Biomedical subjects

Yoko Yamaguchi

Publications and source records attributed to Yoko Yamaguchi.

At least 19 recordsLinked to original sources

PubMed2006

[Nanotechnology for therapy of type 2 diabetes].

All-trans Retinoic Acid (atRA), is known as a member of retinoid, and the atRA nano-particle with coated by CaCO3 (nanoegg -atRA), was recently developed as a new drug delivery system (DDS). This nanoparticles stimulated insulin secretion from islets in a glucose-dependent manner at streptozotocin (STZ)-induced diabetes. The stains on pancreas of Wistar rat at STZ induced diabetes, which was subcutaneous administered nanoegg -atRA 6 mg/head/week for 141 days, showed not only the expression of PDX-1 but also the presence of beta cell in islet of Langerhans. Furthermore, the increase of insulin concentration in plasma was also observed. Our data indicate that nanoegg -atRA might contribute to the regeneration of beta cells in vivo, and provide useful information for future therapy of diabetes mellitus.

Animals↗

PubMed2005

Dopamine D2 receptor plays a role in memory function: implications of dopamine-acetylcholine interaction in the ventral hippocampus.

RATIONALE: The role of the hippocampal dopaminergic system in mnemonic function has not been clarified yet. OBJECTIVE: We previously reported that the dopamine D2 receptor (D2R) is involved in the regulation of acethylcholin (ACh) release in the hippocampus. In this study, we further investigated ACh-dopamine (DA) interaction in the hippocampus and its involvement in mnemonic function. METHODS: For experiment 1, rats fed with Cholin (Ch)-deficient chow were used. We examined the effects of D2R antagonist, raclopride, on cognitive performance using a passive avoidance task. We further carried out in vivo microdialysis to assess the effect of infusion of D2R agonist, quinpirole, into the ventral hippocampus on its capacity to release ACh. For experiment 2, rats fed with normal chow were used. The performance of a radial arm maze task was assessed to examine the effects of hippocampal injection of D2R agonist, quinpirole, on memory impairment induced by scopolamine, a muscarinic ACh antagonist. RESULTS: In experiment 1, rats fed with Ch-deficient chow showed impaired performances indicated by prolonged latency on retention trials of a passive avoidance task following the hippocampal injection of D2R antagonist, and showed reduced capacity to release ACh following the injection of D2R agonist compared with rats fed with normal chow. In experiment 2, memory impairment induced by the intraperitoneal injection of scopolamine was ameliorated by the injection of D2R agonist into the ventral hippocampus. CONCLUSION: These results indicate the possible involvement of hippocampal ACh-DA interaction in mnemonic processing.

Acetylcholine↗

PubMed2005

Conserving total synaptic weight ensures one-trial sequence learning of place fields in the hippocampus.

The hippocampus plays a critical role in the rapid acquisition of information from a novel experience. Recent theoretical studies on the rat hippocampus have shown the possibility of behavioral sequence learning in a single traversal experience by theta phase coding. Specifically, previous work using computer simulations demonstrated that the extent of overlap among individual events of sequence and rat running velocity should be quantitatively incorporated into the learning rule to ensure one-trial sequence learning. These extents of overlap- and running velocity-dependent properties in the learning rule are called the input-dependent regulation of the learning rule. However, the biological meaning of such learning properties remains poorly understood. In this study, we quantitatively derive these learning properties with mathematical analyses. We further find that the input-dependent regulation of the learning rule allows maintenance of total synaptic weight over a given neuron during one-trial learning. Our results predict that a homeostatic plasticity mechanism should exist for conserving total synaptic weight on a rapid timescale.

Action Potentials↗

PubMed2005

Successful treatment of photo-damaged skin of nano-scale atRA particles using a novel transdermal delivery.

We show a novel drug delivery system (DDS) for improved all-trans retinoic acid (atRA) therapy for external treatments of photo-damaged skin. We prepared inorganic-coated atRA nanoparticles, in turn an egg-like structure in nano-scale (Nano-atRA), using boundary-organized reaction droplets. The interfacial properties of organic architectures, in atRA micelles, were used to template the nucleation of inorganic minerals. As a result, irritation and inflammation associated with atRA therapy were substantially reduced due to the complete encapsulation of the carboxylic function. Both irritative symptoms and physicochemical instability of the atRA micelle were improved. Since Nano-atRA which is prepared following to this new DDS system developmentally improved the permeability to the stratum corneum, the remarkable pharmacological effects were resulted in comparison with atRA as such as follows: (1) thicker epidermis than classical atRA treatment and (2) the overexpression of mRNA for heparin-binding epidermal growth factor (HB-EGF) as the provocation epidermal hyperplasia. Furthermore, we found a surprising boost in production of hyaluronan (HA) among the intercellular spaces of the basal and spinous cell layers in epidermis. Nano-atRA technology for atRA therapy could not only efficiently regulate keratinocyte cell proliferation and differentiation, but also markedly produce the additional benefit. Severely injured human skin by chronic ultraviolet irradiation will completely repair due to the accelerated turnover of skin tissue, which is induced by Nano-atRA.

Administration, Cutaneous↗

PubMed2005

Lecithinized brain-derived neurotrophic factor promotes the differentiation of embryonic stem cells in vitro and in vivo.

The addition of lecithin molecules to brain-derived neurotrophic factor (BDNF) has been reported to markedly enhance its pharmacological effect in vivo. In the current study, we show that lecithinized BDNF (PC-BDNF) has a higher affinity than BDNF for neural precursor cells. Although BDNF only slightly increased the expression of the genes for Mash-1, p35, 68 kDa neurofilament, and TrkB receptor, PC-BDNF caused a significant increase in their expression. PC-BDNF also increased the level of neurofilament protein and dramatically increased TrkB mRNA gene expression, which was followed by a sustained activation of the p42/p44 extracellular-regulated kinases. Finally, transplantation of PC-BDNF-treated cells was more effective than BDNF-treated cells at improving impaired motor function caused by spinal cord injury. These findings showed that PC-BDNF has a better potential than BDNF for promoting neural differentiation, partly due to a higher cellular affinity. Furthermore, PC-BDNF-treated cells could be useful for transplantation therapy for central nervous system injuries.

Animals↗

PubMed2005

Brain-derived neurotrophic factor bound with lecithin derivative showed a markedly enhanced pharmacological potency due to its potent cell membrane affinity followed by prolonged MAPK activation.

We synthesized lecithinized brain-derived neurotrophic factor (lecithinized-BDNF), in which an average of three molecules of a lecithin derivative were bound to recombinant human BDNF. We evaluated its pharmacological activity in C57BL/KsJ-db/db mice, and assessed its targetability and affinity for the nervous system. Subcutaneously administered lecithinized-BDNF markedly reduced the plasma glucose level, food intake, and body weight in C57BL/KsJ-db/db diabetic mice. Its potency was more than 20 times greater than that of unmodified BDNF. We then studied the mechanism for the markedly enhanced pharmacological activity. In vitro cell growth activity of lecithinized-BDNF using the MTT assay was lower than unmodified BDNF, probably due to steric hindrance of the lecithin moieties. While the plasma BDNF level after subcutaneous administration of lecithinized-BDNF was not higher compared with unmodified BDNF. However, higher amount of lecithinized-BDNF accumulated in the spinal cord was observed. Lastly, we found that in vitro binding capacity of lecithinized-BDNF for PC-pAB1 neural cells was much higher than unmodified BDNF. Moreover, lecithinized-BDNF bound to PC-pAB1 cells did not exchange with an excessive amount of unmodified BDNF or an excess of lecithinized-BDNF. PC-pAB1 cells treated with lecithinized-BDNF showed sustained mitogen-activated protein kinase (MAPK, ERK1/2) activation. These data would indicate that the high affinity of lecithinized-BDNF for the target cells, followed by prolonged MAPK activation, would play an important role in its potent pharmacological activity.

Animals↗

PubMed2005

Crystallization and preliminary crystallographic analysis of bacterial fructosyl amino acid oxidase.

Bacterial fructosyl amino acid oxidase [fructosyl alpha-L-amino acid:oxygen oxidoreductase (defructosylating); EC 1.5.3] has been crystallized by the hanging-drop vapour-diffusion technique using sodium citrate as the precipitant. Two types of crystals were grown: one type are rhombic prismatic yellow crystals that belong to space group C2 with unit-cell parameters a = 101.08, b = 63.36, c = 83.07 A, beta = 108.80 degrees and diffract to at least 1.8 A resolution, while the second type are rod-like crystals that belong to space group P4(1)22 or P4(3)22 with unit-cell parameters a = b = 119.09, c = 164.66 A and diffract to 2.7 A resolution.

Amino Acid Oxidoreductases↗

PubMed2005

Online formation of a hierarchical cognitive map for object-place association by theta phase coding.

Object-place associative memory, the storage of object and place conjunctions based on a one-time experience, is hippocampal-dependent in humans. Theta phase precession, a type of neural dynamics observed in the rat hippocampus, has recently been suggested to serve a role in instantaneous memory formation based on a one-time experience, while its functional role in associating distinct types of information (object and place information) is unclear. In this study, we hypothesize that theta phase encoding with theta phase precession contributes to the storage of object-place associations. To examine this hypothesis, we propose a neural network model of the corticohippocampal system, including central-peripheral visual pathways and theta phase coding in the hippocampus. Memory storage computer experiments demonstrate that the hippocampal network successfully stores the object-place associations of a one-time experience. Interestingly, it is also found that a random visual input sequence results in a robust formation of asymmetric connections between objects and scenes instantaneously after a single trial. Furthermore, it is found that scene-object connections and scene-scene connections form a hierarchical network representing the spatial alignment of scenes and objects in the environment. Our findings indicate that the theta phase coding, as observed in the rat hippocampus, can facilitate the online memory storage of complex environments in humans as a hierarchical cognitive map.

Action Potentials↗

PubMed2005

Long-range EEG phase synchronization during an arithmetic task indexes a coherent cortical network simultaneously measured by fMRI.

An open question lies in whether or not distributed activities in the distant brain regions are integrated into a coherent ensemble for cognitive information processing. Long-range phase synchronization is often observed by scalp EEG measurements during cognitive tasks and is considered to provide a possible neural principle for the functional integration of distributed neural activities. Synchronization could be reflected at the neuron firing level or at the local field potential and could appear in the scalp EEG under certain conditions on neural spatial and temporal coherence. To examine if phase synchronization is concerned with the integration of distant regions, we proposed a method to extract brain activities associated with task-dependent phase synchronization by combining simultaneous fMRI and EEG. By applying this method in a mental arithmetic task, we found a dominant task-dependent increase of phase synchronization around 14 Hz (in beta frequency) across bilateral parietal sites that were associated with both negative and positive BOLD responses. Functional connectivity analyses of these regions demonstrated that an increase in hemispheric beta synchronization was associated with a linking between the cross-hemispheric regions (left angular gyrus and right superior parietal gyrus) and also among the anterior-posterior regions (right dorsolateral prefrontal cortex, putamen, and right superior temporal gyrus). These findings indicate that the positive BOLD regions (dorsolateral prefrontal cortex and superior parietal lobule) are linked with other negative BOLD regions. We also discussed the possible importance of beta synchronization in the formation of a working memory network.

Adult↗

PubMed2005

Analysis of tetracycline antibiotics using HPLC with pulsed amperometric detection.

The analysis of tetracycline, oxytetracyline, chlortetracycline and doxycycline by high-performance liquid chromatography with pulsed amperometric detection using an anodized boron-doped diamond thin film (BDD) electrode is originally reported. The analyses were carried out using the mobile phase, phosphate buffer (0.01 M, pH 2.5)-acetonitrile (80:20; v/v), on a C18 column (250 x 4.6 mm i.d., 5 microm) at a flow rate of 1.0 mL/min. The optimal PAD waveform parameters at the anodized BDD were 1.5 V (versus Ag/AgCl) detection potential (E(det)) for 290 ms (200 ms delay time and 90 ms integration time), 2.0 V (versus Ag/AgCl) oxidation potential (E(oxd)) for 200 ms oxidation time (t(oxd)) and 0.4 V (versus Ag/AgCI) reduction potential (E(red)) for 200 ms reduction time (t(red)). The proposed method showed the simultaneous determination of tetracycline, oxytetracyline, chlortetracycline and doxycycline with a linear range of 0.1 - 100 microg/mL, detection limits of 0.05 - 0.1 microg/mL and recoveries of 70.8 - 96.0%. The application of this method to real samples was demonstrated and validated using a shrimp sample.

Animals↗

PubMed2005

Basic evaluation of cast joining for electroformed coping using multi-purpose alloys.

The purpose of this study was to evaluate the bonding interface and bonding strength of electroformed coping when cast joining was used with a multi-purpose alloy. The multi-purpose alloy was cast at a mold temperature of 700, 750 or 800 degrees C. A high noble alloy tab was also soldered onto an electroformed coping as a control. Sectioned surfaces of cast joining and soldered specimens were observed using a scanning electron microscope and analyzed using an electron probe micro analyzer. Shear bonding strength of specimens cast at 750 degrees C and that of soldered specimens were determined. The edge of the cast joining alloy was round, but this improved as temperature increased. Diffusion of elements from the cast joining alloy and electroformed coping was detected at the interface, which contributed to a significantly higher bonding strength in the cast joining specimen than in the soldered specimen. These results suggested that the cast joining could be potentially employed for electroformed copings.

Dental Abutments↗

PubMed2004

A long-range cortical network emerging with theta oscillation in a mental task.

Human scalp EEG has demonstrated that global coherence among distant areas increases during cognitive tasks, suggesting that oscillating neural activities work to generate global neuronal assemblies for cognitive functions. The theta oscillation in a frequency range of 4-8 Hz with large amplitudes which emerges during mental tasks around the frontal midline region is called fm theta. If theta oscillation concerns the global neuronal assemblies, fm theta should be associated with regional activities that depend on task conditions. In the present study, we examine the EEG-related brain activities by developing simultaneous EEG and fMRI during a mental calculation task. EEG-related negative BOLD was dominant over anterior medial regions, suggesting a major contribution of negative BOLD to fm theta. Negative and positive BOLD were found over distant regions. Functional connectivity analyses revealed that the connectivity varied remarkably according to mental conditions. In the rest condition, the connectivity was localized, whereas in the task condition, a long-range coherent network was formed by the anterior midline, posterior cingulate and right middle temporal cortices with linking between the right middle temporal and left lateral cortices during numerical processing. Further EEG analyses indicate that the long-range coherent network executing cognitive functions is coordinated in the time window of theta oscillations.

Action Potentials↗

PubMed2004

Optimum formulation for sustained-release insulin.

Our aim was to prepare an optimum formulation for a sustained-release preparation of insulin using biodegradable polymer composed of co-poly(D,L-lactic/glycolic) acids (PLGA)(L/G ratio: 50/50). Various kinds of PLGA microcapsules containing 3% insulin were administered subcutaneously (250 U/kg) as a single dose to rats with streptozotocin-induced diabetes, and plasma insulin levels were monitored. The following results were obtained. (1) Glycerin and water were suitable additives to prepare a reproducible injectable formulation. (2) Addition of zinc compounds was essential to diminish rapid insulin release and six-fold molar excess of ZnO to insulin was desirable. (3) The size of insulin particles showed the following order: human insulin > lyophilized human insulin > Zn-free human insulin. Zn-free insulin was similar to lyophilized insulin with respect to control of rapid release, so a smaller particle size was essential. (4) The size of the microcapsules also affected the release of insulin. With larger microcapsules (approximately 30 microm), there was gradual release and a significant second phase of insulin release, while smaller microcapsules did not allow sustained release. Some variation in microcapsule size contributed to more constant and sustained release. (5) Based on the insulin release profile in vivo, a suitable molecular weight for PLGA was around 6000. The biological activity of insulin extracted from the formulation was similar to that of normal insulin. These experiments allowed us to prepare a desirable sustained-release insulin formulation.

Animals↗

PubMed2004

Input-dependent learning rule for the memory of spatiotemporal sequences in hippocampal network with theta phase precession.

Theta phase precession in rat hippocampal place cells is hypothesized to contribute to memory encoding of running experience in the sense that it provides the ideal timing for synaptic plasticity and enables the asymmetric associative connections under the Hebbian learning rule with asymmetric time window (Yamaguchi 2003). When the sequence of place fields is considered as the episodic memory of running experience, a given spatial route should be accurately stored in spite of differing overlap extent among place fields and varying running velocity. Using a hippocampal network model with phase precession and the Hebbian learning rule with asymmetric time window, we investigate the memory encoding of place field sequences in a single traversal experience. Computer experiments show that place fields cannot be stored correctly until an input-dependent feature is introduced into the learning rule. These experiments further indicate that there exists an optimum value for the saturation level of synaptic plasticity and the speed of synaptic plasticity in the learning rule, which are correlated with, respectively, the overlap extent of place field sequence and the running velocity of animal during traversal. A comparison of these results with biological evidences shows good agreement and suggests that behavior-dependent regulation of the learning rule is necessary for memory encoding.

Computer Simulation↗

PubMed2004

Decomposing EEG data into space-time-frequency components using Parallel Factor Analysis.

Finding the means to efficiently summarize electroencephalographic data has been a long-standing problem in electrophysiology. A popular approach is identification of component modes on the basis of the time-varying spectrum of multichannel EEG recordings--in other words, a space/frequency/time atomic decomposition of the time-varying EEG spectrum. Previous work has been limited to only two of these dimensions. Principal Component Analysis (PCA) and Independent Component Analysis (ICA) have been used to create space/time decompositions; suffering an inherent lack of uniqueness that is overcome only by imposing constraints of orthogonality or independence of atoms. Conventional frequency/time decompositions ignore the spatial aspects of the EEG. Framing of the data being as a three-way array indexed by channel, frequency, and time allows the application of a unique decomposition that is known as Parallel Factor Analysis (PARAFAC). Each atom is the tri-linear decomposition into a spatial, spectral, and temporal signature. We applied this decomposition to the EEG recordings of five subjects during the resting state and during mental arithmetic. Common to all subjects were two atoms with spectral signatures whose peaks were in the theta and alpha range. These signatures were modulated by physiological state, increasing during the resting stage for alpha and during mental arithmetic for theta. Furthermore, we describe a new method (Source Spectra Imaging or SSI) to estimate the location of electric current sources from the EEG spectrum. The topography of the theta atom is frontal and the maximum of the corresponding SSI solution is in the anterior frontal cortex. The topography of the alpha atom is occipital with maximum of the SSI solution in the visual cortex. We show that the proposed decomposition can be used to search for activity with a given spectral and topographic profile in new recordings, and that the method may be useful for artifact recognition and removal.

Alpha Rhythm↗

PubMed2004

Frequency measuring system using mirror gap stabilized Fabry-Perot interferometer.

The mirror gap of a Fabry-Perot interferometer was stabilized with two laser diodes; one locked to the line frequency 385,243,555.14445 MHz of the F=3<--1 in 5D(3/2)<--5S(1/2) (87Rb) and the other to the 385,284,566.3663 MHz of the F=4<--2 in 5D(5/2)<--5S(1/2) (87Rb) [Opt. Commun. 102 (1993) 432]. The length of the mirror gap was adjusted to generate the zero-cross points simultaneously at both of the two line positions. The fringe signals obtained from an interferometer thus stabilized can be used as frequency markers having accuracies of the order of 10(10) depending on the finesse of the interferometer used. Based on measurement using Cs D1 hyperfine lines reported by Udem et al. [Phys. Rev. Lett. 82 (1999) 3568], the uncertainty of markers in the region 50 THz apart from the reference lines is +/- 5 MHz.

Data Interpretation, Statistical↗

PubMed2004

Novel heat shock protein HspQ stimulates the degradation of mutant DnaA protein in Escherichia coli.

Escherichia coli DnaA protein initiates chromosomal replication and is an important regulatory target during the replication cycle. In this study, a suppressor mutation isolated by transposon mutagenesis was found to allow growth of the temperature-sensitive dnaA508 and dnaA167 mutants at 40 degrees C. The suppressor consists of a transposon insertion in a previously annotated ORF, here termed hspQ, a novel heat shock gene whose promoter is recognized by the major heat shock sigma factor sigma32. Expression of hspQ on a pBR322 derivative inhibits growth of the dnaA508 and dnaA167 mutants at 30 degrees C, whereas growth of dnaA46 and other dnaA mutants is insensitive to changes in the level of hspQ. Cellular DnaA508 protein is degraded rapidly at elevated temperature, but hspQ disruption impedes this process. In contrast, DnaA46 protein is rapidly degraded in an hspQ-independent manner. Gel-filtration and chemical cross-linking experiments suggest that HspQ forms a stable homodimer in solution and can form homomultimers consisting of about four monomers. Heat-shock induced proteases such as Clp contain homomultimers of subunit proteins. We propose that HspQ is a new factor involved in the quality control of proteins and that it functions by excluding denatured proteins.

Alleles↗

PubMed2004

Synchronization of neural oscillations as a possible mechanism underlying episodic memory: a study of theta rhythm in the hippocampus.

Rat hippocampal cells exhibit characteristic phase-dependent firings when oscillation in frequency range around 8Hz is present. Based on the hypothesis that theta phase coding is generated by synchronization of neural activities, an autoassociative network model of the hippocampus and the entorhinal cortex was analyzed to explore mechanisms underlying episodic memory. Phase coding in theta rhythm enables instantaneous acquisition of experienced events including temporal and spatial contents. Further comparison with electrophysiological data from both rodents and primates suggests a possible role of theta oscillations in memory encoding and online processing of episodic events.

Action Potentials↗