Meeting Abstract
The study of sexually differentiated behaviors has focused on the effects of gonadal steroids during development, but the degree to which behaviors retain hormone-dependent plasticity is variable across behaviors and species. African clawed frogs (Xenopus laevis) produce rhythmic, sexually differentiated mating calls driven by a serotonin-dependent hindbrain central pattern generator (CPG). Male courtship vocalizations require circulating androgens. Sexually mature female Xenopus develop male-typical calling when treated with androgens. We wish to determine the hormonal and neuronal mechanisms that underlie this behavioral plasticity in Xenopus. Whole-cell recordings in the vocal CPG identified premotor neurons in T treated female brains with activity closely resembling that of “Fast Trill Neurons”. These cells, previously identified in male brains, spike in patterns closely correlated with masculinized vocal behavior. This finding supports our hypothesis that Fast Trill Neurons, and their female precursors, are essential targets of androgen-mediated behavioral changes. Masculinization of the vocal CPG begins rapidly in response to testosterone; however, testosterone is the primary circulating ovarian steroid. We explored whether the effects of testosterone treatment differed in ovariectomized versus non-ovariectomized females. We found that call rates were similar at all time points across treatments, independent of serum testosterone concentration. Future work is required to determine if masculinization occurs in response to sustained elevation of T, or in response to supraphysiological concentrations of T. Regardless of the outcome, Xenopus vocal behavior is an excellent system for assessing the mechanisms that underlie steroid-dependent plasticity in adult vertebrates.
