Brain in flames - animal models of psychosis: utility and limitations

The neurodevelopmental hypothesis of schizophrenia posits that schizophrenia is a psychopathological condition resulting from aberrations in neurodevelopmental processes caused by a combination of environmental and genetic factors which proceed long before the onset of clinical symptoms. Many studies discuss an immunological component in the onset and progression of schizophrenia. We here review studies utilizing animal models of schizophrenia with manipulations of genetic, pharmacologic, and immunological origin. We focus on the immunological component to bridge the studies in terms of evaluation and treatment options of negative, positive, and cognitive symptoms. Throughout the review we link certain aspects of each model to the situation in human schizophrenic patients. In conclusion we suggest a combination of existing models to better represent the human situation. Moreover, we emphasize that animal models represent defined single or multiple symptoms or hallmarks of a given disease

Weak antilocalization in a strained InGaAs/InP quantum well structure

Weak antilocalization (WAL) effect due to the interference corrections to the conductivity has been studied experimentally in a strained InGaAs/InP quantum well structure. From measurements in tilted magnetic filed, it was shown that both weak localization and WAL features depend only on the normal component of the magnetic field for tilt angles less than 84 degrees. Weak antilocalization effect showed non-monotonous dependence on the gate voltage which could not be explained by either Rashba or Dresselhouse mechanisms of the spin-orbit coupling. To describe magnetic field dependence of the conductivity, it was necessary to assume that spin-orbit scattering time depends on the external magnetic field which quenches the spin precession around effective, spin-orbit related, magnetic fields.Comment: Presented at EP2DS 2003 (Nara), to be published in Physica

The subpopulation of microglia sensitive to neurotransmitters/neurohormones is modulated by stimulation with LPS, interferon-γ, and IL-4

Recently, neurotransmitters/neurohormones have been identified as factors controlling the function of microglia, the immune competent cells of the central nervous system. In this study, we compared the responsiveness of microglia to neurotransmitters/neurohormones. We freshly isolated microglia from healthy adult C57Bl/6 mice and found that only a small fraction (1-20%) responded to the application of endothelin, histamine, substance P, serotonin, galanin, somatostatin, angiotensin II, vasopressin, neurotensin, dopamine, or nicotine. In cultured microglia from neonatal and adult mice, a similarly small population of cells responded to these neurotransmitters/neurohormones. To induce a proinflammatory phenotype, we applied lipopolysaccaride (LPS) or interferon-gamma (IFN-{gamma}) to the cultures for 24 h. Several of the responding populations increased; however, there was no uniform pattern when comparing adult with neonatal microglia or LPS with IFN-{gamma} treatment. IL-4 as an anti-inflammatory substance increased the histamine-, substance P-, and somatostatin-sensitive populations only in microglia from adult, but not in neonatal cells. We also found that the expression of different receptors was not strongly correlated, indicating that there are many different populations of microglia with a distinct set of receptors. Our results demonstrate that microglial cells are a heterogeneous population with respect to their sensitivity to neurotransmitters/neurohormones and that they are more responsive in defined activation states

Time transfer and frequency shift to the order 1/c^4 in the field of an axisymmetric rotating body

Within the weak-field, post-Newtonian approximation of the metric theories of gravity, we determine the one-way time transfer up to the order 1/c^4, the unperturbed term being of order 1/c, and the frequency shift up to the order 1/c^4. We adapt the method of the world-function developed by Synge to the Nordtvedt-Will PPN formalism. We get an integral expression for the world-function up to the order 1/c^3 and we apply this result to the field of an isolated, axisymmetric rotating body. We give a new procedure enabling to calculate the influence of the mass and spin multipole moments of the body on the time transfer and the frequency shift up to the order 1/c^4. We obtain explicit formulas for the contributions of the mass, of the quadrupole moment and of the intrinsic angular momentum. In the case where the only PPN parameters different from zero are beta and gamma, we deduce from these results the complete expression of the frequency shift up to the order 1/c^4. We briefly discuss the influence of the quadrupole moment and of the rotation of the Earth on the frequency shifts in the ACES mission.Comment: 17 pages, no figure. Version 2. Abstract and Section II revised. To appear in Physical Review

Spin Coulomb drag in the two-dimensional electron liquid

We calculate the spin-drag transresistivity $\rho_{\uparrow \downarrow}(T)$ in a two-dimensional electron gas at temperature $T$ in the random phase approximation. In the low-temperature regime we show that, at variance with the three-dimensional low-temperature result [$\rho_{\uparrow\downarrow}(T) \sim T^2$], the spin transresistivity of a two-dimensional {\it spin unpolarized} electron gas has the form $\rho_{\uparrow\downarrow}(T) \sim T^2 \ln T$. In the spin-polarized case the familiar form $\rho_{\uparrow\downarrow}(T) =A T^2$ is recovered, but the constant of proportionality $A$ diverges logarithmically as the spin-polarization tends to zero. In the high-temperature regime we obtain $\rho_{\uparrow \downarrow}(T) = -(\hbar / e^2) (\pi^2 Ry^* /k_B T)$ (where $Ry^*$ is the effective Rydberg energy) {\it independent} of the density. Again, this differs from the three-dimensional result, which has a logarithmic dependence on the density. Two important differences between the spin-drag transresistivity and the ordinary Coulomb drag transresistivity are pointed out: (i) The $\ln T$ singularity at low temperature is smaller, in the Coulomb drag case, by a factor $e^{-4 k_Fd}$ where $k_F$ is the Fermi wave vector and $d$ is the separation between the layers. (ii) The collective mode contribution to the spin-drag transresistivity is negligible at all temperatures. Moreover the spin drag effect is, for comparable parameters, larger than the ordinary Coulomb drag effect.Comment: 6 figures; various changes; version accepted for publicatio

Electron Spin Injection at a Schottky Contact

We investigate theoretically electrical spin injection at a Schottky contact between a spin-polarized electrode and a non-magnetic semiconductor. Current and electron density spin-polarizations are discussed as functions of barrier energy and semiconductor doping density. The effect of a spin-dependent interface resistance that results from a tunneling region at the contact/semiconductor interface is described. The model can serve as a guide for designing spin-injection experiments with regard to the interface properties and device structure.Comment: 4 pages, 4 figure

Some remarks on the isoperimetric problem for the higher eigenvalues of the Robin and Wentzell Laplacians

We consider the problem of minimising the $k$th eigenvalue, $k \geq 2$, of the ($p$-)Laplacian with Robin boundary conditions with respect to all domains in $\mathbb{R}^N$ of given volume $M$. When $k=2$, we prove that the second eigenvalue of the $p$-Laplacian is minimised by the domain consisting of the disjoint union of two balls of equal volume, and that this is the unique domain with this property. For $p=2$ and $k \geq 3$, we prove that in many cases a minimiser cannot be independent of the value of the constant $\alpha$ in the boundary condition, or equivalently of the volume $M$. We obtain similar results for the Laplacian with generalised Wentzell boundary conditions $\Delta u + \beta \frac{\partial u}{\partial \nu} + \gamma u = 0$.Comment: 16 page

Effect of Magnetic Impurity Correlations on Josephson Tunneling

The ordering trend of magnetic impurities at low temperature results in the frustration of the pair-breaking effect and induces a ``recovery'' of superconducting properties. We show that this effect manifests itself in the deviation of the Josephson current amplitude from the values obtained within the Ambegaokar-Baratoff and the Abrikosov-Gor'kov models. We consider both weak and strong-coupling cases. The theory is applied to describe the experimental data obtained for the low-$T_c$ superconductor SmRh$_4$B$_4$. We further predict a ``recovery'' effect of the Josephson current in high-temperature superconductors.Comment: 7 pages, 4 figures. Accepted for publication in Physica

Contact-induced spin polarization in carbon nanotubes

Motivated by the possibility of combining spintronics with molecular structures, we investigate the conditions for the appearance of spin-polarization in low-dimensional tubular systems by contacting them to a magnetic substrate. We derive a set of general expressions describing the charge transfer between the tube and the substrate and the relative energy costs. The mean-field solution of the general expressions provides an insightful formula for the induced spin-polarization. Using a tight-binding model for the electronic structure we are able to estimate the magnitude and the stability of the induced moment. This indicates that a significant magnetic moment in carbon nanotubes can be observed.Comment: To appear in Phys. Rev. B (2003