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J Aoyama

Publications and source records attributed to J Aoyama.

11 recordsLinked to original sources
PubMed2004

Shear properties of the temporomandibular joint disc in relation to compressive and shear strain.

Shear stress can result in fatigue, damage, and irreversible deformation of the temporomandibular joint disc. Insight into the dynamic shear properties of the disc may give insight into the mechanism inducing tissue failure due to shear. We tested the hypothesis that the dynamic shear properties of the disc depend on the amount of shear and compressive strain. Twenty-four porcine discs were used for dynamic shear tests. The specimens were clamped between the plates of a loading apparatus under compressive strains of 5%, 10%, and 15%. Dynamic shear was applied to the specimen by a sinusoidal strain of, respectively, 0.5%, 1.0%, and 1.5%. Both the dynamic elasticity and viscosity were proportional to compressive strain and inversely proportional to shear strain. These shear characteristics suggest a significant role of compressive and shear strain on the internal friction of the disc.

Algorithms↗
PubMed2002

Viscoelastic properties and residual strain in a tensile creep test on bovine temporomandibular articular discs.

This study was designed to evaluate the creep characteristics and residual strain of bovine temporomandibular joint (TMJ) discs in tension. Twenty discs were divided into three specimens each: central, lateral and medial regions. Tension of 1.0 MPa was applied and sustained for 20 min to the specimens from 10 right-side discs, and tension of 1.5 MPa to specimens from 10 left-side discs. After the period of tension for creep, the specimens were removed from the tension devices and restoration observed for 20 min. Time-dependent creep curves showed a marked change in strain during the initial 5s. The essential time delay in strain ceased after 2 min, and strain reached an almost steady level after 3 min. At a tensile stress of 1.5 MPa, a strain of 14.5% on average was produced after 20 min creep in the central specimens; peripheral specimens showed strains of 12.4% on average. There were significant differences in strain between the central and peripheral specimens. The residual strain after 20 min restoration was 0.93% on average and there were no significant regional differences. This creep feature could be well represented by a generalized linear viscoelastic model. It was concluded that the regional differences in viscoelasticity might be caused by the complicated articulating functions of the TMJ, and that the residual strain caused by sustained stress could be an important factor in disc deformation.

Animals↗
PubMed2002

Biomechanical response of bovine temporomandibular joint disc to prolonged tensile stress.

This study was designed to evaluate the influence of prolonged tensile stress on the viscoelasticity of the temporomandibular joint (TMJ) disc. Twenty discs from 10, 3-year-old cattle were used. Tensile stress of 1.5 MPa was applied to specimens from the discs for 10, 20, 40 and 60 min. Following the prescribed period of tension for creep, the specimens were removed from the tension device and any recovery observed for 20 min. In all specimens, strain increased at the onset of stress application and reached almost steady conditions after 5 min. Although, the strain became slightly larger when the creep time was longer, no significant differences were found in the strains between any two tests with different periods of creep. The residual strain increased significantly with creep duration, and similarly the degree of recovery decreased significantly. In 10- and 20-min creep tests, the residual strains were 0.1 and 1.0%, the specimens in 40- and 60-min tests revealed irreversible changes in length. It was concluded that continuous loading for >40 min causes creep damage in bovine TMJ disc, and that prolonged sustained tension affects the recovery of joint homeostasis.

Animals↗
PubMed2002

Dynamic properties of bovine temporomandibular joint disks change with age.

The temporomandibular joint disk exhibits morphological and biochemical age-related changes. However, the possible age-related changes of the dynamic viscoelasticity in the disk are unclear. We tested the hypothesis that the dynamic viscoelastic properties of the disk change with age. Thirty-six disks from young-adult, adult, and mature-adult cattle were used for dynamic tensile tests. In all disks, the magnitudes of the complex modulus, the storage modulus, and the loss modulus increased as the frequency increased. The mature-adult disks had higher values of these moduli than did the younger disks. The loss tangent ranged from 0.1 to 0.3, which means that the disk has relatively large elasticity and relatively small viscosity. It was concluded that both the elasticity and viscosity of the disk increase with age. This may reflect age-related changes in biochemical composition.

Aging↗
PubMed2001

Molecular phylogeny and evolution of the freshwater eel, genus Anguilla.

A molecular phylogenetic analysis was conducted on all of the known catadromous eel species of the genus Anguilla to assess their relationships and evolutionary history. The analyses of a total of 1427 bp of the mitochondrial 16S ribosomal RNA and 1140 bp of the complete cytochrome b gene sequences suggested that the genus Anguilla was monophyletic in origin, with A. borneensis as the most basal species. Four clades/species groups that correspond to their geographical ranges were indicated, Indo-Atlantic (three species), Oceania (two species), tropical Pacific (two species), and Indo-Pacific (five species), with ambiguous positions for A. japonica and A. reinhardti. This grouping conflicts with that of a previous morphological study, since the broad undivided maxillary and short-fin type, which were thought to be phylogenetically important, were paraphyletic in the molecular analysis. However, the molecular phylogeny and the present geographic distribution of species suggested historical dispersion of the genus Anguilla according to the Tethys corridor hypothesis, which proposed that anguillid eels originated near present-day Indonesia and dispersed westward along paleo-circumglobal equatorial currents. The westward-moving strain entered the paleo-Atlantic through the Tethys Sea and was ancestral to present-day European and American species.

Anguilla↗
PubMed2001

Biomechanical behaviour of bovine temporomandibular articular discs with age.

The purpose was to evaluate age-associated changes in the creep and restoration properties of bovine temporomandibular joint (TMJ) discs under and after sustained tensile stress. Forty discs were obtained from 7- and 10-year-old cattle, referred to as the adult and mature adult groups, respectively. Tension of 1.0 MPa was applied and sustained for 20 min to specimens from ten right discs and of 1.5 MPa to specimens from ten left discs. After the period of tension for the study of creep, the specimens were removed from the tension devices and their restoration observed for 20 min. For comparative purposes the relevant results for a young adult group were recruited from data on 3-year-old bovine TMJ discs reported in a previous study on viscoelastic properties. In all the specimens the time-dependent creep curves showed a marked change in strain during the initial 5 s, but the elastic moduli at the onset of stress were significantly larger in the mature adult group than in the other groups. After 20-min creep, the strains were decreased in relation to the age of the specimen and were significantly smaller in the mature adult than in the young adult. With regard to regional differences, the medial specimens exhibited significantly smaller strains than the central ones in all three age groups. Furthermore, the residual strains after 20-min restoration also decreased slightly with age. It is concluded that the bovine TMJ disc becomes stiff and acquires the capacity to recover from continuous deformation during growth and maturation. These findings suggest that the TMJ disc can modify its viscoelasticity in order to withstand extrinsic functional stresses.

Aging↗
PubMed1997

Evolution of the freshwater eels.

The freshwater anguillid eels have an unusual life history and world-wide distribution. Questions about the phylogenetic relationships of this group and how their long spawning migrations and larval phase may contribute to their global distribution have not been addressed. This paper is first presentation of molecular phylogeny of Anguilla species, and based on this phylogenetic tree we suggest new aspect of the evolution of this group. Namely, ancestral eels originated during the Eocene or earlier, in the western Pacific Ocean near present-day Indonesia. A group derived from this ancestor dispersed westward, probably by larval transport in the global circum-equatorial current through the northern edge of the Tethys Sea. This group split into the ancestor of the European and American eels, which entered into the Atlantic Ocean, and a second group, which dispersed southward and split into the east African species and Australian species. Thus the world-wide distribution of the eel family can be understood from knowledge of continental drift, ocean currents, a specialized larva and evolutionary forces favoring dispersal and speciation of segregated gene pool.

Anguilla↗
PubMed1997

Identification of rat and human cytochrome P450 forms involved in the metabolism of the thromboxane A2 receptor antagonist (+)-S-145.

(+)-S-145 [5-(+)-(Z)-7-[(1R, 2S, 3S, 4S)-3-phenylsulfonylaminobicyclo[2.2.1]hept-2-yl]-heptenoic acid] and its beta-oxidized metabolites [two [bisnor or dihydro (DH)-bisnor] or four (tetranor) carbon-shortened products at the carboxyl side chain] are hydroxylated at the C-5 or C-6 position of the bicyclo ring by microsomal monooxygenases. We investigated the oxidative metabolism of (+)-S-145 and its beta-oxidized metabolites with liver microsomes from rats and humans to identify which cytochrome P450 (P450) forms are involved in these reactions. In rats, phenobarbital or dexamethasone treatment significantly increased 5- and 6-hydroxylation activities toward (+)-S-145 and its beta-oxidized metabolites, suggesting the involvement of P4503A forms. Immunoinhibition studies suggested that P4503A2 was mainly responsible for the 5-hydroxylation of (+)-S-145, bisnor, and DH-bisnor and the 6-hydroxylation of bisnor and tetranor. Furthermore, P4502C6, a phenobarbital-inducible 2C form in the rat, was involved in the 6-hydroxylation of (+)-S-145, bisnor, and DH-bisnor. P4502C11, the major constitutive form (male rats), was partly involved in the 5-hydroxylation of DH-bisnor and the 6-hydroxylation of bisnor and DH-bisnor. Reconstitution studies with purified human enzymes and immunoinhibition studies suggest that P4503A4 is primarily involved in the 5-hydroxylation of (+)-S-145 and bisnor and the 6-hydroxylation of tetranor; P4502C9/10 mainly catalyzed the 5-hydroxylation of tetranor and the 6-hydroxylation of (+)-S-145. Results of the present study indicated that the same subfamily P450 forms are responsible for the oxidative metabolism of (+)-S-145 in rats and humans. P4503A enzymes were shown to be involved in the formation of 6-hydroxy tetranor, the main metabolite of S-1452 in vivo.

Animals↗
PubMed1994

Interaction between human polymorphonuclear leucocytes and bacteria released from in-vitro bacterial biofilm models.

The interactions between phagocytic cells (polymorphonuclear leucocytes) and Escherichia coli cells released from a biofilm model formed in vitro on the surface of cotton threads in an artificial medium were compared with those of phagocytes and bacteria released from a newly developed in-vitro biofilm model. This new model of bacterial biofilm on the surface of cotton threads was developed by soaking cotton threads in rat carboxymethylcellulose pouch exudate and culturing E. coli in the exudate. The structure of the biofilm model and the surface structure of the bacteria in the biofilm resembled those observed in vivo in infected pouches, and they were quite different from those observed with the biofilm model in artificial medium. Both bacteria released from biofilm models in an artificial medium and those from biofilms in rat carboxymethylcellulose pouch exudate, in vitro, were almost equally resistant to killing by phagocytes. The sensitivity of these bacteria to phagocytosis was no different from that of normal bacteria grown in artificial medium. Bacteria from both models were also less sensitive to the killing activity of H2O2. Electronmicroscopy showed that bacteria from both models had some products that interacted with ruthenium red on their surfaces, but the respective quantities of these products differed.

Animals↗
PubMed1979

Third complement component in cerebrospinal fluid in neuro-Behçet's syndrome. Conversion patterns by crossed immunoelectrophoresis.

Thirteen cerebrospinal fluid specimens (CSFs) from 10 patients with neuro-Behçet's syndrome (nB) were examined for the presence of conversion products of C3 protein by means of crossed immunoelectrophoresis. C3 conversion products were found in 4 CSFs from nB patients, and the proportions of the split products to the total immunoprecipitate zones were 17, 34, 61 and 63%, respectively. CSFs with C3 conversion patterns showed higher C3 protein (beta 1C/A) levels compared with those with non-conversion, whereas the differences of C4 protein (beta 1E) levels were unremarkable. CSF with C3 conversion patterns also showed apparent inflammatory characteristics indicating blood-CSF barrier involvement which would be deduced from increased alpha 2-macroglobulin and IgA, both being regarded as sensitive internal barrier parameters: but IgA measurement was much higher than usually expected values. It is suggested that the increase in CSF C3 might be initiated by accelerated consumption of complement through the alternative pathway, leading to hypersynthetic or hyperinflux response in CSF.

Behcet Syndrome↗