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Biomedical subjects

M Olivereau

Publications and source records attributed to M Olivereau.

At least 55 records · Page 3Linked to original sources
PubMed1980

Responses of the teleost pituitary (goldfish, eel) to deionized water.

The cytological responses of the pituitary gland during adaptation to deionized water (DW) were investigated in the goldfish and the eel. In both teleost species, a stimulation of the prolactin (PRL) cells could not be detected, although the levels of blood electrolytes (Na+, Ca2+, Cl-) are reduced in the eel. PRL cells appear less active in DW-adapted eels. A striking stimulation of the PAS-positive cells of the pars intermedia occurs in both species after 3 weeks and, in the eel, is still present after 11 weeks. Cell and nuclear hypertrophy, mitoses and a well-developed endoplasmic reticulum are observed. MSH cells are partially degranulated when pigmentation is affected; a reduced activity of MSH cells is evident after 11 weeks. The amount of neurohypophysial tissue is reduced. In the goldfish and the eel, during adaptation to DW, an unknown factor secreted by the PAS-positive cells of the pars intermedia appears to play a more important role than the secretion of PRL. These two species are able to survive in fresh water without the pituitary. The control of the PAS-positive cells by external sodium or calcium is discussed.

Adaptation, Physiological↗
PubMed1980

PAS-positive cells of the pars intermedia are calcium-sensitive in the goldfish maintained in a hyposmotic milieu.

Cytological changes in the pars intermedia of the goldfish were investigated after adding calcium to deionized water (DW). In fish maintained in DW, the PAS-positive cells are highly stimulated in comparison to cells of fish kept in fresh water (FW). In DW supplemented with calcium at the same concentration as in FW (2 mM/l), the hyperactivity of the PAS-positive cells is prevented. When calcium ions are added 60 h before the animals are sacrificed, the PAS positive cells start to show signs of regression and their granules are stored: the release of the granular material appears to be suppressed by calcium. In the goldfish, the PAS-positive cells, homologous to a similar cell type in the eel, react only very weakly with the PAS technique. The name "calcium-sensitive cells" appears to be more appropriate in the goldfish for this particular cell type, secreting an unknown factor. This factor, different from the prolactin produced in the rostral pars distalis of the hypophysis, might be an equivalent of a "hypercalcin".

Animals↗
PubMed1979

Effect of estradiol-17 beta on the cytology of the liver, gonads and pituitary, and on plasma electrolytes in the female freshwater eel.

Female freshwater eels injected with estradiol-17 beta (E2) for 15--78 days appear paler and secrete more mucus than controls. The resulting strongly opalescent blood plasma indicates that vitellogenin synthesis occurs in the liver, which shows a significant hypertrophy, an increased vacuolization (lipid material) and glycogen depletion. Plasma sodium is lowered, but calcium levels are considerably increased. The gonosomatic index increases (0.92 +/- 0.1 to a maximum of 2.21). Oocytes are enlarged, but the incorporation of vitellogenin remains discrete. Gonadotrophs (GTH cells), small and scarcely visible in the pituitary of control eels, are hypertrophied and contain numerous glycoprotein granules after E2-administration. E2 may act on the pituitary and/or hypothalamus via a positive feedback to induce gonadotrophin (GTH) synthesis; GTH release seems to be very limited as indicated by the ovarian response. The differentiation of GTH cells in eels treated with fish pituitary extracts is most probably due to secretion of E2 by the ovary, which reacts on the pituitary. Various hypotheses are considered to explain the low GTH release. Thyrotrophs, somatotrophs and prolactin cells of the pituitary are stimulated. In the pars intermedia, MSH and PAS-positive cells appear less active. A possible antidopaminergic effect of E2 is discussed. E2 administration constitutes a simple and economic technique to induce the synthesis of GTH and will facilitate the biochemical and biological study of the latter hormone in eels.

Animals↗
PubMed1979

Effect of serotonin on prolactin- and MSH-secreting cells in the eel. Comparison with the effect of 5-hydroxytryptophan.

As parachlorophenylalanine appears to reduce release of prolactin (PRL) and melanocyte-stimulating hormone (MSH) in the eel, a stimulating serotoninergic control of these adenohypophysial secretions was suspected. Eels were therefore injected with serotonin (5-HT) (7.5--20 mg/kg) and compared with eels injected with the precursor of serotonin, 5-hydroxytroptophan (5-HTP) (20 mg/kg). In both cases, a darkening of the skin was observed, more rapid and intense with 5-HTP than with 5-HT. Similarly, MSH cell degranulation is more completely in 5-HTP-treated eels, which show simultaneously an unexplained dilatation of the swim-bladder not elicited by 5-HT treatment. In both cases, PRL cells are stimulated, and the nuclear area of PRL and MSH cells increases significantly. These results suggest that a serotoninergic pathway stimulates PRL and MSH release in the eel. An antagonism between the serotoninergic system and the dopaminergic system previously demonstrated in the same species seems apparent, but the interaction of other organs or factors, such as the pineal, are considered.

5-Hydroxytryptophan↗
PubMed1978

Serotonin and MSH secretion: effect of parachlorophenylalanine on the pituitary cytology of the eel.

Parachlorophenylalanine (pCPA), an inhibitor of tryptophan hydroxylase which depletes brain serotonin in higher vertebrates, was injected into freshwater eels. After 4 or 6 injections (200 mg/kg/day) or 10 injections (100 and 140 mg/kg/day), the animals are paler, with a low melanophore index. In the pituitary gland, granules tend to accumulate in the basal part of the MSH cells and in the perinuclear area. Cells appear smaller with a decreased nuclear area (P less than 0.001). In the neurohypophysis, the amount of neurosecretory material is often reduced. Conversely, injections of 5-hydroxytryptophan induce a strong darkening, a result similar to that previously reported in some amphibian species and in one lacertilian species. These data substantiate the hypothesis of a stimulatory influence of 5-hydroxytryptamine on MSH release and possibly its synthesis in the eel and other lower vertebrates.

5-Hydroxytryptophan↗
PubMed1978

Effect of parachlorophenylalanine, a brain serotonin depletor, on the prolactin cells of the eel pituitary.

Parachlorophenylalanine (pCPA), an inhibitor of tryptophan hydroxylase depleting brain serotonin in higher vertebrates, was injected into freshwater eels. After 4 or 8 injections (200 mg/kg/day) or 10 injections (100 and 140 mg/kg/day) plasma electrolyte values were not modified. Prolactin (PRL) cells appear less active, with increased granulation after 6 and 10 injections. Their cell height (P less than 0.01) and their nuclear area (P less than 0.001) are reduced. As injections of 5-hydroxytryptophan stimulate PRL cells, these findings suggest that a serotoninergic system may participate in the regulation of PRL cell activity. Brain serotonin depletion probably decreases granule release in PRL cells, a result comparable to the lowering action of pCPA on the plasma PRL level in some mammals.

Anguilla↗
PubMed1978

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.

Animals↗
PubMed1978

Effect of pimozide on the cytology of the eel pituitary. II. MSH-secreting cells.

Pimozide, a specific blocker of dopaminergic receptors, was injected for 4 or 9 days in freshwater (FW) eels or eels acclimated to sea water (SW) for 10 or 30 days. The daily dose was 100 or 200 microgram/100 g. Melanophore index values increase in FW and in 1 month-SW injected eels. All the treated fish react by a total or subtotal degranulation of the lead-hematoxylin positive cells in the pars intermedia. These cells were previously identified as alpha-MSH-secreting cells. The MSH cell nuclear area is significantly increased, nucleoli are larger and the endoplasmic reticulum more developed. The intensity of the response is similar in FW and SW eels, but it does not increase with the higher dose. The rapid release of pituitary alpha-MSH is also visualized by immunofluorescence and immunoenzymologic techniques. No effect on the second cell type of the pars intermedia (PAS-positive cell) is detected. The amount of neurosecretory material is often reduced in the neurohypophysis. These results suggest that the hypothalamic inhibitory control of MSH release and synthesis is mediated through dopaminergic fibers in the eel, but other factors cannot be ignored in this regulation.

Animals↗
PubMed1978

[Aminergic innervation of the hypothalamo-hypophyseal system in Gambusia sp. (Teleost, Poecilidae) studied by two fluorescence techniques].

Using fluorescence techniques (Falck-Hillarp, de La Torre and Surgeon) 2 paired groups of perikarya were observed in the hypothalamus of Gambusia, one in the nucleus recessus lateralis (NRL) and the other in the nucleus recessus posterioris (NRP). No fluorescent neuron could be detected in the nucleus recessus preopticus (NRPO) nor in the nucleus lateralis tuberis (NLT). Fluorescent aminergic fibers demonstrated in the rostral neurohypophysis and in the neurointermediate lobe might originate from the NRL. These two techniques are complementary, but the last one, more rapidly performed, appears promising.

Animals↗
PubMed1978

Prolactin, hypercalcemia and corpuscles of Stannius in seawater eels.

In intact eels in sea water (SW), ovine prolactin (PRL) treatment induces hypercalcemia, but its mechanism of action, which is discussed, remains to be defined. Corpuscles of Stannius (CSt) are modified simultaneously: two cell categories then become evident. The first cell type (type 1) predominates; it has an oval shape and large granules, it shows a nuclear and nucleolar hypertrophy and a mitotic activity, and appears greatly stimulated by PRL; it may elaborate a hypocalcemic factor (hypocalcin) which would compensate for the PRL-induced hypercalcemia. A similar effect, although slightly less intense, is detected in hypophysectomized-PRL treated eels in SW. A second cell type (type 2), is more elongated, smaller in size, and has an oval nucleus and fine granules. Scarcely less active in SW, it is significantly stimulated by PRL despite an increased blood sodium and potassium level. This experiment does not help to clarify its function.

Animals↗
PubMed1978

[Ultrastructure of gonadotropic cells of the normal eel and after estradiol injection].

Male and female silver eels, in fresh water or sea water, have few gonadotrophs (GTH) poorly differentiated. An oestradiol (E2) treatment induces their development: a well developed Golgi area, abundant secretory granules (200-500 nm), dilated cisterna and large globules 1.2-2.2 micron) are observed. A positive feedback may control gonadotropin synthesis in immature eels. No macroscopic effect is discernible on the gonad.

Anguilla↗
PubMed1977

Long term effect of hypophysectomy and prolactin treatment on kidney structure in the eel in fresh water.

Long term effects of hypophysectomy and ovine prolactin treatment on the histological picture of the kidney were investigated in European eels. The epithelial cell height is very slowly affected after hypophysectomy, the decrease being highly significant after 50 days only in the distal and the initial collecting tubules. Nuclear surfaces were more rapidly reduced, the regressive changes being first detected in the initial collecting tubule (5 days), then in the distal portion and the two proximal segments. No degenerative changes were observed. These structural responses may be correlated with the slow reduction of the urine flow and of the plasma electrolytes in the same species. Ovine prolactin treatment (10mug/g/day) overcompensates the effects of hypophysectomy on the epithelial cell height and the nuclear area, and even after 50 days still induces the proliferation of new tubules although its action remains less intense than in intact eels. Other histological criteria (brush border thickness, mitotic activity, basal structure of proximal 2 cells) and sodium retention do suggest that these structural modifications reflect an increased functional activity of the kidney in addition to the effect of prolactin on sodium fluxes in the gills.

Anguilla↗