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Biomedical subjects

A Tachibana

Publications and source records attributed to A Tachibana.

At least 19 recordsLinked to original sources
PubMed2006

Coordination of fore and hind leg stepping in cats on a transversely-split treadmill.

To gain insight into the mechanism of coordination of stepping in the fore and hind legs of quadrupeds, we examined the kinematics of leg movements and the motor patterns in fore and hind leg flexor muscles in decerebrate walking cats when the two pairs of legs stepped on separate treadmills running at different speeds. When the front treadmill was slowed progressively from 0.6 to 0.3 m/s with the rear treadmill running at 0.6 m/s, the rate of stepping in both the fore and hind legs decreased and a 1:1 stepping ratio was maintained. The decrease in the rate of stepping in the hind legs was due primarily to an increase in the duration of the swing phase. Slowing the speed of the rear treadmill while keeping the front treadmill speed at 0.6 m/s decreased the rate of stepping of the hind legs, but had relatively little influence on the average rate of stepping in the forelegs. In this situation stepping in the fore and hind legs was uncoupled and the time of stepping in one hind leg relative to the ipsilateral foreleg progressively shifted during a walking sequence. Analysis of the timing of electromyographic (EMG) recordings from flexor muscles of the hip and elbow joints yielded insight into the neuronal mechanisms underlying the asymmetry in slowing either the front or rear treadmill. We propose that ipsilateral pattern generating networks are asymmetrically coupled via descending inhibitory pathways and an ascending excitatory pathway. We discuss how the characteristics of these linkages are functionally appropriate for establishing the normal timing of stepping in the hind and forelegs during slow walking.

Animals↗
PubMed2005

Recruitment of gastrocnemius muscles during the swing phase of stepping following partial denervation of knee flexor muscles in the cat.

In walking cats, the biarticular medial and lateral gastrocnemius (MG-LG) muscles act to produce extension and flexion torques at the ankle and knee, respectively, and they usually display only one burst of activity beginning just before ground contact and ending near the end of the stance phase. Currently, the MG-LG muscles are considered to function primarily to control extension movements around the ankle joint during the stance phase. However, their flexion action at the knee means that they have the capacity to regulate rotations at the knee, but this role has not yet been clearly defined. Following partial denervation of the other muscles that normally act to flex the knee during swing, we observed that the MG-LG muscles, but not the Soleus muscle (a pure ankle extensor), often generated strong bursts of activity during early swing. These bursts were enhanced following mechanical stimulation of the paw, and they were especially prominent when the leg trailed over an object. They were absent when the leg led over an object. During treadmill walking the swing-related bursts in MG and LG had little influence on ankle flexion at the beginning of swing, but they were associated with slowing of ankle flexion when the leg trailed over an object. We hypothesized that the recruitment of these bursts functions to partially compensate for the reduction in knee torque resulting from the denervation of other knee flexors. Consistent with this hypothesis was our finding that the magnitude of the swing-related activity in the MG-LG muscles was linearly correlated to the extent of the knee flexion and to the peak angular velocity of knee flexion, and that the timing of the bursts was similar to that in the denervated muscles prior to denervation. Our findings suggest that an excitatory pathway exists from the flexor half-center of the central pattern-generating network to MG-LG motoneurons, and that this pathway is strongly regulated by central and/or peripheral signals.

Animals↗
PubMed2005

A role for hip position in initiating the swing-to-stance transition in walking cats.

In this investigation, we obtained data that support the hypothesis that afferent signals associated with hip flexion play a role in initiating the swing-to-stance transition of the hind legs in walking cats. Direct evidence came from observations in walking decerebrate cats. Assisting the flexion of the hip joint during swing advanced the onset of activity in ankle extensor muscles, and this advance was strongly correlated with a reduction in the duration of hip flexor muscle activity. The hip angle at the time of onset of the flexion to extension transition was similar during assisted and unassisted steps. Additional evidence for the hypothesis that sensory signals related to hip flexion are important in regulating the swing-to-stance transition came from four normal animals trained to walk in a variety of situations designed to alter the coordination of movements at the hip, knee, and ankle joints during the swing phase. Although there were exceptions in some tasks and preparations, the angle of the hip joint at the time of onset of extensor activity was generally less variable than that of the knee and ankle joints. We also found no clear relationships between the angle of the limb and body axes, or the length of the limb axis, and the time of onset of extensor activity. Finally, there were no indications that the stretching of ankle extensor muscles during swing was a factor in regulating the transition from swing-to-stance.

Animals↗
PubMed2005

Increased sensitivity to sparsely ionizing radiation due to excessive base excision in clustered DNA damage sites in Escherichia coli.

PURPOSE: In order to clarify the cellular processing and repair mechanisms for radiation-induced clustered DNA damage, we examined the correlation between the levels of DNA glycosylases and the sensitivity to ionizing radiation in Escherichia coli. MATERIALS AND METHODS: The lethal effects of gamma-rays, X-rays, alpha-particles and H2O2 were determined in E. coli with different levels of DNA glycosylases. The formation of double-strand breaks by post-irradiation treatment with DNA glycosylase was assayed with gamma-irradiated plasmid DNA in vitro. RESULTS: An E. coli mutM nth nei triple mutant was less sensitive to the lethal effect of sparsely ionizing radiation (gamma-rays and X-rays) than the wild-type strain. Overproduction of MutM (8-oxoguanine-DNA glycosylase), Nth (endonuclease III) and Nei (endonulease VIII) increased the sensitivity to gamma-rays, whereas it did not affect the sensitivity to alpha-particles. Increased sensitivity to gamma-rays also occurred in E. coli overproducing human 8-oxoguanine-DNA glycosylase (hOgg1). Treatment of gamma-irradiated plasmid DNA with purified MutM converted the covalently closed circular to the linear form of the DNA. On the other hand, overproduction of MutM conferred resistance to H2O2 on the E. coli mutM nth nei mutant. CONCLUSIONS: The levels of DNA glycosylases affect the sensitivity of E. coli to gamma-rays and X-rays. Excessive excision by DNA glycosylases converts nearly opposite base damage in clustered DNA damage to double-strand breaks, which are potentially lethal.

DNA Damage↗
PubMed2004

Recombination repair pathway in the maintenance of chromosomal integrity against DNA interstrand crosslinks.

DNA interstrand crosslinks (ICL) present a major threat to cell viability and genome integrity. In eukaryotic cells, the ICLs have been suggested to be repaired by a complex process involving Xpf/Ercc1-mediated endonucleolytic incision and homologous recombination (HR). However, the entire feature of the ICL tolerating mechanism is still poorly understood. Here we studied chromosome aberrations (CA) and sister chromatid exchanges (SCE) by the use of the crosslinking agent mitomycin C (MMC), in chicken DT40 cells with the HR genes disrupted by targeted replacement. The disruption of the Rad54, Rad51B, Rad51C, Rad51D, Xrcc2 and Xrcc3 genes resulted in a dramatic reduction of spontaneous and MMC-induced SCEs. Interestingly, while HR-deficient cells were hypersensitive to cell killing by MMC, MMC-induced CAs were also suppressed in the HR-deficient cells except for Rad51D-, Xrcc2- and Xrcc3-deficient cells. These observations indicate that DNA double strand breaks (DSB) at stalled replication forks and those arising as repair intermediates present strong signals to cell death but can be tolerated by the HR repair pathway, where Rad54, Rad51B and Rad51C have an initiative role and repair can be completed by their paralogs Rad51D, Xrcc2 and Xrcc3. The impairment of the HR pathway, which otherwise leads to cell death, may be somewhat substituted by an alternative mechanism such as the Mre11/Rad50/Nbs1 pathway, resulting in reduced frequencies of SCEs and CAs.

Animals↗
PubMed2002

Inhibition by fenoterol of human eosinophil functions including beta2-adrenoceptor-independent actions.

Agonists at beta2 adrenoceptors are used widely as bronchodilators in treating bronchial asthma. These agents also may have important anti-inflammatory effects on eosinophils in asthma. We examined whether widely prescribed beta2-adrenoceptor agonists differ in ability to suppress stimulus-induced eosinophil effector functions such as superoxide anion (O2-) generation and degranulation. To examine involvement of cellular adhesion in such responses, we also investigated effects of beta2 agonists on cellular adhesion and on CD11b expression by human eosinophils. O2- was measured using chemiluminescence. Eosinophil degranulation and adhesion were assessed by a radioimmunoassay for eosinophil protein X (EPX). CD11b expression was measured by flow cytometry. Fenoterol inhibited platelet-activating factor (PAF)-induced O2- generation by eosinophils significantly more than salbutamol or procaterol. Fenoterol partially inhibited PAF-induced degranulation by eosinophils similarly to salbutamol or procaterol. Fenoterol inhibited phorbol myristate acetate (PMA)-induced O2- generation and degranulation by eosinophils, while salbutamol or procaterol did not. Fenoterol inhibition of PMA-induced O2- generation was not reversed by ICI-118551, a selective beta2-adrenoceptor antagonist. Fenoterol, but not salbutamol or procaterol, significantly inhibited PAF-induced eosinophil adhesion. Fenoterol inhibited O2- generation and degranulation more effectively than salbutamol or procaterol; these effects may include a component involving cellular adhesion. Inhibition also might include a component not mediated via beta2 adrenoceptors.

Adrenergic beta-Agonists↗
PubMed2002

Radiation-induced apoptosis in the scid mouse spleen after low dose-rate irradiation.

PURPOSE: To elucidate the process of radioadaptation, the role of DNA-PK activity was examined using the scid mouse defective in DNA-PKcs. MATERIALS AND METHODS: The induction of apoptosis in the spleens of the C.B-17 Icr scid mouse and the parental mouse was studied after chronic irradiation with gamma-rays at 1.5 Gy (0.001 Gy min(-1) for 25 h) followed by challenge irradiation with X-rays at 3.0 Gy (1.0 Gy min(-1) for 3 min). RESULTS: When the wild-type mouse was previously exposed to chronic irradiation (1.5 Gy) at a low dose-rate (0.001 Gy min(-1)), apoptosis induced by acute irradiation (3.0 Gy, 1.0 Gy min(-1)) was significantly suppressed, especially in the splenic white pulp. There was no change by acute irradiation after chronic irradiation in the scid mouse, although an effect was detected in the spleen after acute irradiation alone. CONCLUSIONS: These data suggest that DNA-PK activity might play a major role in the radioadaptive response following pre-irradiation at a low dose-rate.

Animals↗
PubMed2001

Stereoselective synthesis of the axially chiral A-B ring system of vancomycin utilizing a planar chiral arene chromium complex.

[reaction: see text] The axial biaryl ring system of vancomycin was stereoselectively synthesized by utilizing a planar chiral tricarbonyl(arylhalide)chromium complex. Both enantiomers of the planar chiral (arylbromide)chromium complexes, (+)-9 and ent-(-)-9, can be stereoselectively transferred to an absolutely identical key intermediate 23 for the vancomycin A-B ring system by the diastereoselective Suzuki-Miyaura cross-coupling reaction as key step.

Anti-Bacterial Agents↗
PubMed2001

Thiolated dermal bovine collagen as a novel support for bioactive substances--conjugation with lysozyme.

Thiol groups were introduced to dermal bovine collagen (DBC) by the reaction with gamma-thiobutyrolactone. Thiolated DBC reacted with 2-pyridyl disulfide group introduced to lysozyme to form DBC-lysozyme conjugate through disulfide bridge. The enzymatic activity of freshly prepared conjugate was almost unchanged during ten consecutive runs over one month. The DBC-lysozyme conjugate showed the maximum activity at pH 6.3, on the contrary, that of native lysozyme was pH 9.0. Thermal stability of lysozyme was enhanced by the conjugation with DBC. The present results showed that the conjugation using thiolated collagen could be one of the useful alternative approaches to modify collagen with bioactive molecules.

Animals↗
PubMed2001

Radiation response of apoptosis in C57BL/6N mouse spleen after whole-body irradiation.

PURPOSE: Primary conditioning low dose irradiation suppresses the molecular responses against secondary challenge high dose irradiation; this phenomenon has been termed the radioadaptive response. The mechanism of the radioadaptive response is not yet clear. This study was undertaken to elucidate the radiation response of apoptosis in mouse spleen after whole-body irradiation. MATERIALS AND METHODS: The induction of apoptosis was analysed in the spleens of C57BL/6N mice after chronic irradiation with gamma-rays at 1.5 Gy (0.001 Gy/min for 25 h) followed by challenge irradiation with X-rays at 3.0Gy (1 Gy/min). RESULTS: Accumulation of p53 and Bax, and the induction of apoptosis were observed dose-dependently in mouse spleen 12 h after acute irradiation at a high dose-rate. However, it was found that there was significant suppression of the accumulation of p53 and Bax, and induction of apoptosis 12 h after challenge irradiation at 3.0Gy at a high dose-rate following chronic preirradiation at 1.5Gy at a low dose-rate. In addition, the combination of pre-irradiation at 1.5Gy at a high dose-rate and challenge irradiation at 3.0Gy at a high dose-rate could not suppress the accumulation of p53 and Bax or the induction of apoptosis. CONCLUSIONS: Chronic pre-irradiation at a low dose-rate suppressed Bax-mediated apoptosis. These findings suggest that the radioadaptive response in mouse spleen may be due to a suppression of p53-mediated apoptosis.

Adaptation, Physiological↗
PubMed2001

High frequency of deletions at the hypoxanthine-guanine phosphoribosyltransferase locus in an ataxia-telangiectasia lymphoblastoid cell line irradiated with gamma-rays.

The molecular nature of gamma-ray-induced mutations at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus in an ataxia-telangiectasia (A-T) lymphoblastoid cell line was investigated. Twelve of 15 gamma-ray-induced HPRT-deficient mutants showed deletions. Eight of them had lost the entire HPRT gene, one showed a 1.9-kb deletion, and three had deletions of about 40-150 base pairs. Of the eight mutants that lost the entire gene, five had also lost both DXS79 and DXS86, flanking markers of the HPRT locus. The spectrum of mutations induced by gamma-irradiation in the A-T cells showed a high frequency of deletions in comparison with that in a control cell line, WIL2-NS. Sequence analysis of breakpoint junctions in four mutants revealed that three of them had junctions between short identical sequences at each breakpoint, leaving one copy at the junction. These results suggest that non-homologous end-joining is the major mechanism for deletion formation in A-T cells.

Ataxia Telangiectasia↗
PubMed2001

Neonatal thrombocytosis resulting from the maternal use of non-narcotic antischizophrenic drugs during pregnancy.

Neonatal thrombocytosis can result from maternal narcotic drug abuse. The case of a male infant is reported who was born to a woman with schizophrenia treated with non-narcotic psychotropic drugs during pregnancy; he developed severe prolonged thrombocytosis. The platelet count reached 1310 x 10(9)/l on day 15. This thrombocytosis persisted for three months. The patient was treated with dipyridamole. A bone marrow aspirate showed normal myeloid and erythroid precursors with an increased number of megakaryocytes. Plasma concentrations of interleukin 6 and thrombopoietin were suppressed. No obvious complications from the thrombocytosis occurred, and the platelet count fell to within the upper limit of normal after 3 months of age. This case indicates that thrombocytosis may occur in infants born to mothers treated with non-narcotic psychopharmaceutical drugs during pregnancy. The thrombocytosis in this case may have been induced by factors other than interleukin 6 or thrombopoietin.

Dipyridamole↗
PubMed2001

[Development of corneal storage medium--first report. Examination of rabbit cornea].

PURPOSE: To develop and evaluate a new corneal storage medium with a simple formula by histological methods. METHODS: We compared two corneal storage media, containing minimum essential medium (MEM) and 2.5% chondroitin sulfate, pH 7.33 and osmolality of 320 mOsm/kg, to OPTISOL-GS. The differences in the two media were the molecular weight (MW) and source of chondroitin sulfate. MW of Medium I was 27,500 and MW of Medium II was 33,700. A cornea with scleral rim obtained from a Japanese white rabbit was stored in either Medium I or Medium II and the fellow cornea was stored in OPTISOL-GS for 7 or 14 days at 4 degrees C. Histological examination of corneal endothelial cells was performed both by scanning electron microscopy and by transmission electron microscopy. RESULTS: At day 7, there was no significant difference in histological findings among the rabbit corneas stored in OPTISOL-GS, Medium I, or Medium II. At day 14, corneas stored in OPTISOL-GS or Medium I showed similar histological findings. In Medium II, endothelial cells showed marked degeneration. CONCLUSION: The results of experiments with rabbit cornea indicated that OPTISOL-GS and Medium I could preserve endothelial cellular structure better than Medium II. The difference between Medium I and Medium II was only the MW of the chondroitin sulfate used. The MW may be an important factor to determine suitable chondroitin sulfate for developing a corneal storage medium.

Animals↗
PubMed2001

[Development of corneal storage medium--second report. Examination of human cornea].

PURPOSE: To develop and evaluate by histological methods a new corneal storage medium with a simple formula. METHODS: We compared a corneal storage medium which contained minimum essential medium and 2.5% chondroitin sulfate (molecular weight 27,500), pH 7.33, osmolality 320 mOsm/kg with OPTISOL-GS. Paired human donor eyes provided by the Lions Eye Bank of Oregon were stored in a moist chamber until the experiment. A cornea with scleral rim was excised and stored in OPTISOL-GS, and its fellow cornea was stored in the test medium for 5, 10, or 14 days at 4 degrees C. Histological examination of corneal endothelial cells was done by both scanning electron microscopy and transmission electron microscopy. RESULTS: On days 5 and 10, there was no significant difference in histological findings between corneas stored in OPTISOL-GS and those in the test medium. Both corneal groups developed degenerative changes with the increase of storage time, but their histological findings were similar for both storage media. On day 14, corneal endothelial cells showed marked degeneration of intracellular organelles such as a swelling of mitochondria in both media. CONCLUSION: Human corneas stored in the test medium for 14 days maintained their structure as well as those in OPTISOL-GS. This shows that the newly developed corneal storage medium composed can be used for medium-term corneal storage.

Chondroitin Sulfates↗
PubMed2001

Bipedal locomotion by the normally quadrupedal Japanese monkey, M. Fuscata: strategies for obstacle clearance and recovery from stumbling.

This study explored how the normally quadrupedal Japanese monkey adjusts to treadmill perturbations, when trained to walk bipedally. The monkey was required to use the left hindlimb to clear an obstacle that was fixed on the left side of a treadmill belt. The monkey either cleared the obstacle (CL: cleared locomotion), or stumbled over it (SL: stumbled locomotion). For CL, it changed its left hind limb's kinematics according to the obstacle's height and position relative to the left foot. In SL, the monkey used a "defensive posture", which included a rapid lowering of the right foot and forelimb movements, to stabilize the perturbed posture and thereby prevent falling. Then, with powerful extensions of its lower limb joints, the monkey raised its center-of-mass to the appropriate level for continuation of normal bipedal walking. The results show that M. Fuscata recruited both anticipatory and reactive neural mechanisms to accommodate to the obstacle.

Animals↗
PubMed2000

Novel mutations of the FANCG gene causing alternative splicing in Japanese Fanconi anemia.

Fanconi anemia (FA), an autosomal recessive disorder characterized by a progressive pancytopenia associated with congenital anomalies and high predisposition to malignancies, is a genetically and clinically heterogeneous disease. At least eight complementation groups (FA-A to FA-H) have been identified. Previously, we studied mutations of the FANCA gene, responsible for FA-A, and found pathogenic mutations in 12 of 15 unclassified Japanese FA patients. Here, we further studied an additional 5 FA patients for sequence alterations of the FANCA gene and found pathogenic mutations in 2 of them. We further analyzed mutations of the FANCC and FANCG genes, responsible for FA-C and FA-G, respectively, in the remaining 6 FA patients. Although there was no alterations in the FANCC gene in these 6 patients, two novel mutations of the FANCG gene, causing aberrant RNA splicing, were detected in 2 FA patients. One was a base substitution from G to C of the invariant GT dinucleotides at the splice donor site of intron 3, resulting in the skipping of exon 3, as well as the skipping of exons 3 and 4. The other was a base substitution from C to T in exon 8, creating a nonsense codon (Q356X). This mutation resulted in the exclusion of a sequence of 18 nucleotides containing the mutation from the mRNA, without affecting the splicing potential of either the authentic or the cryptic splice donor site. Collectively, 14 of the 20 unclassified Japanese FA patients belong to the FA-A group, 2 belong to the FA-G group, and none belongs to the FA-C group.

Alternative Splicing↗
PubMed2000

Novel prenyltransferase gene encoding farnesylgeranyl diphosphate synthase from a hyperthermophilic archaeon, Aeropyrum pernix. Molecularevolution with alteration in product specificity.

Prenyltransferases catalyse sequential condensations of isopentenyl diphosphate with allylic diphosphates. Previously, we reported the presence of farnesylgeranyl diphosphate (FGPP) synthase activity synthesizing C25 isoprenyl diphosphate in Natronobacterium pharaonis which is a haloalkaliphilic archaeon having C20-C25 diether lipids in addition to C20-C20 diether lipids commonly occurring in archaea [Tachibana, A. (1994) FEBS Lett. 341, 291-294]. Recently, it was found that a newly isolated aerobic hyperthermophilic archaeon, Aeropyrum pernix, had only C25-C25 diether lipids, not the usual C20-containing lipids [Morii, H., Yagi, H., Akutsu, H., Nomura, N., Sako, Y. & Koga, Y. (1999) Biochim. Biophys. Acta 1436, 426-436]. In this report, we describe the isoloation from A. pernix of the novel prenyltransferase gene, fgs, encoding FGPP synthase. The protein encoded by fgs was expressed in Escherichia coli as a glutathione S-transferase fusion protein and produced FGPP as a final product. Phylogenetic analysis of fgs with other prenyltransferases revealed that the short-chain prenyltransferase family is divided into three subfamilies: bacterial subfamily I, eukaryotic subfamily II, and archaeal subfamily III. fgs is clearly contained within the archaeal geranylgeranyl diphosphate (GGPP) synthase group (subfamily III), suggesting that FGPP synthase evolved from an archaeal GGPP synthase with an alteration in product specificity.

Alkyl and Aryl Transferases↗