Signatures of the Self-Similar Regime of Strongly Coupled Stimulated Brillouin Scattering for Efficient Short Laser Pulse Amplification.

Plasma-based laser amplification is considered as a possible way to overcome the technological limits of present day laser systems and achieve exawatt laser pulses. Efficient amplification of a picosecond laser pulse by stimulated Brillouin scattering (SBS) of a pump pulse in a plasma requires to reach the self-similar regime of the strongly coupled (SC) SBS. In this Letter, we report on the first observation of the signatures of the transition from linear to self-similar regimes of SC-SBS, so far only predicted by theory and simulations. With a new fully head-on collision geometry, subpicosecond pulses are amplified by a factor of 5 with energy transfers of few tens of mJ. We observe pulse shortening, frequency spectrum broadening, and down-shifting for increasing gain, signatures of SC-SBS amplification entering the self-similar regime. This is also confirmed by the power law dependence of the gain on the amplification length: doubling the interaction length increases the gain by a factor 1.4. Pump backward Raman scattering (BRS) on SC-SBS amplification has been measured for the first time, showing a strong decrease of the BRS amplitude and frequency bandwidth when SBS seed amplification occurs.

Effect of natriuretic peptides on in vitro stimulated adrenocorticotropic hormone release and pro-opiomelanocortin mRNA expression by the fetal rat pituitary gland in late gestation.

OBJECTIVE AND METHODS: We investigated the effects of individual natriuretic peptides (atrial natriuretic peptide, ANP; brain natriuretic peptide, BNP, and C-type natriuretic peptide, CNP) on rat corticotropin-releasing factor stimulated adrenocorticotropic hormone (ACTH) secretion by the pituitary gland of 21-day-old rat fetuses in vitro and on pro-opiomelanocortin gene expression using in situ hybridization. RESULTS: Graded concentrations of ANP, BNP, or CNP (10(-10), 10(-9), and 10(-8) mol/l) induced a log dose dependent inhibition of ACTH secretion induced by rat corticotropin-releasing factor (10(-10) mol/l). These natriuretic peptides showed equipotent effects on a molar basis. Moreover, ANP, BNP, or CNP at 10(-10) mol/l reduced significantly the pituitary pro-opiomelanocortin mRNA expression. In addition, the immunoreactive ANP, BNP, and CNP cells were localized in the anterior lobe, but not in the intermediate lobe of the fetal pituitary gland. CONCLUSIONS: These data suggest that the fetal pituitary gland may be both a source and a target for natriuretic peptides that might control ACTH synthesis and release via an endocrine and/or paracrine mechanism. The natriuretic peptides could participate, as well as glucocorticoids, in the control of the corticotropin-stimulating activity of the fetal rat in late gestation.

Atrial natriuretic peptide and aldosterone secretions, and atrial natriuretic peptide-binding sites in kidneys and adrenal glands of pregnant and fetal rats in late gestation in response to a high-salt diet.

OBJECTIVE: This study aimed at determining, in the term pregnant rat, whether maternal and fetal plasma atrial natriuretic peptide (ANP) concentrations were modified in response to an oral sodium load, and to investigate whether any changes in plasma concentrations were able to modify the density and affinity of the different ANP-binding site subtypes in maternal and fetal kidneys and adrenal glands. METHODS: Pregnant rats kept in metabolic cages were divided into two groups. The normal sodium diet group had free access to rat chow and tap water whereas the high sodium diet group received 1% NaCl as drinking water for 10 consecutive days from day 11 to day 21 of gestation with free access to standard rat chow. Pregnant rats from both groups were killed by decapitation on day 21 of gestation. The plasma ANP and aldosterone concentrations were determined by RIA. The density and affinity of ANP receptors were determined in the maternal and fetal adrenal glands and kidneys. RESULTS: In the pregnant rats on the high-salt diet, the sodium and water intakes, as well as the urine volume and sodium excretion, were significantly higher than in the control group. After 10 days of high-salt intake, water and sodium retentions were not significantly different in the two groups, indicating that the pregnant rats were able to excrete excess salt. The high sodium intake did not change the body weight of the pregnant rats but did increase the body weight of the fetal rats. Maternal and fetal hematocrits remained unchanged in both groups, the high sodium intake did not modify plasma sodium concentration in the maternal rats but increased that of the fetuses, indicating an accumulation of sodium in the fetal rats. The dietary sodium intake did not change the plasma ANP concentrations but significantly decreased the plasma aldosterone concentrations in both the maternal and fetal rats. In response to the high-salt diet, the density and affinity of total ANP, ANPb and ANPc receptors were not altered in the maternal isolated renal glomeruli or the adrenal zona glomerulosa membranes or the fetal adrenal gland and kidney membrane preparations. CONCLUSION: These results suggest that ANP is not involved in the regulation of water and electrolyte balance in maternal and fetal rats during salt-loaded intake.

Effects of water deprivation on atrial natriuretic peptide secretion and density of binding sites in adrenal glands and kidneys of maternal and fetal rats in late gestation.

The effects of water deprivation for 3 days were studied in pregnant rats and their fetuses on day 21 of gestation. Maternal water deprivation induced a significant decrease of the body weight in both maternal and fetal rats. This weight loss was accompanied by significant increases in plasma osmolality and haematocrit in both maternal and fetal rats. Similarly, dehydration significantly decreased plasma atrial natriuretic peptide (ANP) concentrations and increased plasma aldosterone concentrations in maternal and fetal rats. Water-deprived maternal rats presented a significant increase in total ANP receptor density in isolated renal glomeruli and adrenal zona glomerulosa membranes. This increase was due to a significant increase in ANPc receptor density in both renal glomeruli and adrenal zona glomerulosa. The densities of total ANP, ANPb and ANPc receptors in fetal kidneys and adrenal glands were not affected by maternal dehydration. These results suggest that the dehydrated maternal rat is able to up-regulate the number of its ANP receptors in its kidneys and adrenal glands, in response to a decrease in plasma ANP concentrations. In contrast, the fetal rat does not seem to be able to regulate its own ANP receptors in response to maternal dehydration, in spite of a decrease in plasma ANP concentrations.

Association of 6- and 8-Hydroxyquinolines with Aerosol-OT in Heptane: Competition with Dimerization of 8-Hydroxyquinoline.

The enhancement and shift of the fluorescence spectrum of 8-hydroxyquinoline (8-HQ) in heptane upon gradual additions of the anionic surfactant aerosol-OT (AOT) allowed us to show that monomeric 8-HQ was progressively associated to the polar heads via H-bonding. This association competes with dimerization of 8-HQ in heptane which has been revealed by us in a previous work using vapor pressure osmometry measurements. Similar competition has been qualitatively reported by others in the case of 7-azaindole. In the present work, a comparison between the behaviors of 8- and 6-hydroxyquinoline was undertaken because the positions of the -OH and >/=N functions preclude dimerization in 6-hydroxyquinoline. This comparison resulted in the determinations of the binding constant of 8-HQ to AOT, Kass = 860 +/- 30, and of the dimerization constant in heptane, Kdim = (7.0 +/- 1.5) x 10(7). Hence the dimers of 8-HQ in heptane, never reported before, turned out to be of outstanding stability. Copyright 1998 Academic Press.

Nanocapillarity and Chemistry in Carbon Nanotubes

Open carbon nanotubes were filled with molten silver nitrate by capillary forces. Only those tubes with inner diameters of 4 nanometers or more were filled, suggesting a capillarity size dependence as a result of the lowering of the nanotube-salt interface energy with increasing curvature of the nanotube walls. Nanotube cavities should also be less chemically reactive than graphite and may serve as nanosize test tubes. This property has been illustrated by monitoring the decomposition of silver nitrate within nanotubes in situ in an electron microscope, which produced chains of silver nanobeads separated by high-pressure gas pockets.

Aligned carbon nanotube films: production and optical and electronic properties.

Carbon nanotube material can now be produced in macroscopic quantities. However, the raw material has a disordered structure, which restricts investigations of both the properties and applications of the nanotubes. A method has been developed to produce thin films of aligned carbon nanotubes. The tubes can be aligned either parallel or perpendicular to the surface, as verified by scanning electron microscopy. The parallel aligned surfaces are birefringent, reflecting differences in the dielectric function along and normal to the tubes. The electrical resistivities are anisotropic as well, being smaller along the tubes than perpendicular to them, because of corresponding differences in the electronic transport properties.

Molecular forms of atrial natriuretic peptide in atria and plasma from fetal and adult female rats.

Molecular forms of atrial natriuretic peptide (ANP) were determined by chromatography on Sephadex G50 fine coupled with a radioimmunoassay for rANP(1-28) in left and right atrial extracts and acidified plasmas from 17-, 19- and 21-day-old fetuses and adult female rats. Chromatographic analyses revealed two immunoreactive peaks of rANP with an apparent molecular weight of about 25 and 12 kD, respectively, in all atrial extracts from fetal and adult rats. Only one immunoreactive peak of rANP with an apparent molecular weight of about 3 kD was detected in all fetal plasmas. The 25- and 12-kD ANP molecular forms isolated from fetal atrial tissue and incubated with thrombin for 30 min at 37 degrees C were converted to ANP material with a molecular weight of about 3 kD. These results suggest that the two high molecular weight forms stored in fetal atrial tissue should be precursors of circulating rANP molecules, and the rat fetus should possess the same posttranslational processing of the precursor molecule as the adult rat as early as day 17 of gestation.

Magnetism from the atom to the bulk in iron, cobalt, and nickel clusters.

Molecular beam deflection measurements of small iron, cobalt, and nickel clusters show how magnetism develops as the cluster size is increased from several tens to several hundreds of atoms for temperatures between 80 and 1000 K. Ferromagnetism occurs even for the smallest sizes: for clusters with fewer than about 30 atoms the magnetic moments are atomlike; as the size is increased up to 700 atoms, the magnetic moments approach the bulk limit, with oscillations probably caused by surface-induced spin-density waves. The trends are explained in a magnetic shell model. A crystallographic phase transition from high moment to low moment in iron clusters has also been identified.

Characteristics and developmental changes of ANP-binding sites in rat adrenal glands during the perinatal period.

The binding of rANP(1-28) to receptors was studied on crude adrenal membranes from fetal rats between day 17 of gestation and term and also neonatal rats between weeks 1 and 4. The binding assays were carried out using 125I-rANP(1-28) as radioligand incubated with membrane preparations (2 mg/ml) for 90 min at 22 degrees C. The binding was specific, saturable and reversible. The Scatchard analysis of the binding data revealed a single class of binding sites of high affinity (kd approximately 10(-10) mol/l) which did not change significantly at all stages of development studied. The binding sites presented a higher affinity for ANP analogues which contained the C-terminal phenylalanine arginine residue. The number of ANP receptors expressed per adrenal increased regularly in fetal and neonatal rats and the perinatal evolution of these concentrations of ANP receptors was related to the increase in the size of the adrenals. When the concentrations of ANP receptors was expressed per microgram DNA, the concentrations of ANP receptors were higher in neonatal rats than in fetal rats and reflected the number of receptors per cell. These results suggest that these binding sites mediate the biological actions of ANF in the adrenal gland during the perinatal period.

Effects of rat corticotrophin-releasing factor, arginine vasopressin and oxytocin on the secretions of adrenocorticotrophic hormone and corticosterone in the fetal rat in late gestation: in vivo and in vitro studies.

The effects of rat corticotrophin-releasing factor (rCRF), arginine vasopressin (AVP) and oxytocin (OT) were investigated in vivo in 21-day-old rat fetuses injected through the umbilical vein and in vitro on perifused anterior pituitary glands from 21-day-old rat fetuses. In vivo, rCRF (1.25 pmol.50 microliter-1.fetus-1), AVP (5 pmol.50 microliter-1.fetus-1) alone and rCRF in association with AVP or oxytocin (12.5 pmol.50 microliter-1.fetus-1) increased plasma adrenocorticotrophic hormone (ACTH) and corticosterone levels only 30 min after the start of injection. During the first 10 min of the sampling period, the injection of these peptides alone or in combination and the injection of saline decreased the plasma ACTH concentration, which was lower than that of uninjected fetuses, but had no effect on the plasma corticosterone concentration. In vitro, the release of ACTH by perifused anterior pituitary glands was increased strongly by rCRF (4 pmol/0.5 ml) but only slightly by AVP (92 pmol/0.5 ml) and oxytocin (198 pmol/0.5 ml). Arginine vasopressin and oxytoxin potentiated the release of ACTH stimulated by rCRF in vitro but not in vivo. Our results suggest that rCRF is the major peptide that controls ACTH secretion in the fetal rat at term. In conclusion, the rise of the ACTH level observed only 30 min after injection of rCRF or AVP suggests the existence of a factor able to inhibit the ACTH response after injection of these peptides. This factor might be elicited by the blood volume expansion.

Effect of blood volume expansion on basal plasma atrial natriuretic factor and adrenocorticotropic hormone secretions in the fetal rat at term.

The effect of a blood volume expansion (1-1.5% of body weight) on atrial natriuretic factor (ANF) and adrenocorticotropic hormone (ACTH) secretions were investigated in 21-day-old rat fetuses injected intravenously through the umbilical vein with 50 microliters of isotonic saline. Basal ANF and ACTH concentrations were determined in the plasma with specific radioimmunoassays over a 30-min observation period. The basal plasma ANF concentration increased rapidly 1 min after blood volume expansion and then decreased to the control value 5 min later. The basal plasma ACTH concentration decreased during the first 10 min after injection and then increased to the control value 30 min after intravascular volume load. The results suggest that the fetal rat in late gestation is able to respond to blood volume expansion by increasing ANF secretion.

Effects of corticotropin-releasing factor, arginine vasopressin and oxytocin on the polymorphism of plasma adrenocorticotropic hormone in the rat fetus in late pregnancy.

The effects of rat corticotropin-releasing factor (rCRF, 1.25 pmol/50 microliters/fetus), arginine vasopressin (AVP, 5 pmol/50 microliters/fetus) and oxytocin (OT, 12.5 pmol/50 microliters/fetus) alone or in association were investigated in 21-day-old rat fetuses injected intravenously through the umbilical vein. Blood samples were collected 15 and 30 min after injection for the determination of corticosterone concentration and the different plasma molecular adrenocorticotropic hormone (ACTH) forms isolated by chromatography on Sephadex G50 fine. All the plasma samples chromatographed 15 and 30 min after injection of the different peptides showed 3 different molecular ACTH forms: big ACTH (> 20,000 molecular weight), intermediate ACTH (= 13,000) and little ACTH (= 4,500). The injection of rCRF or AVP alone and rCRF in association with AVP or OT increased the concentrations of big ACTH 15 min and little ACTH 30 min after injection. The injection of OT alone or in association with AVP did not change the concentration of the 3 molecular ACTH forms 15 and 30 min after injection. The rise of big ACTH 15 min after injection was not associated with a significant increase in plasma corticosterone concentration, whereas the increase in little ACTH 30 min later enhanced plasma corticosterone concentration. Our results suggest that rCRF or AVP alone and rCRF in association with AVP or OT injected intravenously in the fetal rat produced a selective release of the molecular ACTH forms and the increase in the plasma corticosterone concentration occurred when the proportion of little ACTH which is the predominant ACTH form in the fetal rat was enhanced.

ACTH secretion from isolated hypophysial anterior lobes of male and female newborn rats: effects of corticotrophin-releasing factor, arginine vasopressin and oxytocin alone or in combination.

ACTH release by the anterior pituitary lobes of 8-day-old newborn rats (males and females) in the presence of rat corticotrophin-releasing factor (rCRF), arginine vasopressin (AVP) and oxytocin, given alone or in association, was measured in vitro. Rat CRF and AVP induced a dose-dependent release of ACTH in both sexes, while oxytocin was unable to stimulate ACTH secretion except at the highest dose tested. No sex-related difference was noted for any of the responses. Oxytocin (1 nmol/l) potentiated the response to rCRF (0.20 nmol/l) by the anterior pituitary lobes of females but not by those of males. This oxytocin potentiation was abolished when female newborn rats were injected at birth with testosterone (1 mg). AVP (1 nmol/l) alone stimulated ACTH release from the anterior pituitary lobes of the newborn rats of both sexes and markedly potentiated the ACTH response to rCRF. Although no difference between the sexes was noted for basal levels of AVP and oxytocin in the hypothalamus, the neurointermediate lobe and the peripheral plasma, the present data on the sex-related effect of oxytocin on the newborn adenohypophysis could, in part, explain why ACTH release in response to ether stress was previously reported to be more lasting in females than in males on day 8 postpartum.

Effect of rat atrial natriuretic factor on in vivo and in vitro aldosterone and corticosterone secretions in the rat during the perinatal period.

The effect of rat atrial natriuretic factor (rANF) on aldosterone and corticosterone secretion was investigated in vivo in 21-day-old rat fetuses injected intravenously through the umbilical vein and in vitro on isolated adrenal cells from 17-, 19- and 21-day-old fetuses and 1-, 2-, 3- and 4-week-old rats. In vivo, rANF (50 pmol/50 microliters/fetus) inhibited both basal levels and secretion of aldosterone stimulated by adrenocorticotropin hormone (ACTH(1-24), 0.25 pmol/50 microliters/fetus), but not corticosterone secretion. In vitro, the addition of graded concentrations of rANF (0.001, 0.01 and 10 nmol/l) to the incubation medium did not affect the basal aldosterone and corticosterone secretions of fetal and neonatal adrenal cells. ACTH(1-24) (0.1 nmol/l) stimulated productions of both corticosterone and aldosterone by the adrenal cells at all stages studied. The addition of graded concentrations of rANF to the incubation medium containing ACTH(1-24) (0.1 nmol/l) induced a dose-dependent inhibition of aldosterone secretion by the adrenal cells from 21-day-old fetuses and newborn rats. In contrast, no effect was observed on cells from 17- and 19-day-old fetuses. At all stages investigated, the three doses of rANF were unable to affect ACTH-induced corticosterone secretion in vitro. In isolated adrenal cells from 2-week-old rats, rANF (10 nmol/l) inhibited the secretion of aldosterone induced by ACTH(1-24) (0.1 nmol/l), and by different steroids of the aldosterone synthetic pathway (progesterone, 11-deoxycorticosterone, corticosterone, 1 mumol/l for each steroid). These results suggest that rANF is a specific inhibitor of aldosterone synthesis in the perinatal period of the rat and that the inhibitory effect of rANF occurs both during the early and late pathways of aldosteroidogenesis.

Development of adenylate cyclase activity in rat adrenal glands during the perinatal period.

Adenylate cyclase activity was studied in crude adrenal membranes from fetal and newborn rats. Basal adenylate cyclase activity was higher in fetal than in newborn rats. ACTH(1-24) (1 mumol/l), guanosine (beta,gamma-imido diphosphate) (Gpp(NH)p) (10 mumols/l) and forskolin (100 mumols/l) stimulated the activity of the enzyme at all stages studied. The sensitivity of the enzyme to ACTH was maximal on days 17 and 19 of gestation. When Gpp(NH)p was added to ACTH(1-24), the response was significantly higher than that induced by Gpp(NH)p alone. Forskolin and Gpp(NH)p alone increased the adenylate cyclase activity and the sensitivity of the enzyme to these compounds was higher in newborn rats than in fetuses. Treatment of 21-day-old rat fetuses with ACTH increased the response of adenylate cyclase to Gpp(NH)p alone or to forskolin whereas treatment with dexamethasone did not modify the response of the enzyme to either Gpp(NH)p alone or forskolin. Our results show that the change in the responsiveness of adenylate cyclase takes place immediately after birth during the first week and ACTH is able to induce a maturation of the fetal adrenal adenylate cyclase system.

Ontogeny of ACTH(1-24) receptors in rat adrenal glands during the perinatal period.

Binding of ACTH to receptors was studied on crude adrenal membranes from fetal and newborn rats. 125I-Labelled ACTH(1-24) was used as the radioligand, the steroidogenic potency of which was 100-fold lower than that of unlabelled ACTH(1-24). Binding was specific, rapidly equilibrated and temperature dependent. Scatchard analysis of the binding data revealed a single class of binding sites with a dissociation constant of about 100 nmol/l at all stages of development studied. The concentration of ACTH receptors expressed per mg membrane proteins decreased in fetuses between days 17 and 21 of gestation and remained stable in newborn rats from weeks 1 to 4. The number of ACTH receptors expressed per adrenal increased regularly in fetal and newborn rats. The perinatal evolution of these concentrations of ACTH receptors is related to the increase in the size of the adrenals and the changes in cytoplasmic structures of the adrenocortical cells. When the number of ACTH-binding sites was expressed per microgram DNA, maximum values occurred in fetuses on day 19 of gestation, and minimum values in newborn rats, 1 week after birth. There was an excellent correlation between the plasma levels of immunoreactive ACTH and corticosterone and the number of ACTH receptors per microgram DNA during the perinatal period. Other results suggest that ACTH is able to up-regulate the number of its own receptors.

Corticotrophin-releasing factor immunoreactivity in the hypothalamus of the rat during the perinatal period.

Corticotrophin-releasing factor-41 (CRF-41) immunoreactivity has been measured in hypothalamic extracts of fetal (on days 17, 19 and 21 of gestation), neonatal (1, 2, 3 and 4 weeks of age) and adult rats with a specific radioimmunoassay developed for synthetic rat CRF-41. The hypothalamic content (fmol) and concentration (fmol/mg protein) of immunoreactive CRF-41 gradually increased with age. Chromatography of hypothalamic extracts on Sephadex G-50 Fine showed one single peak of immunoreactive CRF-41 which co-eluted with synthetic rat CRF-41. The retention time of hypothalamic CRF-41 during high-performance liquid chromatography was identical to that of synthetic rat CRF-41 at all stages investigated. These results are consistent with the development of neurones containing CRF-41-like molecules in both the hypothalamus and the median eminence of the fetus, as well as with the hypothalamic control of the cortico-stimulating function of the pituitary gland as early as day 19 of gestation.