Activation of the Male Rat's Sexual Behavior by Intracerebral Implantation of Androgen

Abstract

The hypothesis that sexual behavior in the male results from the direct action of testosterone on specific brain regions was tested, using intracerebral implantation of crystalline testosterone propionate in castrate male rats. Following establishment of a criterion for the loss of sex behavior in castrates, it was determined that the minimum effective dose of subcutaneously administered testosterone for stimulation of the accessory sex glands was less than that required for restoration of sex behavior. It was found that intracerebral implantation of testosterone could result in reappearance of the complete pattern of male sexual behavior in the absence of any histologically demonstrable stimulation of the seminal vesicles or prostate. These results never followed the implantation of cholesterol, showing that they were not due to lesion production by the implant. Although occasional responses were found following implants in other areas of the brain, all the most effective implants were in the hypothalamic-preoptic region, with the most consistent behavioral reactivation resulting from medial preoptic implants. It is concluded that sexual behavior in the male may be virtually completely independent of androgen-sensitive peripheral mechanisms, and that it is dependent upon activation by testosterone of structures lying within the hypothalamicpreoptic region of the brain.(Endocrinology79: 783, 1966)