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Biomedical subjects

M Tsukada

Publications and source records attributed to M Tsukada.

230 records · Page 13Linked to original sources
PubMed1967

Chenopod and amaranth pollen: electron-microscopic identification.

Electron-microscopic criteria for distinguishing chenopod and amaranth pollen have been found in the number of minute holes and spinules, and especially in the ratio between them, which is 1.5 in amaranths and 1.6 in chenopods. Sixty-eight percent of total fossil pollen from a Classic Maya level (carbon-14 age 1380 +/- 120 B.P.) in a lake-sediment core from El Salvador belongs to wild amaranths, which presumably invaded corn fields. Fossil chenopodiaceous pollen from a depth of 3.85 meters (about 4000 years old) at Tinte, the Netherlands, is mostly Atriplex littoralis, which was evidently very common on coastal marshes in the middle sub-Boreal period.

El Salvador↗
PubMedDate not supplied

Swelling and dissolution of silk fibroin (Bombyx mori) in N-methyl morpholine N-oxide.

Bombyx mori silk fibers were dissolved in N-methyl morpholine N-oxide (MMNO), an organic cyclic amine oxide used for the solvent spinning of regenerated cellulosic fibers. The commercial MMNO monohydrate used in this study as a solvent for silk is a hygroscopic compound crystalline at room temperature, which becomes an active solvent after melting at 76 degrees C. The degree of hydration of MMNO was checked by DSC measurements. The solvation power of MMNO towards silk fibroin drastically decreased at a water content > or = 20-21% w/w. Dissolution of silk required both thermal and mechanical energy. The optimum temperature was 100 degrees C. At lower temperatures dissolution proceeded very slowly. At higher temperatures, rapid depolymerization of silk fibroin occurred. The value of the Flory-Huggins interaction parameter chi for the MMNO-H2O-silk fibroin system was -8.5, suggesting that dissolution is a thermodynamically favored process. The extent of degradation of silk fibroin was assessed by measuring the intrinsic viscosity and determining the amino acid composition of silk after regeneration with an aqueous methanol solution, which was effective in removing the solvent and coagulating silk. Regenerated silk fibroin membranes were characterized by infrared spectroscopy, differential scanning calorimetry and scanning electron microscopy. The prevailing molecular conformation of silk fibroin chains was the beta-sheet structure, as shown by the intense amide I-III bands at 1704, 1627, 1515, 1260, and 1230 cm(-1). The value of the I1260/I1230 intensity ratio (crystallinity index) was 0.68, comparable to that of the fibers. The DSC thermogram was characteristic of a silk fibroin material with unoriented beta-sheet crystalline structure, with an intense decomposition endotherm at 294 degrees C. The SEM examination of fractured surfaces showed the presence of a dense microstructure with a very fine texture formed by densely packed roundish particles of about 100-200 nm diameter.

Amino Acids↗
PubMedDate not supplied

Chaotic stimulus dependent long-term potentiation in the hippocampal CA1 area.

In our previous report [Tsukada, M., Aihara, T., Saito, H., Kato, H., 1996. Neural Netw. 9, 1357-1365], the temporal pattern sensitivity of long-term potentiation (LTP) in hippocampal CA1 neurons was estimated by using Markov chain stimuli (MS) with different values of the serial correlation coefficient rho1 between successive interstimulus-intervals. In this paper, the effect of chaotic stimuli (CS) on induction of LTP in the hippocampal CA1 area was investigated in comparison with that of MS and periodic pattern stimuli (PS). The CS were produced by a modified Bernoulli map, so that interstimulus sequences with various values of rho1 can be generated by changing the parameter B. These stimuli had an identical first order statistics (mean interstimulus-interval), but their higher order statistics such as the serial correlation coefficients were different. The LTP induced by CS at B = 2 was significantly larger in magnitude than that of PS and MS, and also depended on the initial value of CS at B = 2 and 3. These results suggest that chaotic signals play an important role for memory coding in the hippocampal CA1 network.

Hippocampus↗
PubMedDate not supplied

Chemical modification of silk fibroin with cyanuric chloride-activated poly(ethylene glycol): analyses of reaction site by 1H-NMR spectroscopy and conformation of the conjugates.

Solubilized silk fibroin (SF) in 0.1 M borate buffer (pH 9.4) was modified with 2-O-[methoxy(polyethylene glycol)]-4,6-dichloro-s-triazine (actPEG1) at 4 degrees C. The weight of the modified SF (PEG1-SF) was at least 3.2 times that of the starting material SF. Amino acid analysis of PEG1-SF suggested that the nucleophilic epsilon-amino group of the lysine residue and the nucleophilic imidazole group of the histidine residue in SF reacted with actPEG1. The 1H-NMR spectrum of PEG1-SF showed a downfield shift of the aromatic protons of the tyrosine residue from the corresponding protons of SF. The 1H-NMR spectrum of the SF reacted with cyanuric fluoride (CyF), whose fluorine atoms are known to react with the phenolic hydroxyl group of the tyrosine residue, also showed the downfield shift. These results suggested that the reaction site of SF with actPEG1 was the phenolic hydroxyl group of the tyrosine residue in addition to the lysine and histidine residues. The conformation of PEG1-SF in a solid state was examined by means of IR and X-ray measurement. The IR spectrum of PEG1-SF revealed a change in secondary structure from random coil to beta-sheet due to the coexistence of PEG molecules. The X-ray diffraction pattern of PEG1-SF indicated that the PEG molecules covalently bonding to SF narrowed the spacing of the interchain periodicity and promoted the formation of the interchain beta-sheet.

Amino Acids↗
PubMedDate not supplied

A comparative study on anti-inflammatory activities of the enantiomers, shikonin and alkannin.

A pharmacological comparison between the enantiomers, shikonin (R) and alkannin (S), was made with regard to their inhibitory effects on the increased capillary permeability and thermal edema in rats, using phenylbutazone as a positive control in both models. The results of experiments have shown that there is no significant difference in the anti-inflammatory activity between the two compounds.

Animals↗
PubMedDate not supplied

Bradykinin-induced vascular responses in dog isolated lingual artery.

1. Kinin-induced vascular responses were studied and kinin receptor subtypes were characterized in canine isolated and preconstricted lingual arteries. 2. A low dose of bradykinin (BK; < 3 x 10(-14) mol) induced only vasodilation, while a higher dose of BK (> 3 x 10(-13) mol) frequently induced a biphasic response: a transient constriction followed by dilation. 3. The BK-induced vasodilation was mostly endothelium dependent but was also partly endothelium independent because although the dilation response was greatly reduced after removal of the endothelium, it was not completely abolished. 4. The dilation response to BK was significantly inhibited by the B2 kinin receptor antagonist HOE 140 and was partly reduced by indomethacin (10 mumol/L) (P < 0.05). 5. Bradykinin-induced vasoconstriction was enhanced in endothelium-denuded preparations. The constriction was significantly inhibited by HOE 140 (10(-10) mol/L). The BK-induced responses were not affected by the B1 kinin receptor antagonist des-Arg9-[Leu8]-BK (3 x 10(-11) mol/L). 6. The B1 kinin receptor agonist des-Arg9-BK (> 10(-12) mol/L) produced vasodilation in 60% of endothelium-intact preparations. In 20% of the endothelium-intact preparations des-Arg9-BK produced a biphasic response: weak vasoconstriction followed by weak vasodilation. The des-Arg9-BK-induced dilation and constriction were significantly inhibited by des-Arg9-[Leu8]-BK (3 x 10(-11) mol/L), but were not affected by HOE 140 (10(-10) mol/L). 7. In conclusion, it appears that both B1 and B2 kinin receptors are present in the dog lingual artery. Both receptor subtypes mediate either vasodilation or vasoconstriction and BK-induced vasodilation is mostly endothelium dependent, although it may also be partially prostaglandin dependent.

Animals↗
PubMedDate not supplied

Activities of NAD+-dependent aldehyde dehydrogenase and alcohol dehydrogenase in the liver of spontaneously hypertensive rats in the process of development.

The difference in the basal activities of NAD+-dependent aldehyde dehydrogenase (ALDH) and alcohol dehydrogenase (ADH) was investigated in the liver of age-matched spontaneously hypertensive (SH) and normotensive Wistar Kyoto (WK) rats. A significant difference between the SH and WK rats in the basal ALDH activity, ADH activity and the protein content of subcellular fractions was observed. The activities of mitochondrial low Km- and high Km-ALDH in the SH rats at 5-8 weeks of age were higher than those in the WK rats. The microsomal high Km-ALDH activity in the SH rats at 5 and 11 weeks of age was higher than that in the WK rats. The ADH activities in the SH rats at 5-14 weeks of age were lower than those in the WK rats. The mitochondrial protein content in the SH rats at 5-14 weeks of age was higher than those in the WK rats. At 14 weeks of age, an increase in the blood acetaldehyde level was observed after an intraperitoneal injection of 1.5 g/kg of ethanol in the SH rats. No difference in blood ethanol level was observed between the SH and WK rats.

Acetaldehyde↗