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Biomedical subjects

H Shibasaki

Publications and source records attributed to H Shibasaki.

At least 55 records · Page 3Linked to original sources
PubMed2001

Hydrolysis of conjugated steroids by the combined use of beta-glucuronidase preparations from helix pomatia and ampullaria: determination of urinary cortisol and its metabolites.

This study describes the enzymatic hydrolysis of urinary conjugates of cortisol, cortisone, tetrahydrocortisol, allotetrahydrocortisol, and tetrahydrocortisone with beta-glucuronidase preparations from Helix pomatia and Ampullaria. The objective of the present studies was to find optimal hydrolysis conditions for these conjugated steroids. Assay of the isolated steroids was carried out by GC-MS using deuterium-labeled compounds as internal standards. The allotetrahydrocortisol conjugate was clearly the hardest to hydrolyze with enzyme from Helix pomatia and required increased enzyme concentration and prolonged incubation. Hydrolysis of a urine sample for 2.0 h with the simultaneous use of 3400 units/ml Ampullaria and 5400 units/ml Helix pomatia enzymes in 0.5 M acetate buffer at 55 degrees C achieved more complete cleavage of the urinary conjugates of the five steroids examined. It is thus advantageous to use the Ampullaria and Helix pomatia enzymes in combination to obtain the highest yield in the urinary corticosteroid assay.

Adult↗
PubMed2001

Accurate identification of waveform of evoked potentials by component decomposition using discrete cosine transform modeling.

This study introduces a method for accurate identification of the waveform of the evoked potentials by decomposing the component responses. The decomposition was achieved by zero-pole modeling of the evoked potentials in the discrete cosine transform (DCT) domain. It was found that the DCT coefficients of a component response in the evoked potentials could be modeled sufficiently by a second order transfer function in the DCT domain. The decomposition of the component responses was approached by using partial expansion of the estimated model for the evoked potentials, and the effectiveness of the decomposition method was evaluated both qualitatively and quantitatively. Because of the overlap of the different component responses, the proposed method enables an accurate identification of the evoked potentials, which is useful for clinical and neurophysiological investigations.

Adolescent↗
PubMed2001

Tonic and phasic inhibition indices are constant among nights: new indices for evaluating the degree of the two types of motor inhibition during REM sleep.

BACKGROUND: Tonic inhibition index (TII) and phasic inhibition index (PII) were proposed as indices for evaluating the degree of two types of motor inhibition activity during rapid eye movement (REM) sleep. METHODS: In the present study, therefore, six healthy men underwent two consecutive all-night polysomnography, and reproducibility of TII and PII was evaluated. RESULTS: TII was 0.85+/-0.07 (mean+/-SD) on the first night and 0.88+/-0.08 on the second; and PII was 3.4+/-2.1 on the first night and 4.9+/-1.8 on the second. Neither TII nor PII was significantly different between the two nights. CONCLUSION: One night sleep study is considered sufficient for using TII and PII as a tool for evaluating motor inhibition activity during REM sleep in adults.

Journal Article↗
PubMed2001

Dissociable mechanisms of attentional control within the human prefrontal cortex.

Neuropsychological tests that require shifting an attentional set, such as the Wisconsin Card Sorting Test, are sensitive to frontal lobe damage. Although little information is available for humans, an animal experiment suggested that different regions of the prefrontal cortex may contribute to set shifting behavior at different levels of processing. Behavioral studies also suggest that set shifting trials are more time consuming than non-set shifting trials (i.e. switch cost) and that this may be underpinned by differences at the neural level. We determined whether there were differential neural responses associated with two different levels of shifting behavior, that of reversal of stimulus-response associations within a perceptual dimension or that of shifting an attentional set between different perceptual dimensions. Neural activity in the antero-dorsal prefrontal cortex increased only in attentional set shifting, in which switch costs were significant. Activity in the postero-ventral prefrontal cortex increased not only in set shifting but also in reversing stimulus-response associations, in which switch costs were absent. We conclude that these distinct regions in the human prefrontal cortex provide different levels of attention control in response selection. Thus, the antero-dorsal prefrontal cortex may be critical for higher order control of attention, i.e. attentional set shifting, whereas the postero-ventral area may be related to a lower level of shift, i.e. reorganizing stimulus-response associations.

Adult↗
PubMed2001

Chronic cerebral hypoperfusion induces MMP-2 but not MMP-9 expression in the microglia and vascular endothelium of white matter.

White matter lesions are closely associated with cognitive impairment and motor dysfunction in the aged. To explore the pathophysiology of these lesions, the authors examined the expression of matrix metalloproteinase-2 (MMP-2) and MMP-9 in the white matter in a rat model of chronic cerebral hypoperfusion. After bilateral clipping of the common carotid arteries, myelin staining revealed demyelinating changes in the optic tract and the corpus callosum on day 7. Zymographic analyses indicated an increase in the level of MMP-2, but not MMP-9, after the hypoperfusion. Immunohistochemical analyses revealed the presence (most abundantly on day 3) of MMP-2-expressing activated microglia in the optic tract and corpus callosum. In contrast, the capillary endothelial cells expressed MMP-2 later. IgM-immunoreactive glial cells were absent in the sham-operated animals, but were present in the hypoperfused animals by day 3, reflecting the disrupted blood-brain barrier. These findings suggest that the main sources of the elevated MMP-2 were the microglia and the endothelium, and that these cells may contribute to the remodeling of the white matter myelin and microvascular beds in chronic cerebral hypoperfusion.

Animals↗
PubMed2001

Markov process amplitude EEG model for spontaneous background activity.

The Markov process amplitude (MPA) EEG model effectively representing spontaneous brain activity of the EEG was introduced. The relationship between the electrical mechanism for EEG generation and the proposed model was also investigated. The MPA EEG model was described by the sinusoidal waves with the randomly fluctuating amplitude of the first-order Markov process. The parameters of the MPA EEG model were determined optimally based on the real EEG records. The results of model outputs in the frequency domain demonstrated an excellent fit with the power spectrum of the corresponding EEG. The simulated model signal in the time domain also showed good agreement with the EEG time series. The satisfactory results from the MPA EEG model suggest its possible applicability in clinical practice. Furthermore, from the high goodness of fit, the authors think that the neurons oscillate at fixed frequencies and are modulated by synaptic interactions in accordance with the first-order Markov process.

Adult↗
PubMed2001

Parametric modeling of somatosensory evoked potentials using discrete cosine transform.

This paper introduces a parametric method for identifying the somatosensory evoked potentials (SEPs). The identification was carried out by using pole-zero modeling of the SEPs in the discrete cosine transform (DCT) domain. It was found that the DCT coefficients of a monophasic signal can be sufficiently approximated by a second-order transfer function with a conjugate pole pair. The averaged SEP signal was modeled by the sum of several second-order transfer functions with appropriate zeros and poles estimated using the least square method in the DCT domain. Results of the estimation demonstrated that the model output was in an excellent agreement with the raw SEPs both qualitatively and quantitatively. Comparing with the common autoregressive model with exogenous input modeling in the time domain, the DCT domain modeling achieves a high goodness of fitting with a very low model order. Applications of the proposed method are possible in clinical practice for feature extraction, noise cancellation and individual component decomposition of the SEPs as well as other evoked potentials.

Adolescent↗
PubMed2001

Compensation of hand movement for patients by assistant force: relationship between human hand movement and robot arm motion.

As some functional diseases in the brain, such as cerebellum dysfunction and Parkinson's disease, cause the disability related to human movement control, a compensation method was developed for improving the performance of hand movement. The compensation can be carried out by adding assistant force, which is generated from artificial equipment attached to a human arm. From the experiment of visual target tracking, the tracking trajectories recorded from both healthy persons and patients with movement disability were analyzed. It was found that the tracking trajectories were represented sufficiently by a dynamic model of a robot arm in which the differences between healthy persons and patients were characterized by the model parameters. Based on the model, it was demonstrated that the hand movement of patients could be improved by introducing an appropriate compensation. The effectiveness of the proposed compensation method was verified from a simulation study of a robot arm. The design of artificial equipment for compensating the hand movement was also presented and discussed.

Biofeedback, Psychology↗
PubMed2001

Blink artifact elimination in electroencephalographic records based on discrete cosine transform domain modeling.

A method for eliminating blink artifacts that contaminate electroencephalographic (EEG) records is introduced. The proposed method enables a direct estimation of blink artifacts without the use of the simultaneously recorded electroculargraphic (EOG) signal. The estimation of blink artifacts in the EEG was achieved by modeling in the discrete cosine transform (DCT) domain. The DCT coefficients of the blink artifact were sufficiently represented by a system transfer function with a low model order of 4. Two cases were investigated: one was blink artifact elimination for the background EEG and the other was for the somatosensory evoked potentials. The effectiveness of the proposed method was demonstrated in an experimental study based on actual EEG data of 11 healthy subjects. The simplicity and effectiveness of the proposed method suggest that blink artifact elimination using DCT domain modeling can possibly be applied in various areas of neuroscience for improving EEG quality.

Adolescent↗
PubMed2000

Expectation of pain enhances responses to nonpainful somatosensory stimulation in the anterior cingulate cortex and parietal operculum/posterior insula: an event-related functional magnetic resonance imaging study.

Although behavioral studies suggest that pain distress may alter the perception of somatic stimulation, neural correlates underlying such alteration remain to be clarified. The present study was aimed to test the hypothesis that expectation of pain might amplify brain responses to somatosensory stimulation in the anterior cingulate cortex (ACC) and the region including parietal operculum and posterior insula (PO/PI), both of which may play roles in regulating pain-dependent behavior. We compared brain responses with and subjective evaluation of physically identical nonpainful warm stimuli between two psychologically different contexts: one linked with pain expectation by presenting the nonpainful stimuli randomly intermixed with painful stimuli and the other without. By applying the event-related functional magnetic resonance imaging technique, brain responses to the stimuli were assessed with respect to signal changes and activated volume, setting regions of interest on activated clusters in ACC and bilateral PO/PI defined by painful stimuli. As a result, the uncertain expectation of painful stimulus enhanced transient brain responses to nonpainful stimulus in ACC and PO/PI. The enhanced responses were revealed as a higher intensity of signal change in ACC and larger volume of activated voxels in PO/PI. Behavioral measurements demonstrated that expectation of painful stimulus amplified perceived unpleasantness of innocuous stimulus. From these findings, it is suggested that ACC and PO/PI are involved in modulation of affective aspect of sensory perception by the uncertain expectation of painful stimulus.

Adult↗
PubMed2000

High-frequency SEP components generated in the somatosensory cortex of the monkey.

To investigate the origin of high-frequency somatosensory evoked potential (SEP) components, we recorded median nerve SEPs from the scalp and the depth in six monkeys. Laminar field potentials were analyzed in area 3b (N10; corresponding to human N20) and area 1 (P12; corresponding to human P25). After digital filtering (300-900 Hz), 4-6 components were identified, and the 1st to 4th peaks in area 3b (7-11 ms in latency) and the 3rd to 5th in area 1 (9-13 ms) showed clear polarity reversals between the surface and the depth of the cortex. These results provide direct evidence for intracortical origin of early high-frequency components in area 3b and of late ones in area 1.

Action Potentials↗
PubMed2000

Neuroprotective effect of cyclic GMP against radical-induced toxicity in cultured spinal motor neurons.

We have previously reported that nitric oxide-related cyclic guanosine-3',5'-monophosphate (GMP) protected spinal nonmotor neurons, but not motor neurons against chronic glutamate-induced toxicity, which is associated with selective motor neuronal death after glutamate stress. In this report, we investigated the effect of cyclic GMP against reactive oxygen species (ROS)-induced toxicity in cultured neurons from embryonic rat spinal cords. Pretreatment with a cGMP analogue, 8-bromoguanosine monophosphate (8br-cGMP), for 12-24 hours protected both spinal motor neurons and nonmotor neurons against injury induced by either hydrogen peroxide (H(2)O(2)), or a glutathione depletor, L-buthionine-[S,R]-sulfoximine (BSO). This protective effect was reversed by coadministration with the cGMP-dependent protein kinase (PKG) inhibitor Arg-Lys-Arg-Ala-Arg-Lys-Glu. Interestingly, when cultures were exposed to BSO for 24 hours to allow irreversible inhibition of glutathione synthesis, 8br-cGMP protected only nonmotor neurons. Our results indicate that cGMP attenuates oxidative injury to cultured spinal neurons, in a mechanism associated with glutathione synthesis.

Animals↗
PubMed2000

Nonconvulsive focal inhibitory seizure: subdural recording from motor cortex.

The authors obtained an ictal electrocorticogram with chronically implanted subdural electrodes from a 30-year-old man with a low grade glioma in the right postcentral gyrus who had a focal inhibitory seizure of the left arm. During the ictal paresis, the authors observed epileptic discharges in the positive arm motor area of the right precentral gyrus and in its rostral area, but not in the negative motor area. The epileptic activity probably inhibited the spinal motoneuron pool without eliciting excitatory activity in the corticospinal pathway.

Adult↗
PubMed2000

Autosomal dominant temporal lobe epilepsy in a Japanese family.

We described autosomal dominant familial temporal lobe epilepsy in a Japanese family in which three individuals (one man and his two children) were affected. Their seizures commonly consisted of auditory symptoms and infrequent nocturnal generalized seizures. Repeated EEGs did not provide confirmative epileptiform discharges, but cranial MRI in one patient showed mild left hippocampal atrophy, and decreased glucose metabolism in the left temporal area was demonstrated by 18F-deoxyglucose positron emission tomography (FDG-PET). A confirmative diagnosis in one of the patients by FDG-PET was helpful for diagnosis in other patients in the same family. Seizure onset was adolescent commonly among the three patients, but better seizure control was achieved in the father as compared with the two children.

Adult↗
PubMed2000

Attentional modulation of parieto-occipital cortical responses: implications for hemispatial neglect.

Functional magnetic resonance imaging (fMRI) was used to examine whether preattentive and attentive visual processing, the cognitive psychological dichotomy on normal vision, indeed activate the parieto-occipital systems differentially as suggested by recent neuropsychological research. The activation paradigms consisted of feature detection and discrimination of line orientation, and visual fixation, which corresponded to preattentive, attention-requiring, and baseline conditions, respectively. The detection versus fixation contrast revealed activation sites in the right lateral prefrontal cortex and bilateral occipital lobes, whereas the discrimination versus fixation contrast showed broader bilateral activations extending from the occipital lobes through the parietal lobes, prefrontal cortex, thalamus, basal ganglia and upper brainstem. In the discrimination versus detection contrast, significant activations were observed in the right superior and inferior parietal lobules as well as in the subcortical structures. These findings were consistently demonstrated both at intra- and inter-subject levels. The present study provides further evidence to delineate neural substrate for the two distinct modes of visual processing and helps us to understand the neuropsychological mechanism underlying visual attention disorders.

Adult↗
PubMed2000

Glucose metabolism in the rat frontal cortex recovered without the recovery of choline acetyltransferase activity after lesioning of the nucleus basalis magnocellularis.

We measured the cerebral metabolic rate of glucose (CMRglc) by using positron emission tomography (PET) with [18F]fluorodeoxyglucose (FDG) and the choline acetyltransferase (ChAT) activity at 3 days and 3 months after destruction of the nucleus basalis magnocellularis (NBM). Although the frontal ChAT activity remained 20% lower than that of controls even at 3 months post-lesioning, the frontal CMRglc, which was reduced by 40% at 3 days, returned to normal at 3 months, namely CMRglc recovered with time without the recovery of ChAT activity with time. Since glucose metabolism reflects mainly presynaptic neuronal activity, we speculate that presynaptic rearrangement may have some relation to the recovery of CMRglc.

Animals↗
PubMed2000

Simultaneous determination of 6beta- and 6alpha-hydroxycortisols and 6beta-hydroxycortisone in human urine by stable isotope dilution mass spectrometry.

A capillary gas chromatographic-mass spectrometric method for the simultaneous determination of 6beta-hydroxycortisol (6beta-OHF, 6beta,11beta,17alpha,21-tetrahydroxypregn-4-ene- 3,20-dione), 6alpha-hydroxycortisol (6alpha-OHF, 6alpha,11beta,17alpha,21-tetrahydroxypregn-4-ene -3,20-dione) and 6beta-hydroxycortisone (6beta-OHE, 6beta,17alpha,21-trihydroxypregn-4-ene-3,11,20-trione) in human urine is described. Deuterium-labelled compounds, 6beta-[1,1,19,19,19-2H5]OHF (6beta-OHF-d5), 6alpha-[1,1,19,19,19-2H5]OHF (6alpha-OHF-d5) and 6beta-[1,1,19,19,19-2H5]OHE (6beta-OHE-d5) were used as internal standards. Quantitation was carried out by selected-ion monitoring of the characteristic fragment ions ([M-31]+) of the methoxime-trimethylsilyl (MO-TMS) derivatives of 6beta-OHF, 6alpha-OHF and 6beta-OHE. The sensitivity, specificity, precision and accuracy of the method were demonstrated to be satisfactory for measuring 6beta-OHF, 6alpha-OHF and 6beta-OHE in human urine.

Calibration↗