INTERACTIONS BETWEEN ADENOHYPOPHYSEAL, HYPOTHALAMIC AND NASAL PRESUMPTIVE TERRITORIES DURING EARLY NEURULATION PROCESS

In chick embryo, the adenohypophysis shows close morphological relatio nships with hypothalamic and nasal presumptive territories. However, w e do not know how long the adenohypophysis depends on its surrounding tissues for its development and differentiation nor do we know anythin g about factors and mechanisms invovled. This study was undertaken to investigate whether any interactions between these neighbouring tissue s influence adenohypophyseal cell growth and differentiation. The abla tion of the presumptive hypothalamus and neurohypophysis results in th e failure of hypothalamic and infundibular process development. Howeve r, the adenohypophysis was present, although it was drastically modifi ed. Moreover, gonadotrophs and corticotrophs can be detected in the de veloping adenohypophyseal tissue. After the ablation of nasal presumpt ive territory, from where GnRH neurons originate, the adenohypophyseal length and the number of gonadatrophs and corticotrophs are not signi ficantly altered when compared to control embryos. These results sugge st that the presumptive hypothalamus and neurohypophysis are committed during open neural stage. At the following stages, these territories may act to promote the future adenohypophysis development and morphoge nesis. However, it seems that pituitary cells are committed from the v ery early embryonic stages, but interactions between the presumptive a denohypophysis and adjacent territories before the open neural stage c annot be ruled out.