Hippocampal Desynchronization of Functional Connectivity Prior to the Onset of Status Epilepticus in Pilocarpine-Treated Rats

Status epilepticus (SE), a pro-epileptogenic brain insult in rodent models of temporal lobe epilepsy, is successfully induced by pilocarpine in some, but not all, rats. This study aimed to identify characteristic alterations within the hippocampal neural network prior to the onset of SE. Sixteen microwire electrodes were implanted into the left hippocampus of male Sprague-Dawley rats. After a 7-day recovery period, animal behavior, hippocampal neuronal ensemble activities, and local field potentials (LFP) were recorded before and after an intra-peritoneal injection of pilocarpine (350 mg/kg). The single-neuron firing, population neuronal correlation, and coincident firing between neurons were compared between SE (n = 9) and nonSE rats (n = 12). A significant decrease in the strength of functional connectivity prior to the onset of SE, as measured by changes in coincident spike timing between pairs of hippocampal neurons, was exclusively found in SE rats. However, single-neuron firing and LFP profiles did not show a significant difference between SE and nonSE rats. These results suggest that desynchronization in the functional circuitry of the hippocampus, likely associated with a change in synaptic strength, may serve as an electrophysiological marker prior to SE in pilocarpine-treated rats

25th Annual Computational Neuroscience Meeting: CNS-2016

Abstracts of the 25th Annual Computational Neuroscience Meeting: CNS-2016 Seogwipo City, Jeju-do, South Korea. 2–7 July 201

Polarised neutron reflectivity from U/Fe, U/Gd multilayers

U/Fe and U/Gd multilayers constitute magnetic systems, which can be used to probe the hybridisation of the 5f electrons of uranium with 3d and 4f electrons, respectively. A range of samples with varying layer thicknesses was prepared by DC sputtering in a UHV chamber. X-ray and neutron reflectivity and X-ray diffraction were used to characterise the structure of the U/Fe [A.M. Beesley, M.F. Thomas, A.D.F. Herring, R.C.C. Ward, M.R. Wells, S. Langridge, S.D. Brown, S.W. Zochowski, L. Bouchenoire, W.G. Stirling, G.H. Lander, J. Phys.: Condens. Matter 16 (2004) 8491] and U/Gd systems. A combination of polarised neutron reflectivity, SQUID magnetometry and X-ray magnetic circular dichroism have revealed an induced moment on the U site in U/Fe structures and a saturation magnetisation which increases with increasing Fe and Gd thickness. © 2006

A study of uranium-based multilayers: II. Magnetic properties

SQUID magnetometry and polarised neutron reflectivity measurements have been employed to characterise the magnetic properties of U/Fe, U/Co and U/Gd multilayers. The field dependence of the magnetisation was measured at 10K in magnetic fields from -70kOe to 70kOe. A temperature dependent study of the magnetisation evolution was undertaken for a selection of U/Gd samples. PNR was carried out in a field of 4.4kOe for U/Fe and U/Co samples (at room temperature) and for U/Gd samples (at 10K). Magnetic 'dead' layers of about 15 Angstrom were observed for U/Fe and U/Co samples, consistent with a picture of interdiffused interfaces. A large reduction in the magnetic moment, constant over a wide range of Gd layer thicknesses, was found for the U/Gd system (about 4 Bohr magnetons compared with 7.63 for the bulk metal). This could be understood on the basis of a pinning of Gd moments arising from a column-like growth mechanism of the Gd layers. A study of the effective anisotropy suggests that perpendicular magnetic anisotropy could occur in multilayers consisting of thick U and thin Gd layers. A reduction in the Curie temperature was observed as a function of Gd layer thickness, consistent with a finite-size scaling behaviour.Comment: 18 pages, 8 figures, submitted to J. Phys.: Condens. Matte

Polarised neutron reflectivity from U/Fe, U/Gd multilayers

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Magnetism of uranium/iron multilayers: I. Fabrication and characterization

U/Fe multilayers constitute a magnetic system in which the 3d magnetism of the Fe layers will be modified by hybridization with the U 5f electrons. This paper describes a programme of measurements of the magnetic behaviour of these systems beginning with the fabrication and thorough characterization of the samples. Metallic U/Fe multilayers were prepared by DC sputtering in a UHV chamber. A range of samples with measured U thicknesses, t U, in the range 18-66 Å and Fe thicknesses, t Fe, from 7 to 108 Å was fabricated. X-ray and neutron reflectivity measurements showed strong peaks indicating good layer structure and gave a determination of the bilayer thickness. X-ray diffraction analysis showed crystalline α-U and α-Fe for layer thicknesses greater than about 20 Å. The α-Fe is strongly textured with (110) planes in the layer plane. The Fe lattice parameter is larger for the case of thin layers, but approaches the bulk value of 2.866 Å at t Fe ∼ 75 Å. Mössbauer spectra of α-Fe were obtained for t Fe ≥ 18 Å; a non-magnetic component of thickness ∼12 Å per layer is always present. The results from these different experimental techniques are combined to present a detailed description of these multilayer systems

Resonant magnetic reflectivity from U/Fe multilayers

U/Fe multilayers have been produced through dc sputtering. The high quality of these multilayers has been confirmed through x-ray reflectivity measurements and fitting to the resultant spectra. These samples are currently the subject of investigations using techniques including polarized neutron reflectivity, conversion electron Mossbauer spectroscopy, and magnetotransport and magneto-optic measurements. In this article, we report on results obtained from a [U 30 Angstrom/Fe 40 Angstrom]x30 multilayer through resonant magnetic scattering performed on the XMaS beamline at the European Synchrotron Radiation Facility. The asymmetry ratio is defined as (I+-I-)/(I++I-), where I+(I-) is the normalized intensity obtained with circular polarization and the applied field parallel (antiparallel) to the beam direction. Asymmetry data are presented as functions of both energy and momentum transfer. We have identified a Uranium moment with the use of resonant magnetic reflectivity at 12 K. Reversal of the polarity of the asymmetry ratio between the first and second superlattice peaks indicates a nonuniform moment distribution through the uranium layers. Temperature dependence measurements confirm that the moment also exists at room temperature. (C) 2003 American Institute of Physics

Wave-Processing of Long-Scale Information by Neuronal Chains

Investigation of mechanisms of information handling in neural assemblies involved in computational and cognitive tasks is a challenging problem. Synergetic cooperation of neurons in time domain, through synchronization of firing of multiple spatially distant neurons, has been widely spread as the main paradigm. Complementary, the brain may also employ information coding and processing in spatial dimension. Then, the result of computation depends also on the spatial distribution of long-scale information. The latter bi-dimensional alternative is notably less explored in the literature. Here, we propose and theoretically illustrate a concept of spatiotemporal representation and processing of long-scale information in laminar neural structures. We argue that relevant information may be hidden in self-sustained traveling waves of neuronal activity and then their nonlinear interaction yields efficient wave-processing of spatiotemporal information. Using as a testbed a chain of FitzHugh-Nagumo neurons, we show that the wave-processing can be achieved by incorporating into the single-neuron dynamics an additional voltage-gated membrane current. This local mechanism provides a chain of such neurons with new emergent network properties. In particular, nonlinear waves as a carrier of long-scale information exhibit a variety of functionally different regimes of interaction: from complete or asymmetric annihilation to transparent crossing. Thus neuronal chains can work as computational units performing different operations over spatiotemporal information. Exploiting complexity resonance these composite units can discard stimuli of too high or too low frequencies, while selectively compress those in the natural frequency range. We also show how neuronal chains can contextually interpret raw wave information. The same stimulus can be processed differently or identically according to the context set by a periodic wave train injected at the opposite end of the chain