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Biomedical subjects

Kenji Yasuda

Publications and source records attributed to Kenji Yasuda.

34 records · Page 2Linked to original sources
PubMed2004

Stepwise pattern modification of neuronal network in photo-thermally-etched agarose architecture on multi-electrode array chip for individual-cell-based electrophysiological measurement.

We have developed a procedure for stepwise topographical control of network patterns and neurite connection directions between adjacent living neurons using an individual-cell-based on-chip multi-electrode array (MEA) cell cultivation system with an agarose microchamber (AMC) array. This procedure enables flexible and precise control of the cell positions and easy and flexible control of the pattern modification of connections between the cells in AMCs through stepwise photo-thermal etching in which a portion of the agarose layer on the chip is melted with a 1480 nm infrared laser beam even during cultivation. With adequate laser power and this stepwise procedure, we can fabricate narrow micrometer-order grooves (microchannels) during cultivation in a stepwise manner. Using this procedure, we controlled the direction of elongation of axons and dendrites selectively and confirmed the direction by immunostaining. We also demonstrated electrophysiological one-way transmission of signals among aligned hippocampal neurons in which the directions of the neurite connections were controlled using this stepwise photo-thermal etching procedure. These results demonstrate the potential of full direction control of neurite connections between neurons using stepwise photo-thermal etching to form microchannels one by one in an on-chip AMC/MEA cell cultivation system. We can thus better understand the meaning of neuronal network patterns and connection directions.

Animals↗
PubMed2004

Biotechnology approach to determination of genetic and epigenetic control in cells.

A series of studies aimed at developing methods and systems for analyzing epigenetic information in cells are presented. The role of the epigenetic information of cells, which is complementary to their genetic information, was inferred by comparing the predictions of genetic information with the cell behaviour observed under conditions chosen to reveal adaptation processes and community effects. Analysis of epigenetic information was developed starting from the twin complementary viewpoints of cells regulation as an 'algebraic' system (emphasis on the temporal aspect) and as a 'geometric' system (emphasis on the spatial aspect). The knowlege acquired from this study will lead to the use of cells for fully controlled practical applications like cell-based drug screening and the regeneration of organs.

Journal Article↗
PubMed2004

A novel method of cultivating cardiac myocytes in agarose microchamber chips for studying cell synchronization.

We have developed a new method that enables agar microstructures to be used to cultivate cardiac myocyte cells in a manner that allows their connection patterns to be controlled. Non-contact three-dimensional photo-thermal etching with a 1064-nm infrared focused laser beam was used to form the shapes of agar microstructures. This wavelength was selected as it is not absorbed by water or agar. Identical rat cardiac myocytes were cultured in adjacent microstructures connected by microchannels and the interactions of asynchronous beating cardiac myocyte cells observed. Two isolated and independently beating cardiac myocytes were shown to form contacts through the narrow microchannels and by 90 minutes had synchronized their oscillations. This occurred by one of the two cells stopping their oscillation and following the pattern of the other cell. In contrast, when two sets of synchronized beating cells came into contact, those two sets synchronized without any observable interruptions to their rhythms. The results indicate that the synchronization process of cardiac myocytes may be dependent on the community size and network pattern of these cells.

Journal Article↗
PubMed2004

Modification of a neuronal network direction using stepwise photo-thermal etching of an agarose architecture.

Control over spatial distribution of individual neurons and the pattern of neural network provides an important tool for studying information processing pathways during neural network formation. Moreover, the knowledge of the direction of synaptic connections between cells in each neural network can provide detailed information on the relationship between the forward and feedback signaling. We have developed a method for topographical control of the direction of synaptic connections within a living neuronal network using a new type of individual-cell-based on-chip cell-cultivation system with an agarose microchamber array (AMCA). The advantages of this system include the possibility to control positions and number of cultured cells as well as flexible control of the direction of elongation of axons through stepwise melting of narrow grooves. Such micrometer-order microchannels are obtained by photo-thermal etching of agarose where a portion of the gel is melted with a 1064-nm infrared laser beam. Using this system, we created neural network from individual Rat hippocampal cells. We were able to control elongation of individual axons during cultivation (from cells contained within the AMCA) by non-destructive stepwise photo-thermal etching. We have demonstrated the potential of our on-chip AMCA cell cultivation system for the controlled development of individual cell-based neural networks.

Journal Article↗
PubMed2004

Non-destructive on-chip cell sorting system with real-time microscopic image processing.

Studying cell functions for cellomics studies often requires the use of purified individual cells from mixtures of various kinds of cells. We have developed a new non-destructive on-chip cell sorting system for single cell based cultivation, by exploiting the advantage of microfluidics and electrostatic force. The system consists of the following two parts: a cell sorting chip made of poly-dimethylsiloxane (PDMS) on a 0.2-mm-thick glass slide, and an image analysis system with a phase-contrast/fluorescence microscope. The unique features of our system include (i) identification of a target from sample cells is achieved by comparison of the 0.2-microm-resolution phase-contrast and fluorescence images of cells in the microchannel every 1/30 s; (ii) non-destructive sorting of target cells in a laminar flow by application of electrostatic repulsion force for removing unrequited cells from the one laminar flow to the other; (iii) the use of agar gel for electrodes in order to minimize the effect on cells by electrochemical reactions of electrodes, and (iv) pre-filter, which was fabricated within the channel for removal of dust contained in a sample solution from tissue extracts. The sorting chip is capable of continuous operation and we have purified more than ten thousand cells for cultivation without damaging them. Our design has proved to be very efficient and suitable for the routine use in cell purification experiments.

Journal Article↗
PubMed2004

Simultaneous measurement of sensor-protein dynamics and motility of a single cell by on-chip microcultivation system.

Measurement of the correlation between sensor-protein expression, motility and environmental change is important for understanding the adaptation process of cells during their change of generation. We have developed a novel assay exploiting the on-chip cultivation system, which enabled us to observe the change of the localization of expressed sensor-protein and the motility for generations. Localization of the aspartate sensitive sensor protein at two poles in Escherichia coli decreased quickly after the aspartate was added into the cultivation medium. However, it took more than three generations for recovering the localization after the removal of aspartate from the medium. Moreover, the tumbling frequency was strongly related to the localization of the sensor protein in a cell. The results indicate that the change of the spatial localization of sensor protein, which was inherited for more than three generations, may contribute to cells, motility as the inheritable information.

Journal Article↗
PubMed2004

Mixed feed containing dextran improves milk production of holstein dairy cows.

Total 37 Holstein daily cows (body weight: 631.76 +/- 18.45 kg, age: 5.47 +/- 1.94 years, parturition: 3.71 +/- 1.76 times) which became pregnant and gave birth to calves in the same season and lactated continuously were selected for this study. They were randomly divided into two groups: Group A-control, Group B-fed with 30 g/head/day of mixed feed containing supplemental dextran for one year from October 2001. After supplementation of the mixed feed, milk yields and components (fat, protein and solid non-fat) of Group B were compared with those of Group A in the 8th, 10th and 11th months (May, July and August of 2002). Milk yields of Group B were greater than the yields of Group A. In particular, there was a significant difference (p<0.001) between these groups in the July and August values. Milk components of Group B slightly differed from those of Group A before the supplementation, but after the supplementation, concentrations and total amounts of fat, protein and solid non-fat significantly increased more in Group B than in Group A. Thus mixed feed containing dextran can increase the milk production of Holstein dairy cows in the hot season.

Animal Feed↗
PubMed2003

Two-dimensional network formation of cardiac myocytes in agar microculture chip with 1480 nm infrared laser photo-thermal etching.

We have developed a new method that enables agar microstructures to be used to cultivate cells and that allows cell network patterns to be controlled. The method makes use of non-contact three-dimensional photo-thermal etching with a 1480 nm infrared focused laser beam, which is strongly absorbed by water and agar gel, to form the shapes of agar microstructures. It allows microstructures to be easily formed in an agar layer within a few minutes, with cell-culture holes formed by the spot heating of a 100 mW laser and tunnels by the tracing of a 100 microm s(-1), 40 mW laser. We cultivated rat cardiac myocytes in adjacent microstructures and observed synchronized beating in them 90 min after they had made physical contact. Our results indicate that the system can make and use microstructures for cell-network cultivation in a minimal amount of time without any expensive microfabrication facilities or complicated procedures.

Agar↗
PubMed2003

Role of timer and sizer in regulation of Chlamydomonas cell cycle.

To estimate the role that time and size had in controlling the Chlamydomonas cell cycle, we used a new on-chip single-cell microcultivation system, which involved the direct observation of single cells captured in microchambers made on a thin glass slide. The dependence of the pattern of energy supply for cells on its cell cycle was examined through a series of different intensities of continuous illumination in a minimal medium, and we found that cell division occurred when cells reached the critical size, which was 2.2 times larger than that of the newly created cells. When illumination stopped before cells reached the critical size, even though growth had stopped, they continued dividing during the delay time, which was shorter when cells were larger. With re-illumination after darkness, cells began to grow again and the timing of cell division was again controlled by the critical size. This indicates that the co-existence of two cell cycle regulation mechanisms and the sizer mechanism had a stronger influence than the timer.

Animals↗
PubMed2003

On-chip single-cell microcultivation assay for monitoring environmental effects on isolated cells.

We have developed a on-chip single-cell microcultivation assay as a means of observing the adaptation process of single bacterial cells during nutrient concentration changes. This assay enables the direct observation of single cells captured in microchambers made on thin glass slides and having semipermeable membrane lids, in which cells were kept isolated with optical tweezers. After changing a medium of 0.2% (w/v) glucose concentration to make it nutrient-free 0.9% NaCl medium, the growth of all cells inserted into the medium stopped within 20 min, irrespective of their cell cycles. When a nutrient-rich medium was restored, the cells started to grow again, even after the medium had remained nutrient-free for 42 h. The results indicate that the cell's growth and division are directly related to their nutrient condition. The growth curve also indicates that the cells keep their memory of what their growth and division had been before they stopped growing.

Adaptation, Physiological↗
PubMed2002

An agar-microchamber cell-cultivation system: flexible change of microchamber shapes during cultivation by photo-thermal etching.

A new type of cell-cultivation system based on photo-thermal etching has been developed for the on-chip cultivation of living cells using an agarose microchamber array. The method can be used to flexibly change the chamber structure by photo-thermal etching, even during the cultivation of cells, depending upon the progress in cell growth. We used an infrared (1064 nm) focused laser beam as a heat source to melt and remove agar gel at the heated spot on a thin chromium layer. The melting of the agar occurred just near the chromium thin layer, and the size of the photo-thermally etched area depended almost linearly on the power of the irradiated laser beam from 2 microm to 50 microm. Thus by using photo-thermal etching with adequate laser power we could easily fabricate narrow tunnel-shaped channels between the microchambers at the bottom of the agar-layer even during cell cultivation. After 48 h of cultivation of nerve cells, the nerve cells in two adjacent chambers made fiber connections through the fabricated narrow tunnel-shaped channels. These results suggest that photo-thermal etching occurred only in the area where an absorbing material was used, which means that it is possible to photo-thermally etch lines without damaging the cells in the microchambers. The results also suggest that the agar-microchamber cell cultivation system in combination with photo-thermal etching can potentially be used for the next stage of single cell cultivation including the real-time control of the interaction of cells during cell cultivation.

Journal Article↗
PubMed2002

Reconstruction of a large duodenal defect created by resection of a duodenal tubulovillous adenoma using a double-tract anastomosis to a retrocolic roux-en-y loop: report of a case.

Adenomas arising in the duodenum are uncommon. The surgical approach to adenoma of the duodenum remains controversial. We herein report the successful closure of a large defect after a partial duodenectomy for an adenoma. A 60-year-old man developed duodenal adenoma. An upper gastrointestinal roentgenographic series and endoscopy revealed a 2.5-cm tumor located adjacent to the duodenal papilla. The tumor was too large to be removed endoscopically, and therefore it was resected en bloc by a partial duodenectomy. Histology confirmed the diagnosis of benign tubulovillous adenoma. The large duodenal defect created by resection of the tumor was closed with double-tract anastomosis to a retrocolic Roux-en-Y loop. Large duodenal defects represent difficult surgical problems. Closure by direct anastomosis to a Roux-en-Y loop side-to-side is thus considered to be the procedure of choice.

Adenoma, Villous↗
PubMedDate not supplied

On-chip single-cell-based microcultivation method for analysis of genetic information and epigenetic correlation of cells.

We have developed an on-chip single-cell based microcultivation method for analyzing the variability of genetic information stored in single cells and their epigenetic correlations. The method uses four systems: an on-chip cell sorter for purifying the cells in a non-destructive manner; an on-chip single-cell cultivation chip for isolating single cells; an on-chip agarose microchamber system for constructive cell-cell network formation during cultivation; and an on-chip single-cell-based expression analysis system. Using these systems, we could measure the variability of prokaryotic cells and eukaryotic cells having the same DNA and found that, although prokaryotic cells have a large variability in their interdivision times, sister eukaryotic cells having the same DNA synchronized well. We also measured the dynamics of synchronization of beating cardiac myocytes and found that two isolated cells synchronize by one cell following the other after a short pause in beating. These results showed the potential of the on-chip microcultivation method's constructive approach to analyzing cell systems.

Animals↗