Showing papers by "Collège de France published in 1976"

Selective stabilisation of developing synapses as a mechanism for the specification of neuronal networks.

Abstract: The specificity of synapses in the mammalian brain cannot possibly be accounted for by one-to-one biochemical matching. The alternative proposed in this article is that connections are genetically specified between classes of cells, but the final wiring pattern depends on the refinement of those collections by selective stabilisation during neuronal activity.

Selective activation of mesocortical DA system by stress.

Abstract: IT is now well established that an important system of dopaminergic (DA) neurones innervates various parts of the cerebral cortex in the rat and other species1–3. In contrast to noradrenergic (NA) terminals which are widely distributed in this structure, the DA terminals are mainly confined to deep layers, particularly in the frontal, the cingular and the entorhinal areas4,5. The results of lesion studies demonstrated that the terminal endings in the frontal cortex originate from the A10 group of DA cell bodies localised in the mesencephalon6–8. This group also contains the cell bodies of the classical mesolimbic DA system projecting to the tuberculum olfactorium, the nucleus accumbens, the nucleus of the stria terminalis, and the amydgala9. The DA terminals found in the cingulate and entorhinal areas of cortex may originate mainly from the A9 group of DA neurones6–8. This group gives rise to the well known nigrostriatal DA system which is implicated in extrapyramidal processes. Its degeneration is in part responsible for some of the symptoms seen in Parkinsonian patients. Little is yet known about the functions of the mesocortical and mesolimbic DA pathways. Electrocoagulation or 6-hydroxydopamine (6-OHDA)-induced lesions of the ventral tegmental area, containing the A10 group, produce a syndrome characterised by “locomotor hyperactivity, serious impairment in tests requiring inhibition of a previously learned response, facilitation of approach learning and of active avoidance and hypoemotivity”10,11. Various workers have suggested that the antipsychotic effects of neuroleptics are in part related to the blockade of postsynaptic DA receptors localised in areas innervated by the mesolimbic and mesocortical DA systems12,13. It seems important to establish whether neurones of these two DA systems correspond to an homogeneous population of cells with similar functional characteristics. We have therefore explored this problem in the rat by examining the reactivity of the mesocortical and mesolimbic DA pathways as well as that of nigrostriatal DA system to stress induced by electric foot shocks. Our results suggest that the mesocortical DA system is selectively activated by this stress.

Remarks on polyelectrolyte conformation

Abstract: We discuss the conformations of linear polyions assuming that a) the corresponding uncharged chain is flexible ; b) electrostatic forces dominate the monomer-monomer interactions; c) no salt is added. 1) For the dilute case (non overlapping chains) correcting a recent self-consistent calculation by Richmond [1a], we find an overall polyion size R = Nd which is a linear function of the polymerization index N in agreement with the early work of Hermans and Overbeek, [1b], Kuhn, Kunzle, and Katchalsky [1c]. 2) There is a range of very low concentration c (c** c**) : here we expect that the polyions build up a 3-dimensional periodic lattice ; however, the detection of such an extremely dilute lattice appears difficult. 3) Practically all experiments on salt-free polyelectrolytes have been performed at concentrations c > c* where different chains overlap each other. To discuss this regime we restrict our attention to cases where the charge per unit length is near (or above) the condensation threshold : then a single length ξ( c) characterizes the correlation; in 3 dimensions ξ scales like the Debye radius associated with the counter ions. We consider several possible conformations : a) hexagonal lattice of rigid rods ; b) cubic lattice of rigid rods ; c) isotropic phase of partially flexible chains. The various rigid rod structures appear to have very similar electrostatic energies. This suggests that the isotropic phase might possibly be the most favorable. We analyse this latter phase using the same scaling methods which have recently been helpful for neutral polymer solutions (2). In the isotropic model each chain behaves like a succession of segments of size. Inside one segment electrostatic effects are important and similar to case (1) above. Between segments the interactions are screened out, and tach chain is ideal on a large scale, with radius R (c) ∼ c-1/4 N1/2 . If we (tentatively) assume that the dynamical effects of entanglements are weak, we are than led to a viscosity ηsp/c ∼ Nc-1/2.

On a relation between percolation theory and the elasticity of gels

Abstract: 2014 We compare the macroscopic conductance 03A3 of a resistor network with a fraction p of conducting links, and the elastic modulus E of a gel obtained by polymerization of z-functional units (p being the fraction of reacted bonds). LE JOURNAL DE PHYSIQUE LETTRES Classification Physics Abstracts 1.660 5.600 TOME 37, JANVIER 1976, ] Consider a Bravais lattice with nodes (i, j, ...) connected by conductances (Jij, the voltages being Vi, Vj... The entropy source is

Scaling theory of polymer adsorption

Abstract: We discuss the equilibrium properties of flexible chains adsorbed on a flat surface, assuming that a) adsorption is weak, resulting in large thicknesses D for the adsorption layer, b) the chains are very long, c) the solvent is good, so that excluded volume effects become important (contrary to an early opinion of Hoeve). The repulsion between monomers are incorporated through a scaling theory which goes beyond the usual mean field (Flory-Huggins) approximations. The central assumption is that polymer concentrations in the first layer and in the next layers scale in the same way, (although they do differ by a constant factor). We can then predict the surface exponents of interest in terms of standard exponents for self avoiding walks; for the latter we use the Flory values. One then finds three regimes of adsorption : (i) In the dilute limit (separate coils) D is independent of the polymerization index N, and varies with the strength of the effective monomer surface attraction (measured by a small parameter δ) according to D ∼ δ -3/2 instead of D ∼ δ-1 in mean field. (ii) There is a semi dilute regime where the coils begin to overlap, but where D remains essentially the same. (iii) The most important case corresponds to the plateau in the adsorption isotherm : here we show that the correlations inside the layer are similar to those in a three dimensional system. Then D ∼ Nδ(ln cB) -1 where cB is the bulk concentration. The dependence on N is stronger than in mean field (D ∼ N1/2) but not incompatible with existant data.

The role of presynaptic receptors in the release and synthesis of 3H-dopamine by slices of rat striatum.

Abstract: Striatal slices were continuously superfused with l-3,5-3H-tyrosine (50 μCi/ml) and 3H-H2O [index of 3H-dopamine (3H-DA) synthesis] and 3H-DA estimated in 0.5 ml (2.5 min) superfusate fractions. Depolarization with 50 mM K+ for 7.5 min induced a marked increase in 3H-DA release and a biphasic effect on synthesis (slight increase in the first fraction followed by a significant decrease in the third and fourth fractions). The decrease in the rate of 3H-H2O formation induced by K+ was not related to modifications of the specific activity of tyrosine in tissues. The possibility that the inhibition of synthesis was due to alterations in DA concentration in the synaptic cleft was examined. Benztropine in a concentration which produced inhibition of DA uptake (10−6 M) increased the K+ induced overflow of 3H-DA but failed to alter the inhibition of synthesis. On the other hand, when the powerful neuroleptic fluphenazine was added to the superfusion medium in a concentration which only weakly blocked 3H-DA uptake (10−6 M) it potentiated 3H-DA release and prevented the inhibition of synthesis both in the absence or presence of benztropine. A similar effect was seen following the in vivo treatment of rats with fluphenazine (2 mg/kg; 1 1/2 h before sacrifice). The addition of exogenous DA (0.6×10−6 M) or NA (10−6 M) to the superfusion medium increased 3H-DA outflow and reduced DA synthesis while isoproterenol (10−6 M) was without effect. The DA inhibitory effect on synthesis was still observed in the presence of benztropine (10−6 M) while the NA effect was prevented. This concentration of benztropine blocked both DA and NA uptake. The administration of fluphenazine (10−6 M) significantly prevented the decrease in 3H-DA synthesis induced by exogenous DA and partially prevented the effect of NA. In addition, the effect of exogenous DA on the inhibition of synthesis was still seen in the presence of 2-amino-4-hydroxy-6,7-dimethyl-5,6–7,8-tetrahydropteridine hydrochloride (DMPH4) (to protect against end-product inhibition). The present results provide direct support for the concept that activation of presynaptic DA receptors located on DA terminals in the striatum of the rat results in an inhibition of synthesis and release of the transmitter.

Heterogeneity of motor units activating single Golgi tendon organs in cat leg muscles.

Abstract: The aim of this study was to investigate whether an individual Golgi tendon organ can signal the contraction of motor units with different physiological properties The axonal conduction velocity and tetanic tension of motor units were examined in four muscles of the cat leg (peroneus brevis, peroneus longus, tibialis anterior and soleus) The motor units which were found to activate a given tendon organ had contractile properties dispersed over the same range as those of the whole muscle population The proportion of tendon organ-activating motor units found in the studied samples suggests that altogether, the Golgi tendon organs of a muscle monitor the contraction of every motor unit in this muscle

The effects of quipazine on 5-HT metabolism in the rat brain.

Abstract: Since quipazine is a potent 5-HT agonist in peripheral organs, its possible stimulatory effects on serotoninergic receptors in the rat brain were investigated. Quipazine administration (10 mg/kg, i.p.) induced a significant decrease in the synthesis and turnover rates of serotonin in the brain stem as well as in the forebrain. It is not likely that these changes were mediated by a negative feed-back mechanism triggered by a direct action of quipazine on central 5-HT postsynaptic receptors. Indeed, in contrast to LSD and 5-methoxy-N,N-dimethyltryptamine, this compound failed to activate the 5-HT sensitive adenylate cyclase in colliculi homogenates of newborn rats. However, quipazine exerted direct effects on serotoninergic terminals. It inhibited competitively the reuptake process in synaptosomes (Ki=1.38 X 10(-7) M) and stimulated the K+ evoked release of newly synthesized 3H-5-HT in slices of the brain stem. Injected in vivo in a dose which affected 5-HT uptake and release, quipazine did not modify MAO activity. However, this activity was non-competitively inhibited by high concentratin of the drug in vitro (Ki=3.0 X 10(-5) M). These actions are very likely indirectly responsible for the stimulation of central 5-HT receptors.

Mesomorphic Derivatives Of Ferrocene

Abstract: The first series of ferrocene derivatives exhibiting mesomorphic properties (substituted N-(p-benzoyloxybenzylidene) anilines la and 1b) has been synthesized for application in Mossbauer spectroscopy.

Isolation and radioenzymic estimation of picogram quantities of dopamine and norepinephrine in biological samples.

Abstract: — A method was developed to measure small amounts of dopamine or norepincphrine in biological samples. It was based on the radioenzymic assay originally described by Engelmanet al. (1968) and improved by other workers: dopamine and norepinephrine are O-methylated by catechol-O- methyl-transferase in the presence of [3H]S-adenosylmethioniiie as la belled methyl donor. O-Methylated derivatives are extracted and estimated. The optimal conditions for the O-methylation and the extractions were determined. The most important improvement in the method consisted in the selective isolation of catecholamines on microcolumns of alumina under conditions that allowed their subsequent enzymic assay. The assay described can thus be used on any size of biological sample. The assay was not affected by the prescnce of various agents (tissue extracts, CSF salts and particularly calcium, drugs etc.) which were shown to interfere with the O-methylation process, and it allowed the measurement of quantities of dopamine and norepinephrine as low as 0.15 and 0.1 pmol respectively, whatever the origin of the sample (CSF superfusates, cerebral tissue).

Polymeric liquid crystals: Frank elasticity and light scattering

Abstract: We discuss some theoretical features of a nematic phase made of long, partially flexible chains. The bend constant K3 is dominated by the rigidity of the chains. The twist constant K2 is mainly related to the anisotropic couplings between chains. The splay constant is very large (increasing like the square of the molecular mass M). An interesting limit is obtained when the length of the extended chains is larger than the optical wavelength used in a light scattering experiment: then the scattering laws should differ qualitatively from what is known in usual nematics.

Effect of high frequency irradiation on the dynamical properties of weakly bound electrons

Abstract: On etudie comment le comportement d’un electron dans des champs statiques electrique ou magnetique est modifie lorsque cet electron interagit egalement avec une onde electromagnetique haute frequence. Les nouvelles proprietes dynamiques de l’electron sont decrites par un hamiltonien effectif dont l’expression est etablie en utilisant une description quantique du champ electromagnetique et en tenant compte des corrections relativistes jusqu’a l’ordre 1 /c2. Outre une correction de masse bien connue, on trouve que les nouvelles proprietes dynamiques de l’electron peuvent etre comprises en termes de facteurs de forme electrique et magnetique qui ont une interpretation physique simple. Ces resultats generaux sont enfin appliques a 2 cas simples : perturbation des niveaux de Rydberg d’un atome et modification des frequences cyclotron et de precession de spin d’un electron dans un champ magnetique uniforme.

Characterization of polystyrene networks by small‐angle neutron scattering

Abstract: Polystyrene networks prepared by anionic polymerization have been characterized by small-angle neutron scattering. Two kinds of systems have been examined: (A) networks with labelled branch points allowing characterization of the spatial distribution of crosslinking points; (B) networks containing a low proportion of chains labelled with perdeuterated polystyrene in order to characterize the conformation of individual elastic chains of the polymeric network. The dependence of the results on swelling and uniaxial extension is discussed.

Torpedo marmorata acetylcholinesterase; a comparison with the Electrophorus electricus enzyme. Molecular forms, subunits, electron microscopy, immunological relationship.

Abstract: Electron microscopy, sequential degradation by hydrolytic enzymes and the physical-chemical properties of the molecular forms of Torpedo acetylcholinesterase indicate that these molecules are structurally related to each other in the same way as the molecular forms of Electrophorus acetylcholinesterase: all are derived from a complex structure in which three tetrameric groups of subunits are associated with a rod-like 'tail'. In aged preparations the catalytic subunits are split into fragments in a manner similar to those of Electrophorus acetylcholinesterase. Immunological cross-reaction between both enzymes demonstrates the occurrence of common antigenic sites. The enzymes from the two sources, however, are different in their molecular weights and susceptibility to hydrolytic enzymes. Also, Torpedo acetylcholinesterase does not precipitate with either isologous or heterologous antibodies.

Molecular forms of acetylcholinesterase: their de novo synthesis in mouse neuroblastoma cells.

Abstract: — Rat mouse AChE molecular forms are indistinguishable with respect to their sedimentation coefficients and their evolutive proportions during brain maturation. Among rat or mouse erythrocytes, rat C6 glial cells, and mouse 2A and NS 20 neuroblastoma cells, only neuroblastoma cells showed both the ES and HS molecular forms with a 1:1 proportion for NS 20 cells. All these cells lack a third molecular form (16S), which is present in rat and mouse superior cervical ganglia. After irreversible inhibition of pre-existing NS 20 neuroblastoma AchE, the ES form is first synthesized (de novo synthesis). The HS form begins to appear after a lag time of several hours and represents, 24 h after inhibition, only 15% of the total recovered activity, which is near the initial level. The initial relative proportions return by 2 to 3 days after inhibition. The recovery of the HS form is, for the most part, blocked by actinomycin D, which does not block the recovery of activity itself, which remains as an ES form. It seems that integration of the ES form into the HS form more probably depends on the synthesis of a new messenger RNA, which is required for the synthesis of either new AChE polypeptide chain, polymerization initiating protein or activating enzyme.