Showing papers by "Pierre-and-Marie-Curie University published in 1977"

Anatomical, Physiological and Biochemical Studies of the Cerebellum from Reeler Mutant Mouse

Abstract: The cerebellum of the homozygous reeler mouse shows a marked reduction in size and in the number of fissures, its dry mass and DNA content are respectively $\frac{1}{3}$ - $\frac{1}{4}$ and $\frac{1}{7}$ - $\frac{1}{8}$ of those of normal animals. Its high content in the P $_{400}$ protein, which is abundant in the Purkinje cell, indicates that the decrease in cell number associated with the fall in DNA affects primarily the granular cells. The anatomy of the reeler cerebellum is rather unique: a thin cortex with almost normal molecular, granular and Purkinje cell layers embracing a central mass of closely packed large neurons, mostly Purkinje cells. Purkinje cells may therefore be found in four different cellular environments: (1) at their normal position in the superficial cortical structure; (2) within the granular layer; (3) intermingled with white matter in the central mass; (4) overlapping with neurons of the deep cerebellar nuclei. The reeler cerebellum therefore offers a model to study to what extent local cellular interactions are required to achieve the planar organization of the Purkinje cell dendrites and the normal synaptic investment of these cells. Concerning the three-dimensional shape of Purkinje cells, only the rare ones located at their normal position and receiving a normal ratio of all their synaptic afferences succeed to develop a characteristic dendritic pattern. Purkinje cells within the granular layer show three distinct patterns of dendritic arrangements. The variation in shape of the Purkinje cell dendrites located in the central agranular mass mimics that described in other agranular cerebella: in particular they show randomly oriented dendrites devoid of spiny branchlets. Concerning the cerebellar circuitry, the specificity of most of the synaptic connections is preserved, despite important disorders in Purkinje cell distribution. Several important differences with the normal cerebellum have, however, been observed at the level of the Purkinje cell: (i) The density of climbing fibre varicosities increases in the central cerebellar mass, where Purkinje cells are deprived of parallel fibre afferences. In addition, electrophysiological studies reveal that, at this position, the response of the Purkinje cells to climbing fibre stimulation is graded by steps as a function of stimulus intensity instead of being all-or-none as found in the superficial cortex or in normal cerebellum. These deep Purkinje cells receive therefore several climbing fibres instead of only one as in normal adult cerebellum. (ii) Ectopic synapses (somato-dendritic and dendro-dendritic) between the soma and/or the dendrite of the granule cell as presynaptic element and mainly the Purkinje cell dendrites as postsynaptic element may form. (iii) Heterologous synapses between mossy fibres and Purkinje cell spines are found in the granular layer and within the central mass. The electrophysiological studies show that these synapses are functional.

Resonant Photoemission in Nickel Metal

Abstract: A strong resonance effect has been observed for the first time in photoemission: This happens on a metallic nickel (100) surface when the photon energy is close to that of the $3p$ energy level. The effect is interpreted as the autionization of an excited quasidiscrete atomic configuration into a continuum of excitations with two holes in the $3d$ shell.

An Analysis of Response Properties of Spinal Cord Dorsal Horn Neurones to Nonnoxious and Noxious Stimuli in the Spinal Rat

Abstract: Electrophysiological properties of neurones in the spinal cord dorsal horn were studied in decerebrated, immobilized spinal rats. Extracellular recordings were performed at the thoraco-lumbar junction level. Each track was systematically located by extracellular injection of pontamine sky blue. According to their responses to mechanical peripheral stimuli, cells were classified in four classes: Class 1 cells: Cells activated only by nonnoxious stimuli. They were divided into — 1A: hair movement and/or touch and 1B: hair movement and/or touch and pressure or pressure only. Class 2 cells: Cells driven by both nonnoxious and noxious stimuli, divided into — 2A: hair movement and/or touch, pressure, pinch and/or pin-prick, and 2B: pressure, pinch and/or pin-prick. Class 3 cells: Cells only activated by noxious stimuli (pinch and/or pin-prick). Class 4 cells: Cells responding to joint movement or pressure on deep tissues. Peripheral transcutaneous or sural nerve stimulation clearly showed that class 1 cells were activated only by A fiber input while 68% of classes 2 and 3 cells received A and C input. Histological examination indicated that cells driven only by noxious input were located either in the deepest part or in the marginal zone (lamina I) of the dorsal horn. Nevertheless, some lamina I cells were also driven by both nonnoxious and noxious stimuli. In addition, there is a great deal of overlap between class 1 and class 2 cells. This fact was confirmed by considering the wide distribution in the dorsal horn of cells receiving A and C input. However, spinal organization of the different classes of cells consists of a preferential distribution rather than a strict lamination. This study indicates that properties of dorsal horn interneurones in the rat have a high degree of similarity with those previously described in other species (cat and monkey).

Transfer of virulence in vivo and in vitro in Agrobacterium.

Abstract: TRANSFER of virulence from a pathogenic to a non-pathogenic strain of Agrobacterium has been reported to occur in vivo1,2 and is due to the transfer of a plasmid which codes for virulence3,4. In the experimental conditions described, virulence transfer can be detected only after several weeks. The reason for this delay is not clear. The most likely explanations are (1) that infrequent transfer occurs long before it can be detected, detection being dependent on a subsequent increase in the ratio of converted to unconverted recipients or (2) that conditions suitable for virulence transfer occur only after donor and recipient have been in contact for several weeks. The main difficulty in distinguishing between these two alternatives is technical. When pathogenicity testing is used to detect virulence transfer, low frequency transfer is impossible to detect unless thousands of inoculations are made at each assessment. It is known, however, that the virulence plasmid codes for characters other than virulence5–7. One of these is utilisation of octopine and, as Kerr8 has pointed out, this could be used instead of pathogenicity testing to detect plasmid transfer. This communication describes both in vivo and in vitro transfer of virulence using octopine utilisation to detect plasmid transfer.

Use of the Coulomb Green's function in atomic calculations

Abstract: Analytical and numerical results are presented which are related to the following higher-order atomic processes: retardation effects in two-photon bound-bound transitions, evaluation of the Bethe logarithm in excited states, and multiphoton ionization. These calculations are carried out within the framework of the conventional perturbation theory by using different representations of the Coulomb Green's function, each representation offering its own particular advantages.

Synthesis and swelling properties of saponites with increasing layer charge

Abstract: Nine synthetic Na-saponites with charge densities varying between 0.33 and 1.0 have been prepared. Their swelling properties and structural organization in water, ethylene glycol and glycerol show discontinuities in the physico-chemical behaviour of these samples. The layer charge densities caused changes in swelling properties and structural organization of the minerals. These changes also depended upon the nature of the solvation liquid and the interlayer cation involved. Electron diffraction patterns of the Ba-saponites showed no abnormal diffusion making honeycomb- like patterns between Bragg reflections. The results indicate criteria for estimating the layer charge of tetrahedrally substituted trioctahedral 2/1 phyllosilicates. There is no upper limit until x = 1 for the layer charge x which is specific to the smectite-group. Consequentb,, the changes in the swelling properties observed when x = 0.5-0.6 and x = 0.8-0.9 come from the modifications of the interlayer structure, which are mainly a function of cation-liquid and silicate layer-liquid interactions. Consequently, there is an overlap between the saponite and the vermi- culite mineral groups.

Optical constants ofε-GaSe

Abstract: The optical constants for both polarizations of light (E‖C andE⊥C) in e-GaSe have been studied between 30 cm−1 and 22000 cm−1, at room temperature. In the region of the band gap absorption edge, data are given down to 2 K. Infra-red data forE⊥C andE‖C in the (200÷300) cm−1 range have been obtained by reflectivity measurements and Kramers-Kronig analysis. TheE⊥C polarization has been compared with interferometric measurements between 30 cm−1 and 600 cm−1. Verification for the high-frequency range (σ>300 cm−1) has been done by comparison with interference patterns, analysed by the same method as for the visible region.

Differential cross sections and angular distributions of H - from dissociative electron attachment to H 2 between 3.75 eV and 13 eV

Abstract: An electron-impact spectrometer has been modified for the study of negative-ion fragments. This instrument has been used to observe differential cross sections and angular distributions of H- ions produced by dissociative attachment to H2 through the 2 Sigma u+ and 2 Sigma g+ resonances. The measured angular distributions are analysed using the pure resonant scattering with potential scattering theoretical model which is discussed. Vibrational structure observed in the differential cross section between 11.30 eV and 13.30 eV is interpreted as resulting from predissociation of the 'a' resonance bands by the H2- 2 Sigma g+ repulsive state.

Further observations on cell wall morphogenesis and polysaccharide arrangement during plant growth

Abstract: The three-dimensional arrangement of the polysaccharide chains in cell walls was investigated, using ultracryotomy and cytochemistry, in order to test the validity of the previously postulated “ordered fibril hypothesis” and to analyze the characteristics of the primary wall morphogenesis. Both in mung bean hypocotyl (Phaseolus aureus) and pea root (Pisum sativum) cultured in defined conditions, cell to cell endogenous specificity is marked by differences in the numbers of layers, thickness, rhythm and direction of deposition. The occurrence of bow-shaped arrangements and of strata of orientation intermediate between the main crisscrossed multifibrillar layers suggests that the sequential changes of the morphogenetic activity of the cells is progressive. The twisted polysaccharide disposition evokes certain mesomorphic states; a part of the mechanism responsible for the wall arrangement may result from a self-assembly process as in the orientation of the molecules in a liquid cristal. This possibility finds experimental support in the fact that a three-dimensional association of the hemicellulose chains spontaneously appears when precipitated in acellular conditions. Polysaccharide removal associated with shadowing indicates that the ordered disposition within the wall is extensively altered by even a slight extraction. These data may invalidate diverse results which are generally brought forward to explain the wall organization during growth.

Inclusive anomalous muon production in e+e- annihilation

Abstract: We present measurements of inclusive anomalous muon production in ${e}^{+}{e}^{\ensuremath{-}}$ annihilations in three energy ranges. In all three ranges we observe a large anomalous muon production rate in two-prong events which is compatible with the expected decays of pairs of heavy leptons. In the highest energy range there is also appreciable anomalous muon production in multiprong events which, due to its magnitude and momentum dependence, must come in part from a source other than a heavy lepton.

Cytokinins: Metabolism and Biological Activity of N6-(Δ2-Isopentenyl)adenosine and N6-(Δ2-Isopentenyl)adenine in Tobacco Cells and Callus

Abstract: The cytokinin, N6-(Δ2-isopentenyl)adenine, is found to be at least 3.3 times as active as N6-(Δ2-isopentenyl)adenosine in promoting the growth of cytokinin-requiring tobacco (Nicotiana tabacum) callus. Absorption rates of N6-(Δ2-isopentenyl)adenine and N6-(Δ2-isopentenyl)adenosine by tobacco cells in liquid suspension do not differ significantly. In these cells, N6-(Δ2-isopentenyl)adenosine-5′-monophosphate, di-, and triphosphate are synthesized in both cases, but 7-glucosylation occurs significantly only with N6-(Δ2-isopentenyl)adenine, protecting thereby its N6-isopentenyl side chain from cleavage. Degradation by N6-side chain removal appears to be intense, leading to the formation of adenine, adenosine, and adenylic nucleotides. Thus, it is suggested that N6-(Δ2-isopentenyl)adenine-7-glucoside is a protected or storage form of the cytokinin which could account for the higher biological activity of N6-(Δ2-isopentenyl)adenine than of N6-(Δ2-isopentenyl)adenosine.

Differential cross sections for dissociative attachment in CO

Abstract: An electron-impact spectrometer is described which, by means of a modification, is able to observe energy and angular distributions of ion fragments produced by molecular dissociation processes with a good precision and sensitivity. O/sup -/ ion formation through dissociative electron capture in CO has been studied. An analysis of the observed O/sup -/ differential cross sections using the theory of O'Malley and Taylor and two partial waves indicates that the two reactions leading to O/sup -/ both proceed through a /sup 2/Pi resonant state. Both resonances appear to have a sigma/sup 2/..pi../sup 3/..pi../sup 2/ configuration by analogy with isoelectronic NO, and their parents would be the a' /sup 3/..sigma../sup +/, for the process with a 9.62-eV threshold, and possibly the d /sup 3/..delta.. state, for the process with an onset at 10.88 eV. (AIP)