Effects of polyunsaturated fatty acids and prostaglandins on oocyte maturation in a marine teleost, the European sea bass (Dicentrarchus labrax)

Involvement of PLA2, COX and LOX in Rhinella arenarum oocyte maturation

In Rhinella arenarum, progesterone is the physiological nuclear maturation inducer that interacts with the oocyte surface and starts a cascade of events that leads to germinal vesicle breakdown (GVBD). Polyunsaturated fatty acids and their metabolites produced through cyclooxygenase (COX) and lipoxygenase (LOX) pathways play an important role in reproductive processes. In amphibians, to date, the role of arachidonic acid (AA) metabolites in progesterone (P4)-induced oocyte maturation has not been clarified. In this work we studied the participation of three enzymes involved in AA metabolism - phospholipase A2 (PLA2), COX and LOX in Rhinella arenarum oocyte maturation. PLA2 activation induced maturation in Rhinella arenarum oocytes in a dose-dependent manner. Oocytes when treated with 0.08 μM melittin showed the highest response (78 ± 6% GVBD). In follicles, PLA2 activation did not significantly induce maturation at the assayed doses (12 ± 3% GVBD). PLA2 inhibition with quinacrine prevented melittin-induced GVBD in a dose-dependent manner, however PLA2 inactivation did not affect P4-induced maturation. This finding suggests that PLA2 is not the only phospholipase involved in P4-induced maturation in this species. P4-induced oocyte maturation was inhibited by the COX inhibitors indomethacin and rofecoxib (65 ± 3% and 63 ± 3% GVBD, respectively), although COX activity was never blocked by their addition. Follicles showed a similar response following the addition of these inhibitors. Participation of LOX metabolites in maturation seems to be correlated with seasonal variation in ovarian response to P4. During the February to June period (low P4 response), LOX inhibition by nordihydroguaiaretic acid or lysine clonixinate increased maturation by up to 70%. In contrast, during the July to January period (high P4 response), LOX inhibition had no effect on hormone-induced maturation.

Characterization of luteinizing hormone and luteinizing hormone receptor and their indispensable role in the ovulatory process of the medaka

The molecular properties and roles of luteinizing hormone (Lh) and its receptor (Lhcgrbb) have not been studied for the medaka (Oryzias latipes), which is an excellent animal model for ovulation studies. Here, we characterized the medaka Lh/Lhcgrbb system, with attention to its involvement in the ovulatory process of this teleost fish. In the medaka ovary, follicle-stimulating hormone receptor mRNA was expressed in small and medium-sized follicles, while lhcgrbb mRNA was expressed in the follicle layers of all growing follicles. Experiments using HEK 293T cells expressing medaka Lhcgrbb in vitro revealed that gonadotropin from pregnant mare's serum and medaka recombinant Lh (rLh) bound to the fish Lhcgrbb. The fish gonadotropin subunits Gtha, Fshb, and Lhb were essentially expressed at fairly constant levels in the pituitary of the fish during a 24-h spawning cycle. Using medaka rLh, we developed a follicle culture system that allowed us to follow the whole process of oocyte maturation and ovulation in vitro. This follicle culture method enabled us to determine that the Lh surge for the preovulatory follicle occurred in vivo between 19 and 15 h before ovulation. The present study also showed that oocyte maturation and ovulation were delayed several hours in vitro compared with in vivo. Treatment of large follicles with medaka rLh in vitro significantly increased the expression of Mmp15, which was previously demonstrated to be crucial for ovulation in the fish. These findings demonstrate that Lh/Lhcgrbb is critically involved in the induction of oocyte maturation and ovulation.

Prostaglandin (F and E, 2- and 3-series) production and cyclooxygenase (COX-2) gene expression of wild and cultured broodstock of Senegalese sole (Solea senegalensis)

Prostaglandin levels in different tissues and cyclooxygenase (COX-2) gene expression were compared between wild and cultured Senegalese sole (Solea senegalensis) broodstock in which a significantly different fatty acid profile, particularly lower tissue levels of arachidonic acid (ARA, 20:4n-6) and higher levels of eicosapentaenoic acid (EPA, 20:5n-3) in the cultured fish compared to wild had already been described. This is the first report of the COX-2 mRNA expression in Senegalese sole. Cyclooxygenase (COX-2) mRNA expression and prostaglandin (2- and 3-series) levels were determined in tissues from 32 broodstock fish, 16 (8 males and 8 females) from each origin wild and cultured (G1). Transcripts of COX-2 were highly expressed in gills, sperm-duct (s-duct), testis, oviduct and spleen compared to liver, kidney and muscle. Differences in COX-2 transcripts expression were found in response to the origin of the fish and expression was significantly higher in s-duct and gills from wild fish compared to cultured. Wild fish showed significantly higher levels of total 2-series PGs and lower levels of 3-series compared to cultured fish. The significance of the lower COX-2 expression and lower PG 2-series production in some of the tissues of cultured fish was discussed in relation to the previously described differences in fatty acid profile (lower tissue levels of ARA and higher levels of EPA and EPA/ARA ratio in cultured fish) and the reproductive failure to spawn viable eggs from G1 cultured Senegalese sole compared to successful spawning from captive wild broodstock.

Disruption of endocrine function in in vitro H295R cell-based and in in vivo assay in zebrafish by 2,4-dichlorophenol

Chlorophenols in the aquatic environment have been of concern due to their potential effects on human and wildlife. In the present study, the endocrine disrupting effects of 2,4-dichlorophenol (2,4-DCP) were investigated in vitro and in vivo. In the in vitro assay, H295R human adrenocortical carcinoma cells were used to determine the potential effects of 2,4-DCP on steroidogenesis. Exposure to 0, 0.1, 0.3 or 1.0 mg 2,4-DCP/L resulted in less production of 17β-estradiol (E2) and alterations in transcript expressions of genes involved in steroidogenesis, including cytochrome P450 (CYP11A, CYP17, CYP19), 3βHSD, 17βHSD and StAR. In the in vivo study, effects of 0, 0.03, 0.1 or 0.3 mg 2,4-DCP/L on concentrations of steroid hormones in plasma of adult zebrafish (Danio rerio) were measured and expression of mRNA of selected genes in hypothalamic-pituitary-gonadal (HPG) axis and liver were determined. Exposure of zebrafish to 2,4-DCP resulted in lesser concentrations of E2 accompanied by down-regulation of CYP19A mRNA in the females. In males, exposure to 2,4-DCP resulted in greater concentrations of testosterone (T) and E2 along with greater mRNA expression of CYP17 and CYP19A. The mRNA expression of prostaglandin synthase (Ptgs2) gene, which regulates ovulation, was down-regulated in females, but up-regulated in males. The hepatic estrogenic receptor (ERα and ERβ) and vitellogenin (VTG1 and VTG3) mRNAs were up-regulated in both females and males. The average number of eggs spawned was significantly less upon exposure to 2,4-DCP. Exposure of adult zebrafish to 2,4-DCP resulted in lesser rates of hatching of eggs. The results demonstrated that 2,4-DCP modulates transcription of steroidogenetic genes in both H295R cells and in the zebrafish HPG-axis and disrupts steroidogenesis, which in turn, can cause adverse effects on reproduction in fish.

Arachidonic acid induces production of 17,20β-dihydroxy-4-pregnen-3-one (DHP) via a putative PGE2 receptor in fish follicles from the Eurasian perch

The effects of docosahexaenoic, eicosaenoic and arachidonic acids (DHA, EPA and ARA, respectively) on sex-steroid and prostaglandin (PG) production were investigated in Eurasian perch (Perca fluviatilis) follicles using an in- vitro incubation technique. Only ARA was able to induce the production of 17,20β-dihydroxy-4-pregnen-3-one (DHP), the hormone produced by vitellogenic follicles undergoing final meiotic maturation, as well as the production of PGE2 and PGF2α by the follicles. This work also investigated, using a preliminary pharmacological approach, the presence of a functional PGE2-like receptor in fish follicles. Exogenous PGE2 and butaprost (specific agonist of the EP2 receptor) stimulated DHP production. A second experiment assayed the cyclic adenosine monophosphate (cAMP) production by the follicles after 24 h of incubation with the agonist and antagonist of the EP2 receptor. As observed in mammals, we concluded that the cAMP produced in response to PGE2 was probably mediated by an intracellular mechanism via a PGE2-like receptor. This is the first pharmacological indication of this type of receptors in fish follicles. This study also indicates that ARA, and its derivatives, PGE2 and PGF2α, may act on final follicle maturation in Eurasian perch.

Swimming physiology of European silver eels (Anguilla anguilla L.): energetic costs and effects on sexual maturation and reproduction

The European eel migrates 5,000-6,000 km to the Sargasso Sea to reproduce. Because they venture into the ocean in a pre-pubertal state and reproduce after swimming for months, a strong interaction between swimming and sexual maturation is expected. Many swimming trials have been performed in 22 swim tunnels to elucidate their performance and the impact on maturation. European eels are able to swim long distances at a cost of 10-12 mg fat/km which is 4-6 times more efficient than salmonids. The total energy costs of reproduction correspond to 67% of the fat stores. During long distance swimming, the body composition stays the same showing that energy consumption calculations cannot be based on fat alone but need to be compensated for protein oxidation. The optimal swimming speed is 0.61-0.67 m s(-1), which is approximately 60% higher than the generally assumed cruise speed of 0.4 m s(-1) and implies that female eels may reach the Sargasso Sea within 3.5 months instead of the assumed 6 months. Swimming trials showed lipid deposition and oocyte growth, which are the first steps of sexual maturation. To investigate effects of oceanic migration on maturation, we simulated group-wise migration in a large swim-gutter with seawater. These trials showed suppressed gonadotropin expression and vitellogenesis in females, while in contrast continued sexual maturation was observed in silver males. The induction of lipid deposition in the oocytes and the inhibition of vitellogenesis by swimming in females suggest a natural sequence of events quite different from artificial maturation protocols.

Fatty acids as trophic biomarkers in vitellogenic females in an impounded tropical river

Fatty acids have been used in marine biogeochemistry as food chain biomarkers, but in freshwater these studies are rare. In order to evaluate the fatty acid potential as biomarkers in freshwater, their profile was analyzed during vitellogenesis in two fish species, in both waterfall and reservoir environments of the Paraíba do Sul River Basin. Detrivorous Hypostomus affinis and omnivorous Geophagus brasiliensis seem to elongate and desaturate polyunsaturated fatty acids (PUFA) and transfer them to the ovaries' phospholipids. Waterfall Geophagus brasiliensis have more highly unsaturated fatty acids in the liver, but in the reservoir, accumulation mainly occurs in muscle and ovary triglycerides, suggesting trophic opportunism and a plasticity during vitellogenesis. In Hypostomus affinis, PUFA alteration occurs only in the reservoir, suggesting a high phytoplankton occurrence. Eutrophication and water speed is reflected in Hypostomus affinis ovaries by higher PUFAn3 and bacterial fatty acids. As in marine environments, analysis of mono- and polyunsaturated fatty acids during vitellogenesis can be used as a tool in food chain studies in freshwater.

The preconception Mediterranean dietary pattern in couples undergoing in vitro fertilization/intracytoplasmic sperm injection treatment increases the chance of pregnancy

OBJECTIVE

To investigate associations between preconception dietary patterns and IVF/intracytoplasmic sperm injection (ICSI) outcomes validated by biomarkers of the homocysteine pathway.

DESIGN

Observational prospective study.

SETTING

A tertiary referral fertility clinic at the Erasmus University Medical Centre, Rotterdam, The Netherlands.

PATIENT(S)

One hundred sixty-one couples undergoing IVF/ICSI treatment.

INTERVENTION(S)

No interventions other than the Dutch governmental recommendation of folic acid.

MAIN OUTCOME MEASURE(S)

Dietary patterns, blood and follicular fluid concentrations of folate, vitamin B12, vitamin B6, homocysteine, and fertilization rate, embryo quality, and pregnancy.

RESULT(S)

In women, two dietary patterns were identified. The "health conscious-low processed" dietary pattern (variation explained 12.1%) was characterized by high intakes of fruits, vegetables, fish, and whole grains and low intakes of snacks, meats, and mayonnaise, and positively correlated with red blood cell folate (β=0.07). The "Mediterranean" dietary pattern (variation explained 9.1%), that is, high intakes of vegetable oils, vegetables, fish, and legumes and low intakes of snacks, was positively correlated with red blood cell folate (β=0.13), and vitamin B6 in blood (β=0.09) and follicular fluid (β=0.18). High adherence by the couple to the "Mediterranean" diet increased the probability of pregnancy, odds ratio 1.4 (95% confidence interval 1.0-1.9).

CONCLUSION(S)

A preconception "Mediterranean" diet by couples undergoing IVF/ICSI treatment contributes to the success of achieving pregnancy.

Perspectives on fish gonadotropins and their receptors

Teleosts lack a hypophyseal portal system and hence neurohormones are carried by nerve fibers from the preoptic region to the pituitary. The various cell types in the teleost pituitary are organized in discrete domains. Fish possess two gonadotropins (GtH) similar to FSH and LH in other vertebrates; they are heterodimeric hormones that consist of a common alpha subunit non-covalently associated with a hormone-specific beta subunit. In recent years the availability of molecular cloning techniques allowed the isolation of the genes coding for the GtH subunits in 56 fish species representing at least 14 teleost orders. Advanced molecular engineering provides the technology to produce recombinant GtHs from isolated cDNAs. Various expression systems have been used for the production of recombinant proteins. Recombinant fish GtHs were produced for carp, seabream, channel and African catfish, goldfish, eel, tilapia, zebrafish, Manchurian trout and Orange-spotted grouper. The hypothalamus in fishes exerts its regulation on the release of the GtHs via several neurohormones such as GnRH, dopamine, GABA, PACAP, IGF-I, norepinephrine, NPY, kisspeptin, leptin and ghrelin. In addition, gonadal steroids and peptides exert their effects on the gonadotropins either directly or via the hypothalamus. All these are discussed in detail in this review. In mammals, the biological activities of FSH and LH are directed to different gonadal target cells through the cell-specific expression of the FSH receptor (FSHR) and LH receptor (LHR), respectively, and the interaction between each gonadotropin-receptor couple is highly selective. In contrast, the bioactivity of fish gonadotropins seems to be less specific as a result of promiscuous hormone-receptor interactions, while FSHR expression in Leydig cells explains the strong steroidogenic activity of FSH in certain fish species.

Upregulated mRNA expression of desaturase and elongase, two enzymes involved in highly unsaturated fatty acids biosynthesis pathways during follicle maturation in zebrafish

BACKGROUND

Although unsaturated fatty acids such as eicosapentaenoic acid (EPA, C20:5n-3), docosahexaenoic acid (DHA, C22:6n-3) and arachidonic acid (ARA, C20:4n-6), collectively known as the highly unsaturated fatty acids (HUFA), play pivotal roles in vertebrate reproduction, very little is known about their synthesis in the ovary. The zebrafish (Danio rerio) display capability to synthesize all three HUFA via pathways involving desaturation and elongation of two precursors, the linoleic acid (LA, C18:2n-6) and linolenic acid (LNA, C18:3n-3). As a prerequisite to gain full understanding on the importance and regulation of ovarian HUFA synthesis, we described here the mRNA expression pattern of two enzymes; desaturase (fadsd6) and elongase (elovl5), involved in HUFA biosynthesis pathway, in different zebrafish ovarian follicle stages. Concurrently, the fatty acid profile of each follicle stage was also analyzed.

METHODS

mRNA levels of fadsd6 and elovl5 in different ovarian follicle stages were determined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) assays. For analysis of the ovarian follicular fatty acid composition, gas chromatography was used.

RESULTS

Our results have shown that desaturase displayed significant upregulation in expression during the oocyte maturation stage. Expression of elongase was significantly highest in pre-vitellogenic follicles, followed by maturation stage. Fatty acid composition analysis of different ovarian follicle stages also showed that ARA level was significantly highest in pre-vitellogenic and matured follicles. DHA level was highest in both late vitellogenic and maturation stage.

CONCLUSION

Collectively, our findings seem to suggest the existence of a HUFA synthesis system, which could be responsible for the synthesis of HUFA to promote oocyte maturation and possibly ovulation processes. The many advantages of zebrafish as model system to understand folliculogenesis will be useful platform to further elucidate the regulatory and mechanism aspects of ovarian HUFA synthesis.

An investigation into the role of prostaglandins in zebrafish oocyte maturation and ovulation

This study explored the potential for ovarian-derived prostaglandins (PGs) to be involved in the regulation of oocyte maturation and ovulation in zebrafish. It was demonstrated that cultured vitellogenic follicles have the capacity to produce prostaglandin E(2) (PGE(2)) and PGF(2alpha) in response to arachidonic acid (AA) in a concentration-dependent manner, and that AA stimulates the in vitro production of 17beta-estradiol (E(2)). The production of AA-stimulated PGF(2alpha) was significantly reduced by treatment with the non-selective cyclooxygenase (COX) inhibitor, indomethacin (INDO). Treatment of full-grown follicles with AA did not induce oocyte maturation as assessed by germinal vesicle breakdown, but INDO significantly decreased the rate of spontaneous maturation. Using Real-Time PCR, it was shown that follicles of different developmental size classes (primary growth and pre-vitellogenic, early-vitellogenic, and mid- to full-grown vitellogenic) express enzymes that release (cytosolic phospholipase A(2) (cPLA(2)); phospholipase Cgamma1) or metabolize (COX-1, COX-2, and prostaglandin synthase-2) AA to PG metabolites. The expression of cPLA(2) was found to be significantly greater in full-grown follicles compared to follicles of the pre- and early-vitellogenic stages. In vivo studies demonstrated that breeding groups of zebrafish exposed to 100 microg/L INDO exhibited reduced spawning rates and clutch sizes compared with control and 1 microg/L INDO exposed fish. In other studies, it was shown that naturally spawning groups of females exhibit increased ovarian levels of PGF(2alpha), E(2), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (a maturation-inducing hormone in zebrafish) near the time of ovulation compared with non-breeding females. Collectively, these experiments indicate that the AA pathway in zebrafish ovaries is involved in the regulation of oocyte maturation and ovulation and a non-selective inhibitor of COX disrupts these processes.

Changes in the timing of reproduction following chronic exposure to ibuprofen in Japanese medaka, Oryzias latipes

Effluents from wastewater treatment plants and untreated sewage constitute a low concentration but continuous source of pharmaceutical products to the aquatic environment. One such drug, ibuprofen, is a non-steroidal anti-inflammatory agent that primarily acts through inhibition of cyclooxygenase (COX) activity. Oryzias latipes (Japanese medaka) were exposed for 6 weeks via water to three concentrations of ibuprofen (1-100 microg/L nominal concentrations) and a water control. Reproductive parameters, including frequency of spawning, fecundity, egg size, and rate of fertilization, were measured for each pair of adult medaka following 6 weeks of exposure. Livers homogenates from exposed individuals were assayed for COX activity and whole individuals were histologically examined for tissue damage. Increasing exposure to ibuprofen significantly increased the number of eggs per reproductive event, but decreased the number of spawning events per week. Liver tissue collected from females had less variability in COX activity with increasing concentration of ibuprofen exposure, and tended to have elevated hepatosomatic indices. No pathological damage was evident the in the gills, livers and head kidneys of animals from the highest exposure group. The results of this experiment begin to show that exposure to chronic low levels of ibuprofen alter the pattern of reproduction and may produce sex-specific responses in teleosts.

Lipid and fatty acid content in wild white seabream (Diplodus sargus) broodstock at different stages of the reproductive cycle

The lipid and fatty acid content of the gonads, liver and muscle of wild white seabream males and females was studied at different stages of the reproductive cycle. Samples were taken from mature white seabream at pre-spawning (November), mid-spawning (March) and post-spawning (June) stages. The results showed that lipid accumulates in gonads and muscle from November to March. The gonadosomatic index (GSI) was also increased during this period. Male gonads showed a greater increase in polar lipid (PL) than neutral (NL), while female gonads displayed the reverse. The increase in both neutral and polar lipid was higher in the muscle of males than in females. In the same period, male livers showed no changes either in lipid content or the hepatosomatic index (HSI), while female livers registered an increase in both lipid content and HSI. Between March and June, in both males and females, total, neutral and polar lipid decreased sharply in the gonads and muscle. Muscular lipid content reduction was more pronounced in males than females. On the other hand, the lipid content of the liver in males and females remained relatively constant. In general terms, the amounts of major fatty acids (16:0, 18:1n-9, 20:5n-3 and 22:6n-3) in gonadal and muscular polar and neutral lipid in both males and females increased from November to March and declined thereafter. Variations of the liver fatty acid content were less extreme. In the period from mid-spawning to post-spawning, the presence of 20:4n-6 in polar and neutral lipid increased to a notable extent in all organs studied.

Divergent cyclooxygenase responses to fatty acid structure and peroxide level in fish and mammalian prostaglandin H synthases

Prostanoid synthesis in mammalian tissues is regulated at the level of prostaglandin H synthase (PGHS) cyclooxygenase catalysis by the availability and structure of substrate fatty acid and the availability of peroxide activator. Two major PGHS isoforms, with distinct pathophysiological functions and catalytic regulation, have been characterized in mammals; a functionally homologous PGHS isoform pair has been cloned from an evolutionarily distant vertebrate, brook trout. The cyclooxygenase activities of recombinant brook trout PGHS-1 and -2 were characterized to test the generality of mammalian regulatory paradigms for substrate specificity, peroxide activation, and product shifting by aspirin. Both trout cyclooxygenases had much more restrictive substrate specificities than their mammalian counterparts, with pronounced discrimination toward arachidonate (20:4n-6) and against eicosapentaenoate (20:5n-3) and docosahexaenoate (22:6n-3), the latter two prominent in trout tissue lipids. Aspirin treatment did not increase lipoxygenase-type catalysis by either trout enzyme. Both trout enzymes had higher requirements for peroxide activator than their mammalian counterparts, though the preferential peroxide activation of PGHS-2 over PGHS-1 seen in mammals was conserved in the fish enzymes. The divergence in cyclooxygenase characteristics between the trout and mammalian PGHS proteins may reflect accomodations to differences among vertebrates in tissue lipid composition and general redox state.

Effect of meiotic maturation on yolk platelet lipids fromBufo arenarum oocytes

Progesterone induces the resumption of meiosis in Bufo arenarum full-grown arrested oocytes through a nongenomic mechanism called meiotic maturation. Growing evidence indicates that lipids are involved in the maturation process. They are mainly located in yolk platelets, the principal organelles of amphibian oocytes. The aim of the present study was to analyze the effect of progesterone-induced maturation on lipids from B. arenarum yolk platelets. Ovarian oocytes, manually obtained, were incubated with progesterone to induce maturation. Yolk platelets were isolated by centrifugation at low velocity. Lipids were separated by thin-layer chromatography. For compositional analysis, they were derivatized by methanolysis, and were identified and quantified in a gas-liquid chromatograph. Phospholipid content decreased in progesterone-treated oocytes, mainly as a result of a decrease at the level of phosphatidylcholine (PC). The turnover of this lipid is considered crucial for the completion of meiosis. Sphingomyelin also underwent a decrease that could be related to the important role of ceramide as an inducer of germinal vesicle breakdown. Maturation effect on fatty acid composition registered significant changes in PC whose saturated fatty acids increased. A net increase in arachidonic acid was observed in phosphatidylserine after progesterone treatment. The contents of total triacylglycerols and diacylglycerols were not significantly modified by hormone effect while free fatty acids underwent a significant increase as a result of polyunsaturated fatty acids increase. Altogether, our results demonstrate that yolk platelet lipids are involved in the resumption of the meiotic cell cycle, thus suggesting that these organelles participate in a dynamic role during amphibian development.

New insights in developmental origins of different GnRH (gonadotrophin-releasing hormone) systems in perciform fish: an immunohistochemical study in the European sea bass (Dicentrarchus labrax)

The knowledge of the roles and origins of different gonadotrophin-releasing hormone (GnRH) systems could greatly contribute to improve the understanding of mechanisms involved in the physiological control of early development, puberty and spawning. Thus, in this study, we have analyzed the distribution of the cells expressing salmon GnRH, seabream GnRH and chicken GnRH-II forms in the brain and pituitary of developing sea bass using specific antibodies to their corresponding GnRH-associated peptides. The first prepro-chicken GnRH-II-immunoreactive cells arose in the germinal zone of the third ventricle at 4 days after hatching, increasing their number from days 10 to 30, in which they adopted their adult position. The prepro-chicken GnRH-II-immunoreactive fibers became conspicuous in the first week and from day 26 they reached almost all brain areas, especially the hindbrain, being never detected in the pituitary. First prepro-salmon GnRH-immunoreactive cells were detected in the olfactory placode at day 7 after hatching and reached the olfactory bulbs at day 10. Migrating prepro-salmon GnRH cells arrived at the ventral telencephalon at day 15, and became apparent in the preoptic area from day 45. The prepro-salmon GnRH innervation was more evident in the forebrain and increased notably between 10 and 30 days, at which fibers already extended from the olfactory bulbs to the medulla. A few prepro-salmon GnRH-immunoreactive fibers were observed in the pituitary from day 30. The prepro-seabream GnRH-immunoreactive cells were first detected at day 26 in the rostral olfactory bulbs. On day 30, prepro-seabream GnRH-immunoreactive cells were also present in the ventral telencephalon, reaching the preoptic area and the hypothalamus at 45 and 60 days, respectively. The prepro-seabream GnRH innervation appeared restricted to the ventral forebrain, increasing notably during the sixth week, when fibers also reached the pituitary. A significant prepro-seabream GnRH innervation was not detected in the pituitary until day 60.

Detailed lipid analysis of yolk platelets of amphibian (Bufo arenarum) oocytes

Yolk platelets, the principal components of amphibian oocytes, have been generally considered as material reservoirs. Their biochemical composition and function during oogenesis and early development have not been fully elucidated. The aim of this study was to carry out a lipidic characterization of yolk platelets from full-grown Bufo arenarum oocytes. Ovarian oocytes were manually obtained and the subcellular fraction was isolated by centrifugation at low velocity. Lipids were separated by thin-layer chromatography. For compositional analysis, they were derived by methanolysis, being identified and quantified in a gas-liquid chromatograph. Phospholipid content indicates that phosphatidylcholine and phosphatidylethanolamine are the main phospholipids followed by phosphatidylinositol, sphingomyelin, phosphatidylserine, and phosphatidic acid. Phospholipidic profile is similar to that in whole oocytes except for the absence of diphosphatidylglycerol in yolk platelets. Oleic, palmitic, and linoleic acids are the main fatty acids in phosphatidylcholine, and oleic acid is the principal one in phosphatidylethanolamine. In phosphatidic acid, palmitic, estearic, palmitoleic, and oleic acids represent 68 mol% of the total acyl groups. Phosphatidylinositol, enriched in arachidonic acid, is the most unsaturated phospholipid while sphingomyelin shows the lowest unsaturation index. The acyl group distribution in triacylglycerols is similar when yolk platelets and whole oocytes are compared. Polar and neutral lipids of yolk platelets determine the lipidic profile of the whole oocyte. The presence of unusual fatty acids as 14:0, 15:0, 15:1, 17:0, and 17:1 in phospholipids and triacylglycerols may indicate an oxidation mechanism different from beta-oxidation in yolk platelets and/or a structural and functional relation with mitochondria. Given that yolk platelets in amphibian oocytes may act in a dynamic fashion in development, their role should be reconsidered.

Nitric oxide-mediated arachidonic acid release from perifused Venus verrucosa oocytes

This study was undertaken in order to investigate the possible interactions between nitric oxide and arachidonic acid (AA) in Venus verrucosa oocytes. We perifused isolated oocytes to determine the effect of the following substances on [3H]arachidonic acid release ([3H]AA): (1) A 23187, a calcium ionophore; (2) nitric oxide (NO) donors; (3) 1,1,1-trifluoromethyl-6,9,12,15 heicosatetraen-2-one (AACOCF(3)), a specific phospholipase A(2) (PLA(2)) inhibitor; (4) [5'-hydroxymethyl-2'-furyl]-1-benzyl indazole (YC-1) and 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), specific soluble guanylyl cyclase activator and inhibitor, respectively; (5) L-arginine, the substrate of nitric oxide synthase; (6) L-nitroarginine methyl esther (L-NAME), an inhibitor of nitric oxide synthase. Our results demonstrated that: (a) the calcium ionophore dose-dependently increased [3H]arachidonic acid release; (b) the NO donors sodium nitroprusside (SNP) and linsidomine (SIN-1) highly increased [3H]arachidonic acid output, while S-nitroso-N-acetylpenicillamine (SNAP) was without effect; (c) AACOCF(3) completely blocked the [3H]arachidonic acid release induced by SNP and SIN-1; (d) YC-1 increased [3H]arachidonic acid release, while ODQ completely counteracted SNP response; (e) [3H]arachidonic acid output was also increased by L-arginine; (f) a similar effect was, paradoxically, obtained in the presence of L-NAME. Furthermore, using RT-PCR we demonstrated in the same cells the presence of a nitric oxide synthase (NOS) mRNA, whose expression was not modulated by interleukin 1beta (IL-1beta). These results demonstrate the presence of a both calcium-dependent and NO-sensitive PLA(2) and of nitric oxide synthase in V. verrucosa oocytes. Our data also suggest a co-action of the two pathways in the control of reproduction in this bivalve.

Role of arachidonic acid and protein kinase C during maturation-inducing hormone-dependent meiotic resumption and ovulation in ovarian follicles of Atlantic croaker

The roles of arachidonic acid (AA) and protein kinase C (PKC) during in vitro maturation-inducing hormone (MIH)-dependent meiotic resumption (maturation) and ovulation were studied in ovarian follicles of Atlantic croaker (Micropogonias undulatus). The requirement for cyclooxygenase (COX) metabolites of AA was examined using a nonspecific COX inhibitor, indomethacin (IM), as well as two COX products, prostaglandin (PG) F(2alpha) and PGE(2), whereas the role of lipoxygenase (LOX) was investigated using a specific LOX inhibitor, nordihydroguaiaretic acid (NDGA). The involvement of PKC was examined using phorbol 12-myristate 13-acetate (PMA), a PKC activator, as well as GF109203X (GF), a specific inhibitor of PKC and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7), nonspecific inhibitor of protein kinases. Genomic mechanisms were examined with the transcription-inhibitor actinomycin D (ActD) and the functionality of heterologous (oocyte-granulosa) gap junctions (GJ) with a dye transfer assay. The AA (100 microM) and PGF(2alpha) (5 microM) did not induce maturation, and NDGA (10 microM) did not affect MIH-dependent maturation. However, IM (100 microM) partially inhibited MIH-dependent maturation. Conversely, AA and both PGs induced, and IM and NDGA inhibited, MIH-dependent ovulation in matured follicles. The PMA (1 microg/ml) did not induce maturation but caused ovulation in matured follicles, whereas PKC inhibitors (GF, 5 microM; H7, 50 microM) did not affect MIH-dependent maturation but inhibited MIH- and PMA-dependent ovulation. The PMA-dependent ovulation was inhibited by IM but not by NDGA. In addition, ActD (5 microM) blocked MIH-dependent, but not PMA-dependent, ovulation, and PGF(2alpha) restored MIH-dependent ovulation in ActD-blocked follicles. The AA and PGs did not induce, and GF did not inhibit, MIH-dependent heterologous GJ uncoupling. In conclusion, AA and PKC mediate MIH-dependent ovulation but not meiotic resumption or heterologous GJ uncoupling in croaker follicles, but a permissive role of COX products of AA during maturation is possible. A novel model of MIH-dependent ovulation is proposed in which 1). LOX and COX metabolites of AA are both required for ovulation, but at upstream and downstream sites of the pathway, respectively, relative to PKC, and 2). PKC is downstream of genomic activation.