Zur Histologie der Hypophyse des Flussneunauges (Lampetra fluviatilis L.)

Electron microscopic identification of axons containing melanin-concentrating hormone in the lamprey, Lampetra fluviatilis L

Melanin-concentrating hormone-like immunoreactivity (MCH-LI) was examined in the hypothalamo-hypophysial region of the lamprey. At the light microscopic level, MCH-LI neuronal cell bodies were shown with the peroxidase anti-peroxidase method; they were seen in the hypothalamic region close to the third ventricle. MCH-LI axons were observed to run toward the proximal neurosecretory contact region (PNCR) and the most proximal part of the neurohypophysis. Electron microscopic analysis with the immunogold method revealed that presumed secretory granules within axonal profiles showed MCH-LI. MCH-LI axonal profiles were most often seen on or near the basement membrane of connective tissue layer separating the PNCR from the hypophysial pars distalis.

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.

The hypothalamo-hypophysial system of the lamprey, Lampetra fluviatilis L. II. The proximal neurosecretory contact region

The proximal neurosecretory contact region (PNCR) of the lamprey, a homologue of the median eminence of tetrapods, was studied by light, fluorescence and electron microscopy. Paraldehyde fuchsin-positive neurosecretory fibers are seen mainly in the central part of the rostral subdivision of the PNCR. The Falck-Hillarp technique reveals a weak, mainly diffuse yellow-green fluorescence in the PNCR. The ultrastructure of the tanycyte layer of the PNCR is very similar to that in the neurohypophysis of the same species, although the funnel-shaped protrusions of the third ventricle in the rostral part of the PNCR are more frequent than in the neurophypophysis. Peptidergic A1 and A2 neurosecretory fibers are characterized by neurosecretory granules of 120-200 nm and 100-150 nm in diameter, respectively. Monoaminergic B type fibers contain granules 80-100 nm in diameter. Neurosecretory terminals and the vascular endfeet of tanycytes make contact with the basement membrane of the avascular connective tissue layer separating the PNCR from the hypophysial pars distalis. It is suggested that both peptide and monoamine neurohormones diffuse through the thick connective tissue septa into the underlying blood vessels which supply the pars distalis and thus affect the function of its glandular cells.