Biomedical subjects

A Guo

Publications and source records attributed to A Guo.

At least 55 records · Page 3Linked to original sources

PubMed1997

Transformation of sensory signals into commands for saccadic eye movements: a neural network study.

A biological plausible neural network which simulated the input-output transformation performed by primates during saccadic eye movements is constructed using a selective attention module and multi-layered neural networks with improved back propagation and a competitive learning algorithm. Simulation results show that the trained model can make fine saccades directed by the target. Representations and processing mechanisms in the saccade system are investigated. The features of most hidden units resemble those that have been observed in physiological recordings of neurons in primates visual cortex. The hidden layer even developed structures similar to those of area 7a.

Algorithms↗

PubMed1997

An immunoaffinity purified Schizosaccharomyces pombe TBP-containing complex directs correct initiation of the S.pombe rRNA gene promoter.

The multi-protein complex SL1, containing TBP, which is essential for RNA polymerase I catalyzed transcription, has been analyzed in fission yeast. It was immunopurified based on association of component subunits with epitope-tagged TBP. To enable this analysis, a strain of Schizosaccharomyces pombe was created where the only functional TBP coding sequences were those of FLAG-TBP. RNA polymerase I transcription components were fractionated from this strain and the TBP-associated polypeptides were subsequently immunopurified together with the epitope- tagged TBP. An assessment of the activity of this candidate SL1 complex was undertaken cross-species. This fission yeast TBP-containing complex displays two activities in redirecting transcriptional initiation of an S. pombe rDNA gene promoter cross-species in Saccharomyces cerevisiae transcription reactions: it both blocks an incorrect transcriptional start site at +7 and directs initiation at the correct site for S. pombe rRNA synthesis. This complex is essential for accurate initiation of the S.pombe rRNA gene: rRNA synthesis is reconstituted when this S.pombe TBP-containing complex is combined with a S.pombe fraction immunodepleted of TBP.

Base Sequence↗

PubMed1997

Molecular cloning and analysis of Schizosaccharomyces pombe Reb1p: sequence-specific recognition of two sites in the far upstream rDNA intergenic spacer.

The coding sequences for a Schizosaccharomyces pombe sequence-specific DNA binding protein, Reb1p, have been cloned. The predicted S. pombe Reb1p is 24-29% identical to mouse TTF-1 (transcription termination factor-1) and Saccharomyces cerevisiae REB1 protein, both of which direct termination of RNA polymerase I catalyzed transcripts. The S.pombe Reb1 cDNA encodes a predicted polypeptide of 504 amino acids with a predicted molecular weight of 58.4 kDa. The S. pombe Reb1p is unusual in that the bipartite DNA binding motif identified originally in S.cerevisiae and Klyveromyces lactis REB1 proteins is uninterrupted and thus S.pombe Reb1p may contain the smallest natural REB1 homologous DNA binding domain. Its genomic coding sequences were shown to be interrupted by two introns. A recombinant histidine-tagged Reb1 protein bearing the rDNA binding domain has two homologous, sequence-specific binding sites in the S. pomber DNA intergenic spacer, located between 289 and 480 nt downstream of the end of the approximately 25S rRNA coding sequences. Each binding site is 13-14 bp downstream of two of the three proposed in vivo termination sites. The core of this 17 bp site, AGGTAAGGGTAATGCAC, is specifically protected by Reb1p in footprinting analysis.

Amino Acid Sequence↗

PubMed1997

Drug disruption of short-term memory in Drosophila melanogaster.

Recent work on operant visual learning and memory in Drosophila has suggested at least three distinct memory phases. Trying to disrupt memory pharmacologically, we fed flies with ouabain or the depolarizing drugs potassium chloride (KCl), lithium chloride (LiCl) and monosodium glutamate for some specific time before training. The depolarizing drugs abolished memory very soon after training. Ouabain exerted no effect on memory within the first 20 min but abolished it more than 30 min after training. These drugs had no diminishing effects on the visual discrimination and behavioral performance of the flies during training. This result suggests that memory disruption may not be induced by nonspecific effects of the drugs. In addition, reversal training of the KCl-fed flies indicates that KCl appears not to impair the retrieval mechanism of flies. These results suggest that the specific disruptive effects of the drugs on memory formation and the existence of a short-term memory phase, are susceptible to disruption of the depolarizing drugs but unaffected by ouabain.

Animals↗

PubMed1997

[Treatment of malignant or aggressive bone tumors with microwave induced hyperthermia].

Limb-sparing procedures have been well established for dealing with malignant bone tumors. Unfortunately, these procedures have different problems. We used an alternative operation combined with microwave-induced hyperthemia to modify the surgical methods. Thermotherapy with microwave intracorporeal irradiation was used to treat 112 patients with bone tumors. In this series, 79 had malignant tumors and 33 aggressive benigh tumors. Postoperatively, immune therapy was carried out regularly. The patients immunologic functions were monitored by assay of the subpopulation of T cells, IL-2 and sIL-2R (soluble IL-2 receptor). Follow-up varied from 3 to 50 months (mean 23 month) s. Excluding 5 patients with malignancy in the vertebrae treated for palliation, 107 were evaluated by oncological and orthopedic criteria. 10 patients had local recurrence and required amputation. The remaining 97 had excellent local control. In 12 of the 74 patients with malignancy of the extremities, lung metastasis occurred 4 months to 2 years after surgery. Pathological fracture occurred at devitalized bone in 8 patients. In 29 out of 40 tumor-free cases followed for more than 2 years, the knee joints functioned properly with almost full range of motion. Single photon emission computered tomography (SPECT) study revealed revascularization of the devitalized tumor bearing bone segment could accomplish in one year or more. The immune state was improved after thermotherapy plus immunotherapy in the majority of patients. These results indicated that the use of microwave hyperthermia and adjuvant immunotherapy in the surgical treatment of bone tumors can be considered a definitive procedure, which is safe and well-tolerated.

Adolescent↗

PubMed1997

Anterior segment prosthesis development: retinal function following anterior segment removal.

Replacement of the entire anterior segment of the eye is a very ambitious and complex endeavor and it is not known whether the retina remains functional when the anterior structures have been removed. We used routine histo-pathologic evaluation and electroretinographic measurements to determine the structural and functional status of rabbit retinas following surgical removal of the internal anterior structures (iris, ciliary body, and lens) and replacement of the vitreous with silicone oil. In some cases, we were able to record both a scotopic and a photopic electroretinographic response as long as 15 weeks after complete removal of the internal anterior segment structures. Although many hurdles remain and more efficacious surgical techniques and biomaterials need to be developed, our results suggest that, in the rabbit, the retina may continue to function in the absence of critical anterior segment structures.

Animals↗

PubMed1996

T cell antigen receptor ubiquitination is a consequence of receptor-mediated tyrosine kinase activation.

Engagement of the T cell antigen receptor results in both its phosphorylation and its ubiquitination. T cell antigen receptor ubiquitination was evaluated in Jurkat, a well characterized human T leukemia cell line. Treatment of cells with the tyrosine kinase inhibitor herbimycin A resulted in an inhibition of receptor ubiquitination. Consistent with this, pervanadate, which increases cellular tyrosine phosphorylation, enhanced receptor ubiquitination. A requirement for receptor-mediated tyrosine kinase activity for ubiquitination was confirmed in cells lacking the tyrosine kinase p56lck and also in cells that are defective in expression of CD45, a tyrosine phosphatase that regulates the activity of p56lck. The need for tyrosine kinase activation for ubiquitination was not bypassed by directly activating protein kinase C and stimulating endocytosis of receptors. These observations establish ubiquitination of the T cell antigen receptor as a tyrosine kinase-dependent manifestation of transmembrane signaling and suggest a role for tyrosine phosphorylation in the ligand-dependent ubiquitination of mammalian transmembrane receptors.

Cells, Cultured↗

PubMed1996

Anterior segment prosthesis development: evaluation of expanded polytetrafluoroethylene as a sclera-attached prosthetic material.

To further the development of a sclera-attached anterior segment prosthesis we investigated the biocompatibility of expanded polytetrafluoroethylene following its surgical implantation into the rabbit sclera. Thin sheets (250 microns) of expanded polytetrafluoroethylene were cut into pieces measuring either 2 x 2, 2 x 4, 2 x 8, or 4 x 8 mm. The pieces were sterilized and placed individually within surgically prepared pockets in the sclera of rabbit eyes. Animals were sacrificed for routine histopathologic evaluation and transmission electron microscopic study of the eyes at 7 days, 14 days, 1 month, and 4 months following surgical implantation. The implants demonstrated excellent compatibility with the sclera and, by 14 days following implantation surgery, exhibited histiocytes, fibroblasts, and blood vessels infiltrating the internodal spaces of the highly porous material. The number of cells and the amount of extracellular matrix material deposited in the implants appeared to increase with time. Transmission electron microscopic studies revealed deposition of collagen within the implants. Our results suggest that expanded polytetrafluoroethylene has potential for use in the development of a sclera-attached prosthetic device.

Animals↗

PubMed1996

Surgical treatment of bone tumors in conjunction with microwave-induced hyperthermia and adjuvant immunotherapy. A preliminary report.

OBJECTIVE: To develop an alternative approach in conjunction with microwave-induced hyperthermia. PATIENTS AND METHODS: Thermotherapy with microwave intracorporeal irradiation was used to treat 73 patients with bone tumors. The series was composed of 58 patients with malignant tumors and 15 with benign tumors: most of tumors occurred about knee joints (53/73 = 72.6%). The surgical procedure included separating the tumor bearing segment from surrounding normal tissues with a safe margin, cooling the normal tissues including the neurovascular bundle and the intraarticular structures with a water circulation system, while heating the tumor with the antenna array of a microwave system and providing an adequate soft-tissue cover for the dead bone. Postoperatively, an immune therapy regimen was carried out regularly. The patients' immunologic functions were monitored by assay of the subpopulation of T cells, IL-2 and sIL-2 R (soluble IL-2 receptor). RESULTS: Follow-up varied from 3 to 38 months (mean 19 months). Excluding 3 patients with malignancy in the vertebrae treated for palliation, 70 were evaluated according to oncological and orthopedic criteria. Five patients had local recurrence and required amputation. The remaining 65 had excellent local control. In 6 of the 55 patients with malignancy of the extremities, lung metastasis occurred one to two years after surgery. The oncological results were similar to those obtained by other limb-saving procedures. Pathological fracture occurred at devitalized bone in 5 patients. In 72.5% of the patients (29 of 40 tumor-free cases followed more than one year), knee joints functioned well, being stable and painless with almost full range of motion. Single photon emission computered tomography (SPECT) for 16 patients revealed revascularization of the devitalized tumor bearing bone segment could accomplish in one year or more. The immune states were improved in various extends after thermotherapy plus immunotherapy in the majority of patients. CONCLUSION: These results show that the use of microwave hyperthermia and adjuvant immunotherapy in conjunction with the surgical treatment of bone tumors can be considered a definitive procedure, which is safe and well-tolerated. The oncological and orthopedic results are encouraging.

Adolescent↗

PubMed1995

Rice cationic peroxidase accumulates in xylem vessels during incompatible interactions with Xanthomonas oryzae pv oryzae.

A cationic peroxidase, PO-C1 (molecular mass 42 kD, isoelectric point 8.6), which is induced in incompatible interactions between the vascular pathogen Xanthomonas oryzae pv oryzae and rice (Oryza sativa L.), was purified. Amino acid sequences from chemically cleaved fragments of PO-C1 exhibited a high percentage of identity with deduced sequences of peroxidases from rice, barley, and wheat. Polyclonal antibodies were raised to an 11-amino acid oligopeptide (POC1a) that was derived from a domain where the sequence of the cationic peroxidase diverged from other known peroxidases. The anti-POC1a antibodies reacted only with a protein of the same mobility as PO-C1 in extracellular and guttation fluids from plants undergoing incompatible responses collected at 24 h after infection. In the compatible responses, the antibodies did not detect PO-C1 until 48 h after infection. Immunoelectron microscopy was used to demonstrate that PO-C1 accumulated within the apoplast of mesophyll cells and within the cell walls and vessel lumen of xylem elements of plants undergoing incompatible interactions.

Amino Acid Sequence↗

PubMed1995

Three-dimensional structure of CA1 pyramidal cells in rat hippocampus--optical recording of LSM and computer simulation of fractal structure.

The optical recording of three-dimensional (3-D) reconstruction of CA1 pyramidal cells was derived from the studies on the CA1 region of the hippocampus in adult male Wistar rats. The recording was produced by the Confocal Laser Scan Microscope (LSM-10). The attemption was to outline the morphological neural network of CA1 pyramidal cells organization, following the trail of axo-dendritic connections in 3-D spatial distributions among neurons. The fractal structure of neurons with their dendritic and axonal trees using fractal algorithm was noticed, and 2-18 simulated cells were obtained using PC-486 computer. The simulational cells are similar in morphology to the natural CA1 hippocampal pyramidal cells. Therefore, the exploitation of an advanced neurohistological research technique combining optical recording of the LSM-10 and computer simulation of fractal structure can provide the quantitative fractal structural basis for chaosic dynamics of brain.

Animals↗

PubMed1995

[A study on two gut hormones in breast milk].

OBJECTIVE: To determine if motilin and gastrin are present in breast milk and to measure their concentrations in human milk and cow milk. METHODS: The concentration of motilin was measured in 17 samples of human colostrum, 18 samples of human mature milk, 8 samples of cow colostrum and 20 samples of cow mature milk by radioimmunoassay. The concentration of gastrin in human milk was also determined by radioimmunoassay. RESULTS: Motilin concentration in human colostrum was the highest (416.34 +/- 183.95ng/L), being higher than that in human mature milk (272.91 +/- 148.73ng/L, that in cow colostrum (229.51 +/- 63.68ng/L) and that in cow mature milk (35.46 +/- 16.94ng/L). Evidently the difference in motilin concentration was very significant between human milk and cow milk. The gastrin concentration in human colostrum was 17.20 +/- 11.98ng/L, being higher than that in human mature milk (5.62 +/- 2.33ng/L). CONCLUSION: Human milk, especially human colostrum, contains high concentrations of motilin and gastrin. Breast feeding, especially early breast feeding, may promote the maturation of the developing gut in neonates and infants.

Adult↗

PubMed1994

Programmed cell death in plants: a pathogen-triggered response activated coordinately with multiple defense functions.

In plants, the hypersensitive response (HR) to pathogens involves rapid cell death, which is hypothesized to arise from the activation of a cell death program. We describe mutant A. thaliana plants that contain lesions in a single accelerated cell death (ACD) gene called ACD2 and that bypass the need for pathogen exposure to induce the HR. acd2 plants that develop spontaneous lesions show typical HR characteristics both within the necrotic tissue and within the healthy part of the plant, including: modification of plant cell walls, resistance to bacterial pathogens, and accumulation of defense-related gene transcripts, the signal molecule salicylic acid and an antimicrobial compound. We propose that the ACD2 gene is involved in a pathway(s) that negatively regulates a genetically programmed HR.

Apoptosis↗

PubMed1994

A mutation in Arabidopsis that leads to constitutive expression of systemic acquired resistance.

Systemic acquired resistance (SAR) is a nonspecific defense response in plants that is associated with an increase in the endogenous level of salicylic acid (SA) and elevated expression of pathogenesis-related (PR) genes. To identify mutants involved in the regulation of PR genes and the onset of SAR, we transformed Arabidopsis with a reporter gene containing the promoter of a beta-1,3-glucanase-encoding PR gene (BGL2) and the coding region of beta-glucuronidase (GUS). The resulting transgenic line (BGL2-GUS) was mutagenized, and the M2 progeny were scored for constitutive GUS activity. We report the characterization of one mutant, cpr1 (constitutive expressor of PR genes), that was identified in this screen and shown by RNA gel blot analysis also to have elevated expression of the endogenous PR genes BGL2, PR-1, and PR-5. Genetic analyses indicated that the phenotype conferred by cpr1 is caused by a single, recessive nuclear mutation and is suppressed in plants producing a bacterial salicylate hydroxylase, which inactivates SA. Furthermore, biochemical analysis showed that the endogenous level of SA is elevated in the mutant. Finally, the cpr1 plants were found to be resistant to the fungal pathogen Peronospora parasitica NOCO2 and the bacterial pathogen Pseudomonas syringae pv maculicola ES4326, which are virulent in wild-type BGL2-GUS plants. Because the cpr1 mutation is recessive and associated with an elevated endogenous level of SA, we propose that the CPR1 gene product acts upstream of SA as a negative regulator of SAR.

Arabidopsis↗

PubMed1993

Effect of chronic intermittent stress on rat pregnancy and postnatal development.

The present study evaluates the effect of chronic intermittent cold-swimming stress on body weight gain of pregnant rats and subsequent development of the offsprings after birth, till peripubertal stage. When stress was administered during the first half (1-11 days) of gestation, weight gain of pregnant rats was significantly lower at the 9th and 11th days (P < 0.05 vs. control, respectively). No differences of weight gain in comparison with control rats were found at term gestation in pregnant rats exposed to stress continuously. Similarly, stress administered, starting from 12th day till term gestation, had no effect on weight gain. Even though weight gain of pregnant rats during the second half of pregnancy in group stress 1-11 was restored to normal values, a high mortality rate of neonates 1, 2 and 3 weeks after birth was found in this group (P < 0.02, 0.01 and 0.001 vs. controls). There was no significant difference between stressed and control groups with respect to the number or body weight of litters, as well as weight gain of neonates during the first 21 days of life. In addition, in offsprings from all stressed groups, a high number of small for date animals was found after 14 days of life, and 74.4% of these small for date animals died during the peripubertal period. The present data demonstrate that the exposure to stress in utero may induce damaging effects on postnatal development.

Animals↗

PubMed1993

[The diagnosis of pleural diseases with a fiberbronchoscope under open pneumothorax].

Thoracoscopy, using a fiberbronchoscope under open pneumothorax, was performed in 27 cases suffering from pleural diseases undiagnosed. The overall diagnostic rate was 92.3%. The items observed included pulse rate, respiration rate, blood pressure, blood gas analysis, electrocardiography and thoracic pressure measure. It was found that this method has little influence on cardiopneumatic function, no harm fiberbronchoscope, and is simple and safe.

Adult↗

PubMed1992

Increased Activity of a Cationic Peroxidase Associated with an Incompatible Interaction Between Xanthomonas oryzae pv oryzae and Rice (Oryza sativa).

Rice (Oryza sativa L.) cultivar Cas 209 carries the gene Xa-10 for resistance to race 2 of Xanthomonas oryzae pv oryzae, the bacterial blight pathogen. When seedling leaves of Cas 209 plants were infiltrated with bacterial cell suspensions of strain PXO86(Rif) (race 2, incompatible), total peroxidase activity in extracts from extracellular spaces increased almost threefold between 16 and 24 hours after inoculation. The increase in total peroxidase activity in extracellular extracts was correlated with the appearance of a 43-kilodalton peroxidase isoenzyme with an isoelectric point of 8.6. Increases in the activities of two anionic peroxidase isoenzymes also were associated with the incompatible interaction. Later during the interactions, total peroxidase activities increased in both compatible (cv Cas 209 infiltrated with race 1, PXO61(Sm)) and control (Cas 209 infiltrated with water) treatments, but final activity levels were less than that observed in the incompatible combination. Similarly, the cationic peroxidase was detected in all three treatments by 48 hours after infiltration, but at reduced levels in compatible and water-infiltrated control treatments relative to the incompatible combination. Accumulation of this peroxidase in extracellular spaces thus may play a role in the defense response in cultivar Cas 209.

Journal Article↗

PubMed1992

Propionibacterium acnes-enhanced lens-induced granulomatous uveitis in the rat.

Propionibacterium acnes (Corynebacterium parvum) is being implicated more frequently as a cause of intraocular inflammation following cataract surgery. In addition to its role as an infectious agent, P. acnes also may possess adjuvant-like or adjuvant-enhancing properties. The presence of this organism in an eye with residual lens material after extracapsular cataract surgery could augment inflammation resulting from a phacoantigenic (phacoanaphylactic) response. We have modified an established rat model of lens-induced granulomatous uveitis (LIGU) to examine the adjuvant properties of P. acnes. Our results suggest that P. acnes effectively potentiates LIGU.

Adjuvants, Immunologic↗