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Biomedical subjects

M Wu

Publications and source records attributed to M Wu.

At least 487 records · Page 27Linked to original sources
PubMed1991

Effects of administration of dopamine D2 agonist quinpirole on exploratory locomotion.

Injections of the dopamine D2 agonist quinpirole (LY 171555) into the nucleus accumbens reduced exploratory locomotion in a dose-dependent manner. Injections of the dopamine D1 agonist SKF 38393 had no effect on exploratory locomotion. The results are consistent with observations from recent electrophysiological and behavioral experiments which suggest a presynaptic action of the D2 agonist. It is proposed that quinpirole activates D2 receptors on the axon terminals of glutamatergic hippocampal-accumbens neurons that are associated with exploratory locomotion.

Animals↗
PubMed1991

Cellular metabolism of proxyl nitroxides and hydroxylamines.

Previous data from model systems indicated that the proxyl nitroxides should be especially resistant to bioreduction and therefore could be an effective solution to this often problematic characteristic of nitroxides. Therefore, we investigated the rate of reduction by cells and by the usual model system, ascorbate, of four proxyl nitroxides and three reference nitroxides. We found that, while the rate of reduction by ascorbate of the proxyl nitroxides was slower than the rate of a prototypic pyrrolidine nitroxide (PCA), the reverse was true for reduction by cells. We also studied the rate of oxidation of the corresponding hydroxylamines. The rate of oxidation by cells of the proxyl hydroxylamines was relatively fast, especially for the most lipophilic derivative. These results indicate that: (i) proxyl nitroxides may not be unusually resistant to bioreduction by functional biological systems; (ii) accurate knowledge of relative rates of metabolism of nitroxides and hydroxylamines in cells and tissues will require direct studies in these systems because the rates may not closely parallel those observed in model (chemical) systems; and (iii) proxyl nitroxides show potential value as agents to measure oxygen concentrations by the rates of oxidation of their corresponding hydroxylamines.

Animals↗
PubMed1991

Purification and characterization of a gamma-like DNA polymerase from Chlamydomonas reinhardtii.

A crude in vitro system which initiates chloroplast DNA synthesis near the D-loop site mapped by electron microscopy [Wu, M., Lou, J. K., Chang, D. Y., Chang, C. H., & Nie, Z. Q. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 6761-6765] consists of soluble proteins and proteins extracted from purified thylakoid membrane. In this paper, a DNA polymerase activity was purified to near homogeneity from the soluble protein fraction of this in vitro system by sequential chromatographic separations on heparin-agarose, DEAE-cellulose, and single-stranded DNA-agarose columns and sedimentation in a glycerol gradient. In the glycerol gradient, the enzyme activity sedimented at a position corresponding to a 110-kDa protein. Electrophoretic analysis of the highly purified fraction on SDS-polyacrylamide gel revealed a major polypeptide band with an apparent molecular mass of approximately 116 kDa. In situ DNA polymerase activity assay shows that the DNA polymerization function is associated with the 116-kDa band and an 80-kDa band which could be a subunit of the enzyme. Polymerization activity is inhibited by N-ethylmaleimide, ethidium bromide, and dideoxycytosine triphosphate and is relatively resistant to aphidicolin. Poly(dA).(dT)10 and gapped double-stranded DNA are preferred templates. The purified enzyme contains no exonuclease activity and can initiate DNA replication in a supercoiled plasmid DNA template containing the chloroplast DNA replication origin.

Ammonium Sulfate↗
PubMed1991

Encoding repetition rate and duration in the inferior colliculus of the big brown bat, Eptesicus fuscus.

1. Encoding of temporal stimulus parameters by inferior collicular (IC) neurons of Eptesicus fuscus was studied by recording their responses to a wide range of repetition rates (RRs) and durations at several stimulus intensities under free field stimulus conditions. 2. The response properties of 424 IC neurons recorded were similar to those reported in previous studies of this species. 3. IC neurons were classified as low-pass, band-pass, and high-pass according to their preference for RRs and/or durations characteristic of, respectively, search, approach, or terminal phases of echolocation. These neurons selectively process stimuli characteristic of the various phases of hunting. 4. Best RRs and best durations were not correlated with either the BFs or recording depths This suggests that each isofrequency lamina is capable of processing RRs and durations of all hunting phases. 5. Responses of one half of IC neurons studied were correlated with the stimulus duty cycle. These neurons may preferentially process terminal phase information when the bat's pulse emission duty cycle increases. 6. While the stimulus RR affected the dynamic range and overall profile of the intensity rate function, only little effect was observed with different stimulus durations.

Acoustic Stimulation↗
PubMed1991

The sequence-directed bent DNA detected in the replication origin of Chlamydomonas reinhardtii chloroplast DNA is important for the replication function.

We demonstrated that the 1055 bp restriction fragment containing OriA, a chloroplast DNA replication origin of Chlamydomonas reinhardtii, has electrophoretic anomalies characteristic of bent DNA. A tandem dimer of the region was constructed. Quantitative measurement of the relative gel mobility of a set of permuted fragments was used to extrapolate the approximate position of the bent DNA segment. By analyzing the gel mobility of short, sequenced fragments of the bent DNA region, the putative bending locus was identified. Two A4 tracts and two A5 tracts were located in the bending locus. Oligonucleotide-directed mutagenesis was then used to disrupt the A tract or the spacing between A tracts and the effect of site-specific mutation on electrophoretic mobility was analyzed. To assess the functional role of the bent DNA region, subclones containing the bending locus, mutated bending locus, and regions flanking the bending locus were constructed. Each subclone was used as template in an in vitro DNA replication system which preferentially initiated DNA replication at OriA. A 224 bp subclone with the bending locus positioned in the middle displayed the highest replication function and was sufficient to initiate DNA replication in vitro. Site-specific mutations or alterations of the A tracts resulted in decreased DNA bending and decreased DNA replication activity.

Base Sequence↗
PubMed1991

Quinpirole to the accumbens reduces exploratory and amphetamine-elicited locomotion.

Locomotor activity measured in an open-field apparatus was increased by adding partitions to enhance exploratory locomotion and by injecting amphetamine into the nucleus accumbens. Administration of the dopamine D2 agonist, quinpirole, into the nucleus accumbens reduced significantly both exploratory and amphetamine-elicited locomotion. It is suggested that these effects of quinpirole are mediated by different presynaptic mechanisms.

Amphetamine↗
PubMed1991

Recognition of MHC TL gene products by gamma delta T cells.

We have studied the ligand specificity of a gamma delta T-cell receptor (TCR) derived from a mouse T-cell hybridoma (KN6). KN6 cells reacted with syngeneic (C57BL/6) cells from various origins (splenocytes, thymocytes, peritoneal exudate cells, etc.) and cells from many different mouse strains. KN6 reactivity against cells from a panel of congenic and recombinant mouse strains demonstrated that the ligand recognized by KN6 is controlled by an MHC-linked gene that most probably maps in the TL region. We cloned this gene and formally proved that it does map in the TL region. This gene turned out to be a novel class I gene (designated T22b) belonging to a hitherto unidentified cluster of TL region genes in strain C57BL/6. This gene was expressed in many different tissues and cell types. We also examined the tissue expression of several other TL genes. One of these, the structural gene (T3b) encoding the thymus leukemia (TL) antigen from C57BL/6 mice, was specifically expressed in the epithelium of the small intestine. Since the intestinal epithelium of the mouse is known to be the homing site for a subset of gamma delta T cells (i-IEL) bearing diverse TCR with V7 rearranged gamma chains, we propose that the T3b gene product is part of the ligand recognized by some of the i-IEL. Our data support the idea that gamma delta T cells might be specific for non-classical class I or class I-like molecules and suggest that gamma delta TCR and non-classical MHC co-evolved for the recognition of a conserved set of endogenous or foreign peptides.

Age Factors↗
PubMed1991

Macronuclei and micronuclei in Tetrahymena thermophila contain high-mobility-group-like chromosomal proteins containing a highly conserved eleven-amino-acid putative DNA-binding sequence.

HMG (high-mobility-group protein) B and HMG C are abundant nonhistone chromosomal proteins isolated from Tetrahymena thermophila macronuclei with solubilities, molecular weights, and amino acid compositions like those of vertebrate HMG proteins. Genomic clones encoding each of these proteins have been sequenced. Both are single-copy genes that encode single polyadenylated messages whose amounts are 10 to 15 times greater in growing cells than in starved, nongrowing cells. The derived amino acid sequences of HMG B and HMG C contain a highly conserved sequence, the HMG 1 box, found in vertebrate HMGs 1 and 2, and we speculate that this sequence may represent a novel, previously unrecognized DNA-binding motif in this class of chromosomal proteins. Like HMGs 1 and 2, HMGs B and C contain a high percentage of aromatic amino acids. However, the Tetrahymena HMGs are small, are associated with nucleosome core particles, and can be specifically extracted from macronuclei by elutive intercalation, properties associated with vertebrate HMGs 14 and 17, not HMGs 1 and 2. Thus, it appears that these Tetrahymena proteins have features in common with both of the major subgroups of higher eucaryotic HMG proteins. Surprisingly, a linker histone found exclusively in transcriptionally inactive micronuclei also has several HMG-like characteristics, including the ability to be specifically extracted from nuclei by elutive intercalation and the presence of the HMG 1 box. This finding suggests that at least in T. thermophila, proteins with HMG-like properties are not restricted to regions of transcriptionally active chromatin.

Amino Acid Sequence↗
PubMed1991

Cell cycle tyrosine phosphorylation of p34cdc2 and a microtubule-associated protein kinase homolog in Xenopus oocytes and eggs.

We have examined the time course of protein tyrosine phosphorylation in the meiotic cell cycles of Xenopus laevis oocytes and the mitotic cell cycles of Xenopus eggs. We have identified two proteins that undergo marked changes in tyrosine phosphorylation during these processes: a 42-kDa protein related to mitogen-activated protein kinase or microtubule-associated protein-2 kinase (MAP kinase) and a 34-kDa protein identical or related to p34cdc2. p42 undergoes an abrupt increase in its tyrosine phosphorylation at the onset of meiosis 1 and remains tyrosine phosphorylated until 30 min after fertilization, at which point it is dephosphorylated. p42 also becomes tyrosine phosphorylated after microinjection of oocytes with partially purified M-phase-promoting factor, even in the presence of cycloheximide. These findings suggest that MAP kinase, previously implicated in the early responses of somatic cells to mitogens, is also activated at the onset of meiotic M phase and that MAP kinase can become tyrosine phosphorylated downstream from M-phase-promoting factor activation. We have also found that p34 goes through a cycle of tyrosine phosphorylation and dephosphorylation prior to meiosis 1 and mitosis 1 but is not detectable as a phosphotyrosyl protein during the 2nd through 12th mitotic cell cycles. It may be that the delay between assembly and activation of the cyclin-p34cdc2 complex that p34cdc2 tyrosine phosphorylation provides is not needed in cell cycles that lack G2 phases. Finally, an unidentified protein or group of proteins migrating at 100 to 116 kDa increase in tyrosine phosphorylation throughout maturation, are dephosphorylated or degraded within 10 min of fertilization, and appear to cycle between low-molecular-weight forms and high-molecular-weight forms during early embryogenesis.

Animals↗
PubMed1991

Ethanol affects release of TNF and GM-CSF and membrane expression of TNF receptors by human macrophages.

Ethanol intoxication has been associated with bacterial pneumonia and tuberculosis. More recently, ethanol was shown to impair the capacity of pulmonary macrophages to produce superoxide anion and tumor necrosis factor (TNF). Furthermore, exposure to ethanol compromises macrophage's ability to respond to stimulation with TNF and granulocyte-macrophage colony-stimulating factor (GM-CSF), and kill an intracellular pathogen, Mycobacterium avium. Based on these previous findings, we examined whether exposure to ethanol affects superoxide anion production, synthesis of cytokines, and expression of membrane receptors to TNF on human monocyte-derived macrophages. Brief exposure to 10 or 50 micrograms/dl of ethanol significantly reduced the macrophage's response to a subsequent stimulus with phorbol ester (phorbol-12-myristate-13-acetate, PMA), and this unresponsive state lasts for approximately 6 h following removal of ethanol. When macrophages were then treated with lipopolysaccharide (LPS) in the presence of ethanol, high concentrations of TNF and GM-CSF were produced, but subsequent stimulation with LPS (second stimulus) was associated with significant impairment on synthesis and release of both TNF and GM-CSF. In addition, although ethanol had no effect on TNF binding to resting macrophages and to macrophages infected with M. avium, ethanol significantly reduced the expression of TNF receptors on interferon-gamma-stimulated macrophages. The ethanol-induced inhibition of macrophage function suggests potential mechanisms for suppression of the host's immune response and consequently increased susceptibility for infectious diseases.

Cell Membrane↗
PubMed1991

Effects of naloxone on tissue oxygen supply and somatosensory evoked potentials in cat brain during focal cerebral ischemia.

The effects of naloxone on local tissue oxygen partial pressure (pO2) and on the somatosensory evoked potentials (SEP) were studied in the brain of cat during focal cerebral ischemia. Ischemia, produced by clamping of the middle cerebral artery (MCA) by a transorbital approach, was performed in two series of cats for 3 h. In one group of cats (n = 5), naloxone 5 mg.kg-1 was injected i.v. 0.5 h after clamping. The pO2 was continuously recorded on different depths (0-5000 microns) of the median gyrus by a polarographic oxygen microelectrode. After MCA clamping, pO2 (depth of 0-1000 microns) decreased markedly and hypoxia occurred in the ischemic area. But in the deeper brain (1001-5000 microns) pO2 did not change significantly. The amplitude of SEP decreased after MCA clamping, while the conduction time of SEP did not significantly decrease. The mean pO2 values in the ischemic area were increased as compared to the control group after naloxone, especially at the depths of 0-1000 microns, and the hypoxia was improved. The amplitude of SEP was increased after naloxone in comparison to the situation of ischemia without naloxone. The conduction time of SEP was not improved significantly. We conclude that naloxone can improve the oxygen supply and the electrical activity of neurons in the ischemic region of the brain.

Animals↗
PubMed1991

[Genetic polymorphism of alpha 2HS-glycoprotein in the Han population in Chengdu].

The distribution of alpha 2HS-glycoprotein (AHSG) phenotype frequencies in the Han population in Chengdu was studied using polyacrylamide gel isoelectric focusing followed by immunofixation with rabbit anti-human AHSG serum. Two hundred eighty-six serum samples collected at random from unrelated individuals were phenotyped for AHSG. The distribution of AHSG phenotype frequencies was found to be AHSG 1 = 47.20%, AHSG 2 = 8.04% and AHSG 2 - 1 = 44.76%. The observed numbers agreed well with the expected numbers calculated on the basis of the Hardy-Weinberg equilibrium. The allele frequencies were estimated to be AHSG.1 = 0.6958 and AHSG.2 = 0.3042. The discrimination probability of AHSG is 0.5704 and the exclusion probability of parentage 0.1669.

China↗
PubMed1991

Directional sensitivity of bat inferior collicular neurons determined under normal and monaurally plugged ear conditions.

In an effort to further understand the combined effect of binaural intensity difference and pinna position on the directional sensitivity of an auditory neuron, we used free field stimulation to study the directional sensitivity of inferior collicular (IC) neurons of the big brown bat, Eptesicus fuscus, under the following three ear conditions: normal ears, monaurally plugged ear and monaurally plugged plus pinna bending backward. The best frequency (BF) and minimum threshold (MT) of each neuron were first determined for a sound (4 ms duration, 0.5 ms rise-decay times) delivered from 40 degrees contralateral in azimuth, 0 degrees in elevation relative to the recording site. Then, the neuron's MT to a BF sound delivered from 7 selected azimuthal angles with respect to the bat's head were determined. The number of impulses to a BF sound delivered at two intensities (10 and 20 dB re MT determined at 40 degrees contralateral) from each of 7 azimuthal angles was also subsequently determined. Although different IC neurons showed different variations in MT and number of impulses with sound source azimuth, most had a lowest MT and/or maximal number of impulses to BF sounds delivered from contralateral azimuthal angles regardless of ear conditions. However, among 117 neurons studied, there were 12 neurons in which the number of impulses did not vary significantly with sound direction thus showing nondirectional characteristics. Monaural plugging (a wet cotton ball) with or without backward bending of the pinna not only increased the MT of a recorded neuron but also greatly reduced the number of impulses of the neuron so that the directional sensitivity of the neuron was also modified. The effect of monaural plugging on the threshold of a neuron and the degree of modification on directional sensitivity varied among individual IC neurons. Thus, while the directional sensitivity of some IC neurons became sharper, for other neurons the same monaural plugging reduced the sharpness of their directional sensitivity curve. Directional sensitivity of IC neurons is dependent upon stimulus frequency regardless of ear conditions. High frequency neurons generally have sharper directional sensitivity than low frequency neurons. The angle of lowest MT and maximal number of impulses tended to move toward the middle portion of a bat's frontal auditory space with increasing BF.

Acoustic Stimulation↗
PubMed1991

Encoding of acoustic stimulus intensity by inferior collicular neurons of the big brown bat, Eptesicus fuscus.

Using bats as a model system, we studied the isointensity and isofrequency discharge rate functions of inferior collicular (IC) neurons under free field stimulation conditions in order to understand how the midbrain auditory neurons encode stimulus intensity. For each encountered IC neuron, the best frequency (BF), minimum threshold (MT), tuning curve and intensity rate function for the BF were first determined. Then at a fixed stimulus intensity, the number of impulses was measured for several frequencies which were incrementally chosen across the entire range of the neuron's tuning curve. Such an isointensity discharge rate function was determined for at least three different intensities above each neuron's MT. A series of isofrequency discharge rate functions were also obtained by determining the intensity rate function for each of several frequencies chosen. Among 110 intensity rate functions measured at the BF of each IC neuron, 98 (89%) were non-monotonic and 12 (11%) were monotonic. The profiles of the intensity rate functions measured at several chosen frequencies for each neuron varied greatly. Thus, within the same series of isofrequency intensity rate functions, a neuron showed both monotonic and non-monotonic functions when measured at different frequencies. Similarly, the profile of each intensity rate curve within a series of isointensity rate functions might also vary with stimulus intensity. The isointensity discharge rate functions of most IC neurons (62 neurons, 61%) was triangular shaped reaching a peak value when stimulated with BF. The remaining (39 neurons, 39%) IC neurons had isointensity functions in which different curves peaked at different stimulus frequencies. In some extreme cases, some curves had two peaks or fluctuated within a moderate range of discharge rate throughout the whole range of stimulus frequency. Our studies suggest that encoding of a wide range of acoustic stimulus intensity in the IC involves more than the discharge rate of any one individual IC neuron. Different populations of IC neurons with different BFs will have to work coordinately in order to overcome the limitation of the dynamic range of individual neurons and to solve the ambiguity created by the same discharge rate of each individual neuron to different combinations of frequency and intensity within its auditory response area.

Acoustic Stimulation↗