The Pituitary Gland of the RoachLeuciscus rutilus

Ultrastructure of the agranular cells in the adenohypophysis of the South American lungfish, Lepidosiren paradoxa

Light and electron microscopic examination demonstrated two types of non-endocrine agranular cells, cavity boundary cells and stellate cells, in the adenohypophysis of the South American lungfish, Lepidosiren paradoxa. The cavity boundary cells line the hypophyseal cleft and diverticulum and display few microvilli, occasional cilia, prominent junctional complexes, and many cytoplasmic microfilaments. The stellate cells are scattered in the glandular parenchyma and are devoid of microvilli and cilia. When adjacent, they are connected to one another by desmosomes. Pinocytotic vesicles or caveolae are frequently seen along the plasma membrane of the agranular cells adjoining the endocrine cells or abutting on the basement membrane. Possible roles of the agranular cells, physically and metabolically supportive functions, are discussed on the basis of their ultrastractural features.

Fine structure of the rostral pars distalis of the adenohypophysis of the killifish, Fundulus heteroclitus, in fresh and salt water

A fine structural study has confirmed earlier light microscopic observations indicating that prolactin cells are the only endocrine cells present in the main body of the rostral pars distalis of the adenohypophysis of Fundulus heteroclitus, a killifish common in New England coastal waters. Some ACTH cells occurred in thin plaques applied to the neurohypophysial trunk in the posterior part of the region. In freshwater-adapted specimens the volume occupied by the prolactin cell mass was larger than in saltwater-adapted specimens and contained larger prolactin cells. A paucity of contact specializations between the parenchymal cells may facilitate their spatial rearrangement as the prolactin cell population varies with changes in ambient salinity. Many fine neurohypophysial processes penetrated deeply into the rostral pars distalis and contained Type B (aminergic) nerve fibers believed to modulate prolactin secretion. These fibers ended mainly on the basement membrane that separates the neurohypophysial processes from the parenchyma. Synaptic contacts on prolactin cells were not observed but no prolactin cell appeared to be more than five cell widths from such a nerve terminal. The results emphasize the usefulness of the rostral pars distalis of this easily obtained and maintained teleost for studies of prolactin cell function.

Effect of pimozide on the cytology of the eel pituitary. I. Prolactin-secreting cells

Pimozide, a specific blocker of dopaminergic receptors, was injected for 4 to 9 days in freshwater (FW) eels or eels acclimated to sea water (SW), for 10 to 30 days. The daily dose was 100 or 200 microgram/100 g. In FW, pimozide induces a nuclear hypertrophy in the prolactin (PRL) cells of eels; these elongated cells increase in height. The amount of erythrosinophilic granules in the cytoplasm, initially reduced, increases. Plasma electrolyte values are not modified: only the plasma sodium level slightly rises with the higher dose. In SW, PRL cells appear less active. After 10 days, this hypoactivity is not yet fully evident; pimozide stimulates PRL cells without affecting electrolyte values. After 1 month in SW, PRL cells are stimulated with pimozide and a slight regranulation may occasionally occur. The response in SW is never as marked as it is in FW; a high dose is not more effective than a low one. The higher dose significantly raises Na+, Ca2+ and Cl- plasma levels. These data suggest that prolactin synthesis and release increase with pimozide. They corroborate the hypothesis of a hypothalamic inhibitory control on PRL secretion mediated through dopaminergic fibers in the eel, but other factors may also be involved in this regulation in addition to the effect of salinity.