Biomedical subjects

S Dufour

Publications and source records attributed to S Dufour.

At least 55 records · Page 3Linked to original sources

PubMed1998

Long-term inhibitory effects of somatostatin and insulin-like growth factor 1 on growth hormone release by serum-free primary culture of pituitary cells from European eel (Anguilla anguilla).

To investigate the ability of hypothalamic and peripheral factors to directly regulate growth hormone (GH) release in a primitive teleost, the European eel (Anguilla anguilla L.), we used primary cultures of dispersed pituitary cells. When cultured for 12 days in a serum-free medium, pituitary cells continuously released large amounts of GH, which exceeded the initial cellular content. Somatotropin-release inhibiting hormone (SRIH-14) dose-dependently inhibited GH release (EC50 0.75 nM) up to a maximal inhibitory effect of 95%. No desensitization of somatotropes to SRIH was observed over the 12 days of culture. Use of receptor subtype-selective SRIH agonists suggests the existence on eel somatotropes of SRIH receptor(s) related to the mammalian sst2/sst3/sst5 class rather than to the sst1/sst4 class. Insulin-like growth factor 1 (IGF1) dose-dependently inhibited GH release (EC50 0.03 nM) up to a maximal inhibitory effect of 85%, without desensitization. IGF1 and IGF2 were equipotent in inhibiting GH release, whereas insulin was 1,000 times less active, suggesting the implication of a receptor related to the mammalian IGF type 1 receptor. These results indicate that eel somatotropes are active in vitro without any specific additional factors, and suggest the existence of a dominant inhibitory control of GH release in vivo. Two potential candidates for this chronic negative regulation are a neurohormone, SRIH and a circulating factor, IGF1. These data underline the early evolutionary origin of the molecular and functional SRIH-GH-IGF1 neuroendocrine axis in vertebrates.

Anguilla↗

PubMed1998

Distribution, characterization, and growth hormone-releasing activity of pituitary adenylate cyclase-activating polypeptide in the European eel, Anguilla anguilla.

The complementary DNA encoding pituitary adenylate cyclase-activating polypeptide (PACAP) has been cloned from two species of teleost fishes, the Sockeye salmon and the Thai catfish, and the amino acid sequence of PACAP has been determined in another teleost, the stargazer. However, to date, the detailed distribution of PACAP immunoreactivity has never been investigated in the fish brain. In the present study, we have determined the localization of PACAP-immunoreactive neurons in the central nervous system of a primitive teleost fish, the European eel Anguilla anguilla, using an antiserum raised against PACAP27. PACAP-positive perikarya were exclusively observed in the diencephalon, i.e. in the preoptic nucleus of the hypothalamus and in the dorsal and ventral nuclei of the thalamus. PACAP-immunoreactive fibers were detected in various areas of the brain, notably in the ventral telencephalon, the diencephalon, the mesencephalon, the cerebellar valvula, and the medulla oblongata. In addition, a dense accumulation of PACAP-containing nerve terminals was found in the pars distalis of the pituitary. The PACAP-like immunoreactivity contained in the eel brain was characterized by HPLC analysis combined with RIA quantification. The major form of PACAP-immunoreactive material coeluted with mammalian PACAP38. Molecular cloning of the PACAP precursor has previously shown that in fish, PACAP and GH-releasing hormone (GHRH) originate from the same precursor. We have thus investigated the effects of PACAP and GHRH on GH secretion from eel pituitary cells in primary culture. Dose-response experiments revealed that PACAP27 and PACAP38 possessed the same efficacy, but PACAP38 was 12 times more potent than PACAP27 in stimulating GH release (ED50 = 4.3 x 10(-10) and 3.5 x 10(-9) M, respectively). In contrast, GHRH, even at a high concentration (10(-6) M), had no effect on GH release. Taken together, these data indicate that in the eel, PACAP may play a significant role in the regulation of somatotrope cells: 1) PACAP-immunoreactive neurons are exclusively located in the diencephalon and send numerous projections in the pars distalis; and 2) PACAP, but not GHRH, dose dependently stimulates GH secretion from cultured eel pituitary cells.

Anguilla↗

PubMed1998

Insulin-like growth factor-I stimulates gonadotrophin production from eel pituitary cells: a possible metabolic signal for induction of puberty.

Insulin-like growth factor (IGF)-I has been suggested as a potential signal linking growth and puberty in mammals. Using the juvenile European eel as a model, we employed a long-term, serum-free primary culture of pituitary cells to study the direct effect of IGF-I on gonadotrophin (GtH-II=LH) production. IGF-I increased both cell content and release of GtH-II in a time- and dose-dependent manner. IGF-I and IGF-II had similar potencies but insulin was 100-fold less effective, suggesting the implication of an IGF type 1 receptor. Other growth and metabolic factors, such as basic fibroblast growth factor and thyroid hormones, had no effect on GtH-II production. IGF-I did not significantly increase the number of GtH-II immunoreactive cells, indicating that its stimulatory effect on GtH-II production does not result from gonadotroph proliferation. Comparison of IGF-I and somatostatin (SRIH-14) effects showed that both factors inhibited growth hormone (GH) release but only IGF-I stimulated GtH-II production by eel pituitary cells. This indicates that the effect of IGF-I on gonadotrophs is not mediated by the reduction of GH released by somatotrophs into the culture medium. This study demonstrates a specific stimulatory effect of IGF-I on eel GtH-II production, played out directly at the pituitary level. These data obtained in a primitive teleost suggest that the role of IGF-I as a link between body growth and puberty may have been established early in the evolution of vertebrates.

Analysis of Variance↗

PubMed1997

Androgens stimulate gonadotropin-II beta-subunit in eel pituitary cells in vitro.

Primary cultures of juvenile eel (Anguilla anguilla) pituitary cells were used to study the direct effects of sex steroids on gonadotropin (GtH-II) cell content and release (radioimmunoassay) as well as on mRNAs levels for alpha and GtH-II beta-subunits (dot-blot). Testosterone stimulated GtH-II production in a dose- and time-dependent manner by selectively increasing mRNAs for GtH-II beta-subunit but not alpha-subunit. This positive effect was also induced by non-aromatizable androgens (androstanediol and dihydrotestosterone) but not by estradiol, indicating an androgen-specific effect in the eel. The androgen-specific stimulation of eel GtH-II beta appears closer to the regulation of mammalian follicle stimulating hormone-beta (FSHbeta) than that of salmonid GtH-II beta or mammalian luteinizing hormone-beta (LHbeta)-subunits. Comparison with previous in vivo experiments suggests multiple sites of action of sex steroids on the brain-pituitary gonadotropic axis for the positive feedback on GtH-II synthesis in this juvenile fish.

Androgens↗

PubMed1997

Direct role of the carboxy-terminal cell-binding domain of fibronectin in neural crest cell motility.

We have analyzed the interaction of neural crest cells with fragments of fibronectin corresponding to the different spliced variants of the COOH-terminal cell-binding domain (COOH-ter CBD). We have shown that this domain can support cell adhesion and migration and that both the IIICS and HepII regions are involved in these events. The rate of locomotion is high, although undirectional, compared to that of whole fibronectin. Interactions with the COOH-ter CBD are controlled by alpha4beta1 and maybe other beta1 integrins and cell-surface proteoglycans. These receptors act cooperatively to mediate attachment, spreading, and migration on fibronectin.

Animals↗

PubMed1997

NMR studies of inorganic phosphate compartmentation in the isolated rat liver during acidic perfusion.

Mitochondrial inorganic phosphate has been shown to be undetectable by 31P NMR in the isolated rat liver perfused under physiological conditions. Cold perfusion (4 degrees C) with valinomycin (K+ ionophore) induced the appearance of an additional resonance assigned to P(i) from mitochondrial compartment (P(i,mito)) (Thiaudière et al., 1993, FEBS Lett. 330, 232-235). Here we have demonstrated that P(i,mito) can be detected by NMR under normothermic conditions (37 degrees C) in acidic (pH 6.5, bicarbonate-free) perfused liver using 50 nM valinomycin or 10 microM N,N'-dicyclohexylcarbodiimide (DCCD, a mitochondrial H+-ATP synthase inhibitor). These conditions resulted in a significant increase in mitochondrial P(i) content. In the presence of valimomycin, pH values of 7.00+/-0.07 and 6.60+/-0.10 (n = 7) for mitochondria and cytosol, respectively, were determined from the chemical shift values of P(i) resonances. Electron microscopy demonstrated a large matrix swelling under valinomycin perfusion, explaining the increased level of mitochondrial P(i). The amount of mitochondrial P(i) measured by NMR increased linearly with the cellular ATP depletion, suggesting a mitochondrial influx of P(i) from the cytosolic compartment with valinomycin perfusion. Moreover, the level of matrix P(i) was dependent on the cytosolic pH value, the resonance being not detectable at physiological cytosolic pH. During mitochondrial swelling, P(i) influx was likely to be associated with proton influx, owing to the stability of transmembrane pH gradient and matrix proton concentration.

Adenosine Triphosphate↗

PubMed1997

Down-regulation of TSH subunit mRNA levels by thyroid hormones in the European eel.

The effects of 3,5,3'-triiodothyronine (T3) and thyroxine (T4) on alpha and thyroid-stimulating hormone (TSH) beta subunit mRNA pituitary levels were examined in a teleost, the European silver eel. Northern blot analysis showed that the number and length of mRNAs encoding TSH beta varied among individuals, a variability apparently not related to thyroidal status. When several bands were present, their intensities were summed for quantitative analysis. Increasing circulating thyroid hormones (THs) by implantation of T3 or T4 significantly decreased TSH beta mRNA levels. Depression of circulating THs by thiourea treatment increased alpha and TSH beta mRNA levels. In vitro studies showed that T3 and T4 decrease TSH beta mRNA levels in primary cultures of eel pituitary cells. In conclusion, in vivo and in vitro experiments indicate that T3 and T4 exert a negative feedback action on pituitary TSH beta mRNA level in the European eel and that this effect might be exerted, at least partly, through a direct action on the pituitary.

Animals↗

PubMed1996

EGF increases retinoid X receptor-alpha expression in human trophoblastic cells in culture: relationship with retinoic acid induced human chorionic gonadotropin secretion.

In the present study, the effect of retinoic acid (RA) and epidermal growth factor (EGF) on the functions of human trophoblastic cells in culture were analysed. In these cells, RA potentiated the hCG secretion increase induced by EGF. To gain a better understanding of such a synergistic effect, the expression of retinoic acid receptors (RAR alpha and beta) and retinoid X receptor (RXR alpha) was studied by immunoblotting in RA- and EGF-treated cells. EGF treatment specifically increased the level of RXR alpha protein and RXR alpha transcripts. In parallel, we demonstrated that the choriocarcinoma cells JEG 3, which respond to RA by an increase in hCG secretion, express constitutively high levels of RXR alpha protein. Furthermore, RXR alpha-transfected trophoblastic cells also become RA responsive for hCG secretion. All these data suggest that RXR alpha expression is modulated by EGF, and may be involved in the effect of RA on hCG secretion.

Cell Line, Transformed↗

PubMed1996

Top-down control analysis of temperature effect on oxidative phosphorylation.

The effects of temperature on the control of respiration rate, phosphorylation rate, proton leakage rate, the protonmotive force and the effective ATP/O ratio were determined in isolated rat liver mitochondria over a range of respiratory conditions by applying top-down elasticity and control analyses. Simultaneous measurements of membrane potential, oxidation and phosphorylation rates were performed under various ATP turnover rates, ranging from state 4 to state 3. Although the activities of the three subsystems decreased with temperature (over 30-fold between 37 and 4 degrees C), the effective ATP/O ratio exhibited a maximum at 25 degrees C, far below the physiological value. Top-down elasticity analysis revealed that maximal membrane potential was maintained over the range of temperature studied, and that the proton leakage rate was considerably reduced at 4 degrees C. These results definitely rule out a possible uncoupling of mitochondria at low temperature. At 4 degrees C, the decrease in ATP/O ratio is explained by the relative decrease in phosphorylation processes revealed by the decrease in depolarization after ADP addition [Diolez and Moreau (1985) Biochim. Biophys. Acta 806, 56-63]. The change in depolarization between 37 and 25 degrees C was too small to explain the decrease in ATP/O ratio. This result is best explained by the changes in the elasticity of proton leakage to membrane potential between 37 and 25 degrees C, leading to a higher leak rate at 37 degrees C for the same value of membrane potential. Top-down control analysis showed that despite the important changes in activities of the three subsystems between 37 and 25 degrees C, the patterns of the control distribution are very similar. However, a different pattern was obtained at 4 degrees C under all phosphorylating conditions. Surprisingly, control by the proton leakage subsystem was almost unchanged, although both control patterns by substrate oxidation and phosphorylation subsystems were affected at 4 degrees C. In comparison with results for 25 and 37 degrees C, at 4 degrees C there was evidence for increased control by the phosphorylation subsystem over both fluxes of oxidation and phosphorylation as well as on the ATP/O ratio when the system is close to state 3. However, the pattern of control coefficients as a function of mitochondrial activity also showed enhanced control exerted by the substrate oxidation subsystem under all intermediate conditions. These results suggest that passive membrane permeability to protons is not involved in the effect of temperature on the control of oxidative phosphorylation.

Adenosine Triphosphate↗

PubMed1996

Development of a radioimmunoassay for European eel growth hormone and application to the study of silvering and experimental fasting.

A specific and sensitive homologous radioimmunoassay for eel (Anguilla anguilla L.) growth hormone (angGH) has been developed. The antiserum, raised against purified angGH and used at 1:20,000 final dilution, did not cross-react with eel prolactin or thyrotropin, carp gonadotropin II, bovine GH, or serum from hypophysectornized eel. The inhibition curves for eel pituitary extracts and serum were parallel to that of angGH standard. The ED50 value was between 1 and 2 ng/tube and the recovery of purified angGH added to the serum was about 100%. In immunocytochemical studies, the antiserum, used at 1:1000 dilution, specifically labeled the somatotrophs in the pituitaries of the glass, yellow, and silver eels. The GH contents were determined in the pituitaries of glass, yellow, and silver eels and in the serum at the yellow and silver stages. GH variations during the transformation of the yellow to silver eel were examined. The results indicated a decrease in GH production between the yellow and the silver eels, possibly related to the cessation of growth at the silver stage. In contrast to the situation in the naturally fasting silver eel, submitting yellow eels to 3 months of starvation (experimental fasting) greatly increased GH production. This suggests a variation in the regulation of GH according to the type of fasting (natural or experimental) and/or the stage of the fish (yellow or silver).

Anguilla↗

PubMed1996

Primary cultures of dispersed pituitary cells from estradiol-pretreated female silver eels (Anguilla anguilla L.): immunocytochemical characterization of gonadotropic cells and stimulation of gonadotropin release.

To analyze the multihormonal control mechanisms of GTH secretion in the eel, primary culture of pituitary cells from control or estradiol-treated female silver eels, a treatment known to stimulate in vivo GTH synthesis, was developed. Dispersed eel pituitary cells obtained by enzymatic (trypsin/DNAse) and mechanical dispersion were cultured in Earles M199, at 18 degrees. Immunoreactive GTH (ir-GTH) cells were characterized by the immunoperoxidase method, using antiserum to carp GTH beta subunit. Ir-GTH cells from control silver eels were small and represented 14% of the dispersed pituitary cells. In contrast, ir-GTH cells from estradiol-treated eels were larger (cell area x 2.5) and represented a higher proportion (21%) of the pituitary cells. Intracellular and medium contents of GTH were measured by radioimmunoassay for the GTH beta subunit. In vivo estradiol-treatment increased more than 100-fold the GTH content of cell cultures. GTH release, studied over 1 to 4 hr, was undetectable in cultures from normal eels. In contrast, GTH release was low (less than 2% of cell content) but measurable in cultures from estradiol-treated eels. Subsequent experiments examined effects of various secretagogues on GTH release from primary cultures of pituitary cells from estradiol-pretreated eels. GTH release was significantly increased (x1.5 to x3 basal release) by 10(-6) M GnRH-A as well as by both native GnRHs in the eel (mammalian GnRH, mGnRH, and chicken GnRH-II, cGnRH-II), at the same concentration. Lower GnRH concentrations had no significant effect, indicating a low sensitivity of gonadotrophs to GnRH, likely to be related to their immature state at the silver stage. The similar efficacy of mGnRH and cGnRH-II suggested that the pituitary GnRH receptor had a low specificity toward various molecular forms, in the eel as in the other nonmammalian species. The protein kinase C (PKC) activator (phorbol ester: PMA) also stimulated GTH secretion, with a maximal effect at 10(-8) M, indicating that the PKC pathway was functional. In contrast, a depolarizing agent (50 mM KCl) had no significant effect on GTH release, suggesting lack of a functional voltagesensitive calcium channel (VSCC) secretory pathway. Perifusion experiments on whole pituitary confirmed the lack of effect of KCl on gonadotrophs from E2-pretreated eels and indicated that an additional in vivo treatment with GnRH agonist and dopamine antagonist could induce the differentiation of a functional VSCC pathway. These characteristics of the transduction mechanisms may be related to the immature state of the eel gonadotrophs at the silver stage.

Anguilla↗

PubMed1996

Temperature dependence of NMR relaxation times of nucleoside triphosphates and inorganic phosphate in the isolated perfused rat liver. Effect on Pi compartmentation.

The effect of temperature on 31P NMR spectra from isolated perfused rat livers was studied at 9.4 T. Relaxation times (T1 and T2) of uncleoside triphosphates (NTP) and inorganic phosphate (Pi) were determined at 37, 25, 15, and 4 degrees C. Under hypothermic conditions, an unexpected apparent line sharpening in the Pi spectral region and a clear emergence of an additional Pi resonance were observed. This additional signal was assigned to mitochondrial Pi. T1 values obtained for cytosolic and mitochondrial Pi at 4 degrees C were 1.14 +/- 0.24 s (n = 5) and 0.71 +/- 0.18.s (n = 5), respectively. No significant mitochondrial contribution to the Pi resonance was observed at 37 degrees C. Quantification of Pi and NTP liver contents at 37 and 4 degrees C was performed by comparing the perfused liver spectrum and the corresponding perchloric acid extract spectrum. Under experimental conditions of low external Pi (0.12 mM), it was concluded that intracellular Pi was completely NMR-visible at 4 and 37 degrees C. The observation of the mitochondrial Pi signal at 4 degrees C was well explained by an increase in the Pi level within the matrix, in response to the mitochondrial swelling induced by hypothermia, as observed by electron microscopy. T2 values for the cytosolic Pi at 37 and 4 degrees C were 17 +/- 4 ms (n = 8) and 22 +/- 4 ms (n = 10), respectively. Comparison with measured linewidths indicated that line broadening for the main phosphorylated metabolites--including matrix Pi--was the result of B0 field inhomogeneity. The additional broadening of the cytosolic Pi resonance at 4 and 37 degrees C was attributed to pH heterogeneity within the liver.

Animals↗

PubMed1996

Body temperature and the return of slow wave activity in extended sleep.

The time courses of slow wave sleep (SWS) and EEG slow wave activity (SWA) were examined in relation to core body temperature (CBT) during extended sleep periods of 15 h. Ten subjects (4 male, 6 female; aged 18-29 years) slept in the laboratory for 3 consecutive nights (2 of 8 h, and the last of 15 h). Bedtime was as close as possible to subjects' habitual bedtimes, but was always between 23.00 h and 1.00 h, and was the same on all nights. Standard polysomnographic measures as well as rectal temperature were collected continuously each night. Using 3 h blocks, SWS and SWA declined with time asleep, then showed a significant increase in the final 3 h. Using a more specific measure with 15 min means, 8 of the 10 subjects showed SWA returns late in sleep, that were not related to preceding amounts of waking after sleep onset (WASO), rapid eye movement sleep (REMS), or WASO+REMS. The timing and magnitude of the SWA return was significantly associated with the phase of CBT as indexed by delay from sleep onset to CBT minimum. The findings are consistent with a 12 h rhythm of SWS and SWA that is related to the phase of the CBT rhythm, with the minor pole of SWS/SWA occurring independently of WASO and/or REMS.

Adolescent↗

PubMed1995

Changes in the fibronectin-specific integrin expression pattern modify the migratory behavior of sarcoma S180 cells in vitro and in the embryonic environment.

The molecules that mediate cell-matrix recognition, such as fibronectins (FN) and integrins, modulate cell behavior. We have previously demonstrated that FN and the beta 1-integrins are used during neural crest cell (NCC) migration in vitro as well as in vivo, and that the FN cell-binding domains I and II exhibit functional specificity in controlling either NCC attachment, spreading, or motility in vitro. In the present study, we have analyzed the effect of changes in the integrin expression patterns on migratory cell behavior in vivo. We have generated, after stable transfection, S180 cells expressing different levels of alpha 4 beta 1 or alpha 5 beta 1 integrins, two integrins that recognize distinct FN cell-binding domains. Murine S180 cells were chosen because they behave similarly to NCC after they are grafted into the NCC embryonic pathways in the chicken embryo. Thus, they provide a model system with which to investigate the mechanisms controlling in vitro and in vivo migratory cell behavior. We have observed that either the overexpression of alpha 5 beta 1 integrin or the induction of alpha 4 beta 1 expression in transfected S180 cells enhances their motility on FN in vitro. These genetically modified S180 cells also exhibit different migratory properties when grafted into the early trunk NCC migratory pathways. We observe that alpha 5 and low alpha 4 expressors migrate in both the ventral and dorsolateral paths simultaneously, in contrast to the parental S180 cells or the host NCC, which are delayed by 24 h in their invasion of the dorsolateral path. Moreover, the alpha 4 expressors exhibit different migratory properties according to their level of alpha 4 expression at the cell surface. Cells of the low alpha 4 expressor line invade both the ventral and dorsolateral pathways. In contrast, the high expressors remain as an aggregate at the graft site, possibly the result of alpha 4 beta 1-dependent homotypic aggregation. Thus, changes in the repertoire of FN-specific integrins enable the S180 cells to exploit different pathways in the embryo and regulate the speed with which they disperse in vivo and in culture. Our studies correlate well with known changes in integrin expression during neural crest morphogenesis and strongly suggest that neural crest cells that migrate into the dorsolateral path, i.e., melanoblasts, do so only after they have upregulated the expression of FN receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

Differential regulation of the two forms of gonadotropin-releasing hormone (mGnRH and cGnRH-II) by sex steroids in the European female silver eel (Anguilla anguilla).

The effect of steroids on the two gonadotropin-releasing hormone (GnRH) forms present in the eel (mammalian GnRH, mGnRH and chicken GnRH-II, cGnRH-II), as well as on gonadotropin (GTH), was studied using specific radioimmunoassays. Female silver eels received chronic treatments with various steroids (estradiol, testosterone, androstenedione, 5 alpha-androstane-3 beta, 17 beta-diol). Estradiol or the combination of estradiol and androgens induced increases in brain and pituitary mGnRH levels and pituitary GTH level, whereas androgens given alone had no significant effect. In contrast, androgens or their combination with estradiol reduced brain cGnRH-II levels (this form remaining undetectable in the pituitary), estradiol given alone having no significant effect. This work demonstrates that the two forms of GnRH undergo a differential regulation by steroids, with a positive estrogen-dependent feedback on mGnRH (as well as on GTH) and a negative androgen-dependent feedback on cGnRH-II. These data are in agreement with previous results obtained in experimentally matured female eels (induced by a gonadotropic treatment which stimulates the production of both estrogens and androgens) showing increases in mGnRH and GTH levels, as well as a decrease in cGnRH-II [1]. The positive feedback of steroids on the mGnRH-GTH axis adds credence to the hypothesis according to which mGnRH would be the main form involved in the control of the gonadotropic function. This positive feedback would play an important role, amplifying pubertal stimulation of the gonadotropic axis, in this fish species.

Amino Acid Sequence↗

PubMed1994

The distribution of GABA-immunoreactive neurons in the brain of the silver eel (Anguilla anguilla L.).

The distribution of GABA-immunoreactivity was studied in the brain of the silver eel (Anguilla anguilla) by means of antibodies directed against GABA. Immunoreactive neuronal somata were distributed throughout the brain. Positive perikarya were detected in the internal cellular layer of the olfactory bulb, and in all divisions of the telencephalon, the highest density being observed along the midline. Numerous GABA-reactive cell bodies were found in the diencephalon, particularly in the preoptic and tuberal regions of the hypothalamus, and the dorsolateral, dorsomedial and ventromedial thalamic nuclei. In the optic tectum, the majority of GABA-positive cell bodies were located in the periventricular layer. A number of immunolabeled cell bodies were observed in different tegmental structures, notably the torus semicircularis. In the cerebellum, the Purkinje cells were either very intensely or very weakly immunoreactive. In the rhombencephalon, reactive cell bodies were observed in the eminentia granularis, the valvula cerebellaris, the octavolateral nucleus, the lobus vagus and in the vagal and glossopharyngeal motor nuclei. Intensely immunoreactive axons and terminals were observed in the external granular layer and internal cellular layer of the olfactory bulb. In the telencephalon, the highest density of reactive fibres and boutons was found in the fields of the medial wall. Many immunolabeled fibres were seen in the medial and lateral forebrain bundles. In the diencephalon, intense labelling of fibres and terminals were observed in the nuclei situated close to the midline. In the optic tectum the highest density of reactive fibres was seen in the sfgs, the layer to which the retina projects massively. Finally, in the rhombencephalon the strongest labelling of neurites was observed in the nuclei of the raphé, the nucleus octavocellularis magnocellularis and the nuclei of the IXth and Xth cranial nerves. The GABAergic system of the eel, which is well developed, appears to be generally comparable to that described in tetrapod vertebrates.

Anguilla↗

PubMed1994

Immunocytochemical localization of mammalian GnRH (gonadotropin-releasing hormone) and chicken GnRH-II in the brain of the European silver eel (Anguilla anguilla L.).

Using specific antibodies for the two molecular forms of gonadotropin-releasing hormone (GnRH) present in the European eel, Anguilla anguilla, (mammalian GnRH, mGnRH, and chicken GnRH II, cGnRH-II), we employed immunocytochemistry to determine the distribution of these two peptides in the brain and in the pituitary. The results indicate that mGnRH and cGnRH-II are localized in different neurons: mGnRH-immunoreactive (ir) perikaria were observed in the olfactory bulbs, the junction between olfactory bulbs and telencephalon (nucleus olfactoretinalis), the telencephalon, the preoptic region and the mediobasal hypothalamus. These cell bodies are located along a continuum of ir-fibers that could be traced from the olfactory nerve to the pituitary. Mammalian GnRH-ir fibers were detected in many parts of the brain (olfactory bulbs, ventral telencephalon, hypothalamus, optic tectum, mesencephalon) and in the pituitary. Chicken GnRH-II-ir cell bodies were detected in the nucleus of the medial longitudinal fasciculus of the midbrain tegmentum, but only scattered fibers could be detected in different parts of the brain. The pituitary exhibited very few cGnRH-II-ir fibers, contrasting with an extensive mGnRH innervation. These results are in agreement with our previous data obtained in the same species using specific radioimmunoassays for mGnRH and cGnRH-II. They demonstrate a differential distribution of the two forms of GnRH in the brain of the eel, as in the brain of some other vertebrate species, and suggest differential physiological roles for the two GnRH forms in the eel. They also provide information concerning the evolution of the GnRH systems in vertebrates.

Anguilla↗

PubMed1994

Differential perturbations in the morphogenesis of anterior structures induced by overexpression of truncated XB- and N-cadherins in Xenopus embryos.

Cadherins, a family of Ca-dependent adhesion molecules, have been proposed to act as regulators of morphogenetic processes and to be major effectors in the maintenance of tissue integrity. In this study, we have compared the effects of the expression of two truncated cadherins during early neurogenesis in Xenopus laevis. mRNA encoding deleted forms of XB- and N-cadherin lacking most of the extracellular domain were injected into the four animal dorsal blastomeres of 32-cell stage Xenopus embryos. These truncated cadherins altered the cohesion of cells derived from the injected blastomeres and induced morphogenetic defects in the anterior neural tissue to which they chiefly contributed. Truncated XB-cadherin was more efficient than N-cadherin in inducing these perturbations. Moreover, the coexpression of both truncated cadherins had additive perturbation effects on neural development. The two truncated cadherins can interact with the three known catenins, but with distinct affinities. These results suggest that the adhesive signal mediated by cadherins can be perturbed by overexpressing their cytoplasmic domains by competing with different affinity with catenins and/or a common anchor structure. Therefore, the correct regulation of cadherin function through the cytoplasmic domain appears to be a crucial step in the formation of the neural tissue.

Amino Acid Sequence↗