Sexual differentiation has for a long time been considered as an event taking place before, around or shortly after birth. During the last few years, it has become apparent that this notion is overly simplified. Something must happen in the brain sometime between the late postnatal period and the end of puberty. For example, sexual behavior cannot be activated to adult levels in prebubertal male hamsters, rats or ferrets even when treated with large doses of androgens. Similarly, absence of gonadal hormones during puberty leads to a reduced responsiveness to these hormones when adult. Male hamsters deprived of androgens during puberty mount, intromit and ejaculate less in a test for copulatory behavior than hamsters exposed to physiological concentrations of these hormones. Not only do pubertal androgens enhance male-typical sexual behaviors in response to androgen treatment in adulthood, but they also reduce the expression of female-typical behaviors. Again, male hamsters not exposed to androgens during puberty display the lordosis response as easily as females. On the contrary, hamsters exposed to andro-gens during puberty are less likely to respond with lordosis (reviewed in Sisk and Zehr, 2005; Schulz and Sisk, 2006). All these observations strongly suggest that, in male hamsters, pubertal androgens facilitate the occurrence of male-typical responses while making the display of female-typical responses less likely. About the same conclusion was reached with regard to the consequences of perinatal hormone treatments. There are no data concerning pubertal hormone effects on the choice of sexual partner. As always, scientists are far more interested in the probability of display of copulatory reflexes than in factors determining the choice of partner. Nevertheless, we should not forget that gonadal hormone actions on the brain during puberty may have consequences for adult sexual behaviors including the sex preferred for displaying these behaviors with. The field of pubertal hormone actions and subsequent adult sexual behaviors is very young. I predict that many interesting findings will emerge in this field over the years to come.
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