Can transplantation of neurons facilitate motor recovery in paraplegics? Study of an animal model

This review strives forward at least two goals. First, to take from the literature the arguments demonstrating that hindlimbs locomotion is controlled by a spinal network of neurons (the so-called Central Pattern Generator for locomotion--CPG) known to be able to generate locomotor activity independently of the control of supraspinal nervous structures, as it is after thoracic lesions of the spinal cord. The principles of work of the CPG and its intrinsic possibilities to adapt its working are reviewed. Special reference is made to the various ways used during experiments to activate the CPG in spinal animals or clinical practice in paraplegic men: training to walk, electrical stimulations, pharmacological stimulations. Second, to show, from our own results, obtained from the study of an animal model of paraplegia, the adult spinal rat, how it could be possible to take advantage of the autonomy of the CPG, with special reference to its sensibility to monoamines, to obtain locomotor recovery in hindlimbs after section of the thoracic spinal cord, by means of transplantation of noradrenergic and/or serotonergic embryonic neurons in the lumbo-sacral spinal cord. Section of the spinal cord at a thoracic level results in an important locomotor deficit in hindlimbs, likely linked to degeneration of monoaminergic terminals in the lumbar enlargement. In the adult spinal rat, sub-lesional injection of a suspension of embryonic nervous cells, taken from either locus coeruleus or raphe sites, leads to reinnervation of the lumbar enlargement with monoaminergic terminals. Despite the fact that connections with supraspinal structures are not reestablished, transplanted animals recover progressively a posture convenient for locomotion. The hindlimbs, which are in an extended position a few days after the lesion, become progressively flexed and able to support the body weight. This evolution does not appear in spinal but non transplanted animals. But, the main point is that transplanted animals develop, within the few weeks that follow transplantation, a good-quality locomotor activity in hindlimbs which had no equivalent in spinal but non transplanted animals. The reality of a lumbar CPG for locomotion and the efficacy of pharmacological treatments and training to walk, to elicit recovery of stepping, are discussed in man, in connection with the relevance to use transplantation of monoaminergic nervous cells in the spinal cord of paraplegics.     

Recovery of locomotor activity in the adult chronic spinal rat after sublesional transplantation of embryonic nervous cells: specific role of serotonergic neurons

We have reviewed the genetic structure of HIV-1 from the perspective of understanding viral and cellular regulatory factors that affect viral replication. Comparisons are drawn, as appropriate, with other human retroviruses, such as HIV-2, in regard to our understanding of pathogenesis. The synthesis of viral protein and the manner in which viral assembly takes place is also discussed.     

Hg0.4Cd0.6Te 1.55-μm avalanche photodiodenoise analysis in the vicinity of resonant impact ionization connectedwith the spin-orbit split-off band

The authors describe the electrical and optical characterization of three Hg_1-xCd_xTe avalanche photodiodes manufactured using planar technology with composition parameter x near 0.6. This alloy composition leads to devices that are well suited for 1.55-μm detection. From the noise analysis under multiplication, the authors show the tight dependence of the ratio β/α (of the hole; and electron ionization coefficient, respectively) upon x and the ratio Δ/E_g where Δ is the spin-orbit splitting energy and E _g is the bandgap energy. It turns out that in these alloys around x=0.6, Δ is very close to the bandgap energy so β/α reaches its maximum value. Owing to this property, which is characteristic of II-VI compounds, Hg_1-xCd_xTe is a good candidate for 1.3-μm to 1.6-μm avalanche photodiodes     

Impact ionization resonance and auger recombination in Hg1 - xCdxTe (0.6 ≤ x ≤ 0.7)

The purpose of this paper is the study of the impact ionization and the Auger recombination in Hg1-xCdxTe avalanche photodiodes, with0.6 leq x leq 0.7. Forx sim 0.7it is shown that the spin orbit splitting Δ is lower than the bandgap energy Egso that impact ionization is initiated by holes from the Split-off valence band. Forx sim 0.6, Delta sim E_{g}, the rate of the Auger recombination is maximum, corresponding to a resonant impact ionization and to a maximum ratiok = beta / alphawhere α and β are, respectively, the impact ionization coefficient for electrons and holes.     

Photodétecteurs à avalanche Hg0,3 Cd0,7Te à λ = 1,3 μm: coefficients d’ionisation et bruit

Annals of Telecommunications - On présente les premiers résultats obtenus sur les photodiodes à avalanche Hg0,3Cd0,7Te pour la photodétection à λ = 1,3 μm. A la...     

Limitation des performances des photodétecteurs à avalanche GaAIAsSb par effet tunnel

The high rate long distance fiber optical communications require rapid low noise detectors adapted to wavelengths 1.3 or 1.55 μm. GaAlAsSb/GaSb is a suitable system for this need. Recently, the authors have obtained photodiodes with ternary GaAlSb or quaternary GaAl AsSb as an active layer. Quaternary alloys were latticematched to GaSb substrate [1–6]. But, this system presented large reverse dark currents attributed either to surface currents or tunneling currents [6]. In this paper, we prove that in a large range of polarization the reverse dark current is dominated by band to band tunneling or defect assisted tunneling. This limits the value of the optimum multiplication factor and increases the noise equivalent power.     

Multilayered InGaN/GaN structure vs. single InGaN layer for solar cell applications: A comparative study

We report a comparison of the morphological, structural and optical properties of both InGaN single-layer and multilayered structures, the latter consisting of periodic thin GaN interlayers inserted during InGaN growth. It is shown that such a structure suppresses the In concentration fluctuations and corresponding different states of strain relaxation with depth, both detrimental to solar cell applications. Measurements performed by X-ray diffraction, cathodoluminescence and photoluminescence demonstrate that this multilayer growth is a promising approach to increase both the InGaN layer total thickness and In content in InGaN epilayers. As an example, single-phase 120 nm thick InGaN with 14.3% In content is obtained and found to possess high structural quality.     

Strongly sub-Poissonian electrical noise in 1.55-/spl mu/m DBR tunable laser diodes

We report terminal electrical noise measurements on 1.55-/spl mu/m DBR tunable laser diodes in the 1 Hz-1 MHz frequency range, performed using an electrical correlation method. These measurements are compared with a comprehensive electrical model based on rate equation formalism. Taking into account diffusion phenomenon and structural parameters, we obtain a complete agreement between the model and the measurements above threshold and a quite similar tendency below threshold. The influence of Bragg section bias is also discussed.     

Bragg section effects on linewidth and lineshape in 1.55-/spl mu/m DBR tunable laser diodes

We report linewidth and lineshape measurements on 1.55-/spl mu/m distributed Bragg reflector tunable laser diodes using the heterodyne method. We measure Lorentzian linewidths ranging from 3.5 to 25 MHz without any passive section injection. Biasing the Bragg section enhances the residual linewidth up to 6.2 MHz, changes the linewidth-power product, and brings an additional Gaussian lineshape. The feedback sensitivity of the overall setup is also demonstrated.