Effects of fadrozole on sexual displays and reproductive activity in the female canary

We used fadrozole, a potent inhibitor of the aromatization of androgens to estrogens, to investigate the influence of estradiol on copulation solicitation displays (CSD) and reproductive activity in female canaries (Serinus canaria). Systemic injections of fadrozole during 10 consecutive days were effective in reducing plasma estradiol concentrations in adult female canaries submitted to photostimulation. Fadrozole provides a powerful tool for limiting an individual's exposure to estradiol, and the results of this study emphasize the influence of estradiol secretion in the regulation of behavioral transitions along the reproductive cycle of the female canary. When females were injected at the beginning of photostimulation, the emergence of copulation solicitation displays in response to conspecific songs was delayed. When females were injected later, after they were sexually active, the fadrozole treatment did not affect sexual displays. These results are consistent with the hypothesis that a threshold level of estradiol is critical to activate the neural circuitry mediating the copulation solicitation displays response in the female canary. They also suggest that the magnitude of sexual response is not related in a dose-dependent manner to estrogen concentrations observed during the period of sexual responsiveness. When females were injected at the beginning of photostimulation, egg-laying was delayed; when females were injected later, after they were sexually active, the fadrozole treatment dramatically reduced egg-laying and prevented incubation. (C) 1998 Elsevier Science Inc.