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Biomedical subjects

M Akamatsu

Publications and source records attributed to M Akamatsu.

At least 19 recordsLinked to original sources
PubMed2001

An electromyographic investigation of the effect of stimulus-response mapping on choice reaction time.

The activity of the agonist muscles was recorded during the performance of a two-choice visual reaction time (RT) task in which the compatibility of the stimulus-response mapping was manipulated. Correct trials were distinguished according to whether or not the activation of the agonist of the required response was preceded by an activation of the agonist of the nonrequired response. Double activation trials were more numerous for the incompatible than for the compatible mapping. Furthermore, these trials yielded longer RTs than the single muscular activation trials. These results suggest that initial activations of nonrequired responses are more frequently aborted and corrected when the mapping is incompatible than when it is compatible. This finding supports the dimensional overlap model of stimulus-response compatibility (S. Kornblum, T. Hasbroucq, & A. Osman, 1990).

Adolescent↗
PubMed2000

Changes in spinal excitability during choice reaction time: the H reflex as a probe of information transmission.

The aim of the present study was to investigate the modulations in amplitude of H reflexes elicited in a hand muscle, the flexor pollicis brevis, during the performance of a choice reaction time (RT) task in which this muscle was directly involved. Ten subjects were to choose between a left- or a right-thumb key-press according to the lateral location of a flash of light. The stimulus-response mapping was either compatible or incompatible. Hoffman reflexes were elicited at different times during the RT by stimulation of the median nerve. Twenty-five milliseconds before the voluntary response, the amplitude of the H reflex suddenly increased when the muscle was involved in the response and decreased symmetrically when the muscle was not involved in the response. Mapping compatibility exerted no detectable influence on the changes in spinal excitability. The latter result supports the assumptions that are at the core of Sternberg's additive factor method.

Adult↗
PubMed2000

[Percutaneous tumor ablation therapy for the advanced stage of HCC].

We have performed percutaneous tumor ablation (PTA) including percutaneous ethanol injection therapy (PEIT) for 90% of the patients with hepatocellular carcinoma. Until December 1998, the 793 patients received PTA, 5 years survival rate reached 39.8%. Excluding the patients with Child C whose hepatic function were extremely low, 5 years survival rate reached to the level of 41.2%. Since 5 years survival rate in stage IV-A reached 24.4%, the patients of stage IV-A may be considered to have an indication for PTA. We have confirmed the effectiveness of the local treatment including radiotherapy for advanced hepatocellular carcinoma with portal vein invasion. We are attempting to perform PTA for the extra-hepatic lesions that had no indication of other treatment. However the indication of PTA is limited by the presence of diffuse nodules, exacerbation of the hepatic function, or tumor invasion to portal vein, bile duct, inferior vena cava.

Carcinoma, Hepatocellular↗
PubMed1999

Vinexin forms a signaling complex with Sos and modulates epidermal growth factor-induced c-Jun N-terminal kinase/stress-activated protein kinase activities.

Vinexin, a novel protein that plays a key role in cell spreading and cytoskeletal organization, contains three SH3 domains and binds to vinculin through its first and second SH3 domains. We show here that the third SH3 domain binds to Sos, a guanine nucleotide exchange factor for Ras and Rac, both in vitro and in vivo. Point mutations in the third SH3 domain abolished the vinexin-Sos interaction. Stimulation of NIH/3T3 cells with serum, epidermal growth factor (EGF), or platelet-derived growth factor (PDGF) decreased the electrophoretic mobility of Sos and concomitantly inhibited formation of the vinexin-Sos complex. Phosphatase treatment of lysates restored the binding of Sos to vinexin, suggesting that signaling from serum, EGF, or PDGF regulates the vinexin-Sos complex through the Sos phosphorylation. To evaluate the function of vinexin downstream of growth factors, we examined the effects of wild-type and mutant vinexin expression on extracellular signal-regulated kinase (Erk) and c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) activation in response to EGF. Exogenous expression of vinexin beta in NIH/3T3 cells enhanced JNK/SAPK activation but did not affect Erk activation. Moreover mutations in the third SH3 domain abolished EGF activation of JNK/SAPK in a dominant-negative fashion, whereas they slightly stimulated Erk. Together these results suggest that vinexin can selectively modulate EGF-induced signal transduction pathways leading to JNK/SAPK kinase activation.

3T3 Cells↗
PubMed1999

Sensorimotor polyneuropathy associated with chronic lymphocytic leukemia, IgM antigangliosides antibody and human T-cell leukemia virus I infection.

A 65-year-old man presented with a sensorimotor polyneuropathy associated with B-cell chronic lymphocytic leukemia (CLL) and immunoglobulin M (IgM) antibody to various gangliosides. Electrophysiological studies denoted significant abnormalities of motor and sensory nerve conduction. Although the pathology of sural nerve biopsy looked minimally affected, immunohistochemical studies showed specific binding of IgM to the human peripheral nerve. Our patient also had high titer of antibody to human T-cell leukemia virus I (HTLV-I) in both serum and cerebrospinal fluid (CSF), which might activate B-cell-mediated immunity and facilitate the production of IgM antibody. The other unique feature is the reactivity of antibody to gangliosides. The patient had IgM antibody reactivities to gangliosides with disialosyl residue such as GT1b, GQ1b and GD3, but not to GD1b. IgM antibody to gangliosides with disialosyl residue has been reported in ataxic symptoms, but our patient failed to demonstrate ataxia. Without reactivity to GD1b, sensory ataxic neuropathy might not develop even in the presence of antibody reactive to other gangliosides with disialosyl residue.

Aged↗
PubMed1999

The time-course of preparatory spinal and cortico-spinal inhibition: an H-reflex and transcranial magnetic stimulation study in man.

In a previous study where reaction-time methods were combined with transcranial magnetic stimulation (TMS) of the motor cortex, cortico-spinal excitability was shown to reflect time preparation. Provided that subjects can accurately estimate time, the amplitude of motor-evoked potentials (MEPs) diminish progressively during the interval separating the warning signal from the response signal (i.e., the foreperiod). On the other hand, several experiments have demonstrated that the amplitude of the Hoffman (H) reflex elicited in prime movers diminishes during the foreperiod of reaction-time tasks. The aim of the present study was to compare the time course of the respective decrements of H-reflex and MEP amplitude during a constant 500-ms foreperiod. The subjects (n=8) participated in two experimental sessions. In one session, H-reflexes were induced in a tonically activated, responding hand muscle, the flexor pollicis brevis, at different times during the foreperiod of a visual-choice reaction-time task. In the other session, motor potentials were evoked in the same muscle by TMS of the motor cortex delivered in the same behavioral conditions and at the same times as in the first session. The results show that both H-reflexes and MEPs diminish in amplitude during the foreperiod, which replicates and extends previous findings. Interestingly, the time constants of the two decrements differed. There was a facilitatory effect of both electrical and magnetic stimulations on the subject's performance: reaction time was shorter for the trials during which a stimulation was delivered than for the no-stimulation trials. This facilitation was maximal when the stimulations were delivered simultaneously with the warning signal and vanished progressively with stimulation time.

Adult↗
PubMed1999

Multineuronal spike classification based on multisite electrode recording, whole-waveform analysis, and hierarchical clustering.

We proposed here a method of multineuronal spike classification based on multisite electrode recording, whole-waveform analysis, and hierarchical clustering for studying correlated activities of adjacent neurons in nervous systems. Multineuronal spikes were recorded with a multisite electrode placed in the hippocampal pyramidal cell layer of anesthetized rats. If the impedance of each electrode site is relatively low and the distance between electrode sites is sufficiently small, a spike generated by a neuron is simultaneously recorded at multielectrode sites with different amplitudes. The covariance between the spike waveform at each electrode site and a template was calculated as a damping factor due to the volume conduction of the spike from the neuron to the electrode site. Calculated damping factors were vectorized and analyzed by hierarchical clustering using a multidimensional statistical test. Since a cluster of damping vectors was shown to correspond to an antidromically identified neuron, spikes of different neurons are classified by referring to the distributions of damping vectors. Errors in damping vector calculation due to partially overlapping spikes were minimized by successively subtracting preceding spikes from raw data. Clustering errors due to complex spike bursts (i.e., spikes with variable amplitudes) were avoided by detecting such bursts and then using only the first spike of a burst for clustering. These special procedures produced better cluster separation than conventional methods, and enabled multiple neuronal spikes to be classified automatically. Waveforms of classified spikes were well superimposed. We concluded that this method is particularly useful for separating the activities of adjacent neurons that fire partially overlapping spikes and/or complex spike bursts.

Action Potentials↗
PubMed1999

Structure-activity relationships of RGD mimetics as fibrinogen-receptor antagonists.

The activities of a series of RGD mimetics, which contained a variety of cationic structures, for the inhibition of platelet aggregation and fibrinogen-receptor binding were measured. The stability of the coulombic ion-pairing complex of the model compounds with the acetate anion as a model for the receptor was calculated in terms of the ionic interaction energy. The results suggest that stability is one of the significant factors which govern the inhibitory potency of fibrinogen-receptor binding. The distance between cationic and anionic groups might also affect the potency. A compound which contained an amidinophenyl structure as the cationic moiety showed exceptionally high inhibitory activity, suggesting that some other factors, in addition to coulombic interaction and the distance, affect the potency.

Blood Platelets↗
PubMed1998

[Granulomatous slack skin].

A 48-year-old woman developed granulomatous slack skin (GSS), one of the special forms of cutaneous T-cell lymphoma. The lesional skin slack with an atrophic, poikilodermic surface and granulomatous induration. Histopathological findings included epidermotropism, diffuse lymphoid cell infiltration and foreign body giant cells as well as granulomatous reactions from superficial to deep dermis, including part the subcutis. The diagnosis was established by positive results for rearrangement of the T-cell receptor gene. The therapeutic possibilities, especially with corticosteroids and monitoring the disease course by following serum angiotensin converting enzyme activity are discussed.

Breast↗
PubMed1998

Picrodendrin and related terpenoid antagonists reveal structural differences between ionotropic GABA receptors of mammals and insects.

Twenty-eight picrotoxane terpenoids, including picrodendrins isolated from the Euphorbiaceae plant, Picrodendron baccatum (L.) Krug and Urban, have been evaluated for their ability to inhibit the specific binding of [3H]EBOB, the noncompetitive antagonist of ionotropic GABA receptors, to rat-brain and housefly (Musca domestica L.)-head membranes. Picrodendrin Q was the most potent competitive inhibitor of [3H]EBOB binding, with IC50 values of 16 nM (rat) and 22 nM (Musca). We find that the spiro gamma-butyrolactone moiety at the 13-position, which contains a carbonyl group conjugated with an unsaturated bond, and the substituents at the 4-position play important roles in the interaction of picrodendrins with their binding site in rat receptors. In contrast, such structural features are not strictly required in the case of the interaction with Musca receptors; the spiro saturated gamma-butyrolactone moiety at the 13-position, which bears the 16-sp3 carbon atom, and the hydroxyl groups at various positions are somewhat tolerated. Quantitative structure-activity studies have clearly shown that the electronegativity of the 16-carbon atom and the presence or absence of the 4- and 8-hydroxyl groups are important determinants of the potency of nor-diterpenes in Musca receptors, while the negative charge on the 17-carbonyl oxygen atom is likely important in the case of rat receptors. These findings indicate that there are significant differences between the structures of the complementary binding sites in rat GABA receptors and Musca GABA receptors. We also infer differences between native Musca GABA receptors and the Drosophila Rdl subunit-containing homo-oligomeric GABA receptors in the structures of their binding sites.

Animals↗
PubMed1998

[Anticancer susceptibility test method using general-purpose dissolved oxygen meter].

Drug susceptibility of cell can be rapidly measured by continuously monitoring its metabolic changes. We focused on respiration volume as a signal of metabolic change, and developed a new dissolved oxygen measuring system which can detect respiration volume of cells. The main feature of the system is the use of a new type bare oxygen electrode which can easily detect the changing rate of dissolved oxygen concentration. In this study, single type electrode was used to evaluate this rapid anticancer drug susceptibility test. The result obtained was almost equivalent to that with MTT method, which is a conventional method for susceptibility test of HL-60 to various kinds of anticancer drugs. We have also developed multi-type electrode plate with oxygen electrodes embedded in the bottom of 96-well plate, with which clinical evaluation of this method can be easily made.

Antineoplastic Agents↗
PubMed1998

[Cystic lesions of the pancreas].

The number of the literature and classification of the cystic pancreatic diseases is increasing recently. We describe MR cholangiopancreatography (MRCP) findings of the cystic pancreatic diseases according to the clinical oriented classification. Intraductal papillary tumor, mucinous cystadenoma and serous cystadenoma showed characteristic MRCP findings. However small non-neoplastic true cysts are difficult to differentiate from cystic tumors even by MRCP.

Acute Disease↗
PubMed1997

Lasting effect of NO on glutamate release in rat striatum revealed by continuous brain dialysis.

The effect of nitric oxide (NO) on glutamate release in the brain of freely moving rats was investigated using a new, high time-resolution microdialysis system. Coperfusion with veratridine (VER) and NO donors increased glutamate release above than that obtained with VER alone. When steady-state levels were regained after co-perfusion, perfusion of VER alone further potentiated glutamate release. The effect depended on the initial level of VER-induced glutamate release, and was maximum for intermediate glutamate levels. These results suggest that NO influences the glutamate release system by affecting the level of neural activity and that its effect lasts and increases when steady-state levels are regained in rat striatum.

Animals↗
PubMed1997

Terminal deoxynucleotidyl transferase staining of malignant lymphomas in paraffin sections: a useful method for the diagnosis of lymphoblastic lymphoma.

Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase located in the cell nucleus which catalyses the polymerization of deoxynucleotides at the 3'hydroxyl ends of oligo- or polydeoxynucleotide initiators without a template. TdT is known as a useful marker for the diagnosis of acute lymphoblastic leukaemia/lymphoma, but its detection usually requires fresh tissue specimens or cell suspensions, using either an enzyme analysis or immuno-fluorescence or -peroxidase staining. Until the recent development of the use of microwave-treated paraffin sections for immunoperoxidase staining, detection of TdT in paraffin sections required rather complicated processes. This new simple technique was applied to paraffin sections from the tumour tissue specimens of 16 patients with lymphoblastic lymphoma and of seven patients with non-endemic Burkitt's lymphoma, which is sometimes difficult to differentiate from lymphoblastic lymphoma because of their similar clinicopathological characteristics. In addition, as a control, ten cases each were examined of adult T-cell leukaemia/lymphoma (ATLL) and angioimmunoblastic lymphoma (AILD), which are both peripheral T-cell lymphomas. The tumour cells from 15 of the 16 (94 per cent) patients with lymphoblastic lymphoma were found to be TdT-positive. The specificity of the anti-TdT antibody used was confirmed by immunoblot and the specific 60 kD band was detected only in a specimen of lymphoblastic lymphoma. These results show that the immunostaining of TdT on paraffin-embedded sections is a useful method for differentiating lymphoblastic lymphoma from other lymphomas. This method is applicable to a routine diagnostic service.

Adolescent↗