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Biomedical subjects

T Yamaguchi

Publications and source records attributed to T Yamaguchi.

At least 127 records · Page 7Linked to original sources
PubMed2001

Diamagnetic activity above Tc as a precursor to superconductivity in La2-xSrxCuO4 thin films.

Superconductors show zero resistance to electric current, and expel magnetic flux (the Meissner effect) below the transition temperature (Tc). In conventional superconductors, the 'Cooper pairs' of electrons that are responsible for superconductivity form only below Tc. In the unconventional high-Tc superconductors, however, a strong electron correlation is essential for pair formation: there is evidence that some pairs are formed above Tc in samples that have less than the optimal density of charge carriers (underdoped) and an energy gap-the 'pseudogap'-appears to be present. Moreover, excitations that look like the vortices that carry magnetic flux inside the superconducting state have been reported above Tc (refs 6, 7). Although the origin of the pseudogap remains controversial, phase fluctuations above Tc, leading to some form of local superconductivity or local pairing, seem essential. Here we report magnetic imaging (scanning SQUID microscopy) of La2-xSrxCuO4 thin films. Clear quantized vortex patterns are visible below Tc (18-19 K), and we observe inhomogeneous magnetic domains that persist up to 80 K. We interpret the data as suggesting the existence of diamagnetic regions that are precursors to the Meissner state.

Journal Article↗
PubMed2001

Investigation of the effects of YM-31636, a novel 5-HT3 receptor agonist, on defecation in normal and constipated ferrets.

We examined the effects of YM-31636 (2-(1H-imidazol-4-ylmethyl)-8H-indeno[1,2-d]thiazole monofumarate), a newly synthesized 5-HT(3) receptor agonist, on defecation in normal and constipated ferrets, and evaluated it as an agent against constipation. YM-31636 facilitated defecation without inducing diarrhea or emetic episodes. This effect occurred within 1 h after oral administration, mostly within 30 min, whereas sodium picosulfate, a widely used laxative, tended to increase the frequency of defecation for several hours with much lower peak incidence than that of YM-31636, and induced diarrhea. UK14304 (brimonidine), an alpha2 receptor agonist, and morphine reduced the frequency of defecation and YM-31636 restored it. These effects of YM-31636 were antagonized by ramosetron, a 5-HT(3) receptor antagonist. These results suggest that YM-31636 could be promising in the treatment of constipation. Because of an early and reliable onset of action compared with sodium picosulfate, YM-31636 could make it easier to control the time of defecation.

Animals↗
PubMed2001

Factors affecting the electronic ground state of low-spin iron(III) porphyrin complexes.

To determine the factors affecting the ground-state electron configuration of low-spin Fe(III) porphyrin complexes, we have examined the (1)H NMR, (13)C NMR, and EPR spectra of a series of low-spin bis-ligated Fe(III) porphyrin complexes [Fe(Por)L(2)](+/-), in which the positions of porphyrin substituents and the coordination ability of axial ligands are different. The seven porphyrins used in this study are meso-tetraalkylporphyrins (TRP: R is propyl, cyclopropyl, or isopropyl), meso-tetraphenylporphyrin (TPP), meso-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin, and 5,10,15,20-tetraphenyl-2,3,7,8,12,13,17,18-octaalkylporphyrins (ORTPP: R is methyl or ethyl). The porphyrin cores of TRP are more or less S(4)-ruffled depending on the bulkiness of the alkyl substituents, while those of ORTPP are highly S(4)-saddled. Three types of axial ligands are examined which have the following characteristics in ligand field theory: they are (i) strong sigma-donating imidazole (HIm), (ii) strong sigma-donating and weak pi-accepting cyanide (CN(-)), and (iii) weak sigma-donating and strong pi-accepting tert-butyl isocyanide ((t)BuNC). In the case of the bis(HIm) complexes, only the isopropyl complex, [Fe(T(i)PrP)(HIm)(2)](+), has shown the less common (d(xz), d(yz))(4)(d(xy))(1) ground state; the other six complexes have exhibited the common (d(xy))(2)(d(xz), d(yz))(3) ground state. When the axial imidazole is replaced by cyanide, even the propyl and cyclopropyl complexes have shown the (d(xz), d(yz))(4)(d(xy))(1) ground state; the TPP and ORTPP complexes have still maintained the common (d(xy))(2)(d(xz), d(yz))(3) ground state. In the case of the bis((t)()BuNC) complexes, all the complexes have shown the (d(xz), d(yz))(4)(d(xy))(1) ground state. However, the contribution of the (d(xz), d(yz))(4)(d(xy))(1) state to the electronic ground state differs from complex to complex; the (d(xz), d(yz))(4)(d(xy))(1) contribution is the largest in [Fe(T(i)PrP)((t)()BuNC)(2)](+) and the smallest in [Fe(OETPPP)((t)BuNC)(2)](+). We have then examined the electronic ground state of low-spin [Fe(OEP)((t)BuNC)(2)](+) and [Fe(ProtoIXMe(2))((t)BuNC)(2)](+); OEP and ProtoIXMe(2) represent 2,3,7,8,12,13,17,18-octaethylporphyrin and protoporphyrin-IX dimethyl ester, respectively. These porphyrins have a(1u) HOMO in contrast to the other seven porphyrins that have a(2u) HOMO. The (13)C NMR and EPR studies have revealed that the contribution of the (d(xz), d(yz))(4)(d(xy))(1) state in these complexes is as small as that in [Fe(OETPP)((t)BuNC)(2)](+). On the basis of these results, we have concluded that the low-spin iron(III) porphyrins that have (i) strong axial ligands, (ii) highly saddle shaped porphyrin rings, (iii) porphyrins with a(1u) HOMO, and (iv) electron withdrawing substituents at the meso positions tend to maintain the common (d(xy))(2)(d(xz), d(yz))(3) ground state.

Electron Spin Resonance Spectroscopy↗
PubMed2001

Stimulus time-locked responses of motoneurons during forelimb fictive locomotion evoked by repetitive stimulation of the lateral funiculus.

In cat forelimb fictive locomotion evoked by repetitive stimulation of the upper cervical lateral funiculus, locomotor discharges consisted of activities time-locked to each stimulus, which were rhythmically modulated. The stimulus time-locked activities were investigated by intracellular recording from motoneurons. In both elbow flexor and extensor motoneurons, there observed stimulus time-locked disynaptic EPSPs, trisynaptic IPSPs and polysynaptic EPSPs, all of which were rhythmically modulated with specific patterns. The disynaptic EPSPs of flexor motoneurons were facilitated in the flexor phase of locomotion, whereas those of extensor motoneurons were facilitated from the flexor phase to the flexor-to-extensor transition phase. Modulation depth was larger in flexor motoneurons. Trisynaptic IPSPs changed in amplitude in parallel with the disynaptic EPSPs of the antagonistic motoneurons. Late, polysynaptic EPSPs of both flexor and extensor motoneurons increased in amplitude along with corresponding nerve discharges. After lesions of the lateral funiculus at C6/C7, both the disynaptic EPSPs and trisynaptic IPSPs were abolished in the motoneurons located caudally to the lesions. However, only trisynaptic IPSPs were lost in the rostrally located motoneurons. Furthermore, the lesions disclosed that extensor motoneurons received another kind of stimulus time-locked EPSPs, trisynaptic EPSPs, which were transmitted through the ventral part of the spinal cord, and rhythmically facilitated in the extensor phase. Stimulus time-locked PSPs observed in this study may at least in part be evoked by last-order interneurons of the central pattern generator, which may be reciprocally organized.

Action Potentials↗
PubMed2001

AT oligonucleotides inducing B lymphocyte activation exist in probiotic Lactobacillus gasseri.

This study determined oligonucleotide sequences of mitogenic DNA derived from lactic acid bacteria (LAB). The chromosomal DNA, which was purified from 12 out of 16 strains of Lactobacillus acidophilus group LAB, induced proliferation of splenic lymphocytes. When DNA from L. gasseri JCM1131T was cloned and amplified using PCR, the mitogenic activities of B lymphocytes were significantly increased by 108 of 321 DNA clones. Ten high homologous nucleotide sequences were found as possible DNA sequences of mitogens, and were then chemically synthesized (sOL-LG1 to sOL-LG10). Two nucleotide sequences (sOL-LG7 and sOL-LG10) that consist of only A and T nucleotides (AT oligonucleotides) were characterized as B lymphocyte specific mitogens because they resulted in proliferation of B lymphocytes but not of T lymphocytes. sOL-LG7 preferentially bound to large B lymphocytes and enhanced the expression of the CD86 antigen more than the CD69 antigen on B lymphocytes. The findings show that mitogenic AT oligonucleotides are likely to restrict pre-activated subsets of B lymphocytes. This study demonstrated that novel AT oligonucleotides triggering B lymphocyte mitogenic responses exist in the nucleoids of L. gasseri and proposed that they have potential as applicants for the production of new functional foods, "Bio-Defense Foods".

Animals↗
PubMed2001

Apolipoprotein E deposition and astrogliosis are associated with maturation of beta-amyloid plaques in betaAPPswe transgenic mouse: Implications for the pathogenesis of Alzheimer's disease.

A transgenic mouse expressing the human beta-amyloid precursor protein with the 'Swedish' mutation, Tg2576, was used to investigate the mechanism of beta-amyloid (Abeta) deposition. Previously, we have reported that the major species of Abeta in the amyloid plaques of Tg2576 mice are Abeta1-40 and Abeta1-42. Moreover, Abeta1-42 deposition precedes Abeta1-40 deposition, while Abeta1-40 accumulates in the central part of the plaques later in the pathogenic process. Those data indicate that Abeta deposits in Tg2576 mice have similar characteristics to those in Alzheimer's disease. In the present study, to understand more fully the amyloid deposition mechanism implicating Alzheimer's disease pathogenesis, we examined immunohistochemically the distributions of apolipoprotein E (apoE) and Abeta in amyloid plaques of aged Tg2576 mouse brains. Our findings suggest that Abeta1-42 deposition precedes apoE deposition, and that Abeta1-40 deposition follows apoE deposition during plaque maturation. We next examined the relationship between apoE and astrogliosis associated with amyloid plaques using a double-immunofluorescence method. Extracellular apoE deposits were always associated with reactive astrocytes whose processes showed enhancement of apoE-immunoreactivity. Taken together, the characteristics of amyloid plaques in Tg2576 mice are similar to those in Alzheimer's disease with respect to apoE and astrogliosis. Furthermore, apoE deposition and astrogliosis may be necessary for amyloid plaque maturation.

Alzheimer Disease↗
PubMed2001

Synthesis of branched cyclomaltooligosaccharide carboxylic acids (cyclodextrin carboxylic acids) by microbial oxidation.

Novel branched cyclomaltooligosaccharide carboxylic acid (cyclodextrin carboxylic acid) derivatives were synthesized by microbial oxidation using Pseudogluconobacter saccharoketogenes to oxidize five types of branched cyclodextrins, including maltosyl beta-cyclodextrin (maltosyl-beta-CyD). For each novel cyclodextrin carboxylic acid derivative synthesized, the hydroxymethyl group of the terminal glucose residue in the branched part of the molecule was regiospecifically oxidized to a carboxyl group to give the corresponding uronic acid. In addition, the physicochemical properties of cyclomaltoheptaosyl-(6-->1)-alpha-D-glucopyranosyl-(4-->1)-alpha-D-glucopyranosiduronic acid (GUG-beta-CyD) (1) and its sodium salt were studied more extensively, as these compounds are most likely to have a practical application.

Alcohol Dehydrogenase↗
PubMed2001

Tandem transesterification and intramolecular cycloaddition of alpha-methoxycarbonylnitrones with chiral acyclic allyl alcohols: systematic studies on the factors affecting diastereofacial selectivity of the cycloaddition.

Factors affecting the stereochemical course of the intramolecular cycloaddition of intermediary alpha-allyloxycarbonylnitrone resulting from transesterification of alpha-methoxycarbonylnitrones 1a-d with chiral allyl alcohols 5 or 6 were investigated systematically. It was found that the factors of diastereofacial selection are highly dependent on the geometries of the allyl alcohols. In the cases where primary or secondary chiral (Z)-allyl alcohols are used, A(1,3)-strain arising from the chiralities in the (Z)-nitrone transition states of the intramolecular cycloaddtion is the most important factor. In contrast, in the case of the reaction using chiral nitrones 1c,d and (E)-allyl alcohols, steric interaction between the chiral N-substituent and the trans substituent of the olefin moiety in the intermediate is dominant. These aspects were applied to geometry-differentiated cycloaddition using a mixture of (E)-5 and (Z)-5. As a typical example, treatment of bulky 1b with a 1:1 mixture of (E)-5 and (Z)-5 in the presence of a catalytic amount of TiCl(4) and MS 4A gave 7b as the predominant product among four possible products.

Journal Article↗
PubMed2001

Inhibition of platelet aggregation and the release of P-selectin from platelets by cilostazol.

To evaluate the in vitro effects of cilostazol, a phosphodiesterase III inhibitor, on platelet responses, we measured platelet aggregation and the levels of soluble P-selectin, a glycoprotein present on the alpha-granule membrane in resting platelets, and cAMP. Platelet-rich plasma and washed platelets from healthy human volunteers were treated with cilostazol (5, 25 and 50 microM). Platelet-rich plasma was stimulated by ADP (1 and 5 microM) or collagen (5 microg/ml). Washed platelets were stimulated by thrombin (4 U/ml) in the presence or absence of 1 microM forskolin. In vehicle-treated samples, soluble P-selectin levels in response to 1 microM ADP-induced primary aggregation were similar to those of circulating levels of healthy volunteers but the levels in response to 5 microM ADP-induced secondary aggregation and collagen-induced aggregation increased markedly compared to those in response to primary aggregation. This result suggests that P-selectin is released from platelets according to the extent of platelet aggregation. Cilostazol inhibited platelet aggregation as well as P-selectin release in a concentration-dependent manner. Cilostazol inhibited completely thrombin-induced aggregation in the presence of 1 microM forskolin, when cAMP levels were two-fold higher than those in the absence of forskolin. Cilostazol, which increases intracellular cAMP in platelets, may be useful in the treatment of arterial occlusive diseases.

Adenosine Diphosphate↗
PubMed2001

Behavioral suppression induced by cannabinoids is due to activation of the arachidonic acid cascade in rats.

Tetrahydrocannabinol (THC) is the principle psychoactive ingredient of marijuana and produces various psychoactive effects through the brain cannabinoid (CB1) receptor. The CB1 receptor belongs to the seven-transmembrane domain family of G-protein-coupled receptors and is involved in the arachidonic acid cascade in the brain. Few reports have attempted to clarify the functional role of endogenous cannabinoid and the arachidonic acid cascade through the CB1 receptor using a behavioral paradigm. Therefore, in this study, we clarified the mechanism of cannabinoid-induced suppression of lever pressing in rats, focusing on the arachidonic acid cascade as a novel second messenger of CB1 receptor. Delta(8)-THC and the potent synthetic CB1 receptor agonist HU-210 dose-dependently inhibited lever-pressing performance. The Delta(8)-THC-induced suppression was significantly antagonized by the cyclooxygenase (COX) inhibitors diclofenac (32 mg/kg, i.p.), aspirin (10 mg/kg, i.p.) and indomethacin (10 mg/kg, i.p.). The suppressive effect of HU-210 was also significantly antagonized by 32 mg/kg diclofenac. Prostaglandin E(2) (3.2 microg/rat, i.c.v.), the final product of the arachidonic acid cascade, significantly inhibited lever pressing similar to Delta(8)-THC and HU-210. In conclusion, we found that suppression of lever-pressing behavior induced by cannabinoids was mediated through activation of the arachidonic acid cascade via the CB1 receptor. Therefore, it is possible that the psychoactive effects of cannabinoid are due to an increase in the formation of PGE(2) in the brain.

Animals↗
PubMed2001

Validation of a novel wire-type intravascular ultrasound imaging catheter.

Intravascular ultrasound can be used to characterize atherosclerotic plaques in arteries. This report describes the results of in vitro experiments with a novel wire-type intravascular ultrasound-imaging catheter developed in our laboratory. The ultrasound catheter comprises a 30-MHz transducer mounted on the tip of a wire-type catheter. The outer diameter of the catheter at the distal acoustic site was 0.025". Dimensional measurements of arteries obtained at the time of autopsy were acquired by intravascular ultrasound and direct planimetry. The luminal CSA (cross-sectional area), vessel CSA, and intima-media thickness for arterial samples (n = 22) acquired by ultrasound images and histopathologic microsections correlated closely (r = 0.99, 0.97, and 0.99, respectively). The histopathologic lumen CSA, vessel CSA, and intima-media thickness were less than those of corresponding ultrasound images in 43 of 54 samples (80%), 43 of 54 samples (80%), and 62 of 62 samples (80%), respectively. Intraobserver and interobserver variances of the luminal CSA vessel CSA and intima-media thickness by ultrasound images were excellence. This novel wire-type intravascular imaging catheter provides accurate vessel measurements and plaque thickness. Furthermore, this intravascular imaging catheter can be used in coronary arteries to assess the morphology of small distal coronary arteries.

Aged↗
PubMed2001

Primary angioplasty for isolated right ventricular infarction.

We describe a case of isolated right ventricular infarction that has rarely been diagnosed antemortem. Electrocardiogram showed ST segment elevation in left precordial chest, right precordial chest, and inferior leads, which mimicked those of anterior and inferior left ventricular infarction. Coronary angiography revealed that culprit lesion was totally occluded right coronary artery. Infarcted artery was nondominant right coronary artery with branches supplying only right ventricular wall. Restoration of coronary blood flow was obtained by primary stenting and resulted in prompt ST segment normalization in all leads. Despite extensive right ventricular wall motion abnormality, subsequent right ventricular dysfunction was not observed.

Aged↗
PubMed2001

Morphologic changes in the aorta during elastase infusion in the rat aneurysm model.

BACKGROUND: The morphologic changes in the aorta during elastase infusion, which have not previously been investigated, were examined in the rat abdominal aortic aneurysm model. MATERIALS AND METHODS: A total of 80 Wistar rats were divided into five groups. A 1.0-cm segment of infra-renal abdominal aorta was infused with 25 U of elastase in 1 mL saline for 10 (n = 14), 20 (n = 14), 30 (n = 14), 60 (n = 19), or 120 min (n = 19). In the 120-min group, transparency and aortic diameter were recorded every 10 min. In each group, 7 rats were killed immediately after infusion. The aortas were excised for histologic examination. The aortic diameters were measured 7 days after infusion in the remaining rats. RESULTS: The infused aorta became transparent within 50 min of elastase infusion. The aortic diameter increased rapidly for the first 30 min of infusion. Histologically, the elastic tissue was completely absent after 60 min of infusion. The aortic diameters in the 60- and 120-min groups were not significantly different 7 days after infusion. CONCLUSIONS: Morphologic changes in the infused aorta are complete after 60 min of elastase infusion. It may be possible to shorten the elastase infusion time from 120 to 60 min in this model.

Animals↗
PubMed2001

Synergistic analgesic effects of intrathecal midazolam and NMDA or AMPA receptor antagonists in rats.

PURPOSE: To investigate the interaction of midazolam and N-methyl-D-aspartate (NMDA) receptor or -amino-3-hydroxy-5-methyl isoxazole-4-propionic acid (AMPA) receptor antagonist on the effects of persistent inflammatory nociceptive activation. METHODS: Male Sprague-Dawley rats were implanted with lumbar intrathecal catheters and were tested for their responses to subcutaneous formalin injection into the hindpaw. Saline, midazolam (1 to 100 microg), AP-5 (I to 30 microg), a NMDA receptor antagonist, or YM872 (0.3 to 30 microg), an AMPA receptor antagonist was injected intrathecally 10 min before formalin injection. The combinations of midazolam and AP-5 or YM872 in a constant dose ratio based on the 50% effective dose (ED50) were also tested and were analysed with an isobologram. RESULTS: Dose-dependent effects were observed with midazolam (ED50 was 1.34 microg and 1.21 microg in phase 1 and 2 of the formalin test, respectively), AP-5 (7.64 microg and 1.4 microg) and YM872 (0.24 microg and 0.21 microg). Synergistic effects in both phases were obtained when combining midazolam with AP-5 or YM872. The ED50 of midazolam decreased to 0.012 microg (phase 1) and 0.27 microg (phase 2) with AP-5 and to 0.09 microg (phase 1) and 0.35 microg (phase 2) with YM872 (P < 0.01). CONCLUSIONS: These results suggest a functional coupling of benzodiazepine-aminobutyric acid (GABA)A receptor with NMDA and AMPA receptors in acute and persistent inflammatory nociceptive mechanisms in the spinal cord.

2-Amino-5-phosphonovalerate↗
PubMed2001

Effects of epidural fentanyl and intravenous flurbiprofen for visceral pain during cesarean section under spinal anesthesia.

PURPOSE: Despite adequate levels of sensory blockade, patients sometimes complain of abdominal pain during cesarean section performed under spinal anesthesia. The aim of this study was to evaluate the effects of epidural fentanyl and intravenous flurbiprofen on visceral pain during cesarean section in patients having spinal anesthesia. METHODS: Thirty ASA physical status I and II patients undergoing elective cesarean section were studied. Spinal-epidural anesthesia was performed in all groups. Group A received no additional analgesics, group B received epidural fentanyl 100 mug, and group C received flurbiprofen 50 mg i.v. immediately after the delivery. Postdelivery, intraoperative visceral pain was evaluated by using the visual analog scale. Incidence and visual analog scale scores of visceral pain and incidence of intraoperative nausea and vomiting were obtained from each patient. RESULTS: Visual analog scale scores of pain were significantly lower in group B than in the other groups (P < 0.05). The incidence of nausea was comparable in all groups. The incidence of intraoperative vomiting was lower in group C than in the other groups (P < 0.05). CONCLUSION: Epidural fentanyl, but not intravenous flurbiprofen, decreases the incidence and severity of visceral pain during cesarean section.

Journal Article↗
PubMed2001

Sevoflurane reduces dysrhythmias during reperfusion in the working rat heart.

PURPOSE: The effects of sevoflurane on myocardial reperfusion injury have not been well studied. The purpose of this study was to determine the effects of sevoflurane on myocardial function, arrhythmia, and metabolism during reperfusion in an isolated working rat heart model. METHODS: Thirty-two hearts were divided into four groups according to the timing of 2.5% sevoflurane administration: group I, control, no sevoflurane; group II, sevoflurane administered only before ischemia; group III, sevoflurane only during reperfusion; group IV, sevoflurane during the whole study period. Myocardial contractility, myocardial ATP, lactate, and glycogen levels were assessed in the reperfusion period following global heart ischemia of 15 min duration. The incidence and duration of ventricular fibrillation were also observed in the reperfusion period. RESULTS: There was no difference in cardiac output and left ventricular dP/ dt max among the four groups at 10, 15, and 20 min after reperfusion. There was no difference in myocardial ATP, lactate and glycogen contents between the groups. The incidences of ventricular fibrillation during reperfusion were 100%, 63%, 100%, and 25% (P < 0.05 vs control), and the durations of ventricular fibrillation during reperfusion were 375 +/- 269, 104 +/- 98 (P < 0.05 vs control), 303 +/- 189, and 93 +/- 245 (P < 0.05 vs control) in groups I, II, III, and IV, respectively (mean +/- SD). CONCLUSION: The administration of sevoflurane prior to reperfusion appears to provide myocardial protection, as assessed by reduced dysrhythmias during reperfusion.

Journal Article↗
PubMed2001

Successful reconstruction of extensive laryngotracheal strictures after inhalation burn injury: report of a case.

We report a rare case of long segmental laryngotracheal stenosis following inhalation burn injury. The patient presented 2 months after his injury with progressive stridor and dyspnea necessitating tracheostomy. A computed tomographic scan of the neck revealed stenosis extending from the vocal cords to the top of the sternum. Repair was successfully carried out with multiple surgical procedures employing hinge-flap closure tented with autogenous tissue.

Adult↗