COMPARISON OF AFFERENT AND EFFERENT COMPETENCE OF TRANSPLANTED GNRH CELLS IN THE BRAINS OF HYPOGONADAL FEMALE MICE

A deletion in the gene encoding gonadotropin-releasing hormone (GnRH) induces hypogonadism in mice caused by the deficiency of GnRH, Activat ion of the reproductive axis can be achieved in these hypogonadal (hpg ) mice by third cerebro-ventricular transplantation of preoptic area ( POA) containing GnRH neurons, obtained from normal fetal mice, The pre sent study was carried out in female hpg mice with POA grafts (hpg/POA ) to investigate anatomical integration of the GnRH cells required for the functional activation of the reproductive system. Ovarian develop ment was present only in mice in which the graft tissue was located cl ose to the median eminence (ME), The total lack of ovarian development in individuals with grafts containing GnRH cells located elsewhere in the brain suggests that the mere presence of GnRH cells does not guar antee ovarian development, but that the location of the graft may be i mportant. Activation of the grafted GnRH cells following mating, as ev idenced by the induction of Fos immunoreactivity, was observed in hpg/ POA mice in which there was no ovarian development or detectable GnRH immunoreactive fiber innervation of the ME. Although ovarian developme nt was evident in individuals with grafts located close to the ME, rel ease of luteinizing hormone (LH) in response to mating was apparent in only some of these mice. The occurrence of mating and pregnancy only in hpg/POA mice with ovarian development and the reflex release of LH in response to mating suggests that both the efferent and afferent con nections of the GnRH system are important for the full functioning of the system.