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Biomedical subjects

M Ichikawa

Publications and source records attributed to M Ichikawa.

At least 55 records · Page 3Linked to original sources
PubMed2000

Spectroscopic and Kinetic Studies of the Reaction of CO+H(2)O and CO+O(2) and Decomposition of HCOOH on Au/H-Mordenite Catalysts.

The surface species formed from the reaction of CO+H(2)O and CO+O(2) and decomposition of HCOOH on Au incorporated into H-mordenite zeolite have been studied by means of in situ FTIR spectroscopy. On H-mordenite, a bidentate formate species (2912, 1536, and 1390 cm(-1)) is produced upon exposure to the CO+H(2)O gas mixture at 323 K, as well as different carbonate-like species (1956, 1852, 1705, and 1360 cm(-1)). The latter species was extensively formed in a short time and was responsible for hindering the CO(2) adsorbed species. However, Au/H-mordenite presented different vibration modes of formate species with a high emphasis on the monodentate ones (2950, 2916, 2896, 1690, and 1340 cm(-1)). The HCOOH adsorption on Au/H-mordenite showed two bands at 1622 and 1590 cm(-1) of the nu(as)(OCO) species, suggesting the formation of two types of formate species. The decomposition rate of the formate species formed on Au moieties was faster than that formed on H-mordenite. This was consistent with the calculated activation energies of CO(2) formation that showed a lower value (40.1 kJ/mol) on the former sample than on the latter one (63.3 kJ/mol). A dehydrogenation mechanism is proposed (HCOOH-->H(2)+CO(2)) for the decomposition of HCOOH on the Au/H-mordenite catalyst. On the other hand, the Au/H-mordenite catalyst activated the CO oxidation reaction. This reaction proceeded mainly through the formation of carboxylate species at first, which tended to obviate with time, preferring the formate species. The latter species resulted from the interaction of CO with OH stretching of the zeolite assisted by the presence of gas phase O(2). The formate species is further decomposed with time to carbonate species. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Quantification of optical signals with electrophysiological signals in neural activities of Di-4-ANEPPS stained rat hippocampal slices.

We have quantified the optical signals of synaptically induced neural activities in an in vitro brain slice preparation in terms of electrophysiological signals. The qualification was done using electrophysiologically well known neural activities in the CA1 area of rat hippocampal slices stained with externally applied fluorescent voltage-sensitive dye (VSD; Di-4-ANEPPS). Together with a newly designed CCD-based digital high-speed camera system and epi-fluorescent optics, our improvements were made on a protocol for staining using a newly designed chamber system. These improvements enabled us to make stable and reliable recordings of optical signals and electrophysiological measurements without affecting the physiological status and to make a quantitative comparison between them. The time course and amplitude of the optical signal showed fair agreement with intracellular and extracellular recordings, and was stable over 2 h. The optical signal followed synaptically induced long-term potentiation (LTP) as monitored by the electrophysiological signals. A regional difference in the amount of LTP was found in optical signals and was confirmed in the electrophysiological signals. These results demonstrate the capabilities of our improved method as an alternative but more potent tool to measure the neuronal activities of brain slice in addition to electrophysiological method.

Action Potentials↗
PubMed2000

Reductive activation of mitomycin C by neuronal nitric oxide synthase.

Mitomycin C (MC) requires bioreduction prior to the generation of alkylating moieties. NADPH-cytochrome P450 reductase is predominant in metabolic activation of MC in hypoxic cancer cells. In this study, neuronal nitric oxide synthase (nNOS), whose reductase domain is structurally similar to that of NADPH-cytochrome P450 reductase, was assessed for its ability to activate MC. nNOS under anaerobic conditions catalyzed the reduction of MC, which was measured as the decrease in absorbance at 375 nm. Neither the heme blocker potassium cyanide (1 mM) nor the nNOS competitive inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 1 mM) affected the bioreduction of MC, whereas 0.1 mM diphenyleneiodonium chloride, which binds to the reductase domain of nNOS, inhibited MC reduction completely. The reduction of MC by nNOS was influenced by Ca(2+)/calmodulin. In the absence of Ca(2+)/calmodulin, the rate of MC reduction decreased by 28% at pH 6.6. The formation of an alkylated complex of 4-(p-nitrobenzyl)pyridine occurred in a manner analogous to that observed in MC metabolic experiments. The rate of MC reduction and the formation of the alkylated complex of 4-(p-nitrobenzyl)pyridine at pH 6.6 were increased by 43 and 54%, respectively, as compared with that at pH 7.6. nNOS-activated MC resulted in the consumption of oxygen in air. The rate of oxygen consumption decreased by 50% in the presence of 2000 U/mL of catalase. MC inhibited nNOS activity in a noncompetitive manner. These findings demonstrate that nNOS is capable of catalyzing the bioreduction of MC.

Alkylation↗
PubMed2000

Decreased UV sensitivity, mismatch repair activity and abnormal cell cycle checkpoints in skin cancer cell lines derived from UVB-irradiated XPA-deficient mice.

Xeroderma pigmentosum group A gene (XPA)-deficient mice are defective in nucleotide excision repair (NER) and are therefore highly sensitive to ultraviolet (UV)-induced skin carcinogenesis. We established cell lines from skin cancers of UVB-irradiated XPA-deficient mice to investigate the phenotypic changes occurring during skin carcinogenesis. As anticipated, the skin cancer cell lines were devoid of NER activity but were less sensitive to killing by UV-irradiation than the XPA(-/-) fibroblast cell line. The lines were also more resistant to 6-thioguanine (6-TG) than XPA(-/-) and XPA(+/+) fibroblasts, which was suggestive of a mismatch repair (MMR) defect. Indeed, in vitro mismatch binding and MMR activity were impaired in several of these cell lines. Moreover, these cell lines displayed cell cycle checkpoint derangements following UV-irradiation and 6-TG exposure. The above findings suggest that MMR downregulation may help cells escape killing by UVB, as was seen previously for methylating agents and cisplatin, and thus that MMR deficient clones are selected for during the tumorigenic transformation of XPA(-/-) cells.

Animals↗
PubMed2000

Studies of in vivo mutations in rpsL transgene in UVB-irradiated epidermis of XPA-deficient mice.

We have established xeroderma pigmentosum group A (XPA) gene-knockout mice with nucleotide excision repair (NER) deficiency, which rapidly developed skin tumors when exposed to a low dose of chronic UV like XP-A patients, confirming that the NER process plays an important role in preventing UVB-induced skin cancer. To examine the in vivo mutation in the UVB-irradiated epidermis, we established XPA (-/-), (+/-) and (+/+) mice carrying the Escherichia coli rpsL transgene with which the mutation frequencies and spectra in the UVB-irradiated epidermal tissue can be examined conveniently. The XPA (-/-) mice showed a higher frequency of UVB-induced mutation in the rpsL transgene with a low dose (150 J/m(2)) of UVB-irradiation than the XPA (+/-) and (+/+) mice, while, at a high dose (900 J/m(2)) they showed almost the same frequency of mutation as the XPA (+/-) and (+/+) mice, probably because of cell death in the epidermis of the XPA (-/-) mice. However, CC-->TT tandem transition, a hallmark of UV-induced mutation, was detected at higher frequency in the XPA (-/-) mice than the XPA (+/-) and (+/+) mice at both doses of UVB. This rpsL/XPA mouse system will be useful for further analyzing the role of NER in the mutagenesis and carcinogenesis induced by various carcinogens.

Animals↗
PubMed2000

Spectroscopic Identification of Adsorbed Intermediates Derived from the CO+H(2)O Reaction on Zeolite-Encapsulated Gold Catalysts.

Identification of reaction intermediates in the water-gas shift reaction (WGSR: H(2)O+CO-->H(2)+CO(2)) on Au(n+) (1</=n<3) incorporated into NaY, Na-mordenite, and Na-ZSM-5 zeolites has been studied by means of in situ FT-IR spectroscopy. Exposure of Au(n+)/zeolites to a gas mixture consisting of CO+H(2)O at 323 K produced IR carbonyl spectra characterized by Au(+)-CO at 2192 cm(-1) and Au(0)-CO at 2128 cm(-1). On Au(n+)/NaY, a unidentate formate species (1710, 1620, and 1340 cm(-1)) is produced as a surface intermediate, which was very readily removed upon evacuation at 323 K. The reduction of the catalyst by H(2) at 423 K prior to the admission of the reacting gas mixture caused inhibition of formate species formation. This result suggests that Au(+) is the dominant species on which the reaction took place. Au(+)/Na-mordenite displayed unidentate formate and organic carbonate species (1936 and 1850 cm(-1)). The latter bands showed a significant increase in intensity with time at the expense of the adsorbed CO(2) bands at 2384 and 2338 cm(-1). On the other hand, Au(+)/Na-ZSM-5 resulted in the formation of different carbonate-like species (1936, 1850, 1730, and 1400 cm(-1)) as well as the rapid appearance of deformation vibrations of adsorbed water molecules at 1630 cm(-1) that built up very quickly compared to that in the Au(+)/Na-mordenite sample. These results were consistent with the catalytic activity data that showed the highest formation rates of CO(2) on Au(+)/NaY compared to those on Au(+)/Na-mordenite and Au(+)/Na-ZSM-5 catalysts. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Thermal decomposition of an ultrathin Si oxide layer around a Si(001)-(2 x 1) window.

We examine the thermal decomposition of an ultrathin Si oxide layer around a Si(001)-(2 x 1) window opened by electron-beam-induced selective thermal decomposition. The decomposition progresses at the oxide/Si(001)-(2 x 1) boundary and follows two rate-limiting steps with activation energies of 4.0 and 1.7 eV. We propose that the former and latter energies correspond to the reaction of Si monomer with the oxide and the desorption of the SiO into the vacuum, respectively.

Journal Article↗
PubMed2000

Effects of long-term, light exercise under restricted feeding on age-related changes in physiological and metabolic variables in male Wistar rats.

The effects of long-term, light exercise under restricted feeding on age-related changes in physiological and metabolic functions were examined in male Wistar rats. Adult (100 days old) rats were divided into sedentary (R10S) and exercise (R11E) groups, and given 10 and 11 g/day, respectively, of a 20% casein diet until they reached 900 days of age. Group R11E simultaneously underwent 3000 m/day of running exercise throughout the test period. As compared with the sedentary group, long-term, light exercise significantly increased body nitrogen retention and serum protein levels, decreased body fat and plasma insulin levels, prevented age-related decline in the basal metabolic rate, and reduced age-associated histopathological changes in the kidney and liver. Long-term, light exercise further enhanced the benefits of restricted feeding on age-related deterioration in physiological and metabolic variables and improved body composition, but did not prolong survival at 900 days of age.

Aging↗
PubMed2000

Anti-IL-12 antibody prevents the development and progression of multiple sclerosis-like relapsing--remitting demyelinating disease in NOD mice induced with myelin oligodendrocyte glycoprotein peptide.

Treatment with monoclonal anti-IL-12 antibody injected on day 0, 7 and 10 after immunization with myelin oligodendrocyte glycoprotein (MOG) peptide 35-55 in NOD mice resulted in significant suppression of the development and the severity of the chronic relapsing-remitting experimental autoimmune encephalomyelitis (EAE) both clinically and histologically. The spleen cells from anti-IL-12 antibody treated mice displayed markedly inhibited MOG35-55 specific proliferation and IFN-gamma production. MOG35-55 specific antibody production was enhanced by anti-IL-12 antibody treatment. These results suggest that IL-12 is critically involved in the pathogenesis of MOG-induced EAE and that antibody to IL-12 could be an effective therapeutic agent in the clinical treatment of autoimmune demyelinating diseases such as multiple sclerosis (MS).

Animals↗
PubMed2000

A rat model for investigation of bladder dysfunction associated with demyelinating disease resembling multiple sclerosis.

Myelin basic protein (MBP) can be used as an antigen for inducing experimental allergic encephalomyelitis (EAE). In various studies, EAE animals have been used as an experimental model of demyelinating diseases. The aim of this study was to determine whether EAE, induced by MBP in rats, can be useful for investigation of bladder dysfunction associated with demyelinating disease. Female Lewis rats were used. In Study 1, the time course of behavioral and cystometric changes were observed consecutively after MBP sensitization. In Study 2, the correlations between behavioral, cystometric, and histologic abnormalities were studied. The degree of paralysis and histologic findings were evaluated. In Study 1, transient hind limb paralysis was observed in all rats. Cystometric findings were characterized by three different patterns: 1) detrusor areflexia (DA), 2) detrusor hyperactivity (DH), and 3) normal. Ten (77%) of the 13 rats given MBP showed bladder dysfunction, including DA (seven), DA/DH (two) and DH (one). Study 2 showed DA in 10 rats, DH in one, and normal findings in nine animals. The difference in degree of paralysis between the DA and the cystometrically normal animals was statistically significant (P<0.01). The mean value of the degree of inflammation in the spinal cord (L6-S1) in the DA group was significantly (P<0.05) higher than that in the cystometrically normal group. The degrees of paralysis and spinal inflammation were weakly correlated (R = 0.47, P = 0.05). The present rat model seems useful for studies of bladder dysfunction associated with spinal myelitis/demyelinating diseases.

Animals↗
PubMed2000

Surface changes in the rat vomeronasal epithelium during degeneration and regeneration of sensory receptor cells.

To investigate cell turnover in the vomeronasal epithelium we used electron microscopy to obtain quantitative measurements of changes observed at the surface of the sensory epithelium. Receptor cell degeneration was induced by sensory nerve transection and animals were examined at postoperative recovery times of 2, 4, 6, 10, 15, 35 and 60 days. We measured the number and density of receptor and supporting cells, and membrane length at the surface of the sensory epithelium. The number of receptor cells rapidly decreased during the degeneration period, reaching a minimum at 6 days. After 15 days of recovery the number and density of receptor cells returned to control levels. The surface membrane length for regenerated receptor cells was similar to that of controls, however the morphological appearance was characteristic of immature cells. In contrast to the receptor cells, the number and density of supporting cells did not change during degeneration and regeneration. However, there was a significant increase in the length of supporting cell-surface membranes. These results suggest that during receptor cell degeneration, supporting cell membranes compensate for the loss of receptor cells by expanding their surface membrane length to help to maintain the continuity of the epithelial surface. Thus, an important role of vomeronasal supporting cells may be to maintain the structural integrity of the epithelium during turnover of the receptor cell population.

Animals↗
PubMed2000

Projection pattern of vomeronasal neurons to the accessory olfactory bulb in goats.

Goats have a well-developed vomeronasal (VN) system and exhibit pheromone-induced reproductive facilitation, but there are no reports on the projection pattern of VN neurons in this species. Rodent, guinea pig and opossum accessory olfactory bulbs (AOBs) have been shown to have a segregated pattern of projection of the VN neurons, which express the two alpha-subtypes of the G-protein, namely Gi2 and Go, to the rostral and caudal regions of the AOB, respectively. In this study we investigated the projection pattern of VN nerve terminals by immunocytochemical staining of the goat vomeronasal organ (VNO) and the AOB with antibodies to Gi2 and Go. Gi2-immunoreactivity was found on the luminal surface of the sensory epithelium of the VNO, and in the VN nerve and glomerular layer throughout the AOB. On the other hand, Go-immunoreactivity was not identified in either the VNO or the VN nerve layer of the AOB. These results indicate that the projection pattern of VN neurons from the VNO to the AOB in the goat is considerably different from that in rodents which show a distinct segregated pattern.

Animals↗
PubMed2000

The diurnal rhythm of energy expenditure differs between obese and glucose-intolerant rats and streptozotocin-induced diabetic rats.

Otsuka Long Evans Tokushima Fatty (OLETF) rats were developed as a model of noninsulin-dependent diabetes mellitus (NIDDM) with mild obesity. Changes in carcass composition and in the daily profile of energy expenditure were examined before and after manifestation of diabetes (8 and 24 wk, respectively), and compared with the normal control Long Evans Tokushima (LETO) rats and streptozotocin (STZ)-induced diabetic LETO rats. OLETF rats had greater body weights than LETO rats and significantly greater absolute and relative fat weights. A diurnal rhythm of energy expenditure associated with two peaks was observed in LETO rats, but the two peaks were not apparent in OLETF rats at 24 wk of age. A diurnal rhythm associated with one peak was observed in STZ-induced diabetic LETO rats. Energy derived from fat constituted this peak; the pattern of the daily energy expenditure was significantly different from that of either nontreated LETO or OLETF rats at 24 wk of age. NIDDM in OLETF rats at 24 wk of age has only a small role in modification of the diurnal rhythm of energy expenditure, whereas STZ-induced diabetes significantly affected the rhythm.

Animals↗
PubMed2000

Molecular cloning and characterization of a new neuron-specific homologue of rat polypyrimidine tract binding protein.

Cancer-associated retinopathy (CAR) is a rare form of retinal degeneration and also one of the paraneoplastic neurologic disorders. Sera of CAR patients usually contain high titers of antibodies against retinal proteins, and CAR is believed to be an autoimmune disease. Using serum from a CAR patient as a molecular probe, a homologue of the polypyrimidine tract-binding protein (PTB) was isolated from a cDNA library of rat neonatal retina. This homologue, named PTB-like protein (PTBLP), encodes a 532 amino acid residue protein and has 73.5 and 68.8% homology with PTB and with a regulator of differentiation 1, respectively. Functional domains in the PTB, such as nuclear localization signals and four RNA recognition motifs (RRMs), were highly conserved. The expression of PTBLP mRNA was observed in the retina and brain but not in liver, kidney, spleen, or lung. The expression of PTBLP protein in rat retina was distributed in most of the cells in the ganglion cell layer and some cells in the inner nuclear layer. The PTBLP protein was localized in the nuclei of these cells. These results suggest that PTBLP is a new member of the PTB gene family and a neuron-specific homologue.

Amino Acid Sequence↗
PubMed2000

Observation and nucleation control of Ge nanoislands on Si(111) surfaces using scanning reflection electron microscopy

Using a high-resolution scanning reflection electron microscope with multifunctions, we investigate Ge nucleation processes on clean Si(111) surfaces and form Ge islands on them by controlling step arrangements of Si(111) surfaces and by using focused electron beam (EB)-induced surface reactions. It is found that three-dimensional (3D) Ge islands grow selectively at step band areas on the surfaces without growth of the islands at terrace areas. Three-dimensional Ge nanoislands are formed at given points by stimulating the Ge wetting layer using focused electron beams and scanning tunnelling microscopy. Ge nanoislands are also formed by depositing Ge on Si windows in ultrathin SiO2 films and subsequent annealing of the sample. The islands are formed only at the window positions. These results imply new methods for forming Ge quantum dots or nanostructures at given areas.

Journal Article↗