Showing papers by "Collège de France published in 1989"

Scaling of hard thermal turbulence in Rayleigh-Bénard convection

Abstract: An experimental study of Rayleigh-Benard convection in helium gas at roughly 5 K is performed in a cell with aspect ratio 1. Data are analysed in a ‘hard turbulence’ region (4 × 107 < Ra < 6 × 1012) in which the Prandtl number remains between 0.65 and 1.5. The main observation is a simple scaling behaviour over this entire range of Ra. However the results are not the same as in previous theories. For example, a classical result gives the dimensionless heat flux, Nu, proportional to . A new scaling theory is described. This new approach suggests scaling indices very close to the observed ones. The new approach is based upon the assumption that the boundary layer remains in existence even though its Rayleigh number is considerably greater than unity and is, in fact, diverging. A stability analysis of the boundary layer is performed which indicates that the boundary layer may be stabilized by the interaction of buoyancy driven effects and a fluctuating wind.

Molecular layering in the spreading of wetting liquid drops

Abstract: THE details of the mechanisms involved in the spreading of liquids on solid substrates are still poorly understood, partly because dominant phenomena may occur in the range 0 to 100 A from the substrate. Experimental investigation at the molecular level should provide information on the basic physical process involved. Here we present the results of studies on the time-dependent thickness profile of tiny drops spreading completely on a smooth surface (a silicon wafer). We use simple liquids which lack any orientational or structural order in the bulk. Using ellipsometry, an optical technique that provides measurements of thickness with sub-molecular resolution, we show that there is strong, dynamic structuring of the fluid near the solid surface, in that the spreading droplet advances as a series of distinct molecular layers. These observations may provide a clue to the nature of the molecular interactions or fluid flow phenomena involved in the spreading process.

Development of the origin of the coronary arteries, a matter of ingrowth or outgrowth?

Abstract: Inconsistencies still exist with regard to the exact mode of development of proximal coronary arteries and coronary orifices. In this regard 15 quail embryos were investigated using a monoclonal anti-endothelium antibody, enabling a detailed study of the development of endothelium-lined vasculature. Coronary orifices emerged at 7–9 days of incubation (Zacchei stages 24–26) and were invariably present at 10 days of incubation (Zacchei stage 27).

Dynamics of wetting of tiny drops: Ellipsometric study of the late stages of spreading.

Abstract: Via ellipsometry, we study the profile evolution of very small drops (about ${10}^{\mathrm{\ensuremath{-}}4}$ \ensuremath{\mu}l) of nonvolatile liquids, spreading completely on silicon wafers. The evolution of the profiles are studied at molecular thicknesses, and for the first time it is shown that (i) the final stage of spreading in the cases studied is not a pancake, as predicted by the theory of de Gennes and Joanny (for S/\ensuremath{\gamma}\ensuremath{\ll}1), but rather is a two-dimensional gas and (ii) short-range forces and molecular dymanics may drastically affect the profile of the droplet.

Catecholamine-containing neurons in the sheep brainstem and diencephalon: immunohistochemical study with tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) antibodies.

Abstract: The present study describes the distribution and morphological characteristics of neurons and nerve fibers containing the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the sheep brainstem and diencephalon on the basis of immunohistochemical procedures. Neurons and fibers were considered to be dopaminergic if they showed anti-tyrosine hydroxylase immunoreactivity, without corresponding anti-dopamine-beta-hydroxylase immunoreactivity. The structures labeled with both antisera were considered noradrenergic or adrenergic. The distribution of catecholaminergic neurons corresponds to that described by other authors with similar methods in the rat and in primates. The noradrenergic neurons belong to cell groups A1 to A7 and the dopaminergic neurons to cell groups A8 to A15. In almost all studied areas, the catecholaminergic innervation is similar to that observed in the other species. However, the central catecholaminergic systems of the sheep showed some specific characteristics: (1) groups A3 and A4, described in the rat, were not found, (2) group A14 contains fewer neurons than in the rat, (3) group A15 does not contain a dorsal but only a ventral portion, (4) there is a larger dispersion of neurons within each group, especially A6 and A7, than in rodents, and (5) there is a larger noradrenergic innervation of the catecholaminergic groups than in the other species.

Influence of extracellular matrix proteins on the expression of neuronal polarity

Abstract: The influence of laminin (LN) and fibronectin (FN) on the differentiation of individual neurones from the embryonic rat central nervous system was studied in vitro. In control cultures or in the presence of soluble FN, most neurones had several dendrite-like and one axon-like processes. On substratum-bound LN, multipolar and unipolar cells were present. Soluble LN and bound FN induced a very simple neuronal morphology, most neurones having only one axon-like neurite as defined by morphological and immunocytochemical characteristics. The significant reduction of neuronal adhesion and spreading in conditions leading to the growth inhibition of dendrite-like processes suggests that, contrary to that of axons, dendrite growth strongly depends on neuronal adhesion. We propose a model in which the different dependency of axonal and dendritic outgrowth towards adhesion and spreading is explained by the respective physical properties of the two types of neurites.

Secretion of nerve growth factor in cultures of glial cells and neurons derived from different regions of the mouse brain.

Abstract: The regional ability of central neurons and glial cells to produce nerve growth factor (NGF) was studied in vitro. NGF secretion was compared in cultures of perinatal astrocytes or embryonic neurons that were derived from various mouse brain structures. No regional differences were detected among cultures of post-natal day 2 glial cells of hippocampal, cortical, striatal, or mesencephalic origin. In all cases, levels of NGF released by the cells were very similar. They were closely correlated to the growth rate as shown by the fact that exponentially growing cells produced relatively more factor than did confluent cells, a finding in agreement with previous observations. Unlike growth-phase cells, primary astrocytes immediately plated at high cell density did not secrete any assayable factor before the 7th day of culture. Levels of NGF found during the following days remained low. In contrast, striking differences were observed among cultures of embryonic neurons. NGF was found in relatively large amounts in cultures of embryonic day 17 or 19 striatal neurons, whereas media conditioned by neurons from the mesencephalon, cortex, or septum contained much less factor. Amounts of NGF assayed in cultures of hippocampal neurons varied with the time of sampling of this brain structure. Levels of factor were significantly higher in media conditioned by embryonic day 19 neurons than in media of embryonic day 17 neurons. However, amounts of NGF found in supernatants of hippocampal neurons remained smaller than those present in cultures of striatal nerve cells. Altogether, the results suggest that, in addition to astrocytes, central neurons may also synthesize and secrete NGF in vitro and that this phenomenum is dependent on both the origin and the developmental stage of the neuronal population.

Tachykinin receptors of the NK1 type (substance P) coupled positively to phospholipase C on cortical astrocytes from the newborn mouse in primary culture.

Abstract: Specific 125I-Bolton-Hunter substance P (125I-BHSP) binding sites are present on intact cortical astrocytes of the newborn mouse in primary culture. Therefore, these cells were used to ascertain the existence of functional substance P (SP) receptors coupled positively to phospholipase C. SP stimulated phosphoinositide breakdown with an EC50 value (4.5 x 10(-10) M) similar to its IC50 value (3.8 x 10(-10) M) for inhibiting 125I-BHSP binding. The maximal response to (10(-6) M SP for 60 min) obtained was approximately 500% of control values. The rank order of potency of tachykinins was SP greater than neurokinin (NK) A greater than NKB. Long SP C-terminal fragments were more potent than shorter ones in stimulating the accumulation of 3H-inositol phosphates. SP free acid and SP N-terminal fragments were without effect. [L-Pro9]SP and SP methyl ester, two selective agonists of NK1 receptors, were almost as potent as SP. An excellent correlation was found when the abilities of tachykinins and their analogs for stimulating phosphoinositide breakdown and for inhibiting 125I-BHSP binding were compared. Finally, when used at a concentration of 3 x 10(-6) M, spantide [( D-Arg1, D-Trp7,9, Leu11]SP), an SP antagonist, competitively reduced the stimulatory effect of SP on accumulation of 3H-inositol phosphates. These results demonstrate the presence of functional SP receptors (NK1) on cortical astrocytes from the newborn mouse in primary culture.

Distinct presynaptic control of dopamine release in striosomal and matrix areas of the cat caudate nucleus.

Abstract: By use of a sensitive in vitro microsuperfusion method, the cholinergic prsynaptic control of dopamine release was investigated in a prominent striosome (areas poor in acetylcholinesterase activity) located within the core of cat caudate nucleus and also in adjacent matrix area. The spontaneous release of [3H]dopamine continuously synthesized from [3H]tyrosine in the matrix area was found to be twice that in the striosomal area; the spontaneous and potassium-evoked releases of [3H]dopamine were calcium-dependent in both compartments. With 10(-6) M tetrodotoxin, 5 x 10(-5) M acetylcholine stimulated [3H]dopamine release in both striosomal and matrix areas, effects completely antagonized by atropine (10(-6) M), thus showing the involvement of muscarinic receptors located on dopaminergic nerve terminals. Experiments without tetrodotoxin revealed a more complex regulation of dopamine release in the matrix: (i) In contrast to results seen in the striosome, acetylcholine induced only a transient stimulatory effect on matrix dopamine release. (ii) Although 10(-6) M atropine completely abolished the cholinergic stimulatory effect on [3H]dopamine release in striosomal area, delayed and prolonged stimulation of [3H]dopamine release was seen with atropine in the matrix. The latter effect was completely abolished by the nicotinic antagonist pempidine (10(-5) M). Therefore, in the matrix, in addition to its direct (tetrodotoxin-insensitive) facilitatory action on [3H]dopamine release, acetylcholine exerts two indirect (tetrodotoxin-sensitive) opposing effects: an inhibition and a stimulation of [3H]dopamine release mediated by muscarinic and nicotinic receptors, respectively.

A neuroglial cooperativity is required for the potentiation by 2-chloroadenosine of the muscarinic-sensitive phospholipase C in the striatum.

Abstract: In rat striatal slices, 2-chloroadenosine, which had no direct effect on inositol phosphate formation, potentiated in a dose-dependent manner the accumulation of inositol phosphates induced either by carbamylcholine (10(-3) M) or by noradrenaline (10(-4) M). Experiments made on pure populations of striatal neurons or striatal glial cells in primary culture from mouse embryos indicated that 2-chloroadenosine potentiated the noradrenaline-elicited phosphoinositide breakdown in striatal glial cultures but did not modify the responses evoked either by noradrenaline or by carbamylcholine in striatal neuronal cultures. However, 2-chloroadenosine enhanced both the carbamylcholine and the noradrenaline-induced accumulation of inositol phosphates in neuroglial cocultures just as it did in rat striatal slices. The potentiation by 2- chloroadenosine of the carbamylcholine response, which is neuron specific, involved a cooperative effect between neurons and glial cells and, as shown by additional experiments, required a brief contact only between the 2 types of cells. The potentiating effect of 2- chloroadenosine was blocked completely by a nonselective A1, A2 adenosine antagonist isobutylmethylxanthine either on rat striatal slices or on mouse embryonic cocultures (noradrenaline and carbamylcholine responses) or on mouse embryonic glial cultures (noradrenaline response). These data indicate the involvement of an extracellular membrane-bound adenosine receptor, possibly of the A1 subtype since N6-cyclohexyladenosine, an A1 adenosine receptor agonist, was more efficient than 5′-N-ethylcarboxamide-adenosine, a rather selective A2 adenosine receptor agonist. We propose that 2- chloroadenosine acts through an adenosine receptor located on glial cells and induces the synthesis of a substance that improves the coupling between carbamylcholine or noradrenaline and phospholipase C located in glial cells or neurons.

Differential Modulation of D1 and D2 Dopamine‐Sensitive Adenylate Cyclases by 17β‐Estradiol in Cultured Striatal Neurons and Anterior Pituitary Cells

Abstract: Primary cultures of anterior pituitary cells from female rats and of mouse embryonic striatal neurons were used to study the effects of 17 beta-estradiol on D1- and D2-dopamine (DA)-sensitive adenylate cyclase. 17 beta-Estradiol pretreatment (10(-9) M, 72 h) suppressed the D2-DA-induced inhibition of adenylate cyclase activity in anterior pituitary cells. The steroid (10(-9) M, 24 h) also blocked the D2-DA-evoked response in striatal neurons whereas it enhanced by twofold the D1-DA-induced stimulation of the enzyme activity in these neurons. All these effects of the steroid were dose dependent and specific, as neither 17 alpha-estradiol, dexamethasone, nor progesterone used at the same concentration (10(-9) M) was effective. Furthermore, the modulation of DA-sensitive adenylate cyclases by the steroid required long-term exposure of living cells to 17 beta-estradiol since neither 17 beta-estradiol pretreatment for 4 h nor its addition to broken cells directly into the adenylate cyclase assay induced any alteration in the DA-sensitive adenylate cyclase activity. These results are in agreement with a genomic effect of the steroid. Using both anterior pituitary cells and striatal neurons in culture, 17 beta-estradiol affected neither the total number of DA (D1 and D2) receptors nor the estimated number of adenylate cyclase catalytic units. Therefore, it is suggested that the steroid modifies the coupling process by a mechanism that still has to be elucidated. These results demonstrate an effect of 17 beta-estradiol on DA target cells in both systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple mRNAs encode peripherin, a neuronal intermediate filament protein.

Abstract: Three cDNA clones of 16 (3u), 12 (5g) and 06 (5b) kbp, specific for peripherin, a neuronal intermediate filament protein (IFP), have been isolated from a murine neuroblastoma cell lambda gt11 library by immunoscreening using peripherin antiserum Antibodies eluted from the fusion proteins produced by clones 3u and 5g recognize the peripherin spots on immunoblots Where they overlap the three cDNAs have identical sequences cDNA 5g exhibits the closest homology to type III IFP cDNAs cDNA 3u is identical to the corresponding region of cDNA 5g, except for the insertion of a 96 bp fragment at a position corresponding to the junction of exons 4 and 5 in type III IFP cDNAs cDNA 5b is also identical to the corresponding region of cDNA 5g, except for the deletion of a 62 bp fragment at the junction of exons 8 and 9 in type III IFP cDNAs S1 mapping experiments performed with probes covering the 3' end of the two unexpected regions show that three distinct mRNAs correspond to the three cDNAs Moreover, three peripherin products, two minor 61 and 56 kd products in addition to the major 58 kd peripherin, are observed when poly(A)+ RNA is in vitro translated, the 61 kd peripherin being translated from the 3u-selected RNA The three RNAs originate from alternative splicing of a unique peripherin gene, thus generating polymorphism of peripherin

Studies of intermediate vector boson production and decay in UA1 at the CERN proton-antiproton collider

Abstract: An extensive study of production and decay properties of charged and neutral Intermediate Vector Bosons (IVB) at the CERN proton-antiproton collider is presented. Intermediate Vector Bosons were detected in the electron, muon, and tau decay modes at centre-of-mass energies of 0.546 and 0.630 TeV. This paper is a summary, based on all the available data from the UA1 experiment from the running periods 1982–1985. Results are presented and compared with expectations of the Standard Eletroweak Model and QCD-improved Drell-Yan annihilation processes. The general conclusion is that there is an excellent agreement between the predictions of the Standard Model and our measurements.

Weak adhesive junctions

Abstract: Weak mechanical junctions can be found (1) at glass/rubber interfaces ; (2) between two rubber blocks with a few interblock crosslinks ; (3) between two glassy polymers A/B with a monolayer of AB copolymer ; (4) between two identical copolymers after partial interdiffusion. When a fracture propagates along such a junction, the dissipation tends to be localized in the junction region. We present a phenomenological description of this process in termes of two ingredients : (a) a threshold stress σc associated with chemical scission in cases (1, 2) and with plastic flow in cases (3, 4) ; (b) a « succion » process — with a succion velocity proportional to the local stress σ, — ending when the volume transfer (per unit area) has reached a certain limit hf. We restrict (for the moment) our attention to cases without cavitation (no crazes). From a very crude analysis of the mechanical behavior around the weak junction, we are led to expect two fracture regimes : (α) at low fracture velocities V, the process is quasi static and the fracture energy GIC scales like σc hf ; β) beyond a velocity V*, the length of the succion region is very much spread out, and GIC increases with V. But we have not yet built a precise mechanical analysis of our model.

Cytosolic free calcium in single microdissected rat cortical collecting tubules.

Abstract: Cytosolic free Ca2+ ([Ca2+]i) was measured in single fragments of rat cortical collecting tubule (CCT) by using fura-2 and a tubule superfusion device. Under basal conditions, i.e. with 1 mM of external Ca2+ ([Ca2+]o), the average steady state [Ca2+]i was 179±16 nM (n=44 tubules). Random alterations of [Ca2+]o between 0 mM and 4 mM led to corresponding variations in steady state [Ca2+]i levels, which were linearly correlated with [Ca2+]o (average slope 93±34 nM [Ca2+]i per 1 mM [Ca2+]o for six tubules). In contrast, [Ca2+]i was little affected by decreasing external Na+ concentration. Cell membrane depolarization with 100 mM of external K+ induced a sustained drop in [Ca2+]i (21% as an average). The data suggest that steady state [Ca2+]i in CCT cells resulted from a non-saturable passive entry of calcium ions across cell membranes balanced with an active extrusion by calcium ATPase (pump and leak mechanism). The passive component cannot be accounted for either by Na+/Ca2+ exchangers nor by voltage-dependent calcium channels; it is best explained by the presence of voltage-independent calcium channels in cell membranes.