Neuroanatomical Correlates of Hormone Sensitive Behaviors in Frogs and Birds

Abstract

In this paper I review some aspects of neural and endocrine interactions in the control of reproductive behaviors of frogs and song birds. In Xenopus laevis , we have shown that castration will eliminate a male sex behavior, clasping, and that this behavior can be restored by the administration of exogenous testosterone or dihydrotestosterone but not by estradiol. This difference in hormone action is paralleled by differences in the locations of androgen and estrogen concentrating cells in the CNS of Xenopus . Certain brain regions contain autoradiographically demonstrable labelled cells only after the administration of tritiated testosterone; others only after estradiol injection. The possibility that label in a third group of nuclei, which contain radioactive steroid after either hormone, is due to metabolism of testosterone to estradiol is discussed. Studies in other anuran species have demonstrated that regions of hormone uptake are also involved in neural control of frog sex behavior. The song of oscine birds represents another hormone sensitive reproductive behavior whose neural control is probably inlluenced by the activity of hormone concentrating CNS cells. Some of the brain nuclei which comprise the efferent pathway for control of song in the canary have been shown to concentrate tritiated androgen in autoradiographic studies on song birds. The uptake of androgens by medullary motor neurons involved in the control of reproductively important vocalizations is common to anurans and oscine song birds. Whether this feature of hormone action on the CNS represents a special feature of the frog and bird brain or whether the phenomenon may also be present in other vertebrate groups awaits further investigation.