Tateaki Ogata

An ESR-CT imaging of the head of a living rat receiving an administration of a nitroxide radical

Three-dimensional ESR imaging of a living rat has been performed by an L-band ESR system, which is composed of an L-band ESR spectrometer, a field gradient coil, and a data processor. The imaging was carried out by Lauterburs method. A nitroxide, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (Carbamoyl-PROXYL), was used as an imaging agent in saline solution at a concentration of 0.2 M and administered intraperitoneally to obtain a constant concentration in the head for about an hour. It took about 40 min to obtain one set of ESR-CT images. The cross-sectional images were made, both as coronal and horizontal images. In the images of the rat head the nitroxide-rich region was clearly distinguished from the deficient region. The nitroxide-deficient areas corresponded well to the brain of the rat.

EPR imaging for in vivo analysis of the half-life of a nitroxide radical in the hippocampus and cerebral cortex of rats after epileptic seizures.

Recently, we developed an in vivo temporal electron paramagnetic resonance (EPR) imaging technique to be applied to the brain of a rat, into which a blood-brain barrier (BBB)-permeable nitroxide radical, 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (PCAM) was injected intraperitoneally. This imaging technique made it possible to measure decay rates of a nitroxide radical in multiple regions of the brain simultaneously. Using this technique, the half-life of PCAM was estimated from the exponential decay of the signal intensity derived from the temporal EPR images in the hippocampus and cerebral cortex of rats after a kainic acid (KA)-induced seizure. The hippocampal half-life of PCAM after KA-induced seizures was significantly prolonged (p < .01), whereas the prolongation of the cortical half-life was not significant. These findings suggest that following a KA-seizure, the intrahippocampal ability to reduce the nitroxide radical is impaired, but the ability is intact in the cerebral cortex. This is the first in vivo quantitative EPR imaging study that has a bearing on the pathogenesis of KA-induced seizures in the brain.

A spatiotemporal study on the distribution of intraperitoneally injected nitroxide radical in the rat head using an in vivo ESR imaging system

We have developed a rapid-scan in vivo electron spin resonance (ESR) imaging system operating at 700 MHz based on an air-cored two-coil Helmholtz designed resistive magnet. Using this system, we performed ESR-CT for the intraperitoneally injected nitroxide radical, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, in the rat head. The imaging data were collected over the time course range from 5 to 47 min after injection at an interval of 3 min and a series of ESR-CT images were reconstructed at the same slice plane (1 cm anterior to interaural line). The series of ESR-CT images thus obtained by rapid scans provided detailed spatiotemporal information on the distribution of the injected nitroxide radical in the rat head. The brain was imaged as a nitroxide-deficient area while the blood vessels and/or extracranium tissues as a nitroxide-rich area. During periods when high intensities of ESR signals were maintained, spots of nitroxide-accumulation were imaged at the central part of the brain. The spots were assigned to the middle sized blood vessels in the brain.

Reversible half-wave potentials of reduction processes on nitroxide radicals

Abstract The reversible half-wave potential ( E 1 2 rev ) of the reduction process was determined for six nitroxide radicals by cyclic voltammetry as the midpoint potential between reduction and reoxidation peaks. The variations of E 1 2 rev with pH were interpreted as the protonation induced by the one-electron reduction of nitroxide radicals.

Preparation of thin films of MnO2 and CeO2 by a modified chemical bath (oxidative-soak-coating) method

Thin films of MnO2 and CeO2 were deposited on glass substrates directly from aqueous solutions in a temperature range from 313 to 333 K by a modified chemical bath deposition technique. The principle of the film deposition was based on the oxidation of Mn2+ and Ce3+ ions in homogeneous solutions and subsequent heterogeneous nucleation of MnO2 and CeO2 on the substrates. We have named this method as “oxidative-soak-coating” method. The film thicknesses after a 24-hour deposition were 1 μm and 60 nm, respectively. Thin films consisting of Mn3O4 and MnOOH were also deposited by changing the pH of the starting solutions for the deposition of MnO2. The effects of the composition of the starting solution, deposition temperature, and the compatibility of the substrates to the film substances were investigated.

Evaluation of the hepatic reduction of a nitroxide radical in rats receiving ascorbic acid, glutathione or ascorbic acid oxidase by in vivo electron spin resonance study

Background:  A nitroxide radical, 4‐hydroxyl‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPOL), is directly reduced to hydroxylamine by ascorbic acid (AsA). Ascorbic acid is oxidized to dehydroascorbic acid (DHA) by ascorbic acid oxidase (AAOx), and DHA is reduced to AsA by glutathione (GSH). In the present study, in vivo and ex vivo reduction of  TEMPOL in the rat liver under various conditions of AsA supply was investigated using an electron spin resonance (ESR) spectrometer equipped with a surface coil‐type resonator.

Proteome analysis of Oncorhynchus species during embryogenesis.

To understand the molecular mechanisms underlying normal and abnormal development of two salmonids, masu salmon (Oncorhynchus masou) and rainbow trout (O. mykiss), we used two‐dimensional (2‐D) electrophoresis to construct a series of 2‐D maps during the embryonic period. We identified all visible protein spots on the 2‐D map by assigning numbers for masu salmon and rainbow trout, and we determined N‐terminal sequences of proteins for one hundred of the spots, that appear at very high concentrations in the whole embryos of masu salmon and rainbow trout. We also characterized embryonic stages according to the periods of appearance of spots. Most of the N‐terminal sequences were identical or at least highly similar to partial sequences reported for vitellogenin (Vtg) of O. mykiss. A potential proteolytic processing of Vtg for rainbow trout is discussed in relation to the time of appearance and relative position of Vtg fragments within the complete protein sequence.

Surface-coil-type resonators for in vivo temporal ESR measurements in different organs of nitroxide-treated rats

Three kinds of surface-coil-type resonators (SCRs) operating at 720 MHz were fabricated for in vivo temporal electron spin resonance (ESR) measurements. The inner diameter of the singleturn coil of the SCRs was 3, 4, or 10 mm. ResonatorQ increases and the detection limit decreases with coil diameter. The distance across which the microwave magnetic field can penetrate in the direction facing to the coil was about the same (about 2 mm) for all SCRs. In vivo kinetic studies of intravenously injected 4-hydroxy-2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPOL) were performed at the liver, kidney, stomach, rectum, vein, and skin of rats with SCRs suited to the target areas. The halflife of TEMPOL was estimated from the exponential decay of the ESR signal intensity (the peak-to-peak height). Different sites in the rat showed apparent differences in the half-life of TEMPOL. This suggests that the apparent differences in the reducing ability of TEMPOL are related to the organ or tissue where measurement is taken because no excretion of TEMPOL was observed.

A reaction kinetics model of water sonolysis in the presence of a spin-trap

The time development of the concentration of a spin-trapped OH radical was studied by electron spin resonance at various sound intensities and various 5,5-dimethyl-1-pyrroline N-oxide (DMPO) concentrations in water sonolysis. The lifetime of the spin-trapped OH radical was also studied, and factors governing sonolysis are discussed. We found that the production of spin-trapped OH radical increases with increasing ultrasound intensity. The lifetime of a spin-trapped OH radical decreases linearly with increase in sonication time. This result suggests that an unknown scavenger is produced by ultrasound. Based on the above results, we suggested a model of the reaction kinetics and estimated the production rate of OH radical from this model.

In vivo electron spin resonance analysis of nitroxide radicals injected into a rat by a flexible surface-coil-type resonator as an endoscope- or a stethoscope-like device

The flexible surface-coil-type resonator (FSCR) operating in a 700 MHz microwave electron spin resonance (ESR) system was applied to measure the nitroxide radicals at a specific area in rats. The FSCR was composed of a single-turn coil with a diameter of 5 mm and two flexible coaxial lines of 450 mm in length. For an endoscope-like application, the FSCR was inserted into the rectum of the rat and sequential changes in the ESR signals of the intravenously injected nitroxide radical (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl; TEMPOL or 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidine-1-yloxy; carbamoyl-PROXYL) were measured. The ESR signal intensity of the nitroxide decreased according to first-order kinetics. For a stethoscope-like application, the FSCR was placed at several sites on the abdominal skin of the rats receiving a subcutaneous injection of carbamoyl-PROXYL, and diffusion and/or metabolism of the radical in the skin was observed.