotestosterone (DHT) were essentially identical during the winter and the summer while in males, summer values for both androgens were 7 to 8x winter values. For DHT, circulating values in males significantly exceeded those in females in both winter and summer while for T, values differed significantly only in summer. Sex differences in circulating androgen arise at late juvenile stages (PM4 and PM5); T values are higher in males than in females and higher, for both sexes, in winter than in summer. During early juvenile stages (PM1-PM3), there were no seasonal or sex differences in circulating androgens. While androgens were detected in liver during late tadpole stages (stage 56-66), no sex differences were apparent. Androgens can be detected in tadpole tissues, as early as tadpole stage 47. delta 5-3 beta-Hydroxysteroid dehydrogenase (HSD) histochemistry indicates that tadpole gonads and interrenals (and, to a much lesser extent, kidneys) are the only tissues capable of steroid biosynthesis. Interrenal HSD activity was present throughout tadpole development; in gonads, activity began before sexual differentiation. Thin-layer chromatographic separation of steroid metabolites following in vitro incubation with radioactive precursors indicated that the interrenals were more active than the gonads in tadpoles but not in juveniles. Thus, interrenals and gonads of developing X. laevis can synthesize delta 4 steroids (which include androgens) and, from early tadpole stages, are capable of metabolizing pregnenolone and testosterone, early and late compounds in the steroid synthetic pathway, respectively. The absence of dramatic sex differences in T or DHT levels during late tadpole and early juvenile stages suggests that while necessary, androgen secretion is not sufficient for masculinization of vocal neuroeffectors.
General and Comparative Endocrinology 01/1996; 100(3):293-307. · 2.82 Impact Factor
[show abstract][hide abstract] ABSTRACT: The relative contributions of innervation and androgen to three muscle fiber properties--twitch type, size, and number--were examined in the sexually dimorphic, androgen-sensitive laryngeal muscle of Xenopus laevis. In adults, the muscle contains all fast-twitch fibers in males and fast- and slow-twitch fibers in females; laryngeal muscle fibers are larger and more numerous in males than in females. Juvenile larynges are female-like in both sexes; male laryngeal muscle is subsequently masculinized by androgen secretion during postmetamorphic development. Because both laryngeal motor neurons and muscle fibers are androgen sensitive during masculinization, we examined the role of the nerve in androgen-regulated muscle fiber development. Laryngeal muscle of male and female juvenile frogs was unilaterally denervated, and effects on muscle fiber type, size, and number were examined 4 weeks later. Half of the frogs received a dihydrotestosterone pellet at the time of denervation. Androgen treatment converts laryngeal muscle from mixed slow and fast to all fast twitch in both innervated and denervated muscle. Thus, the nerve is not required for androgen-regulated fiber type expression in either sex. Denervation produces muscle fiber atrophy and androgen treatment induces muscle fiber hypertrophy in male and female larynx. Nerve and hormone effects are independent and additive; fiber size in androgen-treated denervated muscle is greater than in untreated innervated muscle, and fiber size in androgen-treated denervated muscle is smaller than in androgen-treated innervated muscle. There is no sex difference in the effects of innervation or androgen on fiber size. Denervation causes laryngeal muscle fiber loss in males but not in females. Androgen treatment protects male laryngeal muscle from denervation-induced fiber loss and causes fiber addition in innervated female laryngeal muscle. We conclude that there is a sexually dimorphic interaction between innervation and androgen in control of laryngeal muscle fiber number.
Journal of Neuroscience 02/1993; 13(1):324-33. · 6.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Three laryngeal properties associated with the production of masculine song--laryngeal muscle tension, fiber twitch type, and fiber recruitment--are markedly sexually dimorphic in adult Xenopus laevis frogs. To elucidate the pattern of sexual differentiation, tension and fiber recruitment in male and female larynges and fiber twitch type in male larynges were examined throughout postmetamorphic development. Masculinization of male laryngeal properties begins early in postmetamorphic development and continues until adulthood. In contrast, tension and fiber recruitment in females do not change after the end of metamorphosis. Laryngeal muscle tension and fiber type are gradually and progressively masculinized; the temporal pattern of masculinization is very similar for these properties. Fiber recruitment, on the other hand, appears to masculinize in a stepwise manner. Masculinization of all three properties is highly correlated with larynx weight in males. We have used this relation to divide postmetamorphic development into seven stages associated with key events in sexual differentiation. This staging scheme provides an important experimental tool for studying the hormonal regulation of sexual differentiation, the subject of the accompanying paper.
[show abstract][hide abstract] ABSTRACT: Temporal constraints on androgen regulated masculinization of three sexually dimorphic laryngeal properties—tension, fiber type, and fiber recruitment—were examined in Xenopus laevis frogs. Endocrine state was manipulated at PM0 when the larynx is similar in males and females, at PM2 when the larynx begins sexual differentiation, and at PM6 when sexual differentiation is complete. Removing the testes in developing males (PM0 or PM2) completely arrests laryngeal masculinization. Masculinization resumes when testosterone is replaced later in development (PM2 or PM6, respectively). Thus, testicular secretions, in particular androgens, are required for laryngeal masculinization. The ability of androgens to masculinize tension, fiber type, and fiber recruitment in developing and adult larynges was also determined. Five weeks of testosterone treatment in PM0 or PM2 males and females completely masculinizes laryngeal tension and fiber type, but only partially masculinizes fiber recruitment. However, fiber recruitment can be fully masculinized in PM6 males castrated at PM2. We conclude that androgen induced masculinization of tension and fiber type are not temporally constrained but that androgen induced masculinization of fiber recruitment is. Prolonged androgen treatment can override the temporal constraints on masculinization of the larynx. Testosterone treatment for more than 6 months fully masculinizes fiber recruitment in developing (PM0 or PM2) females. In addition, prolonged treatment (>9 months) completely masculinizes tension, fiber type, and fiber recruitment in adult females; these properties were not fully masculinized by shorter (1–3 months) treatments in adult females. Testosterone induced masculinization in females is maintained for up to 8 months following testosterone removal; thus androgen effects are long lasting and possibly permanent.
[show abstract][hide abstract] ABSTRACT: The number of muscle fibers in the vocal organ of the adult male African clawed frog, Xenopus laevis, exceeds that of adult females. This sex difference is the result of rapid fiber addition in males between the end of metamorphosis, post-metamorphic stage 0 (PM0) and PM2. At PM0, male and female frogs have similar numbers of laryngeal muscle fibers. Males then add more muscle fibers than females and achieve an adult value that is 1.7 times the female number. Males castrated at PM0 have the same fiber number as females. Ovariectomy at PM0 does not alter muscle fiber addition in females. Gonadectomy at PM2 has no effect on fiber addition in either sex. Females attain masculine muscle fiber number if their ovaries are replaced with a testis at metamorphosis. Exogenous testosterone treatment at PM0 significantly increases fiber number in females but not in males. Exogenous testosterone given at PM2 has no effect on fiber number in females but decreases fiber number in males. We conclude that the testes are necessary for the marked addition of laryngeal muscle fibers seen in male X. laevis between PM0 and PM2. The masculine pattern of muscle fiber addition can be induced in females provided with a testis. Androgen secretion from the testes most probably accounts for masculinization of laryngeal muscle fiber number. After PM2, androgens are no longer necessary for muscle fiber addition and cannot increase fiber number in females.
Development 12/1990; 110(3):703-11. · 6.21 Impact Factor