PubMed Health⌕ Search

Biomedical subjects

Hiroshi Ashida

Publications and source records attributed to Hiroshi Ashida.

At least 19 recordsLinked to original sources
PubMed2007

Shigella chromosomal IpaH proteins are secreted via the type III secretion system and act as effectors.

Shigella possess 220 kb plasmid, and the major virulence determinants, called effectors, and the type III secretion system (TTSS) are exclusively encoded by the plasmid. The genome sequences of S. flexneri strains indicate that several ipaH family genes are located on both the plasmid and the chromosome, but whether their chromosomal IpaH cognates can be secreted from Shigella remains unknown. Here we report that S. flexneri strain, YSH6000 encodes seven ipaH cognate genes on the chromosome and that the IpaH proteins are secreted via the TTSS. The secretion kinetics of IpaH proteins by bacteria, however, showed delay compared with those of IpaB, IpaC and IpaD. Expression of the each mRNA of ipaH in Shigella was increased after bacterial entry into epithelial cells, and the IpaH proteins were secreted by intracellular bacteria. Although individual chromosomal ipaH deletion mutants showed no appreciable changes in the pathogenesis in a mouse pulmonary infection model, the DeltaipaH-null mutant, whose chromosome lacks all ipaH genes, was attenuated to mice lethality. Indeed, the histological examination for mouse lungs infected with the DeltaipaH-null showed a greater inflammatory response than induced by wild-type Shigella, suggesting that the chromosomal IpaH proteins act synergistically as effectors to modulate the host inflammatory responses.

Animals↗
PubMed2006

FMRI adaptation reveals separate mechanisms for first-order and second-order motion.

A key unresolved debate in human vision concerns whether we have two different low-level mechanisms for encoding image motion. Separate neural mechanisms have been suggested for first-order (luminance modulation) and second-order (e.g., contrast modulation) motion in the retinal image but a single mechanism could handle both. Human functional magnetic resonance imaging (fMRI) has not so far convincingly revealed separate anatomical substrates. To examine whether two separate but co-localized mechanisms might exist, we used the technique of fast fMRI adaptation. We found direction-selective adaptation independently for each type of motion in the motion area V5/MT+ of the human brain. However, there was a total absence of cross-adaptation between first-order and second-order motion stimuli. This was true in both of the two subcomponents of MT+ (MT and MST) and similar results were found in V3A. This pattern of adaptation was consistent with psychophysical measurements of detection thresholds in similar stimulus sequences. The results provide strong evidence for separate neural populations that are responsible for detecting first- and second-order motion.

Adaptation, Physiological↗
PubMed2006

High vaccine efficacy against shigellosis of recombinant noninvasive Shigella mutant that expresses Yersinia invasin.

Live attenuated Shigella vaccines elicit protective immune responses, but involve a potential risk of inducing a strong inflammatory reaction. The bacterial invasiveness that is crucial for Ag delivery causes inflammatory destruction of infected epithelial cells and proinflammatory cell death of infected macrophages. In this study, the noninvasive Shigella mutant DeltaipaB was equipped with Yersinia invasin protein, which has been shown to mediate bacterial invasion and targeting to M cells located in follicle-associated epithelium. Invasin-expressing DeltaipaB (DeltaipaB/inv) was internalized into epithelial cells and retained in the intraphagosomal space. DeltaipaB/inv did not induce necrotic cell death of infected macrophages nor cause symptomatic damage after intranasal vaccination of mice. DeltaipaB/inv was safer and more effective than the conventional live vaccine, DeltavirG. Infection by DeltaipaB/inv caused polymorphonuclear neutrophil infiltration in the lung, but did not induce production of large amounts of proinflammatory cytokines. We concluded that the low experimental morbidity and high vaccine efficacy of DeltaipaB/inv are primarily based on high protective immune responses, which may be enhanced by the polymorphonuclear neutrophil infiltration unaccompanied by tissue injury.

Adhesins, Bacterial↗
PubMed2006

Assessment of stimulus-induced changes in human V1 visual field maps.

Visual cortex contains a set of field maps in which nearby scene points are represented in the responses of nearby neurons. We tested a recent hypothesis that the visual field map in primary visual cortex (V1) is dynamic, changing in response to stimulus motion direction. The original experimental report replicates, but further experimental and analytical investigations do not support, the interpretation of the results. The V1 map remains invariant when measured using stimuli moving in different directions. The measurements can be explained by small and systematic response amplitude differences that arise when probing with stimuli moving in different directions.

Algorithms↗
PubMed2006

A positive correlation between fixation instability and the strength of illusory motion in a static display.

A stationary pattern with asymmetrical luminance gradients can appear to move. We hypothesized that the source signal of this illusion originates in retinal image motions due to fixational eye movements. We investigated the inter-subject correlation between fixation instability and illusion strength. First, we demonstrated that the strength of the illusion can be quantified by the nulling technique. Second, we concurrently measured cancellation velocity and fixation instability for each subject, and found a positive correlation between them. The same relationship was also found within a single observer when the visual stimulus was artificially moved in the simulation of fixation instability. Third, we confirmed the same correlation with eye movements for a wider variety of illusory displays. These results suggest that fixational eye movements indeed play a relevant role in generating this motion illusion.

Adult↗
PubMed2006

Photoacoustic monitoring of neovascularities in grafted skin.

BACKGROUND AND OBJECTIVE: In skin grafting, evaluation of graft adhesion to the recipient site in the early postgrafting period is important. However, conventional diagnoses such as visual observation and thermography required about 1 week to obtain results and these methods cannot give quantitative information on the adhesion of a skin graft. We proposed a new method for monitoring adhesion of grafted skin that is based on measurement of photoacoustic signals. To investigate the validity of the method, we performed experiments using rat autografts models. STUDY DESIGN/MATERIALS AND METHODS: Grafted skin in a rat was irradiated with 200 microJ, 532-nm nanosecond laser pulses, and photoacoustic signals were detected with a piezoelectric transducer placed on the skin at various postgrafting time. Temporal profiles of the signals were converted to depth profiles using an assumed sound velocity of 1,500 m/second. Histological analysis was performed to observe neovascularities formed in the grafts. RESULTS: At 6 hours postgrafting, a photoacoustic signal peak appeared in the depth region corresponding to the graft. The results of histological analysis also showed formation of neovascularities in the graft after 6 hours postgrafting, indicating that photoacoustic signal peaks observed in the graft originated from the neovascularities, which are an indication of graft adhesion. For up to 24 hours postgrafting, no significant difference was observed between the results of visual observation and laser Doppler imaging of the same grafted skins. CONCLUSION: We have demonstrated that photoacoustic signals originating from neovascularities in grafts can be sensitively detected in the early postgrafting period, suggesting the validity of photoacoustic measurement for adhesion monitoring of skin grafts.

Acoustics↗
PubMed2005

Hollow-waveguide-based nanosecond, near-infrared pulsed laser ablation of tissue.

BACKGROUND AND OBJECTIVE: Short-pulse solid-state lasers have recently received much attention as new coherent light sources for medical applications, but steady transmission of their high-energy output pulses through a solid quartz fiber is difficult because of the onset of laser-induced breakdown. We previously demonstrated that hollow waveguides could be used to deliver nanosecond laser pulses for tissue ablation. The aim of this study was to determine the optimum laser pulse energy and range of defocused distance for obtaining a deep and sharp ablation channel in myocardial tissue with laser pulses transmitted through a hollow waveguide. STUDY DESIGN/MATERIALS AND METHODS: Cyclic-olefin-polymer-coated silver hollow waveguides of 1 mm in inner diameter and 1 m in length were used. A vacuum-cored scheme was applied to the waveguides to suppress laser-induced air breakdown. Porcine myocardial tissue was irradiated with 300 laser pulses that were delivered through the waveguide in vitro at various laser energy levels and defocused distances, and depths and diameters of channels were measured. Histological analysis of the ablated tissues was also performed. RESULTS: At an ablation energy of approximately 60 mJ/pulse, deep (>4.5 mm) and sharp (depth-to-diameter ratio of > 6) channels were created in tissue in the range of defocused distances of -4 approximately + 0.5 mm. Under these conditions, waveguide bending did not cause a remarkable change in ablation characteristics. Histological analysis of ablated tissue showed limited thermal damage but suggested a certain extent of mechanical effects in the tissue. CONCLUSION: With near-infrared, nanosecond laser pulses delivered through a cyclic-olefin-polymer-coated silver hollow waveguide, efficient and sharp ablation of myocardial tissue can be achieved, suggesting the usefulness of the hollow waveguide as a new flexible delivery system for high-intensity laser pulses.

Animals↗
PubMed2005

A new variant of the Ouchi illusion reveals Fourier-component-based processing.

We report that anomalous motion illusion in a new variant of the Ouchi figure is well predicted by the strength of its Fourier fundamentals and harmonics. The original Ouchi figure consists of a rectangular checkerboard pattern surrounded by an orthogonal rectangular checkerboard pattern, in which illusory relative motion between the two regions is perceived. Although this illusion has been explained in terms of biases in integrating one-dimensional motion signals to determine the two-dimensional motion direction, the physiological mechanism has not been clarified. With our new stimuli, which consisted of thin lines instead of rectangles, we found that the perceived illusion is drastically reduced when the position of each line element is randomly shifted. This is not predicted by simple models of local motion integration along the visible edges. We demonstrate that the relative amplitude of the relevant Fourier fundamentals and harmonics leads to a quantitative prediction. Our analysis was successfully applied to other variants of the Ouchi figure (Khang and Essock 1997 Perception 26 585-597), closely predicting the reported rating. The results indicate that the underlying physiological mechanism is sensitive to the Fourier components of the stimuli rather than the visible edges.

Adult↗
PubMed2005

Photoacoustic diagnosis of burns in rats.

BACKGROUND: Accurate burn depth assessment is important for determining the appropriate treatment plan for severe burn patients. However, conventional methods of diagnoses, such as visual observation and pinprick test, are often inaccurate. We previously proposed a new method for burn diagnosis in which photoacoustic signals originating from the blood in healthy tissue under the injured tissue are measured. In this study, we investigated the validity of this method by an experiment using rat scald burn models. METHODS: Superficial dermal burns (SDBs), deep dermal burns (DDBs), and deep burns (DBs) were made in the dorsal skin of rats by using a Walker-Mason template. Wounds were irradiated with low-energy, 550-nm, nanosecond pulsed light, and photoacoustic signals induced were measured with a piezoelectric film as a function of postburn time. Measurement in normal skin as a control was also performed. Temporal profiles of the photoacoustic signals were converted into depth profiles using sound velocity of tissue, and for each profile, a peak showing highest signal intensity was selected. For this peak, the depth at which the signal rose (signal rise depth) and the depth that gave a peak value (signal peak depth) were recorded. Statistical analysis was performed to clarify the difference in depth information of signals between burn groups. RESULTS: Depth profiles of photoacoustic signals showed unique features depending on the degree of burn; pronounced peaks shifted to deeper tissue as the burn severity increased. This indicates that the zone of stasis formed due to injuries can be monitored. There were significant differences in both the signal rise depth and the peak depth between the control and SDB groups, SDB and DDB groups, and DDB and DB groups (p < 0.001). CONCLUSION: SDBs, DDBs, and DBs can be differentiated by photoacoustic signals, suggesting that the method proposed is useful for diagnosing burn injuries.

Acoustics↗
PubMed2004

Attention-based motion perception and motion adaptation: what does attention contribute?

Attention-based motion perception refers to the phenomenon that a stimulus with ambiguous motion energy can be seen to move in a direction that is under attentive control of the observer. The role of attention is obvious when the stimulus is ambiguous: it makes the stimulus move in one direction. The goal of the current experiment is to investigate what the contribution of attention under attentive tracking conditions actually is, especially while viewing-time progresses. We had our observers look at a circular array of four evenly spaced discs whose motion direction was biased in the clockwise direction. Observers either viewed the stimulus moving around a circular path passively or actively. In the latter case they attentively tracked one of the discs. The observer's task was to indicate the perceived direction of motion. As time progresses, this kind of stimulus will undergo spontaneous motion direction reversals. We analyzed the time course of the reversals and show that actively attentive tracking the stimulus massively delays the reversal time. These results suggest that attention can temporarily overrule lower level adaptation.

Adaptation, Physiological↗
PubMed2004

Serial change in airway lumen and wall thickness at thin-section CT in asymptomatic subjects.

PURPOSE: To retrospectively analyze serial changes in airway lumen and wall thickness (WT) at multi-detector row computed tomography (CT) in asymptomatic subjects. MATERIALS AND METHODS: Institutional review board did not require its approval or informed patient consent. Airway dimensions were analyzed in 52 patients (30 men and 22 women) without known cardiopulmonary disease. Contiguous 2-mm CT sections were obtained after reconstruction, extending from origin of right posterior basal segmental bronchi to posterior subsegmental bronchi. Following parameters were determined with semiautomatic image-processing program: luminal area (LA), total airway area (TA), short axis of lumen (LSD), and short axis of total airway (TSD). In airways in which adjacent vessel or branching of small bronchus abutted boundary of airway, extrapolated line was traced by one radiologist. Airway wall area (WA) was calculated as TA - LA, and WT was calculated as (TSD - LSD)/2. Relative WA (WA% = [WA/TA] . 100) and ratio of airway WT to total diameter (D) (WT/D = WT/TSD) were calculated. Linear regression analysis and Spearman rank correlation were used to evaluate relationship between airway parameters (LA, WA%, and WT/D ratio) and distance from origin of segmental bronchi. RESULTS: LA decreased as CT proceeded from hilum to periphery (r = -0.765, P < .001). In 308 (32.7%) of 943 bronchi, however, LA increased as CT proceeded from hilum to periphery. LA increased by 10% or more in 101 (10.7%) of 943 bronchi. Mean changes in WA% and WT/D ratio between two contiguous sections were 0.66 +/- 5.05 (standard deviation) and 0.003 +/- 0.024, respectively. WA% changed by more than 5% between two contiguous sections in 274 (29.0%) of 943 bronchi. WT/D ratio changed by more than 0.02 between two contiguous sections in 338 (35.8%) of 943 bronchi. CONCLUSION: Variation of airway lumen and WT is found in asymptomatic subjects without known cardiopulmonary disease.

Adult↗
PubMed2004

Gene transfer into mammalian cells by use of a nanosecond pulsed laser-induced stress wave.

Plasmid DNA has been successfully delivered to mammalian cells by applying a nanosecond pulsed laser-induced stress wave (LISW). Cells exposed to a LISW were selectively transfected with plasmids coding for green fluorescent protein. It was also shown that transient, mild cellular heating (approximately 43 degrees C) was effective in improving the transfection efficiency.

Animals↗
PubMed2004

In vivo targeted gene transfer in skin by the use of laser-induced stress waves.

BACKGROUND AND OBJECTIVES: Much interest has been shown in the use of lasers for nonviral targeted gene transfer, since the spatial characteristics of laser light are quite well defined. The aim of this study was to demonstrate in vivo gene transfer by the use of laser-induced stress waves (LISWs). STUDY DESIGN/MATERIALS AND METHODS: After reporter genes had been intradermally injected to rat skin in vivo, a laser target was placed on the gene-injected skin. LISWs were generated by the irradiation of an elastic laser target with 532-nm nanosecond laser pulses of a Q-switched Nd:YAG laser. RESULTS: Levels of luciferase activities for the skin exposed to LISWs were two orders of magnitude higher than those for the skin injected with naked DNA. Expressions of enhanced green fluorescent protein (EGFP) and beta-galactosidase were observed only in the area that was exposed to LISWs, and in addition, epidermal cells were selectively transfected. No major side effects were observed, and luciferase activity levels as high as 10(5) RLU per mg of protein were sustained even 5 days after gene transfer. CONCLUSION: Highly efficient and site-specific gene transfer can be achieved by applying a few pulses of nanosecond pulsed LISWs to rat skin in vivo.

Animals↗
PubMed2004

Action-specific extrapolation of target motion in human visual system.

Neuropsychological studies have indicated two distinct visual pathways in our brain, one dedicated to conscious perception and one to visuomotor control. Some psychophysical results support this idea with normal subjects, but they are still controversial. This study provides new psychophysical evidence for the dissociation by showing action-specific extrapolation of the visual target trajectory. When a moving target disappears, the perceived final position is liable to be shifted forward (representational momentum). In experiment 1, larger and more robust forward shifts were found when the position was directly touched without seeing the screen (open-loop pointing) than when the position was judged perceptually. The most striking dissociation was that fixation did not affect the forward shift in open-loop pointing while it almost abolished the shifts in perceptual judgements. In experiment 2, this action-specific result was found to disappear after a response delay of 4000 ms. Experiments 3 and 4 confirmed that the results were not affected by the external reference frames. The specific forward shifts found in open-loop pointing suggest that the visuomotor system compensates for the neural delays by extrapolating the target motion. The results, together with earlier findings, lead to a psychophysical double dissociation of the two visual pathways.

Adult↗
PubMed2003

EEG activity of aviators during imagery flight training.

OBJECTIVE: Imagery flight training (IFT) is widely used in aviation without neurophysiological evaluation. Electroencephalogram (EEG) during IFT was compared between experienced fighter pilots (FP) and novice pilots (NP). METHODS: Six FP and 9 NP performed imagery right bank, left bank, right roll, and left roll maneuvers. Each task was repeated 5 times in a random order. Instantaneous EEG power was calculated by the intertrial variance method. RESULTS: In FP, 3 waves of event-related desynchronization (ERD) were observed. The third ERD (ERD3) was observed at all the electrode positions except Fp1 which began 0.25 s before the beginning of IFT and reached its peak 0.25 s after the beginning of IFT. In NP, ERD was not related to the start of IFT. The difference in event-related EEG at the peak of ERD3 was not significant between FP and NP. However, the negative change to the peak of ERD3 was significantly larger in FP than in NP. CONCLUSIONS: It is speculated that ERD3 in FP may indicate the activation of cortical areas including visual- and motor-related areas involved in IFT. SIGNIFICANCE: It is speculated that the representation of IFT was programmed in visual- and motor-related cortical areas as an aviator's career advances.

Adult↗
PubMed2003

Vector analysis of electrogastrography during motion sickness.

Although the dominant frequency at 3 cpm of electrogastrography (EGG) is reported to shift to a higher frequency during motion sickness (MS), it is unclear whether the normal slow wave (NSW) disappears or not. The authors investigated changes in NSW using vector analysis of EGG. Fourteen subjects were exposed to a Coriolis stimulation to evoke MS. EGG was recorded from two sets of bipolar leads, placed perpendicular to each other representing x and y axes. Trajectories for each frequency were drawn on the x-y plane. The amplitude and phase difference at NSW were compared before, during, and after the stimulus for each subject. In those with a change in phase difference, changes in NSW and tachygastria were negatively correlated (P = -0.048), whereas in those without a change, they were not correlated. This indicated two different kinds of tachygastria due to MS: tachygastria with and without a change in NSW.

Adult↗
PubMed2003

Proposal of a model for medical records for international disaster relief operations.

The triage of a large number of victims in an international disaster relief operation is very important. To ensure the correct way of registration of patients and effective triage and treatment, useful medical records are necessary. The authors proposed a model for medical records (Shinchi's Medical Record (SMR)) for international disaster relief operations for medical teams from our experience of the Honduras Disaster Relief Operation in November 1998. Our medical unit, which was part of the Japan Self-Defense Forces International Disaster Relief Operation, was confronted with many patients who needed immediate medical care. SMR was developed using only one sheet of paper including the medical record, laboratory data sheet, and prescribed drug sheet. SMR also registers urgency classes and the primary diagnosis. SMR is simple, inexpensive, and easy to prepare for many patients.

Disasters↗