Studies on the Endocrine Glands of a Salmonoid Fish, the Ayu, Plecoglossus altivelis Temminck et Schlegel-IX Seasonal Changes in the Cells of the Adenohypophysis, Especially the Prolactin Producing Cells

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Specimens of the annual salmonoid fish, Ayu, were collected from different places along the course of the Tassha-gawa River in Sado Island of the Japan Sea. The adenohypophysis was studied histologically to determine the cell types. For the purpose of examining the gland of marine life, some fish just entering the river were transferred to sea water.The rostral pars distalis consists mainly of two glandular cells: the dorsally shifted chromophobe cells facing the pars nervosa may correspond to the corticotrophs, and anteroventrally shifted acidophil cells are equivalent to the prolactin producing ones. Three types of cells are found in the proximal pars distalis: they are small, aldehyde fuchsin positive thyrotrophs bordering the pars nervosa; large, aldehyde fuchsin positive gonadotrophs which occur in the ventral region of the hypophysis and occupy an extensive portion of the pars distalis in parallel with sexual maturation; and the oval shaped orangenophil cells considered to be somatotrophs, lying between these two cell types mentioned above. The pars intermedia includes two cell types, larger and smaller ones, which could not be differentiated by their tinctorial responses.The acidophil cells in the rostral pars distalis undergo a marked hypertrophy and degranulation during the upstream migration of immature fish, whereas the cells in the fish kept in sea water showed only few of these changes.
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