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Biomedical subjects

L Guan

Publications and source records attributed to L Guan.

At least 55 records · Page 3Linked to original sources
PubMed1997

[An investigation of precipitation of airborne fungi particles in the rooms of university library].

Precipitation of airborne fungi particles in the rooms of an University library and the influencing factors were studied in May 1994 with the fallen plate method. The total average precipitation of airborne fungi particles was 11.68 per dish in 5 minutes. The differences were significant from different room patterns, floors and times, so were the humidity assayed. The book-store rooms and reading rooms had an average precipitation of 15.01 and 8.35 per dish in 5 minutes respectively (P < 0.05), and humidity of 41.7 and 11.4 percent respectively (P < 0.01). The influencing factors were: different floors and room patterns, the people's activity, the different time, humidity, ventilation and book pollution.

Air Microbiology↗
PubMed1997

[The development of a special instrument for measuring propagation velocity distribution of compound active potential using collision method].

This paper introduced a special instrument for measuring the propagation velocity distribution of compound active potential using collision method. In briefly, the principle of collision method is introduced. The structure and operation principle of the neuroelectrical amplifier, A/D converter and computer interface circuit are emphatically discussed. The instrument has the advantage of usable and low costing. It has considerable application value in clinical pathological diagnosis and research experiments of nervous system.

Action Potentials↗
PubMed1997

[A study on TF no-mix orthodontic adhesive].

A no-mix orthodontic adhesive composed of primer and paste was developed. The adhesive eliminated the spatulation procedure to which most commercially available products were imperative, could quickly polymerize and cure by means of contact and slight compression of the primer with the paste. It featured high bond strength, convenient handling, enough working time, easy removal of extra adhesive around the bracket and no objectionable odour. The biological tests showed it was safe to use in orthodontic practice, and the results of clinical trials certified the reliable performance, effective bond and convenient use of the adhesive.

Adhesives↗
PubMed1997

[A study on bonding performance of DPR dental adhesive].

Phosphoric acid esters can be used as restorative materials for human teeth and bones. The authors investigated bonding performance of phosphoric acid diester (DPR) with tensile bond test. The results showed: (1) DPR dental adhesive could markedly improve the tensile bond strength (TBS) to human enamel, dentin, dental nonprecious metals and self-curing denture plastics, it is used widely; (2) Three kinds of the etchants could also improve markedly TBS. 37% phosphoric acid and DT-I were respectively applicable to enamel and dentin. DT-II was available to both of them.

Dental Enamel↗
PubMed1997

[Studies on the flavonoids from Dendranthema lavandulifolium].

From the whole plant of Dendranthema lavandulifolium, two flavonoides (I, II) and two flavone glycosides (III, IV) were isolated. They were identified as luteolin (I), apigenin (II), 5-hydroxy-4'-methoxy-flavone-7-O-alpha-L-rhamnopyranosyl(1-->6)-beta- D-glucopyranosyl (acaciin III) and 5-hydroxy-4'-methoxy-flavone-7-O-alpha-L-rhamnopyranosyl (1-->6) [2-O-acetyl-beta-D-glucopyranosyl(1-->2)]-beta-D-glucopyranoside (IV) by means of IR, UV, 1H-NMR, 13C-NMR, EI-MS, HRFAB, etc. Among these four compounds, I, II were isolated for the first time from this plant, IV is a new compound.

Apigenin↗
PubMed1996

Isolation, characterization and expression of the maize Cat2 catalase gene.

The maize Cat2 gene was isolated by direct cloning and PCR. The clones were mapped and sequenced. The start site of transcription was determined by primer extension. Computer analysis of the 1.6 kb Cat2 promoter sequence has revealed an obvious TATA box, tow GC boxes, a putative GA response element, and several ACGT core sequences known to have diverse regulatory functions in plants. Several other protein binding motifs were also identified within 800 bp upstream from the transcriptional start site. Five introns were identified in the Cat2 coding region. All five Cat2 introns are located in exactly the same position as five of the six introns in Cat1. Two of the Cat2 introns are located in the same position as the two Cat3 introns. The identical positioning of these introns suggests an evolutionary link between all three maize catalase genes. The response of the CAt2 gene to plant growth regulators was examined. Results clearly showed that the response of CAt2 to several environmental factors are developmental stage-dependent. Thus, complex regulatory mechanisms appear to be involved in the regulation of Cat2 expression in maize.

Amino Acid Sequence↗
PubMed1996

Molecular evolution of maize catalases and their relationship to other eukaryotic and prokaryotic catalases.

We have compared the nucleotide and protein sequences of the three maize catalase genes with other plant catalases to reconstruct the evolutionary relationship among these catalases. These sequences were also compared with other eukaryotic and prokaryotic catalases. Phylogenies based on distances and parsimony analysis show that all plant catalases derive from a common ancestral catalase gene and can be divided into three distinct groups. The first, and major, group includes maize Cat1, barley Cat1, rice CatB, and most of the dicot catalases. The second group is an apparent dicot-specific catalase group encompassing the tobacco Cat2 and tomato Cat. The third is a monocot-specific catalase class including the maize Cat3, barley Cat2, and rice CatA. The maize Cat2 gene is loosely related to the first group. The distinctive features of monocot-specific catalases are their extreme high codon bias at the third position and low degree of sequence similarity to other plant catalases. Similarities in the intron positions for several plant catalase genes support the conclusion of derivation from a common ancestral gene. The similar intron position between bean catalases and human catalase implies that the animal and plant catalases might have derived from a common progenitor gene sequence.

Catalase↗
PubMed1996

Interaction between the caudal brainstem and the lamprey central pattern generator for locomotion.

Because of its remarkable simplicity and the robustness of the isolated preparation, the lamprey has been used as a model system to study locomotion and its central pattern generator. The function of the spinal cord is relatively well understood in this context, but the role of the brain or even the caudal brainstem remains less so. We here present a study of the interaction between the caudal brainstem and the spinal pattern generator for locomotion. We show that the interaction is highly complex, with both feedforward input from the brainstem to spinal cord and feedback input from the spinal cord to brainstem playing a significant role in the motor output during locomotion. The brainstem, when diffusely stimulated pharmacologically, can initiate fictive locomotion, or it can disrupt or alter the ongoing D-glutamate initiated motor output. The nature of the disruptions vary greatly, and can induce generalized irregularity, while the alterations can include accelerating or decelerating of the bursting. All behaviors are displayed with spectrograms of the motor nerve discharge. We also show that the unstimulated brainstem can disrupt as well as slow the bursting, but in a complex fashion. Finally, a slow episodic behavior initiated from the caudal brainstem is also described. This can be elicited either by D-glutamate to the brainstem or by ascending activity from the spinal cord pattern generator. Thus, we demonstrate that the interaction between the brainstem and the spinal cord during the production of locomotion is highly complex. The locomotion that is exhibited by the combined brainstem-spinal cord preparation is extremely variable. This is in striking contrast to the variability of the locomotor output pharmacologically induced in the spinal cord alone. The latter preparation exhibits remarkable regularity, or upon occasion, irregularity, but not the routine irregularity or the systemic up and down changes in frequency seen with the brainstem present. However, the pattern of frequency changes induced by the brainstem is not predictable, and remains to be understood.

Animals↗
PubMed1996

Visual search performance with complete and incomplete visual lobe areas.

A simulation study of the effects of visual lobe shape and search strategy on search performance is reported. Using a homogeneous pattern search task that did not dictate eye fixation movements (as in reading), three basic categories of strategy and two lobe shapes were tested. Random strategies with controlled overlap of lobe areas, representing various degrees of memory, were found to produce better performance (faster search times with equal or better detection rates) than either a completely random strategy or systematic strategies with various degrees of controlled visual lobe area overlap. The controlled overlap random strategies were far better able to compensate for non-optimum interfixation distances and distortion of visual lobe shape than systematic strategies.

Attention↗
PubMed1996

[A study of corneal transplantation and human leukocyte antigen matching].

OBJECTIVE: The effect of human leukocyte antigen (HLA) matching on immune rejection after keratoplasty was studied. METHODS: Immunoserologic HLA typing was performed on thirty-three eyes with corneal vascularization of 33 high-risk patients before keratoplasty, and HLA matching was made before the surgery. The donor corneas used for these cases were selected on the basis of obtaining a negative HLA cross-match test and matched ABO antigen compatibility of blood group before surgery. The mean follow-up was fifteen months. RESULTS: The findings suggested that there should be highly statistic significance (t = 7.36, P < 0.01) between the rate of rejection of well matched group and that of the poorly matched one. There was no correlation between the number of HLA antigen matched and the rejection rate (t = 0.917, P > 0.05). CONCLUSION: Lower incidence of corneal graft failure from allograft rejection occurs when well HLA matching is used for selecting donor in high-risk patients with corneal vascularization.

Adult↗
PubMed1996

[Effects of saponins from stems and leaves of Panax quinquefolium L. on the contraction of rabbit aortic strips].

It has been found out that the saponins from stems and leaves of Panax quinquefolium (PQS) can non-competitively antagonize the dose-response curves of norepinephrine (NE), potassium chloride and calcium chloride on the isolated aortic strips of rabbits, and obviously inhibit intracellular and extracellular Ca2(+)-dependent contraction of the aortic strips induced by NE. These effects of PQS are similar to verapamil.

Animals↗
PubMed1995

Developmentally related responses of maize catalase genes to salicylic acid.

The response of the maize catalase genes (Cat1, Cat2, and Cat3) to salicylic acid (SA) was examined at two distinct developmental stages: embryogenesis and germination. A unique, germination-related differential response of each maize catalase gene to various doses of SA was observed. During late embryogenesis, total catalase activity in scutella increased dramatically with 1 mM SA treatment. The accumulation of Cat2 transcript and CAT-2 isozyme protein provided the major contribution to the observed increase in total catalase activity. This increase was paralleled by the enhanced growth of germinated embryos at that stage. In a CAT-2 null mutant line, a full compensation of total catalase activity by the CAT-1 isozyme was observed in the presence of SA. This suggests that catalase is important for maintenance of normal cellular processes under stress conditions. SA at 1 mM, which enhances growth of precociously germinated embryos, appeared to inhibit seed germination at 1 day after inhibition. Furthermore, Cat2 transcript accumulation was inhibited at this stage. SA is probably not a direct signal for the induction of the catalase genes. Other signals, possibly germination-related regulator(s), might be responsible for the induction of the catalase genes. The effect of SA on the activity of purified catalase protein was also examined.

Catalase↗
PubMed1995

Modulation of macrophage phagocytic activity by cell wall components of Candida albicans.

Cell wall components of the pathogenic yeast Candida albicans have been shown to possess significant immunomodulatory activity both in vivo and in vitro. We have previously found that an ethylenediamine (EDA) extract of the Candida cell wall exhibits significant immunosuppressive activity. In an effort to further characterize the immunomodulatory activity of the EDA extract, we attempted to determine the effect of this extract on macrophage phagocytic activity. Our results show that nonelicited peritoneal macrophages treated for 24 or 48 hr with the EDA extract fail to phagocytize Candida yeast cells normally. We have observed that the phagocytosis of Candida is mediated by a combination of lectin-like receptor-, Fc receptor-, and complement receptor-type 3 (CR3)-dependent processes. Results show, however, that the most efficient uptake of this organism is dependent on CR3-mediated phagocytosis. Experiments carried out under various opsonic conditions suggest that the level of CR3-mediated phagocytosis of Candida is depressed following EDA extract treatment. These results show that a substantial mechanism of macrophage phagocytosis is depressed following contact with cell wall components of Candida.

Animals↗
PubMed1995

Characterization of an alternative superantigen binding site expressed on a renal fibroblast cell line.

It is well established that the bacterial superantigens bind to both TCR beta-chain and, with moderate affinity, to MHC class II molecules. Class II-bearing cells bind the superantigen and present the superantigen to T cells expressing certain TCR beta-chain variable region alleles. We have observed that the superantigen staphylococcal enterotoxin (SE) B binds to COS-1, an African green monkey kidney fibroblast-like cell line. This cell line fails to express class II and the binding of SEB is saturable. Scatchard analysis of radiolabeled ligand binding data reveals a binding affinity for COS of 51 nM, while binding to DR1-transfected L cells is measured at 150 nM. Further analysis shows that SEB bound to COS cells, unlike SEB bound to DR1-bearing L cells, is not recognized by T cells in the presence or absence of accessory cytokines or anti-CD28. Studies carried out with chemical cross-linking agents show that radiolabeled SEB associates with a membrane protein of approximately 85 kDa. These studies suggest that the alternative superantigen binding molecule (p85) binds SEB with an affinity roughly equivalent to SEB binding by class II molecules, but at a site which does not permit recognition by the TCR.

Animals↗
PubMed1995

[In vitro effect of metronidazole ester on Trichomonas vaginalis and Entamoeba histolytica].

Metronidazole ester, a new nitroimidazole drug, was synthesized by the Department of Physical Chemistry, School of Pharmacy, Shanghai Medical University. The trichomonadicidal and amoebicidal activity of metronidazole ester was evaluated in vitro by the cultivation of Trichomonas vaginalis and Entamoeba histolytica at different drug concentrations. The results indicated that the 100% lethal concentration for T. vaginalis and E. histolytica was 2.6 micrograms/ml and 40 micrograms/ml, respectively after incubation with metronidazole ester for 48 h. In comparison with metronidazole, the effect of metronidazole ester for both protozoa was similar.

Animals↗
PubMed1994

Both T cells and macrophages are targets of kappa-opioid-induced immunosuppression.

We have previously shown that antibody responses are inhibited following administration of kappa-opioid agonists. We found that the inhibition was blocked by either naloxone or the kappa-selective antagonist norbinaltorphimine. This inhibitory activity is apparent after short-term treatment with the kappa-opioid agonist. In an attempt to identify the cell populations which serve as the target for this immunosuppressive effect, we have carried out cell fractionation analyses to generate isolated T cells and macrophages. Using multiple cell fractionation methods, we have determined that short-term treatment of either T cells or macrophages with the kappa-opioid agonist U50,488H results in significant inhibition of in vitro antibody responses. We also find that the inhibition of both T cell and macrophage activity can be blocked by naloxone. These studies demonstrate that resting T cells and macrophages express kappa-opioid receptors and exhibit significant opioid responsiveness prior to activation by antigen.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1994

[Leishmaniasis in Karamay. XIV. Identification of promastigote isolates from naturally infected Phlebotomus major wui].

Phlebotomus major wui, an anthropophilic species, was predominant among sandflies in Karamay, Xinjiang of China. The females of this species collected in the wild and houses were detected to be infected with promastigotes. Three isolates of promastigotes obtained from P. major wui were inoculated intraperitoneally and subcutaneously into normal hamsters or BALB/c mice which developed visceral leishmaniasis later. The mean size of amastigotes in hamster viscera (smear observation) artificially inoculated with the cultured parasite originated from sandfly was significantly smaller than those in control hamster inoculated with the cultured Leishmania turanica from great gerbils in situ. The promastigotes from P. major wui hardly grew in NNN medium. In addition, 32P labeled gene gp63 was used as probe to hybridize DNA prepared from L. infantum, L. turanica and Leishmania from this sandfly showed that marked homogeneity existed between the isolates from P. major wui and L. infantum. At the present time, visceral leishmaniasis did not occur in Karamay but cutaneous leishmaniasis (CL) has been evidenced. Thus, what is the source of natural infection of P. major wui? Whether L. turanica or L. infantum is the pathogen of human CL in this area? These are interesting aspects to deal with in the further study.

Animals↗