Cellular organization and neuronal inducer (inhibitor) in Xenopus adenohypothesis.

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The adenohypophysis consists of two distinct parts, the pars distalis and the pars intermedia, both derived from a common embryonic rudiment called Rathke's pouch and regulated by the hypothalamus. However, the control mechanisms of the pars distalis and the pars intermedia are different from each other. Hormone-producing cells in the pars distalis are controlled by hypothalamic hormones produced by hypothalamic neurons carried via hypothalamo-hypophysial blood vessels, whereas the melanotrope cells in the pars intermedia are controlled directly by the hypothalamic neurons. Evidence of these mechanisms is the great number of blood vessels located in the pars distalis, whereas in the pars intermedia, the blood vessels are not nearly so well developed, and also by the many axons penetrating the pars intermediate. Such histological observations create a working hypothesis that the pars intermedia produces some factors that induce neurons, whereas the pars distalis secretes some factors in … More ducing morphogenesis of blood vessels. To identify these factors, I have tried to establish an in vitro bioassay system for quantitating the presence and length of the axons projecting from hypothalamic neurons into the pars intermedia. I co-cultured suprachiasmatic nuclei from hypothalamus of Xenopus tadpoles in collagen-matrix with pars intermedia from identical stages of development or from the adult toad, and counted the number of axons growing from the superchiamatic nuclei a fixed period of incubation. I observed a slight difference in the outgrowth of the axons when the suprachiasmatic nuclei were co-cultured with either the pars distalis or the pars intermedia, but the quantity and reproducibility of the observation were low. In the course of studies on the characterization of melanotrope cells in the Xenopus pars intermedia, I have found that the prohormone convertases PC1 and PC2 are involved in the proteolytic processing of proopiomelanocortin into alpha-MSH by using specific antibodies against the mammalian enzymes. Less