Experimental analysiss of morphogenesis of hypothalamohypophyseal system

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Using Bufo embryos of wild type (rich in melanin granules) and of albino (devoid of melanin granules) transplantation experiments were carried out to identify the origin of the pituitary cells. The anterior part of the neural ridge was found to be the almost exclusive source of the secretory cells in the epithelial pituitary. It was also found that the pituitary primordium and the anlage of the hypothalamus are closely apposed at the open neurula stage. Some of anterior neural ridge-originated cell groups were observed to migrate into the hypothalamus long after the formation of neural tube. One of them is known to be LHRH neurons. But there is another cell group which migrates together with the pituitary primordium and penetrates into the anterior hypothalamus when the pituitary primordium attaches to the infundibulum. Although these cells are not characterized, it is highly probable that they differentiate into hypothalamic neurons. Thus, we concluded that the hypothalamus and the hypophysis are in an intimate clonal relationship. In the hypophyseal primordium developed without contact with the hypothalamus, POMC cells did not appear. Without pituitary primordium, neither development of the median eminence nor extension of hypophysiotripic neurons occurred. This indicates that stimulatory signals that induce differentiation of the hypophysis and hypothalamus are bidirectional ; from hypothalamus to the hypophysis and vice versa.