Electrophysiological studies of rat substantia nigra neurons in an in vitro slice preparation after middle cerebral artery occlusion

We studied sequential changes in electrophysiological profiles of the ipsilateral substantia nigra neurons in an in vitro slice preparation obtained from the middle cerebral artery-occluded rats. Histological examination revealed marked atrophy and neurodegeneration in the ipsilateral substantia nigra pars reticulata at 14 days after middle cerebral artery occlusion. Compared with the control group, there was no significant change in electrical membrane properties and synaptic responses of substantia nigra pars reticulata neurons examined at one to two weeks after middle cerebral artery occlusion. On the other hand, there was a significant increase in the input resistance and spontaneous firing rate of substantia nigra pars compacta neurons at 13-16 days after middle cerebral artery occlusion. Furthermore, inhibitory postsynaptic potentials evoked by stimulation of the subthalamus in substantia nigra pars compacta neurons was suppressed at five to eight days after middle cerebral artery occlusion. At the same time excitatory postsynaptic potentials evoked by the subthalamic stimulation was increased. Bath application of bicuculline methiodide (50 microM), a GABA(A) receptor antagonist, significantly increased the firing rate of substantia nigra pars compacta neurons from intact rats. These results strongly suggest that changes in electrophysiological responses observed in substantia nigra pars compacta neurons is caused by degeneration of GABAergic afferents from the substantia nigra pars reticulata following middle cerebral artery occlusion. While previous studies indirectly suggested that hyperexcitation due to deafferentation from the neostriatum may be a major underlying mechanism in delayed degeneration of substantia nigra pars reticulata neurons after middle cerebral artery occlusion, the present electrophysiological experiments provide evidence of hyperexcitation in substantia nigra pars compacta neurons but not in pars reticulata neurons at the chronic phase of striatal infarction.     

Compatibility of alkaline earth metal (Mg, Ca, Sr)-doped lanthanum chromites as separators in planar-type high-temperature solid oxide fuel cells

The mechanical, electrical and thermal properties of alkaline earth metal (Mg, Ca and Sr)-doped LaCrO₃ have been examined as separators in planar-type high-temperature solid oxide fuel cells. The maximum three-point bending strength at 1000°C in air was measured and found to be 186 MPa for LaCr_0.9Mg_0.1O₃, 36 MPa for La_0.9Ca_0.1CrO₃ and 77 MPa for La_0.9Sr_0.1CrO₃. The La_0.8Sr_0.2CrO₃ separator placed in both an oxidizing and a reducing environment at 1000°C showed almost the same electrical conductivities of the H₂ atmosphere, and the conductivity was independent of sample thickness in the range 0.5–3.0 mm. For all the doped LaCrO₃ perovskites, a difference between the thermal expansion behaviours of air and the H₂ atmosphere was observed. In particular, the thermal expansion slope for the first heating cycle under the H₂ atmosphere showed a marked change. The volume changes were due to the formation of oxygen defects in the perovskite structure. This revised version was published online in November 2006 with corrections to the Cover Date.     

Slot-coupled microstrip antenna with a triplate line feed whereparallel-plate mode is suppressed

In a slot-coupled microstrip antenna with a triplate line feed, the parallel-plate mode is excited by the slot, resulting in a decrease of radiation efficiency. The authors present a technique for suppressing the parallel-plate mode in this type of the antenna. Measured results confirm the effective performance of the proposed method     

Volumetric properties of mixtures of 1,4-dioxane and water at high pressures

Densities of aqueous of 1,4-dioxane have been measured at temperatures from 298 to 348 K and at pressures up to 40 MPa by a vibrating-tube method. Molar volumes obtained with an estimated uncertainty of ±0.2°,% are correlated with pressure by the Tait equation within the experimental uncertainty. Pressure and composition dependences of the excess molar volume, partial molar volume, and isothermal compressibility are determined and they are compared with those of other aqueous solutions.     

Lipopolysaccharide primes human alveolar macrophages for enhanced release of superoxide anion and leukotriene B4: self-limitations of the priming response with protein synthesis

Human alveolar macrophages (AM) can produce potent reactive oxygen intermediates (ROI) and arachidonic acid metabolites (eicosanoids), which have important roles in host defense and the pathogenesis of some diseases of the lung. Bacterial lipopolysaccharide (LPS) is believed to cause profound lung injury and can prime mouse peritoneal macrophages for the enhanced secretion of ROI and eicosanoids. Therefore, we investigated the effect of LPS pretreatment on the ability of AM to release superoxide anions (O2-) and leukotriene B4 (LTB4). LPS can prime AM for the enhanced secretion of O2- and LTB4, regardless of whether they are derived from nonsmokers or smokers. Moreover, judging from the time-response characteristics, this priming for LTB4 release could be inhibited in the later stages of pretreatment, when the O2(-)-releasing capacity was enhanced. The priming inhibition was prevented, at least in part, by cycloheximide, but not by SOD and/or catalase. In addition, cycloheximide also inhibited the priming for O2- release. Hence, protein synthesis might be necessary for the priming for O2- release and for inhibiting the priming for LTB4 release. This phenomenon of self-limiting the priming response with LPS seems to be very important when we consider the high oxygen tension in the lungs and the many bacterial substances inspired into alveoli.     

Construction of the plasmid PMEX8-HAK1 and random site-directed mutagenesis of human cytosolic adenylate kinase

The pMEX8-hAK1 vector was devised from the pAK plasmid (Kim J. H. et al., 1989, Protein Engineering 5, 379-386), which could directly express human adenylate kinase proteins without recombination and its single strand DNA could be withdrawn with helper phage for random site-directed mutagenesis. The conserved key residues at Lys21, Lys27, and Thr39 were engineered to obtain mutants for kinetic analysis. Three mutants were obtained as K21P, K27R, and T39S, their specific activities were strikingly reduced compared to those of wild type adenylate kinase. This pMEX8-hAK1 will be a powerful tool for site-directed mutagenesis to detect the substrate-enzyme interaction for human adenylate kinase including various other enzymes.     

Control of volatile organic compounds by an AC energizedferroelectric pellet reactor and a pulsed corona reactor

Two laboratory-scale plasma reactors, an alternating current (AC) energized ferroelectric (high dielectric ceramic) packed bed reactor and a nanosecond pulsed corona reactor, were constructed. This study was done to develop baseline engineering data to demonstrate the feasibility of the application of plasma reactors to the destruction of various volatile organic compounds (VOCs) at PPM levels. Complete destruction was obtained for toluene. Conversions of methylene chloride at 95% and trichlorotrifluoroethane (known as CFC-113) at 67% were achieved for the plasma reactors used. The conversion was dependent on the mean electron energy in the reactor and was also related to how strongly halogen species were bonded with carbon     

High-efficiency finishing process for metal mold by large-area electron beam irradiation

A new finishing process for metal molds by large-area electron beam (EB) irradiation is proposed in this study. In the large-area EB irradiation equipment used here, an EB with high-energy density is irradiated without focusing the beam, and so the EB with a maximum diameter of 60 mm can be used for melting or evaporating metal surface instantly. Experimental results show that the surface roughness decreases from 6 μmRz to less than 1 μmRz in just a few minutes under proper machining conditions. The corrosion resistance of metal mold surface also could be greatly improved by large-area EB irradiation. Furthermore, the surface roughness of tilting surface close to 90° could be well improved. Therefore, large-area EB irradiation method has a possibility to become a high-efficiency finishing process for metal molds.     

Novel anion exchange membranes having fluorocarbon backbone: Preparation and stability

Anion exchange membranes with excellent durability were prepared by chemical modification of Nafion. The modification was achieved by transformation of the sulfonic acid group into quaternary ammonium group. Namely, Nafion membrane was first converted into an amide-type membrane. Reduction of the carbonxyl group to methylene followed by quaternarization with alkyl iodide resulted in the formation of an anion exchange membrane. The electric resistance of the resulting membranes depends on the equivalent weight of the starting membranes (4.4–6.0 Ω cm² in 0.5N NaCl). The characteristics of the membranes are the excellent stability toward chemical substances such as organic solvents, oxidizing agents, acids, etc. For example, the membranes are stable in aqueous saturated chlorine solution at 60°C for 1000 hr.