Pilocarpine-Induced Status Epilepticus in Rats Involves Ischemic and Excitotoxic Mechanisms

The neuron loss characteristic of hippocampal sclerosis in temporal lobe epilepsy patients is thought to be the result of excitotoxic, rather than ischemic, injury. In this study, we assessed changes in vascular structure, gene expression, and the time course of neuronal degeneration in the cerebral cortex during the acute period after onset of pilocarpine-induced status epilepticus (SE). Immediately after 2 hr SE, the subgranular layers of somatosensory cortex exhibited a reduced vascular perfusion indicative of ischemia, whereas the immediately adjacent supragranular layers exhibited increased perfusion. Subgranular layers exhibited necrotic pathology, whereas the supergranular layers were characterized by a delayed (24 h after SE) degeneration apparently via programmed cell death. These results indicate that both excitotoxic and ischemic injuries occur during pilocarpine-induced SE. Both of these degenerative pathways, as well as the widespread and severe brain damage observed, should be considered when animal model-based data are compared to human pathology

Rodent models of focal cerebral ischemia: procedural pitfalls and translational problems

Rodent models of focal cerebral ischemia are essential tools in experimental stroke research. They have added tremendously to our understanding of injury mechanisms in stroke and have helped to identify potential therapeutic targets. A plethora of substances, however, in particular an overwhelming number of putative neuroprotective agents, have been shown to be effective in preclinical stroke research, but have failed in clinical trials. A lot of factors may have contributed to this failure of translation from bench to bedside. Often, deficits in the quality of experimental stroke research seem to be involved. In this article, we review the commonest rodent models of focal cerebral ischemia - middle cerebral artery occlusion, photothrombosis, and embolic stroke models - with their respective advantages and problems, and we address the issue of quality in preclinical stroke modeling as well as potential reasons for translational failure

SFDU documentation for CLAES - data set change history document

SFDU - Standard format data units CLAES - Cryogenic Limb Array Etalon Spectrometer This document describes the CLAES data set change history for each version of the cataloged data

Isentropic formation of the tropopause

Large-scale horizontal rolls can have a significant influence on turbulent transport across the atmospheric boundary layer. The formation and maintenance of such rolls is dependent on the thermal and dynamic stability of the boundary layer (BL). The authors present aircraft observations of boundary layers, both with and without roll circulations, off the coast of California. The contribution of the rolls to the turbulent fluxes of heat, moisture, and momentum, and the variances of the three velocity components are determined for four cases. The fractional roll contributions to the u and w variances, and the sensible heat and along-wind momentum fluxes, show a near linear increase with altitude, from less than 10% at 30 m to more than 70% at the top of the BL. The variance in v and crosswind momentum flux are more scattered, although the variance shows a slight increase with altitude from about 40% to 60%. The latent heat flux also shows a great deal of scatter, especially in the lower third of the BL where the total flux is small; above this, values range between about 40% and 85% but show no clear trends. A stability parameter in the form of a bulk Richardson Ri number is calculated for each of 13 profiles through the boundary layer; it is found that the Richardson number successfully identifies those cases where rolls are present, and its value corresponds to some extent with the strength of the rolls. Values close to zero correspond to cases with well-defined rolls; for 0.1 < Ri < 0.25 rolls are found to exist, but they tend to be weak and patchy; and no rolls are found where Ri is greater than the critical value of approximately 0.25. Reynolds numbers are calculated from a number of different definitions and indicate the dynamic instability of the shear dominated boundary layers

Global evolution of the Mt Pinatubo volcanic aerosols observed by the infrared limb-sounding instruments CLAES and ISAMS on the Upper Atmosphere Research Satellite

The cryogenic limb array etalon spectrometer (CLAES) and the improved stratospheric and mesospheric sounder (ISAMS) instruments on board the Upper Atmosphere Research Satellite (UARS) have been used to produce global information on the Mt. Pinatubo volcanic aerosol for the period from October 1991 to April 1993, The Satellite infrared extinction measurements near 12 mu m are converted into the aerosol-related parameters necessary for modelling the effects of the volcanic aerosol on the aeronomy of the stratosphere and are presented as zonal mean distributions for 80 degrees S to 80 degrees N averaged over similar to 35-day periods. The aerosol composition is derived from the CLAES and ISAMS temperature measurements and the water vapour abundances are obtained from the microwave limb sounder (MLS). The aerosol volume density is obtained from the extinction measurements from which the Surface area density and the effective particle radius are estimated. The maximum aerosol surface area density has a value of about 50 mu m(2) cm(-3) at a height of 24 km at the equator in October 1991, before decaying exponentially with a time constant of 443 +/- 10 days. The surface area density remained well above preeruption values in April 1993. The effective particle radius in the tropics decays monotonically from 0.65 mu m in October 1991 to 0.4 mu m in April 1993. The global aerosol sulphate mass loading is 19.5 Mt in October 1991 and decays exponentially with a time constant of 342 +/- 8 days to a value of 4.3 Mt by April 1993. Four months after the eruption the calculated optical thickness at 1.02 mu m was similar to 0.25 in the tropics. Rate constants are derived for the heterogeneous reactions of N2O5 and ClONO2 on the sulphate aerosols. The application of the aerosol parameters to the investigation of tracer transport, heterogeneous chemistry, and radiative transfer is discussed

UARS first global N2O5 data sets: Application to a stratospheric warming event in January 1992

For the first time, global measurements of N2O5 are available for study. N2O5 has long been a missing link in large-scale observations of stratospheric nitrogen species, the chemical family that comprises the major global loss cycle for ozone above about 25 km [McElroy et al., 1992]. N2O5 is also an important intermediate in conversion of NOx to HNO3, thus limiting the effect of nitrogen-catalyzed ozone destruction below about 25 km [Fahey et al., 1993]. The new N2O5 observations come from both the Cryogenic Limb Array Etalon Spectrometer (CLAES) and Improved Stratospheric and Mesospheric Sounder (ISAMS) instruments on the Upper Atmosphere Research Satellite (UARS), providing near-global coverage at high spatial and temporal resolution for almost 20 months. Here we focus on data obtained near 40 km during a stratospheric warming in January 1992. The N2O5 fields show globally coherent structures with large variation in response to global transport coupled with highly temperature dependent chemistry. Comparison of the data with chemistry and transport models indicates that our understanding of processes controlling N2O5 amounts and the interaction with other reactive nitrogen species is largely accurate under most conditions; however, an exceptional disagreement is found in the prolonged polar dark. This example demonstrates the utility of global data to understand the combined effects of chemistry and transport on N2O5 under a wide range of conditions

Coupled aerosol-chemical modeling of UARS HNO3 and N2O5 measurements in the arctic upper stratosphere

Gas-phase photochemical models do not account for the formation of a secondary altitude HNO3 maximum in the upper stratosphere at high latitudes during winter, suggesting that some processes are missing in the currently accepted chemistry of reactive nitrogen species [Kawa et al., 1995]. Heterogeneous chemistry on aerosol particles had been discounted as the cause because the aerosol surface area is expected to be very low at these altitudes. We have coupled a sulphate aerosol microphysical model to a chemical transport model to investigate this model deficiency in the Arctic during January 1992. The aerosol model predicts the formation of small sulphate particles at 1100 K. Comparisons with cryogenic limb array etalon spectrometer (CLAES) HNO3 and improved stratospheric and mesospheric sounder (ISAMS) N2O5 observations show that the heterogeneous conversion of N2O5 to HNO3 on the modeled small sulphate particles can account for some of the unexpected features seen in Upper Atmosphere Research Satellite (UARS) observations

Simultaneous observations of Polar Stratospheric Clouds and HNO3 over Scandinavia in January, 1992

Simultaneous observations of Polar Stratospheric Cloud (PSC) aerosol extinction and HNO3 mixing ratios over Scandinavia are examined for January 9-10, 1992. Data measured by the Microwave Limb Sounder (MLS), Cryogenic Limb Array Etalon Spectrometer (CLAES), and Improved Stratospheric and Mesospheric Sounder (ISAMS) experiments on the Upper Atmosphere Research Satellite (UARS) are examined at locations adjacent to parcel trajectory positions. Regression coefficients, obtained from Mie calculations, are used to transform aerosol extinctions into aerosol volume densities. Graphs of volume density versus temperature, and importantly, HNO3 mixing ratio versus temperature, show volume increases and simultaneous loss of HNO3 as temperatures decrease. The data is consistent with initial PSC growth processes which transform sulfate droplets into ternary droplets or nitric acid dihydrate (NAD) particles