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Masataka Watanabe

Publications and source records attributed to Masataka Watanabe.

44 records · Page 3Linked to original sources
PubMed2002

Release of neurotransmitters in the monkey frontal cortex is related to level of attention.

Attention is reported to be maintained by monoamines, acetylcholine and amino acids systems. Changes in the releases of these neurotransmitters during the three stages comprising quiet wake (QW) and two arousal states (AW), which are activated from different sources, were investigated. Norepinephrine releases during AW were significantly higher than that during QW. Conversely, the levels of acetylcholine and serotonin that were released did not change significantly among these three stages. The interesting observation was the dissociation of the increase between glutamate and dopamine releases in the two AW states. The results indicate that attention level is related to the amount of norepinephrine release, and that attention quality is related to the interaction between dopamine and glutamate releases.

Animals↗
PubMed2002

Succession of bacterial community structure along the Changjiang River determined by denaturing gradient gel electrophoresis and clone library analysis.

Bacterial community structure along the Changjiang River (which is more than 2,500 km long) was studied by using denaturing gradient gel electrophoresis (DGGE) and clone library analysis of PCR-amplified 16S ribosomal DNA (rDNA) with universal bacterial primer sets. DGGE profiles and principal-component analysis (PCA) demonstrated that the bacterial community gradually changed from upstream to downstream in both 1998 and 1999. Bacterial diversity, as determined by the Shannon index (H'), gradually decreased from upstream to downstream. The PCA plots revealed that the differences in the bacterial communities among riverine stations were not appreciable compared with the differences in two adjacent lakes, Lake Dongting and Lake Poyang. The relative stability of the bacterial communities at the riverine stations was probably due to the buffering action of the large amount of water flowing down the river. Clone library analysis of 16S rDNA revealed that the dominant bacterial groups changed from beta-proteobacteria and the Cytophaga-Flexibacter-Bacteroides group upstream to high-G+C-content gram-positive bacteria downstream and also that the bacterial community structure differed among the stations in the river and the lakes. The results obtained in this study should provide a reference for future changes caused by construction of the Three Gorges Dam.

Bacteria↗
PubMed1997

Chaos in Neural Networks Composed of Coincidence Detector Neurons.

Chaotic behaviour is observed in neural network models composed of coincidence detector neurons. We use a continuous time and deterministic point process model with uniform synaptic strength and random delay, and apply periodical external inputs to a few neurons in the network. We show that the network dynamics becomes chaotic when the length of "chain firing" starting from an external input becomes practically infinite. Copyright 1997 Elsevier Science Ltd.

Journal Article↗
PubMedDate not supplied

Spatial localization of synapses required for supralinear summation of action potentials and EPSPs.

Although the supralinear summation of synchronizing excitatory postsynaptic potentials (EPSPs) and backpropagating action potentials (APs) is important for spike-timing-dependent synaptic plasticity (STDP), the spatial conditions of the amplification in the divergent dendritic structure have yet to be analyzed. In the present study, we simulated the coincidence of APs with EPSPs at randomly determined synaptic sites of a morphologically reconstructed hippocampal CA1 pyramidal model neuron and clarified the spatial condition of the amplifying synapses. In the case of uniform conductance inputs, the amplifying synapses were localized in the middle apical dendrites and distal basal dendrites with small diameters, and the ratio of synapses was unexpectedly small: 8-16% in both apical and basal dendrites. This was because the appearance of strong amplification requires the coincidence of both APs of 3-30 mV and EPSPs of over 6 mV, both of which depend on the dendritic location of synaptic sites. We found that the localization of amplifying synapses depends on A-type K+ channel distribution because backpropagating APs depend on the A-type K+ channel distribution, and that the localizations of amplifying synapses were similar within a range of physiological synaptic conductances. We also quantified the spread of membrane amplification in dendrites, indicating that the neighboring synapses can also show the amplification. These findings allowed us to computationally illustrate the spatial localization of synapses for supralinear summation of APs and EPSPs within thin dendritic branches where patch clamp experiments cannot be easily conducted.

Action Potentials↗
PubMedDate not supplied

Absolute stereochemistry of chiral C60 fullerene bis-adducts.

To determine the absolute configuration of chiral fullerene bis-adducts, we have studied the double Bingel reaction of C60 with chiral tether (2S,3S)-(-)-9 derived from (R,R)-(+)-tartaric acid, and have succeeded in isolating two possible chiral bis-adducts 10a (5%) and 10b (2%) in addition to the Cs-symmetrically added derivative 10c (40%). The CD spectra of chiral bis-adducts [CD(+)281]-10a and [CD(-)281]-10b show very intense Cotton effects, which are almost of mirror image, indicating that their chiral C60 pi-electron systems are enantiomeric each other. The 1H and 13C NMR spectra of 10a and 10b indicate that they have C2-symmetrical structures, and the vicinal coupling constants between two equivalent protons H-2 and H-2' were determined as 1.2 Hz for 10a and 1.8 Hz for 10b, respectively by the 13C satellite band method. From the conformational analyses, the absolute configurations of these chiral C60 fullerene bis-adducts were unambiguously determined as [CD(+)281]-(S,S,fC)-10a and [CD(-)281]-(S,S,fA)-10b, respectively.

Journal Article↗
PubMedDate not supplied

Comparison of CD spectra of (2-methylphenyl)- and (2,6-dimethylphenyl)-phenylmethanols leads to erroneous absolute configurations.

Enantiopure (2,6-dimethylphenyl)phenylmethanol (+)-(3) and analog (+)-(4) were prepared and their CD spectra were found opposite to that of (2-methylphenyl)phenylmethanol (R)-(-)-(2), the absolute configuration of which was previously established by X-ray crystallography. Therefore the S absolute configuration was once assigned to (+)-3 and (+)-4. After that we have succeeded in the X-ray analyses of chiral dichlorophthalate esters of (+)-3 and (+)4, which clearly indicated R absolute configuration. It is thus evident that comparison of the CD spectra of alcohols 2, 3, and 4 leads to erroneous absolute configurations.

Journal Article↗
PubMedDate not supplied

Crystalline state conformation of 2-methoxy-2-(1-naphthyl)propionic acid ester.

The enantioresolution method using (S)-(+)-2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid 1) was applied to 1,2,3,4-tetrahydro-4-phenanthrenol (4). Racemic alcohol (+/-)-4 was esterified with (S)-(+)-1, and a diastereomeric mixture of esters formed was separated by HPLC on silica gel giving the first-eluted ester 5a and the second-eluted one 5b. Ester 5a was reduced with LiAlH4 yielding enantiopure alcohol (+)-4. A single crystal of ester 5a was subjected to X-ray crystallography to determine its absolute configuration as (S,S), and therefore to assign the S absolute configuration to (+)-4. The most striking finding in the X-ray analysis is that the methoxyl oxygen atom is syn to the ester carbonyl oxygen even in the crystalline state. This is just the preferred conformation of MalphaNP acid esters assumed in the 1H NMR anisotropy method. The S absolute configuration of (+)-4 was also confirmed by the CD and 1H NMR anisotropy methods.

Journal Article↗