[Development of magnocellular neurosecretory neurons in embryonic hypothalamic tissue transplanted into the cavity of the 3d cerebral ventricle of adult rats].

Magnocellular neurosecretory cell (MSC) ontogenesis was comparatively assessed in normal rat hypothalamus and in fetal hypothalamic tissue transplanted into the third ventricle of the adult rat brain. 3H-thymidine uptake has shown that the time of origin of NSC in grafted tissue and supraoptic nucleus of normal rat fetuses was similar. NSC pericarions in grafts were well developed and contained neurosecretory material (NSM). Nuclear and nucleolar volumes did not differ from those in adult animals. Water deprivation was followed by a significant increase in nuclear and nucleolar volumes and NSM content in pericarions of grafted tissue, which suggests that raised synthetic activity was not accompanied by an increased NSM release. It is concluded that proliferation and specific differentiation of NSC precursor cells are invariably determined by genetic factors. The origin of neurosecretory nuclei and their specific connections is considerably influenced by conditions of tissue surroundings.