The ultrastructure of the cell types and of the neurosecretory innervation in the pituitary of Mugil cephalus L. from fresh water, the sea, and a hypersaline lagoon : I. The rostral pars distalis

Abstract

The ultrastructure of the cells of the rostral pars distalis and their neurosecretory innervation were studied in the pituitaries of Mugil cephalus from fresh water (FW), the sea (SW), and a hypersaline lagoon (HL). The secretory granules of the eta cells have a median diameter of 2600 Å in FW, 2300 Å in SW, and 1800 Å in HL. Large-sized nucleus and nucleolus, a well developed endoplasmic reticulum, and abundance in secretory granules in FW eta cells were interpreted as indicating high synthetic activity, while scarcity of granules, decrease of cellular size as well as reduction of the volume of the RPD in HL specimens were interpreted as indicating high release and inadequate synthesis. An intercellular channel system formed by specialized channel cells in the eta cell region is described. In the epsilon cell region, a channel system is formed by invaginating membranes of the epsilon cells. Neurosecretory granules in the rostral neurohypophysis are of two types: (1) presumably peptidergic, which accompany the capillaries and probably most of them empty into the capillaries before the latter penetrate the epithelial region; and (2) presumably aminergic granules which are close to the interface which separates the neurohypophysis from the rostral pars distalis. Neurosecretory elements in the adenohypophyseal region between the eta cells, are of the aminergic type. The possible roles of the different neurosecretory granules are discussed.