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Biomedical subjects

C Li

Publications and source records attributed to C Li.

At least 1,027 records · Page 57Linked to original sources
PubMed1994

Neonatal 6-hydroxydopamine and adult SKF 38393 treatments alter dopamine D1 receptor mRNA levels: absence of other neurochemical associations with the enhanced behavioral responses of lesioned rats.

To study potential biochemical correlates of dopamine (DA) and serotonin receptor supersensitivity, rats were lesioned at 3 days after birth with 6-hydroxydopamine (6-OHDA; 67 micrograms in each lateral ventricle; desipramine pretreatment, 20 mg/kg i.p., 1 h) and then sensitized with the DA D1 agonist, SKF 38393 HCl (3.0 mg/kg i.p. per day) either ontogenetically (daily, for 28 consecutive days from birth) and/or in adulthood (four weekly injections, 6-9 weeks from birth). Controls received vehicle in place of 6-OHDA or SKF 38393. Enhanced locomotor responses were observed after SKF 38393 at 6 weeks, only in rats that received SKF 38393 + 6-OHDA in ontogeny. Locomotor responses were further enhanced in this group after the last of four weekly SKF 38393 injections at the 9th week. These weekly SKF 38393 treatments also produced enhanced responses in 6-OHDA rats that did not receive SKF 38393 in ontogeny. When striata were studied at 11 weeks, the percentages of high and low affinity DA D1 binding sites were not altered. Basal as well as DA-, NaF-, and forskolin-stimulated adenylyl cyclase activities also were not changed. Dot blot analysis showed that there was a reduction of mRNA levels for DA D1, but not serotonin1C, receptors in the 6-OHDA groups. However, SKF 38393 at 6-9 weeks eliminated this alteration. Based on these findings it can be proposed that supersensitization may be a consequence of altered neuronal cross talk rather than an imbalance of receptor elements per se.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1994

The design and use of a device to detect deer pedicle growth.

The design, construction and use of a device to detect changes in deer pedicle volume are described. The device is highly sensitive for detecting the initiation of pedicle growth. Between-sample differences of 170 mm3 in the pedicle volume of live deer were detected (triplicate measurements) using the detector; these correspond to a change in height of the pedicle of at most 0.67 mm. The within sample coefficient of variation was 1.4%. The pedicle growth detector enables more precise measurements to be obtained for identifying the onset of pedicle development to the nearest week than is currently possible with palpation.

Journal Article↗
PubMed1994

Human dTMP kinase: gene expression and enzymatic activity coinciding with cell cycle progression and cell growth.

dTMP kinase (E.C.2.7.4.9.) catalyzes the phosphorylation of dTMP to the corresponding diphosphate. This enzyme is essential for DNA synthesis in vivo and is an important intermediate enzyme in the pathway of many pyrimidine analog drugs. In this report, we describe the isolation of the human dTMP kinase gene by functional complementation of a Saccharomyces cerevisiae cell cycle mutant, cdc8. The cDNA sequence revealed an open reading frame that encodes a protein with the molecular weight of 23,806. The deduced protein sequence was compared to known dTMP kinase sequences from different organisms. Although functionally complementary and structurally conserved, expressed human dTMP kinase in yeast shows little enzymatic activity. In contrast, active human dTMP kinase can be expressed from the gene cloned into the baculovirus expression system, as evidenced by increased enzymatic activity by four- to five-fold. Unlike yeast dTMP kinase, human dTMP kinase does not contain a cysteine residue after the conserved glycine-rich loop, but its enzymatic activity is still affected by the sulfhydryl inhibitor, 5,5'-dithio-bis(2-nitrobenzoic acid) (DTNB). The levels of dTMP kinase mRNA and its enzymatic activity fluctuate during the cell cycle, peaking at the S phase. Thus, like Saccharomyces cerevisiae CDC8 (encoding dTMP kinase), the human homolog mRNA and enzymatic activity are also cell cycle regulated. We have also examined four neuroblastoma cell lines for dTMP kinase mRNA levels and its kinase activities, which appear to vary according to cell growth rate. Our results suggest that the expression of the dTMP kinase gene and its activity coincide with various stages of cell growth. The identification of the human dTMP kinase gene and expression of its product in the baculovirus expression system should facilitate study of the mechanism of gene regulation and its role in pyrimidine metabolism.

Amino Acid Sequence↗
PubMed1994

Production and characterization of monoclonal antibodies against guinea pig tracheal mucins.

Thirty-five hybridomas that secrete mouse monoclonal antibodies (MAb) against guinea pig (G.P.) tracheal mucins were established. The MAbs were characterized immunologically, biochemically, and immunohistochemically at both light and electron microscopic levels. Isotyping of the MAbs revealed 14 to be IgM, 13 IgG1, 3 IgG2, and 5 IgG3. The MAbs demonstrated various patterns of binding in immunoblots against mucins derived from G.P. tracheal explants. This suggested the presence of "subpopulations" of G.P. tracheal mucins with specific MAbs binding to different epitopes on the mucin molecules. Periodate oxidation indicated that 33 of the 35 MAbs recognized carbohydrate epitopes on the mucin molecules. Ten of the MAbs also reacted with both bovine and ferret tracheal mucins, while 7 and 6 MAbs bound only to bovine and ferret tracheal mucins, respectively. The generated MAbs should be useful for immunomeasurement of mucin secretion in vivo (e.g., in bronchoalveolar or airway lavage fluid) and in vitro (e.g., cell and organ cultures) from cells of guinea pig and (with certain MAbs) bovine and ferret origin.

Animals↗
PubMed1994

Demographic impact of HIV infection in rural Rakai district, Uganda: results of a population-based cohort study.

OBJECTIVES: To examine HIV-1-related mortality and demographic impact in a high HIV prevalence rural district of Uganda. DESIGN: One-year follow-up (1990-1991) in a population-based rural cohort. SETTING AND PARTICIPANTS: Annual enumeration of all consenting residents of 1945 households in 31 randomly selected community clusters in Rakai District. Subjects provided yearly HIV serological samples, behavioral and health information. MAIN OUTCOME MEASURE: Mortality in HIV-infected and uninfected persons. RESULTS: Mortality among HIV-seropositive adults aged > or = 15 years of 118.4 per 1000 person-years (PY) was substantially higher than in HIV-seronegative adults [12.4 per 1000 PY; relative risk (RR), 9.5; 95% confidence interval (CI), 6.0-14.9]. Infant mortality among offspring of HIV-infected mothers was almost double that for uninfected women (210 compared with 111 per 1000 live births; RR, 1.9; 95% CI, 1.0-3.5). Adult HIV-related mortality was associated with HIV prevalence and, in this cohort, with higher education, non-agricultural occupation and residence in roadside trading centers. We estimate that adult HIV prevalence in the district is 13% and adult HIV attributable mortality 52%. For all ages combined, district HIV attributable mortality is 28%. CONCLUSION: HIV is the leading cause of adult death in Rakai. Its effects on mortality are particularly marked in the most economically active sectors. However, the overall crude birth rate in the district (45.7 per 1000 population) remains higher than the crude death rate (28.1 per 1000 population), resulting in continued rapid population growth.

Adolescent↗
PubMed1994

Preparation, characterization, and evaluation of ioxilan carbonate particles for computed tomography contrast enhancement of liver.

RATIONALE AND OBJECTIVES: To prepare and characterize a new particulate contrast medium, cyclic carbonate of ioxilan (IX-C) particles, as a macrophage imaging agent for computed tomography (CT) enhancement of the liver. METHODS: Cyclic carbonate of ioxilan was synthesized from ioxilan, a nonionic water-soluble contrast agent. The IX-C particles prepared by a solvent extraction-evaporation method were characterized by size distribution, degradability, suspension stability, and median lethal dose. Pharmacokinetics of IX-C particles and their effectiveness in enhancing liver attenuation and in detecting hepatic tumors were evaluated using normal and VX2-tumor-bearing rabbits. RESULTS: The IX-C particles were biodegradable, with ioxilan and carbon dioxide as the degradation products. The particles had an average size of 1 to 2 microns and were stable in saline suspension. The median lethal dose determined for IX-C particles was 2.6 and 3.1 g/kg body weight for female and male rabbits, respectively. A dose of 200 mg iodine/kg body weight caused an increase of 38 Hounsfield units in liver attenuation. In rabbit, hepatic clearance of the contrast medium occurred in 2 days. A tumor barely visible in precontrast scans could be detected after contrast injection. CONCLUSIONS: Development of particulate contrast medium from nonionic contrast agents represents a new approach. Ioxilan carbonate particles have suitable physicochemical properties that warrant further studies before clinical evaluation.

Animals↗
PubMed1994

The measured electrical properties of normal and malignant human tissues from 50 to 900 MHz.

The electrical conductivity and relative permittivity of malignant and normal human tissues were measured at frequencies from 50 to 900 MHz. The measurements were made between 23 and 25 degrees C using a network analyzer connected to a flat-ended coaxial probe that was pressed against the freshly excised tissue samples. The malignant tissues were of the following normal tissue origin: bladder, colon, kidney, liver, lung, lymph nodes, mammary gland, spleen, and testes. The normal tissues included: colon, kidney, liver, lung, mammary gland, and muscle. Normal tissue samples of bladder, lymph, spleen, and testes were not available. In general, at all frequencies tested, both conductivity and relative permittivity were greater in malignant tissue than in normal tissue of the same type. For tissues of the same type, the differences in electrical properties from normal to malignant were the least for kidney (about 6% and 4% average differences over the frequency range in permittivity and conductivity, respectively), and these differences were the greatest for mammary gland (about 233% and 577% average differences in permittivity and conductivity, respectively). To illustrate a potential use of these data in hyperthermia applications, frequency-selective heating of malignant tissue (modeled as a sphere) surrounded by host normal tissue is calculated from the measured electrical properties for certain tissues.

Biophysical Phenomena↗
PubMed1994

A new gene involved in stationary-phase survival located at 59 minutes on the Escherichia coli chromosome.

We determined the DNA sequence of a 2,232-bp region immediately upstream of the pcm gene at 59 min on the Escherichia coli chromosome that encodes an L-isoaspartyl protein methyltransferase with an important role in stationary-phase survival. Two open reading frames of 477 and 1,524 bp were found oriented in the same direction as that of the pcm gene. The latter open reading frame overlapped the 5' end of the pcm gene by 4 bp. Coupled in vitro transcription-translation analysis of DNA containing the 1,524-bp open reading frame directly demonstrated the production of a 37,000-Da polypeptide corresponding to a RNA species generated from a promoter within the open reading frame. The deduced amino acid sequence showed no similarity to known protein sequences. To test the function of this gene product, we constructed a mutant strain in which a kanamycin resistance element was inserted at a BstEII site in the middle of its coding region in an orientation that does not result in reduction of Pcm methyltransferase activity. These cells were found to survive poorly in stationary phase, at elevated temperatures, and in high-salt media compared with parent cells containing the intact gene, and we thus designate this gene surE (survival). surE appears to be the first gene of a bicistronic operon also containing the pcm gene. The phenotypes of mutations in either gene are very similar and indicate that both gene products are important for the viability of E. coli cells under stressful conditions.

Acid Phosphatase↗
PubMed1994

A gene at 59 minutes on the Escherichia coli chromosome encodes a lipoprotein with unusual amino acid repeat sequences.

We report a 1.432-kb DNA sequence at 59 min on the Escherichia coli chromosome that connects the published sequences of the pcm gene for the isoaspartyl protein methyltransferase and that of the katF or rpoS (katF/rpoS) gene for a sigma factor involved in stationary-phase gene expression. Analysis of the DNA sequence reveals an open reading frame potentially encoding a polypeptide of 379 amino acids. The polypeptide sequence includes a consensus bacterial lipidation sequence present at residues 23 to 26 (Leu-Ala-Gly-Cys), four octapeptide proline- and glutamine-rich repeats of consensus sequence QQPQIQPV, and four heptapeptide threonine- and serine-rich repeats of consensus sequence PTA(S,T)TTE. The deduced amino acid sequence, especially in the C-terminal region, is similar to that of the Haemophilus somnus LppB lipoprotein outer membrane antigen (40% overall sequence identity; 77% identity in last 95 residues). The LppB lipoprotein binds Congo red dye and has been proposed to be a virulence determinant in H. somnus. Utilizing a plasmid construct with the E. coli gene under the control of a phage T7 promoter, we demonstrate the lipidation of this gene product by the incorporation of [3H]palmitic acid into a 42-kDa polypeptide. We also show that treatment of E. coli cells with globomycin, an inhibitor of the lipoprotein signal peptidase, results in the accumulation of a 46-kDa precursor. We thus designate the protein NlpD (new lipoprotein D). E. coli cells overexpressing NlpD bind Congo red dye, suggesting a common function with the H. somnus LppB protein. Disruption of the chromosomal E. coli nlpD gene by insertional mutagenesis results in decreased stationary-phase survival after 7 days.

Amino Acid Sequence↗
PubMed1994

Craniospinal axis irradiation: an improved electron technique for irradiation of the spinal axis.

In this work we review the dosimetric features of craniospinal axis irradiation in the areas of matching cranial and spinal fields, with reference to the normal structures within the spinal field. The implications of the use of photon or electron modalities for the spinal port were evaluated. A novel method of matching the cranial photon and the spinal electron fields involving a computer-aided junction design is presented. The technique involves moving the photon beam in three steps to degrade its penumbra to match that of the electron field. Thermoluminescent dosimetry in a Rando phantom and computed tomography-based dose-volume histogram study for an illustrative paediatric case were used to compare the dose to normal structures within the spinal field. Our results show that the use of electrons for the spinal field leads to better sparing of deep seated normal structures. In the case of bone marrow, the use of a customized bolus for the spinal field results in an improved dose distribution, making electrons potentially superior to photons for radiobiological reasons.

Bone Marrow↗
PubMed1994

Neuroimaging in patients with olfactory dysfunction.

This review summarizes neuroimaging findings in patients with olfactory dysfunction. Neuroimaging techniques offer a valuable means for evaluating and distinguishing disorders of olfaction. The new or refined techniques make it possible to pinpoint the anatomic and pathologic changes of many disorders of the sinonasal cavity and brain that cause olfactory deficits. From an anatomic point of view, the causes of olfactory deficits generally can be classified as peripheral or central (intracranial). In the assessment of the peripheral causes, CT and MR imaging reveal anatomic information and structural changes, enable a differential diagnosis, and provide a road map for surgical intervention. In the evaluation of the central causes, MR imaging, positron emission tomography, or single-photon emission computed tomography can provide the links between olfactory dysfunction and structural or functional changes in the brain.

Brain Diseases↗
PubMed1994

Electrochemical therapy in the treatment of malignant tumours on the body surface.

From November 1988 to May 1991, 113 patients with malignant tumours on their body surface, who were at great operative risk or had refused surgery, underwent local treatment with electrochemical therapy (ECT). After 2.6 years' follow up, total effective rate of the cure was 79.7%. The clinical results were considered satisfactory.

Adolescent↗
PubMed1994

[Antigenic changes in skin after cryopreservation].

It is well accepted impression that antigenic properties of skin are lowered after cryopreservation. In order to prove it, this experiment was done. Fresh guinea pig and cadaveric skin homogenates with appropriate adjuvants were injected hypodermically separately to rabbits once a week. Five week later, blood was withdrawn from rabbits, thus anti-guinea pig skin serum (AGS) and anti-cadaveric skin serum (ACS) were obtained. Homogenates of fresh guinea pig skin (FG) and guinea pig skin stored at -196 degrees C (SG), homogenates of fresh cadaveric skin (FC) and cadaveric skin stored at -196 degrees C (SC) were used as antigens. Microimmunoelectrophoresis and rocket immunoelectrophoresis were performed between related antigens and antibodies. The results of microimmunoelectrophoresis showed that there were four dense and wide precipitated are lines in AGS vs FG and ACS vs FC groups, while only two light and thin precipitated are lines in AGS vs SG and ACS vs SC groups. Rocket immunoelectrophoresis showed that the rocket precipitated area in AGS vs FG and ACS vs FC groups are larger (longer in axis, and broader in width) than in AGS vs SG and ACS vs SC groups. The antigenicity of skin is lowered after being stored at -196 degrees C as compared with that of the fresh one as shown by electrophoresis method.

Animals↗