Attaining and maintaining strong vocal synapses in female Xenopus laevis

Abstract

Synaptic efficacy at the laryngeal neuromuscular synapse differs markedly in adult male and female Xenopus laevis. Here, we examined the relation between circulating estrogen and synapse strength in developing and adult female frogs. Circulating estrogen levels in males and females during juvenile and adult stages were measured using radioimmunoassays. Synaptic strength was determined by quantal analysis in isolated female larynges. In males, estrogen levels are low (<40 pg/mL) throughout development. In females, estrogen levels are similar to those in males until 9 months after metamorphosis is complete and then increase throughout development. Female laryngeal synapses have low quantal contents until 24 months; quantal content increases significantly between 24 and 26 months, and high quantal contents are maintained thereafter. Measures of reproductive maturation, ovary, and oviduct weights, are strongly and positively correlated with estrogen level in 16- to 26-month females, while oocyte maturation is age dependent. Estrogen level and quantal content are not well correlated in these females. Ovariectomy at 24 months prevents the expected increase in quantal content and ovariectomy at 28 months results in a decrease in quantal content. Thus, the sex difference in efficacy of the laryngeal synapse develops under the influence of the ovary and requires the ovary for maintenance of strong synapses in adulthood. While the influence of the ovary is most likely due to estrogen secretion, the pattern of estrogen secretion required for maturation of the synapse in females is not known.

Plasma sex steroid concentrations and gonadal aromatase activities in African clawed frogs (Xenopus laevis) from South Africa

“…These results indicate that NCGR frogs were still at the peak of their reproductive activity, and thus the differences in the absolute concentrations of plasma sex steroids measured in the study by Paolucci et al [35] and our study may be due to differences among species. In our study, males from the NCGR exhibited greater E2 concentrations than those reported for males from another study [41], but were similar to those in R. clamitans (control group) that were confined under laboratory conditions [42]. The reasons for these discrepancies are unknown.…”

Species-specific loss of sexual dimorphism in vocal effectors accompanies vocal simplification in African clawed frogs (Xenopus)

“…Rapid, intensity-modulated calls require an entirely fast-twitch complement of muscle fibers, and a weak and facilitating neuromuscular synapse responsible for EMG potentiation (Ruel et al, 1998;Tobias et al, 1998). Given the widespread rapidity and intensity modulation of male advertisement calls in Xenopus and Silurana (Tobias et al, 2011), an entirely fast-twitch complement of laryngeal muscle fibers and a facilitating synapse may also represent the male ancestral state.…”

Endocrine Toxicology

“…This results in the appearance of VTG in the plasma, vitellogenic oocytes in the ovary, and the development of the oviducts (Olmstead et al, 2009d). Oviduct development appears to be regulated by estrogens as development correlates with blood E2 levels in X. laevis (Tobias et al, 1998) and X. tropicalis (Olmstead et al, 2009d). Jelly coats are applied to the outside of oocytes as they pass through the oviduct and collect in the ovisac, ready for fertilization.…”