MEG responses during rhythmic finger tapping in humans to phasic stimulation and their interpretation based on neural mechanisms

 The phase-resetting experiment was applied to human periodic finger tapping to understand how its rhythm is controlled by the internal neural clock that is assumed to exist. In the experiment, the right periodic tapping movement was disturbed transiently by a series of left finger taps in response to impulsive auditory cues presented randomly at various phases within the tapping cycle. After each left finger tap, the original periodic tapping was reestablished within several tapping cycles. Influences of the disturbance on the periodic right finger tapping varied depending on the phase of the periodic right finger tapping at which each left finger tap was made. It was confirmed that the periodic tapping was disturbed not by the auditory cues but by the left finger taps. Based on this fact, in this paper each single left tap was considered as the stimulus, and the phase of the periodic tapping of the right index finger when the left tap was executed as the phase of the stimulus. Responses of the neural activities (magnetoencephalography, MEG), the tapping movement, and the corresponding muscle activities (electromyography) were simultaneously measured. Phase-resetting curves (PRCs) representing the degree of phase reset as a function of the phase of the stimulus were obtained both for the left sensorimotor cortex MEG response and for the right index finger tapping response. The shapes of both PRCs were similar, suggesting that the phase reset of the left sensorimotor cortex activities and that of the finger tapping rhythm were the same. Four out of eight subjects showed type-0 reset in Winfree's definition, and the others showed type-1 reset. For general limit-cycle oscillators, type-0 reset is obtained for relatively strong perturbations and type 1 for weak perturbations. It was shown that the transient response of MEG to the single left tap stimuli in type-0 subjects, where the phase was progressively reset, were different from those in type-1 subjects. Based on detailed analysis of the differences, a neural network model for the phase reset of the tapping rhythm is proposed. Received: 10 February 2000 / Accepted in revised form: 15 January 2002     

Conversion of gastric mucosa to intestinal metaplasia in Cdx2-expressing transgenic mice

Gastric intestinal metaplasia occurs as a pathological condition in the gastric mucosa. To clarify how an intestine-specific homeobox gene, Cdx2, affects the morphogenesis of gastric mucosa, we generated transgenic mice expressing Cdx2 in parietal cells. Until Day 18 after birth, the number of parietal cells inthegastric mucosa of transgenic mice was the same as for their normal littermates. However, at Day 19, we detected several glands in which parietal cells disappeared and the proliferating zone moved from the isthmus to the base of the glands. Thereafter, parietal cells decreased gradually and disappeared at Day 37. All of the gastric mucosal cells, except for enterochromaffin-like (ECL) cells, were completely replaced by intestinal metaplasia, consisting of goblet cells, enteroendocrine cells, and absorptive cells expressing alkaline phosphatase. Pseudopyloric gland metaplasia was also formed. The transgenic mouse is a very useful model for clarifying physiological differentiation of gastric and intestinal cell lineages and analyzing the molecular events from intestinal metaplasia to adenocarcinoma.     

The specific mitochondrial DNA polymorphism found in Klinefelter's syndrome

Hypervariable segments of mitochondrial DNA (mtDNA) (HV1 and HV2) were analyzed in Klinefelter's syndrome and compared to normal population data. One pair of samples consisting of a Japanese mother and affected son with Klinefelter's syndrome (involved in a criminal case), and seven unrelated DNA samples from Caucasian Klinefelter males (two involved in criminal cases and five diagnosed) were collected in Japan and the United States. The diagnosis of Klinefelter's syndrome was established previously by multiplex XY-STR typing detecting two X alleles and one Y allele in the samples. Haplotype analysis of the mtDNA sequence in Klinefelter males was found to be identical, unique, and specific, as it was not found in the normal population. Astonishingly, family data exhibited that the haplotype of the mtDNA in the son was apparently different from the mother's, suggesting that the mtDNA of Klinefelter male would not be inherited from mother to son. Our data indicate that possible interaction of the sex chromosome and the mtDNA exists, and suggests that the specific mtDNA haplotype could cause the abnormal cell to fertilize and reproduce itself.     

Isolation of single-stranded DNA from loop-mediated isothermal amplification products.

Loop-mediated isothermal amplification (LAMP), in which a specific DNA sequence can be directly amplified under isothermal conditions, yields DNA in large quantities of more than 500 microg/ml. We have developed a method to isolate single-stranded DNA fragments from LAMP products that are stem-loop DNAs with several inverted repeats of the target DNA. This method requires the TspRI restriction enzyme, a primer hybridized to the 3' overhanging sequence at its cleavage site, and a DNA polymerase with strand displacement activity. The LAMP products are digested with TspRI and are then extended using the primer, producing the strand-specific DNA fragments. All processes, from LAMP reaction to primer extension, can be carried out at the same temperature. The use of strand-specific DNA would be conducive for detection by hybridization technique such as DNA microarrays.     

Two lignan dimers from bamboo stems (Phyllostachys edulis)

Phyllostadimers A and B, two bis-lignans in which the two lignan units are directly connected by a C-C bond, were isolated from stems of bamboo, Phyllostachys edulis. Their structures were determined on the basis of spectral evidence. In addition, 14 known compounds were also obtained throughout the investigation. Phyllostadimer A significantly inhibited liposomal lipid peroxidation.     

A new method for enzymatic preparation of isopentenyladenine-type and<Emphasis Type="Italic"> trans</Emphasis>-zeatin-type cytokinins with radioisotope-labeling

We describe a new enzymatic reaction method for the preparation of the radioisotope-labeled cytokinins isopentenyladenine (iP), trans-zeatin (tZ), and their ribosides. The method is based on the three enzyme activities of an adenylate isopentenyltransferase (IPT; EC 2.5.1.27) from Arabidopsis thaliana, an alkaline phosphatase (EC 3.1.3.1) from calf intestine, and a purine-nucleoside phosphorylase (EC 2.4.2.1) from Escherichia coli. The A. thaliana IPT, AtIPT7, utilized both dimethylallyldiphosphate and 4-hydroxy-3-methyl-2-(E)-butenyl diphosphate as isoprenoid donors. The dual specificity of the substrates enabled us to produce iP-type and tZ-type cytokinins separately in the same system simply by switching the substrates. Our method affords a much higher yield of the labeled products than the chemical reaction methods previously used. These labeled compounds will be useful tools for cytokinin research, such as receptor–ligand assays and cell metabolism studies.     

Development of catheter-type optical oxygen sensor and applications to bioinstrumentation

A catheter-type optical oxygen sensor based on phosphorescence lifetime was developed for medical and animal experimental use. Since the sensor probe should have biocompatibility and high oxygen permeability in vivo, we focused attention on acceptable polymer materials for contact lenses as the substrates of probes. Pd-porphyrin was doped in silicone-based polymer, and was fixed at the edge of an optical fiber inserted in a catheter tube. The shape of the probe was 600 μm in diameter and 100 μm in thickness, and the probe had high oxygen permeability of Dk value 455. In accuracy evaluation, there found an excellent correlation between the pO₂ values measured through phosphorescence lifetime using the oxygen sensors and those measured as the calibrating data using oxygen electrodes. The response time required to achieve 90% from reversible default value to be from 150 to 0 mmHg, and from 0 to 150 mmHg was 15.43 and 7.52 s, respectively. In addition, other properties such as temperature and pH dependency, response, and durability of our optical oxygen sensor were investigated. In animal experiments, the catheter-type oxygen sensor was inserted via the femoral artery of a rat, and arterial oxygen pressure was monitored under asphyxiation. The sensor was valid in the range of oxygen concentration sufficient for biometry, and expected to be integrated with an indwelling needle.