Ultrastructure of the Pro-adenohypophysis of the River Lamprey,Lampetra fluviatilis, During Gonad Maturation

Development of the hypophysis of the arctic lamprey, Lampetra japonica

The hypophysis of early larval stages, from the moment of hatching on the 18th day after fertilization to the 101st day of larval life, of the arctic lamprey Lampetra japonica was studied with scanning and transmission electron microscopes. A solid cord of cells of the distal part of the nasopharyngeal duct represents the early adenohypophysis. On the 20th day after fertilization, several of the epithelial cells of this structure showed first indications of secretory activity with an extensive Golgi apparatus and small electron-dense secretory granules. On the 26th day, non-secretory, stellate (=supporting) cells and secretary cells can be distinguished. Already on the 39th day, two different parts can be distinguished in the adenohypophysis: the pars distalis with cells containing small dense granules, and the pars intermedia with cells containing larger granules of medium density. The number of granulated cells increases steadily; on the 101st day two pars distalis cell types can be distinguished. The neurohypophysis consists of a thin anterior and a thick posterior part. Already on the 20th day single nerve terminals in the ependymal layer of the diencephalic (=infundibular) floor contain dense elementary granules. The number of granule-containing terminals increases steadily; on the 101st day almost all terminals contain granules. The present observations suggest an early secretory function of the lamprey hypophysis.

Localization of acid phosphatase in lysosomes of pituitary folliculo-stellate cells following estrogen withdrawal from primed male rats

Acid phosphatase was localized in lysosomes of non-granulated, folliculo-stellate pituitary cells 72 h after estrogen was withdrawn from primed male rats. The appearance of lysosomes and the accumulation of lipid droplets in folliculo-stellate cells coincide with the clearance of lipid from pituitary mammotropes. Positive identification of lysosomes supports our proposal in a previous study that folliculo-stellate cells are phagocytic.

Immunoreactivity for Met-enkephalin and substance P in cells of the adenohypophysis of larval and adult sea lampreys, Petromyzon marinus

Procedures for localizing immunoreactive Met-enkephalin and substance P were applied to the adenohypophysis of larval and adult sea lamprey, Petromyzon marinus. Immunopositive reaction to anti-Met-enkephalin antiserum was found in certain adenohypophysial cells of both larvae and adults. This reaction was specific, as judged by preabsorption of the antiserum with synthetic Met-enkephalin and subsequent elimination of the immunoreaction. An immunopositive response to one of three anti-substance P antisera, also selective for certain adenohypophysial cells was obtained in both larval and adult glands. This reaction was not completely eliminated by preabsorption with authentic substance P. Although the substance P immunoreaction is not specific for authentic mammalian substance P, its localization is characteristic and distribution of cells exhibiting it is described. Immune-staining of Met-enkephalin was seen in most of the cells of the rostral pars distalis, and it was as strong or stronger in larvae (ammocoetes) of Petromyzon as it was in adults. The substance P response was found in about half of the cells of the caudal pars distalis and in a few cells of the rostral pars distalis. In ammocoetes substance P staining was limited to a few cells of the caudal pars distalis, and no cells in the rostral pars distalis were stained. Thus, Met-enkephalin staining in Petromyzon is a general property of cells in the rostral pars distalis both in larvae and adults and cannot be correlated with such events in the life cycle as metamorphosis or reproduction. On the other hand, cells containing materials reactive with the anti-substance P serum appear at a very low level in the larva and grow in number and intensity of staining in a time pattern that parallels development of reproductive capacity. Furthermore, the disparity in time of synthesis and adenohypophysial and cellular distribution of Met-enkephalin-like and substance P-like materials indicates that these two peptides are not functionally related, as has been suggested for some higher vertebrates.

Pituitary cysts in the sea lamprey of the Great Lakes, Petromyzon marinus L

Large epidermal cysts that occur in the adenohypophysis of spawning lampreys develop as a consequence of destructive invasion of the parenchyma by an epithelium derived from the same anlage as the medial nasopharyngeal duct. The lumina of the cysts contain a carbohydrate-rich secretory material which is a mixture of epithelial mucins. An array of histochemical methods was used to show the kinship of the cysts with the mucin-secreting epidermis of the duct. These cysts appear to be unique to the cyclostomes and to have no obvious adaptive benefit.

Immunocytochemical study of growth hormone, prolactin, and thyroid-stimulating hormone in the adenohypophysis of the sea lamprey, Petromyzon marinus L., during its upstream migration

Immunoreactivity to growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) was found in the adenohypophysis of the sea lamprey, Petromyzon marinus L., during its upstream migration, by immunoperoxidase techniques with antisera to mammalian pituitary hormones. Cross-reactivity to GH and PRL was found in two different cell populations in the proximal pars distalis. Specific immunostaining for GH and PRL was absent in other parts of the lamprey pituitary. Immunoreactive TSH cells were located only in the rostral pars distalis, and corresponded in shape and size to the large basophils in this region of the lamprey pituitary. These results suggest that mammalian-like GH, PRL, and TSH are produced in the pituitary of the lamprey.

Ultrastructure of the adenohypophysis in the larval anadromous sea lamprey, Petromyzon marinus L

The ultrastructure of the adenohypophysis (AH) in the larval anadromous sea lamprey, Petromyzon marinus L., was examined. The AH is subdivided into three regions, the pro-, meso-, and meta-AH. Cells of the nasopharyngeal stalk extend directly beneath the pro- and meso-AH to form the ventral surface of the gland. Some cells in the pro- and meso-AH are arranged into small follicles. Each region of the AH is characterized by a single granulated (secretory) cell type. Granulated cells constitute 80-90% of the pro-AH and contain secretory granules that range from 800 to 2400 A in diameter. Only 10-20% of the cells in the meso-AH are granulated and they contain much smaller secretory granules (400 to 1250 A diameter) than those in the pro-AH. Granulated cells constitute 80-90% of the meta-AH and contain only a few secretory granules, ranging from 1000 to 2500 A in diameter, and many vesicles containing either a loose flocculent or dense granular material. Non-granulated (stellate) cells are found in all regions. They are characterized by their long cell processes, abundant cytoplasmic filaments, and variable electron density. The appearance of organelles in these cells suggests they are nonsecretory. They may play a role in maintaining the structural integrity of the gland and the regulation of granule release in the pro-AH. Two types of nongranulated cells make up 80-90% of the meso-AH. Type I are stellate cells, type II may be undifferentiated cells. The functional significance of the secretory cells in the larval AH is discussed.

Ultrastructure of the nongranulated cells and morphology of the extracellular spaces in the pars distalis of adult and pouch-young tammar wallabies (Macropus eugenii)

Differentiated nongranulated (folliculo-stellate) cells were observed in the centre and periphery of the cords of cells in the pars distalis of the adult tammar wallaby (Macropus eugenii). The nongranulated cells formed follicles containing a small lumen: the cell apices were joined by junctional complexes including zonulae adhaerentes and maculae adhaerentes (desmosomes). Follicles of granulated cells were also occasionally found. Follicles were rarely observed in the adult, but were numerous and generally larger in pouch-young wallabies. Moreover, whereas the involvement of granulated cells in the follicles of the adult was infrequent, they were common components of follicular structures in the pouch-young. The marginal cells at the periphery of the pars distalis in contact with the hypophysial cleft had many of the cytological characteristics of the nongranulated cells in the central pars distalis. In both adult and pouch-young wallabies, nongranulated cells at the periphery of the cell cords were juxtaposed such that they formed "sinusoid-like" spaces or lacunae, presumably as part of the extravascular channel system. The observations are discussed in light of the proposed phagocytotic, metabolite and/or hormone transport and "stem cell" roles attributed to these cells.

Phasic secretion by follicular cells of the bat adenohypophysis during the prearousal period of their annual life cycle

The fine structure of the follicular (nongranulated) cells of the adenohypophysis of the bat was examined at different periods of the annual life cycle. Follicular cells were found in all regions of the pars distalis of both active and hibernating bats. Throughout the active phase of the life cycle and during most of the hibernating period, the structure of follicular cells is unchanged. Toward the end of hibernation, however, striking ultrastructural changes occur. The most obvious of these alterations is the appearance in follicles of dense rod-shaped bodies within the follicular luminal space. Just prior to arousal, the rodlike bodies become much wider and appear more as paracrystalline aggregates of dense material. Images indicate that the dense rod-shaped bodies are packaged in vesicles in the cytoplasm of the follicular cells. The fusion of the membrane of filled vesicles with the plasma membrane of the follicular cell results in the release of their dense rod-shaped bodies into the follicular lumen by exocytosis. These cyclic ultrastructural changes indicate that follicular cells have a phasic secretory activity.