The effects of aromatase and 5α-reductase inhibitors, antiandrogen, and sex steroids on Bidder's organs development and gonadal differentiation inBufo bufo tadpoles

Abstract

Embryos of toads (Bufo bufo) were treated with aromatase (4‐OHA) and 5α‐reductase (17βC) inhibitors, antiandrogen (CPA), estradiol‐17β, testosterone, and 5α‐dihydrotestosterone in order to study the role played by sex steroids in the development and sex differentiation of gonads. Test compounds were administered to tadpoles in water and morphometric and cytometric analyses were carried out on histological sections of the cephalic Bidder's organ (a rudimentary ovary) and of the gonadal region. In Bidder's organs, the number and size of oogonia and oocytes were modified by the treatments. However, the female commitment of the Bidder's organ occurs independently from steroid treatments that lead to an acceleration or slackening of the processes of proliferation and differentiation of oogonia. 4‐OHA and androgens caused various degrees of inhibition of ovarian differentiation, with gonads maintaining an undifferentiated condition. Estrogen provoked a shift of the sex ratio towards the female sex, yet slackened gonadal growth. 17βC accelerated ovarian differentiation in females while CPA enhanced gonadal differentiation in both sexes by promoting the germ and somatic cell proliferation. We suggest that sex hormones may have a local regulatory role in gonadal differentiation during early developmental stages. Furthermore, the strong tendency of Bidderian germ cells to develop in the oogenetic way regardless of sex genotype and steroid treatments, and the quantitative sex differences found in the control Bidder's organs and gonads, suggest that other factors (such as intracellular mechanisms) may be involved in the initial steps of the process of germ cell differentiation. J. Exp. Zool. 280:245–259, 1998. © 1998 Wiley‐Liss, Inc.

Patterns of Reproductive Isolation in Toads

“…Interestingly, 1.6% ( N  = 8) of hybrid males contained eggs in association with the Bidder's organ. The Bidder's organ is a unique organ present in male bufonids composed of rudimentary ovarian tissue that normally does not produce functional eggs [46].…”

The Bidder's organ of the toad Rhinella arenarum (Amphibia, Anura). Presence of steroidogenic enzymes

“…In Bufo ictericus , the structure of this organ is similar to a typical ovary, composed by a cortex with follicular cells and follicles in different stages of development and, also, a medulla containing blood vessels and cells pigmented with melanin (Farias et al, 2002). BO differentiation has been previously described by several authors (Beccari, '25; Ponse, '25, Ponse and Dovaz, '43; Vitale‐Calpe, '69; Petrini and Zaccanti, '98). BO develops in both sexes very early during the larval stage and prior to the first appearance of ovarian and testicular differentiation.…”

Exposure of Xenopus laevis tadpoles to finasteride, an inhibitor of 5-α reductase activity, impairs spermatogenesis and alters hypophyseal feedback mechanisms

“…The single finding of one female gonad without the forming of an ovarian cavity may be an effect of FIN, but has to be verified in future experiments. In tadpoles of Bufo bufo and Rana dalmatina, the inhibition of 5-a reductase activity accelerated the ovarian differentiation in females, suggesting an inhibiting role for 5-a-reduced metabolites regarding the timing of ovarian differentiation and maybe also for oocyte maturation in females (Zaccanti et al 1994, Petrini & Zaccanti 1998). However, this finding could not be confirmed in the present study.…”