Biomedical subjects

M Y Li

Publications and source records attributed to M Y Li.

At least 19 recordsLinked to original sources

PubMed2001

Global stability of an SEIS epidemic model with recruitment and a varying total population size.

This paper considers an SEIS epidemic model that incorporates constant recruitment, disease-caused death and disease latency. The incidence term is of the bilinear mass-action form. It is shown that the global dynamics is completely determined by the basic reproduction number R(0). If R(0) 1, a unique endemic equilibrium is globally stable in the interior of the feasible region and the disease persists at the endemic equilibrium.

Communicable Diseases↗

PubMed2001

Monomeric destetrapeptide human insulin from a precursor expressed in Saccharomyces cerevisiae.

Destetrapeptide insulin (DTI, human insulin with B27-30 removed) was obtained from a monomeric precursor (MIP) expressed in Saccharomyces cerevisiae through tryptic transpeptidation in the presence of synthetic tetrapeptide Gly-Phe-Phe-Tyr. The in vivo biological activity of DTI, determined by mouse convulsion assay, is 22 IU/mg. Its binding activity with insulin receptor on human placental membrane is 80% and its in vitro biological activity, determined by free fat cell assay, is 77%. Compared with native insulin, DTI molecules do not associate in solution but exist in the monomeric form, thus leading to its rapid utilization in vivo.

Amino Acid Sequence↗

PubMed2001

Quenching of singlet molecular oxygen (1O2) by azide anion in solvent mixtures.

The azide ion is a strong physical quencher of singlet molecular oxygen (1O2) and is frequently employed to show involvement of 1O2 in oxidation processes. Rate constants (k(q)) for the quenching of 1O2 by azide are routinely used as standards to calculate k(q) values for quenching by other substrates. We have measured k(q) for azide in solvent mixtures containing deuterium oxide (D2O), acetonitrile (MeCN), 1,4-dioxane, ethanol (EtOH), propylene carbonate (PC), or ethylene carbonate (EC), mixtures commonly used for many experimental studies. The rate constants were calculated directly from 1O2 phosphorescence lifetimes observed after laser pulse excitation of rose bengal (RB), used to generate 1O2. In aqueous mixtures with MeCN and carbonates, the rate constant increased nonlinearly with increasing volume of organic solvent in the mixtures. k(q) was 4.78 x 10(8) M(-1) s(-1) in D2O and increased to 26.7 x 10(8) and 27.7 x 10(8) M(-1) s(-1) in 96% MeCN and 97.7% EC/PC, respectively. However, in EtOH/D2O mixtures, k(q) decreased with increasing alcohol concentration. This shows that a higher solvent polarity increases the quenching efficiency, which is unexpectedly decreased by the proticity of aqueous and alcohol solvent mixtures. The rate constant values increased with increasing temperature, yielding a quenching activation energy of 11.3 kJ mol(-1) in D2O. Our results show that rate constants in most solvent mixtures cannot be derived reliably from k(q) values measured in pure solvents by using a simple additivity rule. We have measured the rate constants with high accuracy, and they may serve as a reliable reference to calculate unknown k(q) values.

Journal Article↗

PubMed2001

[An AFLP marker related to fibrogenesis in upland cotton (Gossypium hirsuturm L.)].

By using AFLP technique polymorphism analysis was performed between a fuzzlesslintless mutant line and its isogenic wild-type line, Xuzhou 142. Out of 6,360 bands produced by 64 pairs primers, a fragment, named as CF1, appearing stably in wild-type line, Xuzhou 142. This polymorphism was further verified using several normal fiber varieties and F2, F3 populations from the cross of fuzzless-lintless mutant line with a high-lint-percentage variety Yumian No. 1. The cosegregation of CF1 and fibrogenesis was proved, which suggested that CF1 can be used as a molecular marker for cotton fibrogenesis. The CF1 segment was cloned into PUCm-T Vector and then sequenced. The putative amino acid sequences, is an analogue to phenol hydroxylase alpha subunit, outer surface protein C, NADH dehydrogenase subunit 1, NADH-ubiquinone oxidoreductase, 2-oxoacid ferredoxin oxidoreduct and hypothetical 14.5kD protein.

Base Sequence↗

PubMed2001

[lambda N gene expression regulated by the leader sequence].

It was reported recently that changing the TIR (translational initiation region) of lambda N gene resulted in the increasing expression of lambda N gene and it was regulated at translational level. According to the alignment, the leader sequence of lambda N gene had three parts: a code region for ORF lambda N, the upstream sequence of ORF lambda N and 17 bp of spacer between ORF lambda N and downstream of lambda N gene. ORF lambda N is an open reading frame located at upstream of lambda N gene coding a peptide of 19 amino acids. To study the mechanism of regulation of lambda N gene expression, three serials of plasmids with mutant leader region of lambda N gene were constructed. (1) pMC1403-XT, in which the start codon or the partial code of ORF lambda N was connected with lacZ to obtain the ORF lambda N-lacZ fusion gene and in which the ORF lambda N-lacZ expression was under the control of a strong trp/lac promoter; (2) The ORF lambda N mutants in which the termination codon TAA was introduced into ORF lambda N at different positions by site-directed mutagenesis to preterminate the ORF lambda N on plasmid pMC1403N; (3) Mutants in which a deletion was located at upstream ORF lambda N in the ORF lambda N mutants above. The results obtained from determination of the beta-galactosidase activity in the transformants harboring the different plasmids showed that the ORF lambda N-lacZ expression was suppressed by the ORF lambda N code region and the lambda N expression was increased in both the second and third serials of mutants. At the same time the results from RNA-DNA dot hybridization showed that the lambda N gene expression was regulated at translational level. Therefore it was predicted that the reason of relatively low expression for lambda N gene in pMC1403N was due to the low efficiency of ORF lambda N translation. There are two ways to increase the expression of lambda N gene. One is to preterminate the translation of ORF lambda N at a suitable position to decrease the ORF lambda N effects on downstream lambda N gene translation; the other is to change the upstream sequence of ORF lambda N to improve its translation efficiency.

5' Untranslated Regions↗

PubMed2000

Vitamin B6 (pyridoxine) and its derivatives are efficient singlet oxygen quenchers and potential fungal antioxidants.

Vitamin B6 (pyridoxine, 1) and its derivatives: pyridoxal (2), pyridoxal 5-phosphate (3) and pyridoxamine (4) are important natural compounds involved in numerous biological functions. Pyridoxine appears to play a role in the resistance of the filamentous fungus Cercospora nicotianae to its own abundantly produced strong photosensitizer of singlet molecular oxygen (1O2), cercosporin. We measured the rate constants (kq) for the quenching of 1O2 phosphorescence by 1-4 in D2O. The respective total (physical and chemical quenching) kq values are: 5.5 x 10(7) M-1 s-1 for 1; 7.5 x 10(7) M-1 s-1 for 2, 6.2 x 10(7) M-1 s-1 for 3 and 7.5 x 10(7) M-1 s-1 for 4, all measured at pD 6.2. The quenching efficacy increased up to five times in alkaline solutions and decreased approximately 10 times in ethanol. Significant contribution to total quenching by chemical reaction(s) is suggested by the degradation of all the vitamin derivatives by 1O2, which was observed as declining absorption of the pyridoxine moiety upon aerobic irradiation of RB used to photosensitize 1O2. This photodegradation was completely stopped by azide, a known physical quencher of 1O2. The pyridoxine moiety can also function as a redox quencher for excited cercosporin by forming the cercosporin radical anion, as observed by electron paramagnetic resonance. All B6 vitamers fluoresce upon UV excitation. Compounds 1 and 4 emit fluorescence at 400 nm, compound 2 at 450 nm and compound 3 at 550 nm. The fluorescence intensity of 3 increased approximately 10 times in organic solvents such as ethanol and 1,2-propanediol compared to aqueous solutions, suggesting that fluorescence may be used to image the distribution of 1-4 in Cercospora to understand better the interactions of pyridoxine and 1O2 in the living fungus.

Ascomycota↗

PubMed2000

[Effects of media on the production of flavonoids by suspension cultures of Saussurea medusa].

Flavonoids were produced from cell suspension cultures of Saussurea medusa. The results of studies on eight types of culture media showed that the MS medium was the best for cell growth and flavonoids formation, We investigated the effects of all the components of MS medium on the cell growth and flavonoids production, and found that carbon, nitrogen and phytohormone had especially marked effects. With MG medium a modified MS medium, the yield of cell growth was 24.8 g(dwt)/L, with MP medium another modified MS mediums, the yield of flavonoids production was 1. 75 g/L. The yield of cell growth and flavonoids production in MG and MP medium were 32% and 70% higher than that in MS medium respectively.

Cell Division↗

PubMed1999

A highly conserved sequence is a novel gene involved in de novo vitamin B6 biosynthesis.

The Cercospora nicotianae SOR1 (singlet oxygen resistance) gene was identified previously as a gene involved in resistance of this fungus to singlet-oxygen-generating phototoxins. Although homologues to SOR1 occur in organisms in four kingdoms and encode one of the most highly conserved proteins yet identified, the precise function of this protein has, until now, remained unknown. We show that SOR1 is essential in pyridoxine (vitamin B6) synthesis in C. nicotianae and Aspergillus flavus, although it shows no homology to previously identified pyridoxine synthesis genes identified in Escherichia coli. Sequence database analysis demonstrated that organisms encode either SOR1 or E. coli pyridoxine biosynthesis genes, but not both, suggesting that there are two divergent pathways for de novo pyridoxine biosynthesis in nature. Pathway divergence appears to have occurred during the evolution of the eubacteria. We also present data showing that pyridoxine quenches singlet oxygen at a rate comparable to that of vitamins C and E, two of the most highly efficient biological antioxidants, suggesting a previously unknown role for pyridoxine in active oxygen resistance.

Animals↗

PubMed1999

Global dynamics of a SEIR model with varying total population size.

A SEIR model for the transmission of an infectious disease that spreads in a population through direct contact of the hosts is studied. The force of infection is of proportionate mixing type. A threshold sigma is identified which determines the outcome of the disease; if sigma < or = 1, the infected fraction of the population disappears so the disease dies out, while of sigma > 1, the infected fraction persists and a unique endemic equilibrium state is shown, under a mild restriction on the parameters, to be globally asymptotically stable in the interior of the feasible region. Two other threshold parameters sigma' and sigma are also identified; they determine the dynamics of the population sizes in the cases when the disease dies out and when it is endemic, respectively.

Disease Outbreaks↗

PubMed1998

Orphanin FQ/nociceptin modulates glutamate- and kainic acid-induced currents in acutely isolated rat spinal dorsal horn neurons.

The heptadecapeptide orphanin FQ (OFQ), also known as nociceptin (NOC), is a newly discovered endogenous ligand for the opioid-like G-protein coupled receptor, ORL1. In the present study, the effects of OFQ/NOC on glutamate (Glu), kainic acid (KA) and quisqualic acid (QA) induced currents were examined in isolated rat spinal dorsal horn neurons of young rats using whole-cell patch-clamp techniques. Glu, KA and QA elicited rapid inward currents in 90%, 69%, 83% of tested neurons. OFQ/NOC(0.03 approximately 300 nM) failed to induce any changes of membrane currents, but modulated Glu-, KA- and QA-elicited currents. OFQ/NOC inhibited and potentiated Glu-induced currents in 40.6% and 27.3% of examined cells (n=106) respectively. In about one third examined neurons, OFQ/NOC had no detectable effects on Glu responses. OFQ/NOC also inhibited and enhanced KA- and QA-induced currents (inhibition: KA, 67.1%, n=76; QA, 50%, n=36. Potentiation: KA, 23.7%, n=76; QA, 16.7%, n=36). In about 10% of tested cells, Glu-induced currents were potentiated after the application of OFQ/NOC, and lasted for 20 approximately 30 min. The inhibitory effects of OFQ/NOC on KA and QA responses were naloxone-insensitive. The C-terminal fragment OFQ(8-17) presented same effects on EAA-induced responses. Taken together, OFQ/NOC primarily inhibited Glu-, KA- and QA-induced currents in isolated rat spinal dorsal horn neurons via non-opioid mechanism, which might contribute to nociceptive transmission in the spinal level.

Analgesics↗

PubMed1998

Antagonistic effect of orphanin FQ on opioid analgesia in rat.

AIM: To study the effect of orphanin FQ (OFQ), a newly discovered heptadecapeptide, on nociception and opioid analgesia. METHODS: The intracerebroventricular (i.c.v.) and intrathecal (i.t.h.) injections were used to give the drugs. The tail-flick model of rats were used to test the pain threshold. RESULTS: OFQ (i.c.v. or i.t.h.) 0.1 microgram had no effect on nociception but 0.5-10 micrograms induces hyper-reaction of rat to noxious electric stimulus; the decapeptide (OFQ1-10 i.c.v.), a fragment of the OFQ, did not affect the pain reaction of rats. Fentanyl (1 microgram, i.c.v. or i.t.h.), a selective mu-receptor agonist, DSLET (5 micrograms, i.c.v. or i.t.h.), a selective delta-receptor agonist, or U50488H (1 microgram, i.t.h.), a kappa-receptor agonist, induced an increase in pain threshold, when OFQ (0.1 or 1 microgram) was added together with one of them (except for the ith injection of DSLET), the increase of pain threshold was reduced obviously. CONCLUSION: OFQ induces hyperalgesia and antagonizes opioid analgesia mediated by mu- and delta-receptors in the brain and by mu- and kappa- but not delta-receptors in the spinal cord of rats.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1997

Effect of quinine on autoreceptor-regulated serotonin release in the rat hippocampus.

The involvement of K+ channels in the autoregulation of terminal serotonin (5-hydroxytryptamine, 5-HT) release was investigated by microdialysis in the hippocampus of conscious rats. Extracellular 5-HT was increased concentration-dependently by the K+ channel blocker quinine (10, 100 and 1000 microM in perfusate), and tetrodotoxin (10 microM) but not fluoxetine (5 microM) exerted a partially attenuating influence. The 5-HT1/2/6 receptor antagonist methiothepin (50 microM) increased dialysate 5-HT, most likely through 5-HT1B autoreceptors tonically activated in the hippocampus of awake rats as opposed to the previously reported lack of effect 5-HT1B autoreceptor blockade in anesthetized rats. The effect of methiothepin was greatly reduced by preperfusion with quinine (100 microM), consonant with a role for quinine-sensitive K+ channels in the autoregulation of 5-HT release in the hippocampus by 5-HT receptor antagonism. In contrast, the reduction in dialysate 5-HT induced by the 5-HT1 receptor agonist RU 24969 (1 microM), in the presence of fluoxetine (5 microM), persisted in the co-presence of quinine, consonant with the involvement of (extrasynaptic?) 5-HT autoreceptors not coupled with quinine-sensitive K+ channels.

Animals↗

PubMed1997

Carbamazepine increases extracellular serotonin concentration: lack of antagonism by tetrodotoxin or zero Ca2+.

Carbamazepine administration causes large increases in extracellular serotonin concentration and dose-related anticonvulsant effects in genetically epilepsy-prone rats (GEPRs). In order to determine the generality of the effect on serotonin, we determined the anticonvulsant ED50 for carbamazepine against maximal electroshock seizures in outbred, non-epileptic Sprague-Dawley rats. We then administered anticonvulsant carbamazepine doses to Sprague-Dawley rats and observed extracellular serotonin concentration in hippocampi by way of microdialysis. We found that administration of carbamazepine, either systemically or through the dialysis probe, resulted in significant and dose-related increases in extracellular serotonin concentration. Basal serotonin release was decreased by tetrodotoxin administration through the dialysis probe. Tetrodotoxin administration through the dialysis probe did not decrease the effect of systemically or focally administered carbamazepine on extracellular serotonin concentration. Similarly, elimination of Ca2+ from the dialysate did not alter the release of serotonin caused by carbamazepine. These findings suggest that the serotonin releasing effect of carbamazepine does not take place by exocytosis and does not require action potentials in the brain area in which the release takes place. Further they suggest that the effect is mediated by an action of carbamazepine directly on serotonergic nerve terminals.

Animals↗

PubMed1997

Anticonvulsant doses of carbamazepine increase hippocampal extracellular serotonin in genetically epilepsy-prone rats: dose response relationships.

The antiepileptic drug carbamazepine produces dose related anticonvulsant effects in genetically epilepsy-prone rats (GEPRs) and most other animal seizure models. Carbamazepine releases serotonin as part of the pharmacodynamic action by which it suppresses convulsions in GEPRs and it releases serotonin in non-epileptic Sprague-Dawley rats. The two strains which make up the GEPR seizure model (moderate seizure GEPR-3s and severe seizure GEPR-9s) experience anticonvulsant effects in response to different doses of carbamazepine (GEPR-3 ED50 = 25 mg/kg; GEPR-9 ED50 = 3 mg/kg). The present study determined that carbamazepine produces a dose related increase in extracellular serotonin in each of the two GEPR strains. The doses of carbamazepine required to increase extracellular serotonin are similar to the doses required for an anticonvulsant effect in each of the strains. This result provides further support for the hypothesis that release of serotonin by carbamazepine is an important part of the pharmacodynamic action by which this drug suppresses seizures.

Analysis of Variance↗

PubMed1997

Extracellular dopamine, norepinephrine, and serotonin in the ventral tegmental area and nucleus accumbens of freely moving rats during intracerebral dialysis following systemic administration of cocaine and other uptake blockers.

Extracellular levels of dopamine (DA), serotonin (5-HT), and norepinephrine (NE) were measured by microdialysis in conscious rats equipped with dual probes, one in the ventral tegmental area (VTA) and another one in the contralateral nucleus accumbens (NACC). Dialysate content of all amines in both regions was essentially abolished by local infusion of tetrodotoxin (1 microM) or Ca2+-free buffer. Injection of the selective DA uptake blocker GBR 12935 (15 mg/kg i.p.) increased DA, as well as NE and, to a lesser extent, 5-HT in the VTA; it increased DA more than 5-HT in the NACC. The selective NE uptake blocker desipramine (10 mg/kg i.p.) increased NE but also 5-HT in the VTA and NACC; the DA level was persistently enhanced in the VTA, whereas in the NACC it initially rose and then fell below baseline value. The selective 5-HT uptake blocker citalopram (15 mg/kg i.p.) was generally more effective in elevating dialysate level of 5-HT than that of other amines in both regions. Cocaine (20 mg/kg i.p.) was non-selective in enhancing all three amines in both regions. There is considerable crosstalk between monoamine systems occurring upon systemic administration of uptake blockers, and the VTA and NACC are notably different in the time course of the DA effect (long-lasting versus transient).

Animals↗

PubMed1997

[The sterilization effect of formaldehyde fumigating on the catheter place vertically].

UNLABELLED: The aim of this paper is to investigate the effect of formaldehyde fumigating on the sterilization of catheters with different diameters and placed in different positions. The lumen of cleaned catheters with different diameters was filled with a solution of live bacilli coil. The catheters were then dried by a drier and divided into 3 groups for formaldehyde fumigating sterilization. A segment of 5 cm of the middle section of the sterilized catheters was cut and incubated at 36 degrees C for 48 h with bouillon medium. For those segments with positive culture, bacteriologic identification was done. RESULTS: Group A, U = 6.85 and P < 0.01; Group B, chi 2 = 8 and P < 0.01; Group C, chi 2 = 13, P < 0.01. CONCLUSIONS: in the same conditions, fumigating in vertical direction is better than fumigation in horizontal direction and save time; in the same conditions, the positive culture rate is inversely related to the diameter of the catheters; for catheter with a diameter greater than 0.75 cm, fumigating vertically for 2 h is enough to obtain satisfactory sterilization effects.

Catheters, Indwelling↗

PubMed1997

[Effect of intrathecal or intracerebroventricular administrition of OFQ on pain threshold and acpuncture analgesia in rats].

Orphanin FQ (OFQ) is a newly discovered 17-amino-acid peptide capable of inducing hyperalgesia. In the present study, the effects of OFQ on basal pain threshold and acupuncture anlgesia (AA) in rats were observed using the tail-flick test. It was found that intrathecal (i.t.) or intracerebroventricular (i.c.v.) administrition of 0.1 microgram OFQ had no effect on basal pain threshold of rats, while 1 microgram OFQ could lower the threshold. However, OFQ at both the doses (0.1 or 1.0 microgram) administered by either i.t. or i.c.v. injection could antagonize AA with that occuring in the brain being more prominent then in the spinal cord. When the rats were repeatedly treated with antisense oligonucleotide to block synthesis of OFQ receptor, pain threshold increased significantly. At such instance, when the OFQ was combined with acupuncture, the effect of AA showed no obvious change. The above results show that the OFQ at small dose has no effect on pain threshold but can lower it at larger dose; while in both cases OFQ can antagonize AA.

Acupuncture Analgesia↗

PubMed1996

Extracellular dopamine, norepinephrine, and serotonin in the nucleus accumbens of freely moving rats during intracerebral dialysis with cocaine and other monoamine uptake blockers.

Monoamine-uptake blockers were applied focally (0.1-1,000 microM) through a dialysis probe in the nucleus accumbens of freely moving rats, and the extracellular concentrations of dopamine, norepinephrine, and serotonin were measured. The selective dopamine-uptake blocker GBR 12935 increased dopamine preferentially with only a small effect on norepinephrine, whereas the selective serotonin-uptake blocker fluoxetine increased serotonin output preferentially. In contrast, the selective norepinephrine-uptake blockers desipramine and nisoxetine enhanced not only norepinephrine, but also serotonin and dopamine appreciably. Cocaine increased all three amines with the greatest effects on dopamine and serotonin. As in our previous study on the ventral tegmental area, there was a positive association between dopamine and norepinephrine output when all blocker data were taken together. The present results suggest a contribution of the increase in norepinephrine, but not serotonin, to the enhancement of dopamine after cocaine applied focally in the nucleus accumbens.

Animals↗