Abstract
In this chapter the operation of the hypothalamic-pituitary gonadal axis is considered, with special reference to the way that gonadotropin-releasing hormone (GnRH) and gonadotropin secretion is controlled by gonadal hormones. The nature of GnRH neurons and how they function is considered, especially with respect to the way that GnRH secretion is controlled by the feedback effects of gonadal steroids. Feedback effects are also important at the level of the gonadotropes, and this too is covered in detail. With this background, a working model of the female estrous/menstrual cycle is presented.