Abstract
The African clawed frog (Xenopus laevis) has been an invaluable research tool for developmental biology, electrophysiology, biochemistry, and neurobiology for almost a century,1,2 yet literature on amphibian medicine and diagnostics is underrepresented.3 Because of this, disease in laboratory frogs is not well understood, nor are clinicians prepared to utilize and interpret diagnostics, such as imaging. Additionally, X. laevis are a sexually dimorphic species; however, phenotypic signs of sexual maturation can take 1 to 2 years to develop. The ability to sex juvenile frogs has the potential to improve colony management and reduce the number of animals used in research. Ultrasonography provides an easily accessible, noninvasive platform useful for both research and diagnostics, and has recently become more popular in aquatic medicine. Travelling easily through water and the external slime coat of the frog, ultrasound waves allow for easy identification of the majority of X. laevis coelomic organs. Needing only light anesthesia with tricaine methanesulfonate (MS-222), or gentle manual restraint, the normal size, echogenicity, and echotexture of heart, lungs, major arteries and veins, liver, gallbladder, stomach, gastrointestinal tract, kidneys, urinary bladder, and gonads were recorded in 4 adult males and 4 adult females. Half of the females were also imaged before and after hormonally induced ovulation, a noninvasive technique commonly used for egg harvesting in biomedical research. Electronic calipers were used to measure oocyte diameter, and results reflected the asynchrony of oogenesis in this species. Furthermore, juvenile animals (15–22 g) not yet old enough to be sexed by phenotypic characteristics, were imaged with ultrasound before being euthanized and necropsied to correlate the images with sex. This is the first report documenting baseline ultrasonographic anatomy of adult male and female X. laevis, with assessment of oocytes before and after ovulation, providing clinically relevant data for veterinarians and X. laevis investigators. These results also demonstrate the potential use of ultrasonography as an early and noninvasive way to sex juvenile X. laevis.
Acknowledgements
The authors thank Christian Dolf and Ferdinand Kaya for their respective expertise and technical assistance.
* Presenting author
+ Student presenter
Literature Cited
1. Segerdell E, Bowes JB, Pollet N, Vize PD. 2008. An ontology for Xenopus anatomy and development. BMC Dev Biol. 25:92.
2. Callery EM. 2006. There’s more than one frog in the pond: a survey of the amphibia and their contributions to developmental biology. Semin Cell Dev Biol. 17:80–92.
3. O’Rourke DP. 2007. Amphibians used in research and teaching. ILAR J. 48:183–187.