Detection of the Hormone Receptors Controlling the Female Genital Tract throughout the Sexual Cycle of an Oviparous Caecilian Amphibian, Boulengerula taitana

Aims: Hormonal control of the development of the oviducts, as inferred by the distribution of hormone receptors, is described for the first time in the oviparous caecilian, Boulengerula taitana (Gymnophiona: Herpelidae). A comparison is made with the aquatic viviparous caecilian, Typhlonectes compressicauda.

Study Design: The study was performed from histological sections of the left oviduct of three B. taitana females collected at different periods of the sexual cycle in the Taita Hills, Kenia, from April 2003 to March 2004. The hormone receptors were localized with indirect immunohistochemical method. Sixty counts were carried out per antibody and per season in the various parts of the oviduct. Analysis of variance (one-way ANOVA) and Fisher test (LSD) permitted to determine the significant differences between the groups (p≤ 0.05).

Place and Duration of Study: Sciences and Humanities Confluence research Center, UCLy, cedex 02, 69288 Lyon, France

Methodology: By using an immunohistochemical staining method, the specific receptors of steroid hormones (α- and β estrogen, progesterone) and pituitary hormones (gonadotropin, prolactin) were detected in the tissues of the ostium and the oviduct during the female sexual cycle.

Results: The number of immunostained cells reflects the sensitivity of each part of the genital tract to hormonal control, related to its physiological functions. The large number of progesterone receptors detected in tissues during the preovulation period implies the key role of progesterone in preparing the oviduct for ovulation. The two estrogen receptors are differently detected in the tissues, suggesting a specific physiological function of each isoform. The presence of pituitary hormone receptors in the cells during the reproductive period suggests direct control of these hormones on the development and functions of the genital tract. Similarities are observed in the neuroendocrine control of this oviparous species and the viviparous caecilian Typhlonectes compressicauda.

Conclusion: This study indicates the presence of steroid and pituitary hormone receptors in the genital tract of B. taitana, with variations closely related to the key events of seasonal reproductive activity, and confirm that oviduct morphology is closely correlated with ovarian function. A comparative study of the detection of these hormone receptors also revealed correspondence between the parts of the oviduct in the oviparous and the viviparous species T. compressicauda. Despite differences in reproductive mode, similarity in receptor distribution between the two species suggests conservative physiological control of the reproductive cycle in caecilians.