Interactions between adenohypophyseal, hypothalamic and nasal presumptive territories during early neurulation process.

In chick embryo, the adenohypophysis shows close morphological relationships with hypothalamic and nasal presumptive territories. However, we do not know how long the adenohypophysis depends on its surrounding tissues for its development and differentiation nor do we know anything about factors and mechanisms invovled. This study was undertaken to investigate whether any interactions between these neighbouring tissues influence adenohypophyseal cell growth and differentiation. The ablation of the presumptive hypothalamus and neurohypophysis results in the failure of hypothalamic and infundibular process development. However, the adenohypophysis was present, although it was drastically modified. Moreover, gonadotrophs and corticotrophs can be detected in the developing adenohypophyseal tissue. After the ablation of nasal presumptive territory, from where GnRH neurons originate, the adenohypophyseal length and the number of gonadatrophs and corticotrophs are not significantly altered when compared to control embryos. These results suggest 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 morphogenesis. However, it seems that pituitary cells are committed from the very early embryonic stages, but interactions between the presumptive adenohypophysis and adjacent territories before the open neural stage cannot be ruled out.