Cytological Changes in the Prolactin Cells of Medaka, Oryzias latipes, along with the Change of Environmental Salinity

Abstract

The detailed morphological changes of the prolactin cells in the pituitary gland of medada (Oryzias latipes) during a short period after transferring the fish from sea water to fresh-water were investigated by means of light and electron microscopes.
The prolactin cells of the fresh-water medaka are stained strongly with azocarmine G and contain secretory granules measuring 200-300mμ in diameter. On the contrary, the cells of the sea water fish are small in size and weak in staining affinity for azocarmine G. The secretory granules are small in size and number, and are variable in shape. On the other hand, one to three hours after transferring the sea water fish to fresh-water, their cytoplasm is seen to become occupied with newly synthesized small granules. During these stages, the formation of granules in the Golgi apparatus and the extrusion of granules through the cell membrane were frequently observed. Along with the lapse of time after the transfer, the cells showed increase in size and acquire a staining affinity for azocarmine G. Thus, the experimental evidence obtained in the present study seems to support the view that prolactin cells secrete one kind of hormone which plays an important role for the adaptation of the fish to fresh-water.