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Biomedical subjects

M Xu

Publications and source records attributed to M Xu.

At least 253 records · Page 14Linked to original sources
PubMed1997

Dopamine D3 receptor mutant mice exhibit increased behavioral sensitivity to concurrent stimulation of D1 and D2 receptors.

The dopamine D3 receptor is expressed primarily in regions of the brain that are thought to influence motivation and motor functions. To specify in vivo D3 receptor function, we generated mutant mice lacking this receptor. Our analysis indicates that in a novel environment, D3 mutant mice are transiently more active than wild-type mice, an effect not associated with anxiety state. Moreover, D3 mutant mice exhibit enhanced behavioral sensitivity to combined injections of D1 and D2 class receptor agonists, cocaine and amphetamine. However, the combined electrophysiological effects of the same D1 and D2 agonists on single neurons within the nucleus accumbens were not altered by the D3 receptor mutation. We conclude that one function of the D3 receptor is to modulate behaviors by inhibiting the cooperative effects of postsynaptic D1 and other D2 class receptors at systems level.

Amphetamine↗
PubMed1997

Inhibition of 2-amino-3-methylimidazo[4,5-f]quinoline-DNA adducts by indole-3-carbinol: dose-response studies in the rat colon.

Indole-3-carbinol (I3C) inhibits the formation of colonic aberrant crypt foci and DNA adducts in rats given heterocyclic amine colon carcinogens, such as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Mechanism studies indicate that I3C induces cytochromes P4501A1 and 1A2 (CYP1A1 and CYP1A2), isozymes that respectively metabolize IQ via ring hydroxylation or activate the carcinogen by N-hydroxylation. The present study examined the dose-response for induction of CYP1A1 versus CYP1A2 by I3C, and compared the profiles of induction with the dose-response for inhibition of IQ-DNA adducts in the colon of the F344 rat. Dietary equivalent doses of I3C in the range 100-1000 p.p.m. increased in a dose-related manner both ethoxyresorufin O-deethylase (EROD) and methoxyresorufin O-demethylase (MROD) activities in the liver and colonic mucosa, and Western blots showed a corresponding induction of CYP1A1 and CYP1A2 proteins. However, dietary equivalent doses of I3C in the range 10-25 p.p.m. (i) reduced hepatic EROD and MROD activities and CYP1A protein levels compared with controls, (ii) increased the ratio of CYP1A2 versus CYP1A1, and (iii) activated IQ to a more potent mutagen when liver microsomes from rats given I3C were used for metabolic activation in the Salmonella assay. Rats given a single oral dose of I3C shortly before administering IQ (5 mg/kg body wt, p.o.) exhibited dose-related inhibition of colonic IQ-DNA adducts in the range 25-100 p.p.m. I3C, reaching 95% inhibition at doses > or = 100 p.p.m. I3C, but IQ-DNA adducts were elevated slightly at the lowest I3C dose as compared with the controls. The possible significance of the low versus high dose effects of I3C are discussed in the context of human dietary exposures to I3C and the reported chemopreventive mechanisms of I3C in vivo.

Animals↗
PubMed1997

Genomic organization of the rat nuclear factor I-A gene.

The nuclear factor 1 (NF1) protein family functions as a cellular transcription factor as well as an adenovirus DNA replication factor. This family consists of four subtypes, NFI-A, NFI-B, NFI-C, and NFI-X, each encoded by a different gene. Each subtype possesses different isoforms generated by alternative splicing. To date, only a porcine NFI-C gene has been cloned, and the gene structures of the other NF1 proteins have not yet been identified. We recently isolated four kinds of NFI-A cDNA clones from the rat liver. To gain additional insight into the structure of NFI-A, we isolated the rat NFI-A gene. This gene is composed of 11 exons spanning over 70 kb. All of the exon/intron boundaries are consistent with the GT/AG rule, and consensus sequences surrounding the splice boundaries are also found. The 5'-flanking region lacks a canonical TATA box, but contains several GC-box and AP2 binding sites. A 5'-rapid amplification of cDNA end analysis indicated that the transcription of the NFI-A gene is initiated at multiple sites. We also found conservation in the genomic structure between the rat NFI-A and the porcine NFI-C, suggesting that duplication of an ancestral gene occurred rather recently to produce the NFI-A and NFI-C genes.

Animals↗
PubMed1997

Basic fibroblast growth factor reduces the gut and liver morphologic and functional injuries after ischemia and reperfusion.

OBJECTIVE: To explore the possible effects of basic fibroblast growth factor (bFGF) on ischemic gut and liver injuries after trauma. METHODS: Animal models of superior mesenteric artery occlusion (45 minutes) and reperfusion (3 days) were used in this study. Seventy-two Wistar rats were divided into three groups of 24 rats each. The animals in bFGF-treated group were injected with 4 microg bFGF/rat in 0.15 mL normal saline solution containing heparin 0.1% (w/v) through the jugular vein at the onset of reperfusion. In the normal saline control group, all rats received the same vehicle, but without bFGF. Group 3 (sham-operated) underwent the same laparotomy procedure, but without superior mesenteric artery occlusion. Liver function parameters, the levels of serum tumor necrosis factor alpha, nitric oxide, superoxide dismutase, malondialdehyde (MDA), tissue bacterial examination, and pathologic study were used to evaluate the results. RESULTS: In bFGF-treated rats, the amounts of serum alanine transaminase and aspartate aminotransferase and serum tumor necrosis factor-alpha were reduced significantly at 6, 24, and 48 hours when compared with normal saline-treated rats. However, the changes in nitric oxide, superoxide dismutase, and MDA varied from each other as a function of time after injury. The amounts of nitric oxide were increased significantly at 6 hours in intestine in normal saline-treated rats and in liver in bFGF-treated rats (p < 0.05). At 6 hours after reperfusion, the activity of superoxide dismutase in normal saline-treated rats were much lower in liver than those in bFGF-treated and sham-operated rats (p < 0.05), but the levels of MDA were increased in intestine in bFGF-treated rats and in liver in normal saline-treated rats when compared with sham-operated rats (p < 0.05). At 24 hours, the levels of MDA in normal saline-treated rats were much higher than those in both bFGF and sham-operated rats (p < 0.05). Bacterial examination revealed that the ratio and the amounts of bacterial translocation from gut to liver, spleen, and mesenteric lymph nodes in bFGF-treated rats were much lower than those in normal saline-treated rats. The results of pathologic study support the assumption that bFGF provided protective effects against reperfusion injury. CONCLUSIONS: Intravenous administration of bFGF may benefit in reducing gut and liver injuries after ischemia and reperfusion. The mechanisms of those effects may involve mitogenic and nonmitogenic effects of bFGF.

Animals↗
PubMed1997

Inhibitory activity of green and black tea in a free radical-generating system using 2-amino-3-methylimidazo[4,5-f]quinoline as substrate.

Green tea and black tea inhibit colon carcinogenesis in rats exposed to the cooked meat mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). In the present investigation, green tea, black tea and (-)-epigallocatechin gallate (EGCG) were shown to block the production of oxygen free radicals derived from IQ in the presence of NADPH-cytochrome P450 reductase. In kinetic studies using IQ as the substrate and DMPO as a free radical spin trap, EGCG increased the K(m) of the reaction without altering Vmax, suggesting competitive enzyme inhibition (Ki = 9.96 microM). This was confirmed in spectrophotometric studies using cytochrome c as the substrate, in which EGCG acted as a competitive inhibitor of NADPH-cytochrome P450 reductase (Ki = 9.7 microM). These results suggest that the inhibitory activities of green tea and black tea in electron spin resonance assays using IQ as the substrate for the reductase are related to an indirect effect on the enzyme rather than via direct scavenging of the free radicals. The possible implications of these findings are discussed in the context of pathways involved in the activation and detoxification of IQ in the colon.

Animals↗
PubMed1997

Structural studies by 1H NMR of a prototypic alpha-helical peptide (LYQELQKLTQTLK) and homologs in trifluoroethanol/water and on sodium dodecyl sulfate micelles.

The 1H NMR-determined structure and dynamics of a synthetic, amphiphilic alpha-helical peptide, PH-1.0 (LYQELQKLTQTLK), and several homologs were compared in 50% trifluoroethanol-d2 (TFE-d2)/H20 and in sodium dodecyl-d25 sulfate (SDS-d25) micelles. The peptides were designed to test the influence on secondary structure of placement of favored and disfavored residues relative to a "longitudinal, hydrophobic strip-of-helix" defined by the repeating leucines. PH-1.0 was highly ordered as an alpha-helix in 50% TFE-d2/H20 and in SDS-d25 micelles. Homologs PH-1.1, in which L1 was replaced by T, and PH-1,4, in which L12 was replaced by T. were found to be partially helical in both media. Calculated structures in SDS-d25 revealed that the helix of PH-1.1 was slightly disordered at the N-terminus, but that of PH-1.4 was completely disordered at the C-terminus. Examination of distributions of hydrophobic residues in protein structures revealed that, when [symbol: see text] = LIVFM and [symbol: see text] = nonLIVFM, the pattern [symbol: see text] is favored and [symbol: see text] is disfavored in alpha-helices. Several analogs of PH-1.0 incorporating these patterns were studied. Peptide PH-1.12 (LYQELQKLLQTLK) retained alpha-helical structure in both 50% TFE-d2/H20 and in SDS-d25 micelles. However, although PH-1.13 (LYQELQKLTLTLK) was fully helical in 50% TFE, it was helical only through residue 6 in SDS micelles. Two homologs containing an additional loop of the helix and repeats of favored (PH-5.0, NYLQTLLETLKTLLQK) or suppressed LL patterns (PH-5.11, NYLQTLETLKLTQK) gave similar results, i.e. the latter peptide was helical only through residue 6 in SDS micelles. The degree of local order in these SDS micelle-adsorbed peptides correlates to placement of hydrophobic residues in motifs which are favored or disfavored in proteins in general and in alpha-helices specifically.

Amino Acid Sequence↗
PubMed1997

[Effects of L-glutamic acid, gamma-aminobutyric acid and their respective antagonists on spontaneous discharge of nucleus paragigantocellularis lateralis neurons in rats].

Using multibarrel microelectrode techniques, we studied the effects of iontophoretic application of L-glutamic acid (L-Glu), gamma-aminobutyric acid (GABA) and their respective antagonists DL-2-amino-5-phosphonovaleric acid (AP5), bicuculline (BIC) on the spontaneous discharge of the caudal half of nucleus paragigantocellularis lateralis (cPGCL) neurons (including respiratory related neurons) and the influences of AP5 and BIC on the effects of L-Glu and GABA respectively in 22 anesthetized spontaneously breathing Sprague-Dawley rats. The spontaneous discharges of all the cPGCL neurons tested were inhibited by GABA(n = 53). Most of the tested neurons were excitated by L-Glu (30/36). AP5 and BIC both showed three kinds of effects on the cPGCL neuronal spontaneous discharge; excitatory, inhibitory and no-effect. The excitatory effects of L-Glu and BIC and the inhibitory effects of GABA showed a dose-response relationship. AP5 could block partially the excitatory effect of L-Glu on a large part of neurons tested (14/19). BIC blocked, partially or completely, the inhibitory effect of GABA also on a large part of the neurons tested(18/24). The results implicate that there might exist endogenous L-Glu and GABA acting as neurotransmitters in the cPGCL area and excitatory amino acids (EAA, including NMDA and non-NMDA) and GABA-receptors on cPGCL neurons. These neurotransmitters and receptors may mediate the regulatory action of cPGCL on respiration and other functional systems.

2-Amino-5-phosphonovalerate↗
PubMed1997

[Constuction of an improved system for the determination of fidelity of polymerase in PCR].

A system used for the determination of fidelity of DNA polymerase in PCR was developed in E.coli and was used to determine the fidelity of FD DNA polymerase in PCR amplication. Frame shift and base substitution mutations were created in vitro in the lacZ gene in pUC118 and pUC119. As a result, a set of six derived plasmids namely pFDFM118 and pFDFM119 (-1 frame shift), pFDFP118 and pFDFP119 (+1 frame shift), pFDFU118 and pFDFU119 (base substitution) were obtained. All of them failed to carry out lacZ alpha-complementation in E.coli MV1184 and the colonies appeared white on medium with X-Gal and IPTG consequently. PCR reaction was carried out using these derived plasmids as templates and the PCR products were ligated to specially constructed cloning vectors pFDFL118 or pFDFL119, and the ligated products were used to transform MV1184. If any back mutation happens to occur during PCR, the transformants would appear blue on medium with X-Gal and IPTG. By scoring the number of blue and white colonies, the fidelity of DNA polymerase can be calculated. With this system the error of replication of the FD DNA polymerase was found to be 10(-5)-10(-6).

Base Sequence↗
PubMed1997

Synthesis, in vivo evaluation and PET study of a carbon-11-labeled neuronal nitric oxide synthase (nNOS) inhibitor S-methyl-L-thiocitrulline.

UNLABELLED: Reports have implicated neuronal nitric oxide synthetase (nNOS) in the pathological effects of neurodegenerative diseases. S-Methyl-L-thiocitrulline (MTICU), a potent and selective nNOS inhibitor (Ki = 1.2 nM), was chosen as our initial target molecule for positron emitter labeling as a potential nNOS tracer. We report the synthesis, biological evaluation and primate brain images of S-[11C]methyl-L-thiocitrulline ([I11C]MTICU). METHODS: The two-step synthesis of [11C]MTICU consisted of the S-alkylation of alpha-N-Boc-L-thiocitrulline t-butyl ester with [11C]Mel followed by TFA hydrolysis and HPLC purification. The final product was obtained within 50 min (yield = 9.1%-12.5%, based on [11C]Mel S.A. = 27-680 Ci/mmol at end of synthesis). The lipophilicity of [11C]MTICU was determined by octanol/water partition coefficient (LogP). Blood stability of this tracer in vitro and in vivo was measured by HPLC analysis. Biodistribution using female Sprague-Dawley rats was performed, including examination of uptake in cerebellum and olfactory bulb (high nNOS) as well as cortex and brain stem (low nNOS). Carbon-11-MTICU was administered to a female baboon and brain images were obtained using a Siemens ECAT EXACT scanner for determination of brain regional uptake and blood-brain barrier permeability. RESULTS: At 30 min postinjection, [11C]MTICU remained 64% intact in vivo and 95% intact in vitro. Lipophilicity estimation gave Log p = 1.08 +/- 0.08 (n = 6). The brain (0.11% ID/g)-to-blood (0.20% ID/g) ratio was 1:2 at 30 min postinjection. Uptake in the cerebellum was 20% higher than in either the cortex or the brain stem (p < 0.05). Blockage using 1 mg/kg MTICU reduced uptake in the cerebellum and the cortex by 22%, but did not affect the brain stem. PET imaging showed that [11C]MTICU brain uptake, corrected for blood volume, was stable from 10 min to 1 hr at approximately 0.4% ID/organ. PET images of a baboon brain showed increased uptake in the region of the olfactory bulb compared to uniform biodistribution in the rest of the brain. CONCLUSION: The [11C]MTICU is a tracer that is potentially useful in determining nNOS levels in vivo.

Animals↗
PubMed1997

A study of apolipoprotein A-IV genetic polymorphism, serum lipids and lipoproteins in Beijing habitants.

OBJECTIVES: Apolipoprotein (apo) A-IV genetic polymorphism and its effect on serum lipids, apoA-I and apoA-IV were investigated in order to clarify the role of apoA-IV gene during the development of hyperlipidemia. METHODS: Four polymorphic sites (codon 127, 167, 347 and 360) of apoA-IV gene (exon 3) were determined in two groups of inhabitants in Beijing (Group I: 145 healthy individuals; Group II: 41 cases of hyperlipidemic patients and controls) by PCR-RFLP technique. Serum concentrations of HDL-cholesterol (HDL-C), HDL3-C, HDL2-C, triglyceride (TG), total cholesterol (TC), apoA-I and apoA-IV were studied among the individuals with different genotypes of apoA-IV. RESULTS: In Group I, frequencies of the alleles were 0.648 and 0.352 in codon 127; 0.972 and 0.028 in codon 167; 0.817 and 0.183 in codon 347. Two common alleles were 0.941 and 0.059 in codon 360. The results indicated that cases of codon 127 heterozygotes had a significantly higher serum TC level and cases of apoA-IV Ser127 homozygotes kept a markedly low TG level. Both homozygotes and heterozygotes which carried apoA-IV His 360 exhibited a significantly higher concentration of TC in comparing with that of apoA-IV Gln 360 homozygotes. The data from Group II showed that the allele frequency of His 360 had a significant difference between patients and controls. CONCLUSIONS: Certain polymorphic sites of apoA-IV gene might influence the serum lipid levels in both healthy persons and hyperlipidemic patients. His 360 polymorphic position might have a relationship with the development of hyperlipidemia.

Adult↗
PubMed1997

[Endocrine differences between patients with luteal phase deficiency and inadequate endometrial response].

OBJECTIVE: To study the difference of endocrine characteristics between patients with luteal phase deficiency (LPD) and inadequate endometrial response (IER). METHODS: Serum estradiol (E2), progesterone (P), follicle-stimulating hormone, luteinizing hormone and prolactin levels were determined by radioimmunoassay in cycles of LPD, IER and normal controls. Contents of endometrial cytoplasmic estradiol receptors (ERc), nuclear estradiol receptors (ERn), cytoplasmic progesterone receptors (PRc) and nuclear progesterone receptors (PRn) were determined by dextran coated charcoal assay in the same cycle. RESULTS: Serum E2 and P levels in the luteal phase of patients with LPD were significantly lower than those of normal group (P < 0.001), no significant difference of endometrial estrogen receptor and progesterone receptor contents was found between the two groups (P > 0.1). Serum E2 levels in both follicular and luteal phase of IER patients were significantly lower than those of normal groups (P < 0.001), but serum P levels in luteal phase of the two groups showed no difference (P > 0.1). The contents of ERc and PRn in proliferative phase and PRc contents throughout the menstrual cycle were also lower than those of the normal group (P < 0.001, < 0.001 and < 0.05 respectively). CONCLUSIONS: These results indicate that LPD and IER are two distinct entities in terms of endocrine characteristics. To distinguish underdeveloped endometrium caused by either LPD or IER is the key to choose appropriate treatment.

Adult↗
PubMed1997

[Effects of bFGF on succinate dehydrogenase level and oxygen consumption of skin flap in rats].

To investigate the effects of basic fibroblast growth factor (bFGF) on necrosis rate, succinate dehydrogenase level and oxygen consumption of the skin flap, 18 Wistar rats were divided into 2 groups. Caudally based skin flap was raised on the back of each rat. Nine micrograms bFGF or normal saline with heparin was instilled under the flaps respectively after closure of the wounds. After 7 days, the necrosis rate of each wound was measured. The result showed that in bFGF group, the average necrosis rate of skin flap was 18.2%, less than that of the control group (37.14%). Succinate dehydrogenase content and oxygen consumption in bFGF group were higher than those of the corresponding sites in the control group (P < 0.05). It was suggested that the use of bFGF resulted in the decrease rate of necrosis of skin flap, and it maintained higher succinale dehydrogenase level and oxygen consumption. It was concluded that bFGF would probably be valuable for clinical use.

Animals↗
PubMed1997

[Bowel elongation technique by using omentum as vascular pedicle in beagle dogs].

Basing on the establishment of an isolated bowel segement (IBS) in Beagle dog by omentoenteropexy, the possibility of using omentum as vascular pedicle in bowel elongation was investigated. Five young Beagle dogs (3 females, 2 males) with a body weight of 5-9 kg were used. A longitudinal incision (15 cm long) was made down to the seromuscular layer of the jejunal segment on the antimesenteric border, 20 cm distal to the duodenojejunal fold, the mucosal layer should never be injured. Then the free margin of the omentum was attached to the seromuscular border of the jejunum by interrupted sutures. One dog died from volvulus and necrosis of the bowel 3 days after operation. Seven weeks later, the mesentery was ligated in one dog and the bowel lengthening procedure was carried out in the other 3 dogs. The procedure consisted of longitudinal splitting of the isolated bowel segment anteroposteriorly, thus two separated segments of bowel were obtained, each received its own blood supply from either omental or mesenteric blood vessels. Either of the longitudinally splitting segments was rebuilt into one intestinal canal by 3/0 non-traumatic sutures. Then isoperistaltic end-to-end anastomosis of these two isolated segments was carried out, and an jejunostomy was established. The free jejunal ends were rejoined together to restore the continuity of the bowel lumen. Two weeks later, the blood supply of the experimental bowel segment was observed. It was shown that the IBS and elongated bowel segment (EBS) appeared viable, and there was good collateral circulation between the bowel segment and the omentum. The regeneration of lymphatics was observed from injection of methylene blue. It was concluded that a viable IBS and EBS could be established by using omentoenteropexy technique. The application of the this model in the management of short bowel syndrome needed to be further investigated.

Anastomosis, Surgical↗
PubMed1996

Cellular responses to psychomotor stimulant and neuroleptic drugs are abnormal in mice lacking the D1 dopamine receptor.

Stimulation of dopamine D1 receptors has profound effects on addictive behavior, movement control, and working memory. Many of these functions depend on dopaminergic systems in the striatum and D1-D2 dopamine receptor synergies have been implicated as well. We show here that deletion of the D1 dopamine receptor produces a neural phenotype in which amphetamine and cocaine, two addictive psychomotor stimulants, can no longer stimulate neurons in the striatum to express cFos or JunB or to regulate dynorphin. By contrast, haloperidol, a typical neuroleptic that acts preferentially at D2-class receptors, remains effective in inducing catalepsy and striatal Fos/Jun expression in the D1 mutants, and these behavioral and neural effects can be blocked by D2 dopamine receptor agonists. These findings demonstrate that D2 dopamine receptors can function without the enabling role of D1 receptors but that D1 dopamine receptors are essential for the control of gene expression and motor behavior by psychomotor stimulants.

Amphetamine↗
PubMed1996

Induction properties of a transiently transfected glucocorticoid-responsive gene vary with glucocorticoid receptor concentration.

Transient transfections of steroid receptors have yielded much of the data used to construct the current models of steroid hormone action. These experiments invariably examine the ability of receptors to regulate transcription when occupied by saturating concentrations of steroid. We now report that other induction properties of a transiently transfected gene are not constant but vary with the concentration of transiently transfected glucocorticoid receptors. Thus, the percentage of maximal induction seen with subsaturating concentrations of glucocorticoid could be dramatically increased, and an antiglucocorticoid could be converted into a partial glucocorticoid, simply by increasing the concentration of glucocorticoid receptors. This behavior was observed in HeLa cells, containing endogenous receptors, or in CV-1 cells, containing almost no endogenous receptor, with either homologous or heterologous receptors. These increases were relatively insensitive to the concentration of reporter gene, suggesting the titration of some transcription factor(s) involved in regulating the position of the glucocorticoid dose-response curve and the agonist activity of an antiglucocorticoid. This property of transfected glucocorticoid receptors required a full-length, functionally active receptor but was retained, albeit reduced in magnitude, in the absence of binding to a glucocorticoid response element. Furthermore, this phenomenon was specific in that the A form of the human progesterone receptor had no effect under the same conditions. These variations in induction properties of antiglucocorticoids and of subsaturating concentrations of glucocorticoid, in a manner that was proportional to the amount of transfected receptor, reveal processes that are not operative with saturating concentrations of glucocorticoid. These variations also demonstrate that caution should be exercised in making mechanistic conclusions based solely on experiments conducted with saturating concentrations of glucocorticoid.

Animals↗