First Time In Teleosts Research Articles

Differential in Vitro Suppressive Effects of Steroids on Leukocyte Phagocytosis in Two Teleosts, Tilapia and Common Carp

The objectives of this study were to investigate the potential roles of cortisol and gonadal steroids in the phagocytic activity of peripheral blood leukocytes in two teleosts, tilapia (Oreochromis niloticus × O. aureus) and common carp (Cyprinus carpio). An in vitro microtiter plate assay, measuring incorporation of FITC-latex beads into peripheral blood leukocytes, was developed for the first time in teleosts. Peripheral blood leukocytes were cultured in AL medium with tested compounds in a microfluor black plate at 25°C. FITC-latex beads were further incubated for phagocytosis and engulfed fluorescent intensity in phagocytes was detected fluorometrically. Cortisol suppressed leukocyte phagocytosis in a dose (10−14 to 10−4 M)- and time (0.5 to 8 h)-dependent manner in tilapia. The glucocorticoid agonist dexamethasone had a suppressive effect similar to that of cortisol, while cortisone and the mineralocorticoid aldosterone had only a weak effect in tilapia. High doses of estradiol and ethynylestradiol, but not of estrone, suppressed phagocytosis in tilapia. No suppressive effect on phagocytosis was observed with various concentrations of progesterone, testosterone, and 11-ketotestosterone. Triiodothyronine was also inactive on phagocytosis. A combination of estradiol and cortisol potentiatingly suppressed phagocytosis. Actinomycin D and cycloheximide blocked the suppressive effects of cortisol and estradiol. Cortisol had weaker suppressive effects on the phagocytosis of leukocytes in common carp than tilapia. Other steroids had no suppressive action on phagocytosis in common carp. It is concluded that the suppressive effects of cortisol and estradiol on phagocytosis in tilapia are mediated by specific glucocorticoid receptors and estrogen receptors, respectively. Cortisol would play a main and important role on the down-regulation of phagocytic activity. Sexual steroids, such as estradiol, also could interact with cortisol to further suppress immunity in tilapia. Differential responsiveness of the immune system to suppressive effects of steroids, among teleosts species, has been demonstrated.

Do gonadotrophin-releasing hormone neurons express estrogen receptors in the rainbow trout? A double immunohistochemical study.

A double immunocytochemical procedure, with two different chromogens, was used to compare the respective distributions of estrogen receptor-immunoreactive cells and gonadotrophin-releasing hormone-immunoreactive neurons on the same sections of the brains of adult male and female rainbow trout (Oncorhynchus mykiss). Estrogen receptor-immunoreactive cells were observed in the ventral and lateral telencephalon, the preoptic region, the mediobasal hypothalamus, and the ventromedial thalamic nucleus. Gonadotrophin-releasing hormone-immunoreactive perikarya were detected in the olfactory bulbs, the ventral telencephalon, the preoptic area, and the mediobasal hypothalamus. Double-staining studies showed that, although some estrogen receptor-positive cells were in close proximity to gonadotrophin-releasing hormone-immunoreactive perikarya, careful examination of 550 gonadotrophin-releasing hormone-positive cells from five adult females and two adult males failed to demonstrate any evidence that gonadotrophin-releasing hormone neurons coexpress estrogen receptor in the brain of the rainbow trout. The present study provides, for the first time in teleosts, morphological evidence that gonadotrophin-releasing hormone neurons do not represent major direct targets for estradiol, suggesting that the positive feedback effects of estradiol onto the gonadotrophin-releasing hormone system are likely to be conveyed via other cell populations.

Insulin and Insulin-like Growth Factors I and II Induce Final Maturation of Oocytes of Red Seabream, Pagrus major, in Vitro

The effects of various growth factors and peptides on in vitro germinal vesicle breakdown (GVBD) were examined in oocytes of the red seabream, Pagrus major , a daily spawning marine teleost. The oocytes used underwent GVBD in response to HCG but not to 17α,20β-dihydroxy-4-pregnen-3-one (DHP). Insulin (1 μ M) and insulin-like growth factor-1 (IGF-I, 10 n M) and IGF-II (13 n M) induced GVBD. Salmon gonadotropin-releasing hormone (GnRH), chicken GnRH (100 n M), angiotensin II and III (10 μg/ml), inhibin A, activin A (200 ng/ml), and epidermal growth factor (1 n M) were ineffective. IGF-I was the most potent inducer of GVBD. In the presence of DHP, oocytes underwent GVBD in response to low doses of IGF-I or -II or insulin which alone were ineffective. GVBD occurred in response to DHP after oocytes were preincubated with IGF-I or with HCG. Actinomycin D inhibited GVBD induced by HCG alone or in combination with DHP, but actinomycin D did not block GVBD induced by IGF-I alone or in combination with DHP. Cycloheximide totally inhibited induction of GVBD by HCG or IGF-I, alone or in combination with DHP. These results suggest, for the first time in teleost, that growth factors, such as IGF-I, are involved in the induction of GVBD of oocytes. IGF-I appears to act directly on oocytes, and not via maturation-inducing hormone production, to induce GVBD.

Characterization, cerebral distribution and gonadotropin release activity of neuropeptide Y (NPY) in the goldfish

The presence of a peptide closely related to porcine NPY has been demonstrated in the goldfish brain and pituitary by means of radioimmunoassay (RIA) and high performance liquid chromatography (HPLC). The RIA data demonstrate that displacement curves of brain extracts are parallel to a porcine NPY standard and that in HPLC a compound present in brain extracts is co-eluted with porcine NPY. The distribution of this NPY-like factor within the central nervous system was studied by radioimmunoassay and immunohistochemistry. The results indicated that NPY has a widespread distribution with the highest concentrations being found in the telencephalon and diencephalon. In the pituitary gland, NPY immunoreactive terminals characterized at the electron microscope level were found in the different lobes and, in particular, in close association with the gonadotrophin (GTH) secreting cells. Using anin vitro perifusion system, it was shown that NPY causes a dose dependent increase of GTH release from anterior lobe fragments.These data indicate for the first time in teleosts that NPY is present and widely distributed in the brain and pituitary, and that among other putative functions, could be implicated in the multihormonal release of GTH from the pituitary.

Inositol pentaphosphate in erythrocytes of a freshwater fish, piraracú ( [formula omitted

Inositol pentaphosphate (IPP), a characteristic component of avian erythrocytes (RBC), has been found for the first time in teleost. IPP is present in the erythrocytes of a freshwater air-breathing fish, Piraracú, at a level of 1.8 μmoles per ml RBC, representing 39.0 per cent of the total cell phosphate. Guanosine triphosphate (GTP) represents 22.0 per cent of the cell phosphate.