Brain-Steroid Interactions and the Control of Aggressiveness in Birds

A. A. Berthold (1849, cited in 1) is credited with pioneering the field of experimental endocrinology. In his classic experiments with roosters, Berthold observed that crowing, sexual behavior and aggressiveness could be eliminated by castration and restored by reimplanting testes, and he came to the important conclusion that the active principle was a blood-borne substance. Since the time of Berthold, the secreted products of the gonads have been identified as steroids, and our understanding of the molecular mechanisms and behavioral manifestations of steroid action in the central nervous system (CNS) has expanded considerably. Nonetheless, gaps in our knowledge remain, and steroid control of vertebrate behavior continues to be a focus of intense investigation. One important area of research has been focused on the hormonal basis of aggressive behavior. In this paper, we will review results of studies in this laboratory in which we have examined the hormonal basis of individual and sex-related differences in the intensity of aggressive displays in the Japanese quail (Coturnix coturnix japonica). As a preface to this detailed consideration of aggressive behavior and brain-steroid interactions in the control of behavior, it is appropriate to consider landmark technical and conceptual advances which are the foundation of present-day research.