The male sexual revolution: Independence from testosterone

Much of our knowledge concerning the physiology of male sexual behavior has been based on classic work on animal models in which gonadal steroids are intimately tied to the expression of male copulatory behavior. The dominant paradigm in traditional behavioral neuroendocrinology has been that in adult male mammals, copulatory behavior is highly dependent on the concurrent availability of gonadal hormones. In the past few decades, however, there has been a shift away from this paradigm, as accumulating evidence reveals that activation of male sexual behavior in several species occurs in the absence of gonadal steroids. Delineating the underpinnings of gonadal steroid-independent male sexual behavior will help us understand the complex mechanisms that contribute to variability in sexual function. In this review, we summarize the role of gonadal steroids in male sexual behavior and then examine the evidence in both mammalian and nonmammalian examples that demonstrates gonadal steroid-independent male sexual behavior. Lastly, we discuss future lines of research and the clinical significance of identifying the underlying mechanisms by which gonadal steroidindependent male sexual behavior may be mediated.