Basal-medial hypothalamus conducts the development of GnRH neurons

In rats, gonadoliberin- (GnRH-) neurons deriving from the medial nasal placode (NAP) penetrate into the forebrain vesicle and medial septum, and migrate further to various brain parts concerned with hypophysio-gonadal activities or with sexual behaviour. Such heterotaxic migration occurred in a spaciotemporal fashion. In the brain of 21.5-day-old rat (E 21.5) embryo whose nasal cavity had been scratched unilaterally at E 16.5, GnRH neurons were diminished in number in the ipsilateral septo-preoptic area. The presence of the heterotaxic attitude of the neurons was further examined in vitro. In co-culture of E 1.5 nasal placodes with various brain parts of E 14.5 embryos, GnRH neurons emerging from the nasal placodes migrated into all the brain tissue, most frequently, however, into the median eminence-arcurate complex (ME-Arc). Together with our previous findings (Daikoku et al., 1995), it is suggested that the developing medial basal hypothalamus has certain attractions for intracerebral migration and development of GnRH neurons in rats.