Showing papers by "Collège de France published in 1984"

Magnesium gates glutamate-activated channels in mouse central neurones

Abstract: The responses of vertebrate neurones to glutamate involve at least three receptor types. One of these, the NMDA receptor (so called because of its specific activation by N-methyl-D-aspartate), induces responses presenting a peculiar voltage sensitivity. Above resting potential, the current induced by a given dose of glutamate (or NMDA) increases when the cell is depolarized. This is contrary to what is observed at classical excitatory synapses, and recalls the properties of 'regenerative' systems like the Na+ conductance of the action potential. Indeed, recent studies of L-glutamate, L-aspartate and NMDA-induced currents have indicated that the current-voltage (I-V) relationship can show a region of 'negative conductance' and that the application of these agonists can lead to a regenerative depolarization. Furthermore, the NMDA response is greatly potentiated by reducing the extracellular Mg2+ concentration [( Mg2+]o) below the physiological level (approximately 1 mM). By analysing the responses of mouse central neurones to glutamate using the patch-clamp technique, we have now found a link between voltage sensitivity and Mg2+ sensitivity. In Mg2+-free solutions, L-glutamate, L-aspartate and NMDA open cation channels, the properties of which are voltage independent. In the presence of Mg2+, the single-channel currents measured at resting potential are chopped in bursts and the probability of opening of the channels is reduced. Both effects increase steeply with hyperpolarization, thereby accounting for the negative slope of the I-V relationship of the glutamate response. Thus, the voltage dependence of the NMDA receptor-linked conductance appears to be a consequence of the voltage dependence of the Mg2+ block and its interpretation does not require the implication of an intramembrane voltage-dependent 'gate'.

Acetylcholine receptor: an allosteric protein

Abstract: The nicotine receptor for the neurotransmitter acetylcholine is an allosteric protein composed of four different subunits assembled in a transmembrane pentamer alpha 2 beta gamma delta. The protein carries two acetylcholine sites at the level of the alpha subunits and contains the ion channel. The complete sequence of the four subunits is known. The membrane-bound protein undergoes conformational transitions that regulate the opening of the ion channel and are affected by various categories of pharmacologically active ligands.

Prenatal and postnatal development of retinogeniculate and retinocollicular projections in the mouse

Abstract: The development of retinal projections to the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC) has been studied in fetal and neonatal mice of the pigmented C57BL/6 strain, using the anterograde transport of tritiated proline and horseradish peroxidase (HRP). Retinal efferents are present contralaterally just beyond the chiasm at E14. By E16 they have grown into both dLGN and SC. Ipsilateral fibers are limited to the proximal optic tract at E16; their growth into dLGN and SC is delayed until E18-birth. During the first 2 postnatal days, an early population of ipsilateral fibers invades the dLGN. Most of these fibers grow in or around the medio-dorsal sector of the dLGN, i.e., the future binocular segment. Fibers are also present, but at lower densities, in the ventral half of the nucleus and thereafter become dispersed or are lost, without at any stage becoming dense. Some denser labeling is also present ipsilaterally in the outer rim of dLGN, just below the optic tract, and later disappears. On the third postnatal day, the ipsilateral fibers establish a deep and denser projection along the medial and dorsal borders of dLGN; this projection overlaps part of the crossed projection, which at this age extends to the whole nucleus. The segregation of each projection starts on the fourth postnatal day, when crossed fibers begin to disappear from the small region of uncrossed projection. This process goes on for another 4 days. During this period, the ipsilateral fibers withdraw from the deepest layer of dLGN, and their terminal density increases gradually; by the eighth postnatal day, both projections are already well separated. Dense crossed projections first appear near the surface of the SC at birth. Prior to this, retinal fibers course throughout neurons of the collicular plate and underneath the pia. The uncrossed fibers invade the SC between birth and P3. They are located preferentially in the anterior and medial aspect of the SC. Subsequently, there occurs a diminution in the laminar and tangential extent of these projections, simultaneously with an intensification of the ipsilateral input to several small, longitudinally oriented clusters located deep to the crossed projections.

Glial heterogeneity may define the three-dimensional shape of mouse mesencephalic dopaminergic neurones.

Abstract: The shape of a neurone--the projection and branching pattern of axons and dendrites--appears to be determined by a combination of intrinisic and environmental influences. We have previously shown that striatal target neurones influence the biochemical maturation of ascending mesencephalic dopamine (DA) cells in culture, as well as the elongation rate of DA neurites. Using a similar approach in which the morphology of individual DA cells can be studied after 3H-DA uptake and autoradiography, we now report on in vitro neurone-glia interactions and show that glial cells exert a morphogenetic effect on DA neurones. Dopaminergic neurones from the mesencephalon were plated on glial monolayers prepared either from the striatal or the mesencephalic region of the embryonic brain. On mesencephalic glial cells the majority of DA neurones develop a great number of highly branched and varicose neurites, whereas on striatal glia they only exhibit one long, thin and rather linear neurite. These results demonstrate that glial cells from two different brain regions have distinct properties which could be used to define neuronal polarity observed in vivo.

Disc-Like Mesogen Polymorphism

Abstract: Among the various mesogenic polyaromatic cores, only benzene, triphenylene, truxene and anthraquinone hexasubstituted derivatives exhibit one or several D columnar phases and/or a ND lenticular nematic phase. A simple scheme of nomenclature is suggested for the six different types of columnar phase requiring only two structural parameters: firstly the symmetry of the lattice (hexagonal: Dh, rectangular: Dr, oblique: Dob), and secondly the order or disorder within the column. Several examples of disc-like compounds which form phases Dho, Dhd, Drd(P21/a) , Drd(P2/a), Drd(C2/m), Dod.d are described and a discussion of the specificity of the corresponding optical textures is given. Then the complex polymorphism of these new mesogenic materials (normal, inverse, reentrant columnar-nematic sequences) is reviewed. Finally, a simple classification of the various types of lyotropic and thermotropic phase is proposed, based on the shape of the structural element (finite or infinite cylinder, disc, infinite...

Prevention of gastrulation but not neurulation by antibodies to fibronectin in amphibian embryos

Abstract: Gastrulation and formation of the neural plate are major steps in early vertebrate embryogenesis. Although morphogenetic movements leading to the formation of the primary germ layers have been extensively described1–3, the mechanisms governing migration of mesodermal cells and their interactions with ectoderm remain ill-defined. A large body of evidence indicates that fibronectin (FN), a high molecular weight cell-surface-associated glycoprotein, promotes cell adhesion and cell migration throughout embryogenesis4–6. FN has been detected at an early blastula stage in Pleurodeles waltlii7. We now show that FN is a component of a dense fibrillar matrix underlying the blastocoel roof; in contrast, the exterior surface of the embryo is devoid of FN. Microsurgical inversion of part of the blastocoel roof does not prevent mesodermal cell migration except at the site of inversion where no FN matrix is available. Perturbation experiments using antibodies to FN demonstrate that the invagination of presumptive mesodermal cells does not occur when the monovalent antibodies are injected before or at the onset of gastrulation; on the other hand, the formation of a neural plate is not prevented when late gastrula stage embryos are treated with antibodies to FN. We conclude that the presence of FN is required for cell migration during gastrulation.

Ontogeny of primary lymphoid organs and lymphoid stem cells

Abstract: Cells of the immune system go through a series of important developmental steps that begin early in embryonic life and include, first, the various waves of hemopoietic-cell production in the embryo and, second, the homing of these cells to the hemopoietic organs, which are the sites of hemopoiesis and lymphopoiesis in embryonic and adult life. The avian embryo is an important model for investigating these early steps; and this paper presents a comprehensive review of the work done on the early ontogeny of the avian immune system.

Phase diagrams of mesomorphic mixtures

Abstract: We have combined the Maier Saupe theory [1] of the nematic-isotropic transition and the Flory Huggins theory of mixtures to describe the phase diagrams of two nematogens A+B. The two components can have different order parameters S A , S B in the mixture. We can then predict the morphology of the phase diagrams in term of a relatively small number (4) of interaction parameters. The final numerical calculations are restricted to cases where the clearing points of the two components are nearly equal (cases of chemical similarity). For certain sets of parameters we find a rather remarkable phase diagram with two consolute points ― one at high temperatures in the isotropic phase and a second one at lower temperatures in the nematic phase. We also discuss the effects of chain length on the phase diagrams: when one component is a nematogenic polymer [2] with mesogenic side groups; and when the two components are polymers Combinaison de la theorie de la transformation isotrope-nematique de Maier-Saupe et la theorie des melanges de Flory-Huggins pour decrire les diagrammes de phase de deux nematogenes (A, B) qui peuvent avoir des parametres d'ordre differents. Prevision de la forme des diagrammes de phase avec 4 parametres seulement. Discussion de l'effet de la longueur de chaine quand un composant est un polymere nematogene avec des groupes lateraux mesogenes et quand les deux composants sont des polymeres

Concentrated Winsor microemulsions: a small angle X-ray scattering study

Abstract: By small angle X-ray scattering, we have studied the structure of Winsor microemulsions, with brine and oil (toluene) proportions comparable and much larger than the surfactant (sodium dodecyl sulfate, SdS) and co-surfactant (butanol 1) proportions. Three systems were made. In the first (already studied in detail), the microemulsions are in equilibrium with an oil and/or water phase in excess, the microemulsion composition varies as a fonction of the brine salinity. The two other systems are monophases made with a brine of salinity 6.5 %. In the second system, we vary the oil volume fraction Φo from 20 to 90 % at constant SdS concentration (5 x 10-2 g/ml). In the third, we chose the component proportions such that the quantity ΦoΦw/cs (Φw : brine volume fraction, cs : SdS concentration) remains constant as Φo varies from 20 to 80 %. Thus one fixes the theoretical microemulsion characteristic length according to the expression $$ predicted by Talmon-Prager and de Gennes (Σ is the area per SdS polar head). 1) The SdS polar head contribution to the contrast and to the intensity scattered at large angle in the asymptotic domain is large. From this, we deduce a direct proof of the existence of a soap film between the oil and water parts of the microemulsion and also a method of measurement of the area per polar head (Σ ~ 60 A2); 2) We measure the characteristic microemulsion size as a function of cs and Φo . The various scans suggest that, for Winsor microemulsions, starting from the inversion point (Φo = 0.5) and increasing the water or oil proportion, a progressive change occurs from a random bicontinuous water and oil structure $$ to a dispersion made of distinct oil in water or water in oil droplets (Φo 0.7, ξ ∼ $$ or $$; 3) At very small angles (q ∼ 10-2 A-1), we observe correlations or interaction effects not predicted by the existing bicontinuous microemulsion models.

Experimental Brain Ischemia: Neuron‐Specific Enolase Level in Cerebrospinal Fluid as an Index of Neuronal Damage

Abstract: Levels of neuron-specific enolase (NSE) were measured in rat CSF following occlusion of the four major arteries to the brain for 10, 20, or 30 min. In the CSF of rats submitted to 30 min of total ischemia, an up to ninefold increase of NSE level occurred within the first few hours and then slowly diminished. Significant levels were seen for as long as 8 days. Histological observations 3 days after ischemia showed neuronal loss as well as neu- ronal damage in several forebrain regions such as hippocampus, striatum, and thalamus. Ischemia was followed by transient decreases in exploration behavior and neurological states that were no longer visible 24 h later. After 10 or 20 min ischemia, NSE levels were increased to a lesser degree and fewer damaged neurons were observed. The positive correlation between duration of ischemia and amount of NSE release in CSF indicates that the measurement of NSE in the CSF is a sensitive and reliable index of neuronal lesions.

Optical activity due to isotopic substitution. Synthesis, stereochemistry, and circular dichroism of (+)- and (-)-[2,7,12-2H3]cyclotribenzylene

Abstract: The enantiomers of the specified compound, whose chirality is due to isotopic substitution, were synthesized from cyclotriguaiacylene; and their absolute configuration was established as M-(-) or P-(+). The phenolic groups in the starting compound were removed by hydrogenolysis of the corresponding tris(2-phenyl-1-tetrazolyl) ether, and the resulting cyclotrianisylene was demethylated into cyclotriphenolene. Optical resolution of the latter compound followed by deuteriolysis of the phenolic groups then provided the desired (+) and (-)-cyclotribenzylene with a high isotopic purity. The energy barrier for the crown inversion in the titled compound was calculated from racemization rates. Interpretation in terms of vibronic rotation of the B/sub 2u/ transition moment, induced by the deuterium atoms perturbing the breathing mode of each phenyl ring, was qualitatively consistent with the observed spectrum.

Basic and regulatory mechanisms of in vitro release of Met-enkephalin from the dorsal zone of the rat spinal cord.

Abstract: Under control conditions, superfused slices of the dorsal half of the lumbar enlargement from adult rats released Met-enkephalin-like material (MELM) that behaved as authentic Met-enkephalin under two different chromatographic procedures (Bio-gel filtration, HPLC). MELM release increased markedly on exposure of slices to batrachotoxin (0.5 microM) or to an excess of K+ (28 and 56 mM instead of 5.6 mM). The K+-evoked release was totally dependent on the presence of Ca2+ in the superfusing fluid whereas the spontaneous efflux of MELM was only partially Ca2+-dependent. Further experiments performed with tissues of polyarthritic rats indicated that the increase in their MELM levels was associated with a lower fractional rate constant of MELM release, therefore suggesting that spinal Met-enkephalin turnover might be reduced in chronically suffering animals. Examination of the possible modulation of MELM release by various neuroactive compounds present within the dorsal horn revealed that cholecystokinin (10 microM), but not its desulphated derivative, substance P-sulphoxide (10 microM), and to a lesser extent substance P, enhanced the K+-evoked MELM release. In contrast, gamma-aminobutyric acid (10 microM) and (-)-baclofen (1 microM) partially prevented the stimulatory effect of K+ on MELM release. Other compounds such as serotonin, somatostatin, and neurotensin altered neither the spontaneous nor the K+-evoked release of MELM.

Preparation by yeast reduction and determination of the sense of chirality of enantiomerically pure ethyl (−)-4,4,4-trichloro-3-hydroxy- and (+)-4,4,4-trifluoro-3-hydroxybutanoate

Abstract: Reduction of ethyl 4,4,4-trichloro- and 4,4,4-trifluoro-3-oxobutanoate by fermenting baker's yeast (Saccharomyces cerevisiae) on a preparative scale (20–50 g in ca. 3 1 of H2O) gave 70–80% yields of the trichloro- [(−)-(S)-1a] and trifluoro-hydroxyesters [(+)-(R)2a] of ca. 85 and 45% ee, respectively. Both, (−)-1a and (+)-2a could be obtained in > 98% ee by subsequent crystallization (of(−)-1, (+)-2a or the 3,5-dinitrobenzoate (+)-2b. The absolute configuration of both hydroxyesters was determined (a) by chemical correlation ((−)-1a), (b) from the melting diagrams and mixed melting points (differential-scanning calorimetry Fig. 1) of the dinitrobenzoates of the CF3-derivative (+)-2a and its CH3-analogue 8, and c) by X-ray analysis of the ester 2f from (+)-2a and (−)-camphanoyl chloride (Fig. 2 and 3).