Neuroanatomical Correlates of Hormone Sensitive Behaviors in Frogs and Birds

In this paper I review some aspects of neural and endocrineinteractions in the control of reproductive behaviors of frogsand song birds. In Xenopus laevis, we have shown that castrationwill eliminate a male sex behavior, clasping, and that thisbehavior can be restored by the administration of exogenoustestosterone or dihydrotestosterone but not by estradiol. Thisdifference in hormone action is paralleled by differences inthe locations of androgen and estrogen concentrating cells inthe CNS of Xenopus. Certain brain regions contain autoradiographicallydemonstrable labelled cells only after the administration oftritiated testosterone; others only after estradiol injection.The possibility that label in a third group of nuclei, whichcontain radioactive steroid after either hormone, is due tometabolism of testosterone to estradiol is discussed. Studiesin other anuran species have demonstrated that regions of hormoneuptake are also involved in neural control of frog sex behavior.The song of oscine birds represents another hormone sensitivereproductive behavior whose neural control is probably inlluencedby the activity of hormone concentrating CNS cells. Some ofthe brain nuclei which comprise the efferent pathway for controlof song in the canary have been shown to concentrate tritiatedandrogen in autoradiographic studies on song birds. The uptakeof androgens by medullary motor neurons involved in the controlof reproductively important vocalizations is common to anuransand oscine song birds. Whether this feature of hormone actionon the CNS represents a special feature of the frog and birdbrain or whether the phenomenon may also be present in othervertebrate groups awaits further investigation.