Journal of Neuroscience, Vol 7, 3198-3206, Copyright © 1987 by Society for Neuroscience
Androgen regulation of muscle fiber type in the sexually dimorphic larynx of Xenopus laevis
DA Sassoon, GE Gray and DB Kelley
Department of Biological Sciences, Columbia University, New York, New York 10027.
We used histochemical techniques [assays for adenine triphosphatase
(ATPase) and succinate dehydrogenase (SDHase) activity] to identify muscle
fiber types in the larynx of Xenopus laevis. Male muscle is made up of one
fiber type, medium-sized fibers (approximately 9 microns2) that stain
lightly for acid-stable ATPase and intensely for SDHase activity. In
contrast, the female has 3 fiber types: small fibers (approximately 6
microns2) that stain intensely for ATPase and SDHase, medium-sized fibers
(approximately 13 microns2) with moderate staining for ATPase and dark
staining for SDHase, and large fibers (approximately 15 microns2) with
little SDHase or ATPase activity. Long- term castration (6 months) has no
effect on histochemical staining of adult male fibers. Long-term
testosterone treatment (5 months) increases the proportion of medium-sized,
moderately staining fibers in adult females, and reduces the proportion of
both the small, darkly staining fibers and the large, lightly staining
fibers. At metamorphosis, both males and females have 3 fiber types whose
ATPase activity is similar to that of the adult female. However, no SDHase
activity is observed. Treatment of juveniles for 3 weeks with testosterone
results in nearly complete masculinization of muscle fibers, as judged by
increased cross-sectional area, homogeneous ATPase staining, and a marked
increase in SDHase activity. Thus, juvenile muscle is considerably more
responsive to testosterone than is adult female muscle. We propose that the
uniform metabolic properties of male laryngeal muscle contribute to the
production of the rapid (66 Hz) mate call vocalizations characteristic of
this species. Further, our results suggest that androgens direct the
masculinization of laryngeal muscle fibers during postmetamorphic
development.
Previous Article | Next Article
