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>Thin section and freeze fracture studies of the hypophyseal proximal pars distalis in a teleost (Rhamdia hilariiVal.) during different stages of the reproductive cycle
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Thin section and freeze fracture studies of the hypophyseal proximal pars distalis in a teleost (Rhamdia hilariiVal.) during different stages of the reproductive cycle
Chromophilic cells in the proximal pars distalis of the adenohypophysis ofRhamdia hilariiwere studied in thin section and freeze fracture preparations. The gonadotropic cells (GTH-cells) exhibit a diversity of form, the frequency of which can be related to stages (maturation, matureandspent) in the sexual cycle. GTH-cells showing a cytoplasm filled with electron dense polymorphic secretory granules and small rough endoplasmic reticulum (RER) vesicles, have been termed non-vacuolated. During thematuregonadal stage, such cells become increasingly vacuolated. The small RER vesicles become dilated and/or fuse, forming a single enormous cisternum (4–11 μm diameter), the contents of which show direct contact with the inner nuclear membrane. These morphological aspects support the idea thatRhamdia hilariipossesses only one GTH-cell type. Evidence from freeze fracture replicas suggests that membrane-associated events precursory to exocytosis take place in regions where the cell and secretory granule membranes are in close apposition. Thin section analysis of secretory granule formation revealed their derivation from the dilated extremities of the inner Golgi saccule which appears to resemble the rigid lamella described in other cells. After detachment of the inner saccule, the immature secretory granules appear to enlarge by microvesicular transport. Freeze fracture and ultrastructural data on the morphology of the cells that presumably synthetise growth hormone are also present
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