The hypothalamo-hypophysial system of the lamprey, Lampetra fluviatilis L. I. the neuohypophysis

Monoamines in the brain of the lancelet, Branchiostoma lanceolatum. A fluorescence-histochemical and electron-microscopical investigation

Three types of monoamine-containing neurones and fibres can be discriminated in the brain of the lancelet. Two types of elongated cerebrospinal fluid-contacting neurons, located in the ventral and the dorsolateral part of the brain, exhibit formaldehyde-induced catecholamine fluorescence. These neurones contain dense-core vesicles 75-100 nm in diameter. Their apical portion possesses cilia, displaying a 9 X 2 + 2 arrangement of their internal tubuli, and projecting into the ventricle. Basal processes from the ventrally situated perikarya abut upon the meninx and may discharge their catecholamines into the circulatory system. Fibres exhibiting catecholamine fluorescence originate from the dorsolaterally situated perikarya and run ventrocaudally to the neuropil, where they form numerous swellings of the bouton en passant type. A third type of perikarya in the posterior part of the brain displays specific green fluorescence. Further, neurones characterized by a specific yellow fluorescence are present in the anterior part of the brain and the anterior part of the neural tube. The rapid photodecomposition of the latter fluorophore indicates that these cells contain an indolamine.

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.

The hypothalamo-hypophysial system of the lamprey, Lampetra fluviatilis L. III. High-resolution radioautography of monoaminergic structures in neurohemal regions

The distribution of monoaminergic structures was studied in the proximal neurosecretory contact region and neurohypophysis of the lamprey by light and electron microscopic radioautography. Only weak radioautographic reactions were found in the proximal neurosecretory contact region 1 h after injection of 3H-dopamine. High-resolution radioautography revealed some labeled neurosecretory terminals mainly in contact with the basement membrane of the connective tissue layer separating the proximal neurosecretory contact region from the hypophysial pars distalis. The number of silver grains as well as the number of neurosecretory terminals marked by the presence of labeled dopamine was much higher in the neurohypophysis of the same species. In the latter, labeled neurosecretory terminals were found in contact with the connective tissue layer containing blood vessels of the general circulation. Some neurosecretory terminals make synaptoid contacts with tanycyte perikarya and their basal processes. According to their ultrastructure and the size of their granules, the labeled neurosecretory terminals are identical with the B type terminals described in both neurohemal regions (transmission electron microscopy). No labeled neurosecretory terminals were observed in the proximal neurosecretory contact region and the neurohypophysis of lampreys treated with the serotonin precursor, 3H-5-hydroxytryptophan.

The hypothalamo-hypophysial system in Acipenseridae. V. Ecological-histophysiological analysis of the neurohypophysis of the female sturgeon Acipenser güldenstädti Brandt during up-stream migration and after spawning

Neurohypophyses from sexually mature female sturgeons, Acipenser guldenstadti Brandt, killed before, soon after spawning, and during down-stream migration were studied light and electron microscopically. Ovaries were examined only under a light microscope. A large amount of neurosecretory material (3.5-4.5 arbitrary units) is found in the neurohypophysial "roots" during up-stream migration to spawning grounds. Neurosecretory fibres and their terminals are replete with elementary neurosecretory granules. Side by side with the latter some terminals contain single residual granules and few "synaptic" vesicles. Soon after spawning the amount of neurosecretory material decreases markedly in most individuals (content up to 1-3 units), and elementary granules are few in the fibres and their terminals. The number of residual granules increases, and "synaptic" vesicles are especially numerous. Granulated, disintegrating neurosecretory granules and granule-shadows occur in the preterminal parts of the fibres. The number of pituicytes increases becuase some "light" tanycytes seem to migrate from the ependymal into the subependymal layer. The restoration of neurosecretory material (reaching again up to 3.5-4.5 units) occurs within a month after spawning. The number of elementary granules increases in fibres and terminals while that of residual granules and "synaptic" vesicles decreases. These changes in the neurohypophysis of females after spawning are due to discharge of great amounts of peptide neurohorsmones into the general circulation after spawning. Spawning is regarded as a "physiological" stress for these females.

The hypothalamo-hypophysial system in acipenseridae. VI. The proximal neurosecretory contact region

The proximal neurosecretory contact region (PCR) of Acipenseridae, a homologue of the tetrapod median eminence, has been studied by light, fluorescence and electron microscopy. It occupies the rostral and chiefly the ventral surfaces of the hypothalamic tuber cinereum. PAF-positive fibres occur in the zone of the preoptico-hypophysial tract but their terminal enlargements are concentrated mainly in the external zone. They make contact with the primary portal capillaries situated in the pia mater. Monoaminergic fibres and terminals with an intense green fluorescence are localized in the same regions. The fibres of some bipolar monoaminergic neurons of the PCR make contact both with the third ventricle and the primary portal capillaries. Three types of granule-containing neurosecretory fibres and terminals have been recognized in the PCR. Fibres of types A1 (d = 120-300 nm) and A2 (D = 100-170 nm) are peptidergic PAR-positive, although some fibres, including some of type A1, belong possibly to PAF-negative type. Monoaminergic type B fibres have granules 80-100 nm in diameter. Neurosecretory terminals and vascular "endfeet" of tanycytes make contact with the 70 nm thick outer basement membrane of the primary portal capillaries. Several laminae of thin horizontally oriented tanycyte processes form a boundary between the external zone and the preoptico-hypophysial tract. Few neuroglial cells with pale cytoplasm, numerous lysosomes and lipofuscin granules are seen in this region. It is hypothesized that, as in other vertebrates both peptide hypophysiotropic neurohormones and monoamines are discarged from the PCR into the portal circulation and affect the activity of the glandular cells of the pars distalis.