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Biomedical subjects

D Li

Publications and source records attributed to D Li.

At least 631 records · Page 35Linked to original sources
PubMed1996

Myocardial signal response to dipyridamole and dobutamine: demonstration of the BOLD effect using a double-echo gradient-echo sequence.

The purpose of this study was to examine the differential myocardial signal responses due to the blood oxygen level dependent (BOLD) effect in magnetic resonance imaging (MRI) under differing conditions of myocardial oxygen supply and demand. The signal response was measured when myocardial blood flow was increased in excess of oxygen demand or when flow was increased in response to increased myocardial oxygen demand. Normal volunteers were studied using a segmented, interleaved, double-echo, gradient-echo sequence at baseline conditions and during pharmacological stress with either dipyridamole (n = 5) or dobutamine (n = 6). Changes in T2* in the myocardium during stress were calculated. Peak coronary flow velocity was measured at rest and during stress using a breath-hold phase contrast technique. Administration of dipyridamole induced a 124 +/- 27% increase in coronary blood flow which resulted in a 46 +/- 22% increase in T2*, consistent with a decrease in myocardial venous deoxyhemoglobin concentration as myocardial oxygen supply exceeds demand. In contrast, the administration of dobutamine resulted in a 41 +/- 25% increase in coronary blood flow but no significant change in T2* (-5 +/- 19%), consistent with a lack of change in myocardial venous deoxyhemoglobin concentration and balanced oxygen supply and demand. Thus, alterations in the relationship between myocardial oxygen supply and demand appear to be detectable using BOLD MRI.

Adrenergic beta-Agonists↗
PubMed1996

Connectional specification of regenerating entorhinal projection neuron classes cannot be overridden by altered target availability in postnatal organotypic slice co-culture.

Layer II neurons of the entorhinal cortex project to the dentate gyrus and field CA3 and also send collaterals to the subiculum; layer III neurons project to the subiculum and field CA1, but not to the dentate gyrus; and layer IV neurons project to the perirhinal cortex. We have previously shown that these specific differences between the projections of the layer II and III neurons are maintained and can regenerate in organotypic slice culture. In the present experiments we have confronted Postnatal Day 7 (P7) rat entorhinal cortex with P7 tissue selected from restricted parts of the overall entorhinal projection field. (1) When entorhinal slices were co-cultured with target slices containing only dentate gyrus, extracellular uptake of biotin dextran from crystals placed on the dentate gyrus retrogradely labeled neurons in layer II, and those of layer III were not labeled. (2) When entorhinal slices were co-cultured with target slices that contained only the subiculum and the hippocampal field CA1 (but not dentate gyrus), neurons in both layers II and III of the entorhinal area were labeled. (3) When entorhinal slices were co-cultured with target slices containing the perirhinal area and no hippocampal or dentate tissue, the neurons of entorhinal layer IV were labeled, but (4) when co-cultured with control target slices taken from the rostral parietal neocortex, no entorhinal neurons were labeled. Thus the exclusive relationship of layer II entorhinal neurons to the dentate gyrus has already been established by 1 week of age and is maintained by the regenerating entorhinal axons. Layer III entorhinal neurons cannot be induced to project to the dentate gyrus even when deprived of their own target, and layer IV neurons are specified to project to the perirhinal area and will not project to any part of the hippocampal complex or to the rostral parietal cortex. Thus, deprivation of the normal target tissue and presentation of an incorrect target tissue (even when it is the correct target for one of the other classes of entorhinal neurons) are not sufficient to override the specificity of the entorhinal projection neurons.

Age Factors↗
PubMed1996

Construction of expressing plasmids of recombinant FN polypeptides with bifunctional-domain and the characterization of the products expressed in E. coli.

Two expressing plasmids have been constructed and used to express two bifunctional-domain recombinant polypeptides of human fibronectin (FN) in E. coli. One was CH50 (Pro1239-Ser1515 of FN linked with Ala1690-Thr1960 of FN through Met) and the other was CH56 (Pro1239-Thr1960 of FN). Both of two polypeptides were capable of binding heparin and were purified by heparin-agarose affinity chromatography. The purified products were capable of binding cells. The production of CH50 and CH56 polypeptides provided a fundamental basis for further study of the anti-metastatic function of recombinant fibronectin polypeptides.

Escherichia coli↗
PubMed1996

Predischarge respiratory recordings in very low birth weight newborn infants.

PREMISE: There may be a relationship between undiagnosed, ongoing apnea occurring at discharge in infants of very low birth weight and sudden infant death syndrome. OBJECTIVE: To describe patterns of apnea in former very low birth weight (< 1251 gm) infants thought to be ready for hospital discharge, and to determine the relationship between apnea at discharge and later adverse events-in particular, apparent life-threatening events (ALTEs) and sudden infant death syndrome. METHODS: One hundred eighty-seven infants had 24-hour (four-channel) recordings scored for apnea (> 12 seconds in duration) frequency, type, and duration. Infants were followed by telephone interview at 2, 4, and 6 months after discharge from the hospital. RESULTS: Ninety-one percent of recordings displayed significant apnea, the majority of episodes of apnea were obstructive, and about half occurred during feedings. Infants had as many as 43 episodes in a 24-hour period, with a maximum duration of 62 seconds. There was no relationship between severity of pre-discharge episodes of apnea and ALTEs. No infants died during follow-up. CONCLUSIONS: Predischarge multichannel recordings may identify infants with apnea that is not otherwise clinically apparent but do not predict the risk of an ALTE.

Apnea↗
PubMed1996

Cellular mechanisms for bi-directional regulation of tubular sodium reabsorption.

The molecular mechanisms underlying the regulation of sodium excretion are incompletely known. Here we propose a general model for a bi-directional control of tubular sodium transporters by natriuretic and antinatriuretic factors. The model is based on experimental data from studies on the regulation of the activity of Na+,K+-ATPase, the enzyme that provides the electrochemical gradient necessary for tubular reabsorption of electrolytes and solutes in all tubular segments. Regulation is carried out to a large extent by autocrine and paracrine factors. Of particular interest are the two catecholamines, dopamine and norepinephrine. Dopamine is produced in proximal tubular cells and inhibits Na+,K+-ATPase activity in several tubule segments. Renal dopamine availability is regulated by the degrading enzyme, catechol-O-methyl transferase. Renal sympathetic nerve endings contain norepinephrine and neuropeptide Y (NPY). Activation of alpha-adrenergic receptors increase and activation of beta-adrenergic receptors decrease Na+,K+-ATPase activity. alpha-Adrenergic stimulation increases the Na+ affinity of the enzyme and thereby the driving force for transcellular Na+ transport. NPY acts as a master hormone by synergizing the alpha- and antagonizing the beta-adrenergic effects. Dopamine and norepinephrine control Na+,K+-ATPase activity by exerting opposing forces on a common intracellular signaling system of second messengers, protein kinases and protein phosphatases, ultimately determining the phosphorylation state of Na+,K+-ATPase and thereby its activity. Important crossroads in this network are localized and functionally defined. Phosphorylation sites for protein kinase A and C have been identified and their functional significance has been verified.

Animals↗
PubMed1996

Malignant conversion of human cells by antisense cDNA to a putative tumor suppressor gene.

A cell line, SCC83-01-82, derived from a human oral squamous carcinoma, was non-tumorigenic in nude mice, a characteristic of premalignant cells. Conversion of these cells to a tumorigenic phenotype with chemical mutagens did not increase mutations in hot spots or other conserved regions of p53 or H-ras genes. Investigation of the tumorigenic conversion using an expression library resulted in isolation of a previously unidentified gene, CATR1, located on the long arm of chromosome 7 at band approximately q31-32. Evidence for the involvement of this gene in conversion to tumorigenicity was demonstrated by introduction of a eukaryotic expression CATR1 construct into SCC83-01-82 cells. Transfection with the antisense construct reduced the expression of CATR1 in tumors formed by the transfected cells, suggesting that the antisense suppression of endogenous CATR1 expression appeared to be sufficient for tumorigenic conversion. These results are consistent with previous reports of cytogenetic analyses of tumors, that 7q31-32 contains a gene(s) with tumor suppressor activity; CATR1 is a candidate for this putative suppressor gene.

Animals↗
PubMed1996

Mutational scanning of large genes by extensive PCR multiplexing and two-dimensional electrophoresis: application to the RB1 gene.

With the rapid increase in the number of identified human disease genes, the development of accurate and cost-efficient mutation tests has become opportune. Here we present a combination of extensive PCR multiplexing and two-dimensional (2-D) DNA electrophoresis to screen for mutations in 26 exons of the retinoblastoma (RB1) tumor suppressor gene. In 2-D electrophoresis, fragments are separated according to size and base pair sequence in non-denaturing and denaturing gradient gels, respectively. All target fragments, designed to have optimal melting characteristics, were prepared in a two-step PCR (a 6-plex long-PCR pre-amplification and a subsequent 25-plex short-PCR) followed by heteroduplexing. The mixture of PCR amplicons was then subjected to 2-D electrophoresis under a single set of experimental conditions. With this design, 35 previously identified mutations in 18 different exons were detected in 33 bilateral retinoblastoma patients. These results suggest that 2-D electrophoresis in this format provides a generally applicable, practical and fast way to diagnose with high accuracy large genes for a broad spectrum of possible disease-causing mutations.

DNA Mutational Analysis↗
PubMed1996

Intratemporal facial nerve perineurioma.

Forty-two cases of perineurioma have been reported in the literature. This report adds the first intratemporal facial nerve perineurioma to the literature and reviews the others. Unlike schwannoma and neurofibroma, the histological features of perineurioma demonstrate onion bulb-like structures with a strong positive immunoreactivity for epithelial membrane antigen. The clinical history of gradual facial nerve paresis was 15 years in the case presentation and the clinical diagnosis of tumor was overlooked.

Adult↗
PubMed1996

Coronary arteries: three-dimensional MR imaging with retrospective respiratory gating.

Thin-section, three-dimensional (3D) gradient-echo magnetic resonance imaging of the coronary arteries was performed without and with retrospective respiratory gating in 12 healthy volunteers and one patient. In all examinations, results were improved with gating. In five of seven volunteer examinations, coronary artery delineation on images reconstructed by using the least-squares method for motion detection with navigator echoes was found to be equal to that obtained by using edge detection. Images in five other volunteers covered the entire heart with multiple overlapping 3D slabs. The arteries were segmented from the background and could be viewed from any orientation. The lengths of contiguously visible vessels were as follows: left main coronary artery, 11.5 mm +/- 0.4 (mean +/- standard deviation); left anterior descending branch, 115.9 mm +/- 19.7; left circumflex branch, 97.2 mm +/- 12.5; and right coronary artery, 125.9 mm +/- 18.8. This respiratory gating technique clearly improved depiction of the coronary arteries.

Adult↗
PubMed1996

Facial canal dehiscence: a report of 1,465 stapes operations.

We retrospectively reviewed 1,465 stapes operations for facial canal dehiscences. The incidence of facial canal dehiscence was found to be 11.4%. A facial canal dehiscence with protrusion of the facial nerve is more common than a dehiscence without protrusion. In addition, 3 cases (0.2%) had a herniation of the facial nerve. Our data suggests that heredity could be one of the factors associated with a facial canal dehiscence. If an operated ear shows a dehiscent facial canal, there is a 29% possibility that the contralateral ear also has a dehiscence. Bilaterality of facial canal dehiscence is, therefore, exceptional.

Facial Nerve↗
PubMed1996

An oviposition-inducing peptide: isolation, localization, and function of avian galanin in the quail oviduct.

It is well established that avian oviposition is regulated, at least partly, by a neurohypophysial hormone, arginine vasotocin, and ovarian hormones, prostaglandins, are regulated through mechanisms of the induction of uterine contractions. Although abundant nerves are terminated in the musculature in the uterine and vaginal oviduct regions, limited information is available on the neuronal control mechanism of avian oviposition. To identify the oviduct factor that plays an important role in the induction of oviposition as a neurotransmitter or a neuromodulator, a study was conducted to isolate the bioactive substance involved in the vaginal and uterine contractions from mature oviducts of the Japanese quail. Acetic acid extracts of 200 quail oviducts were forced through disposable C-18 reversed-phase cartridges, and then the retained material was subjected to the reversed-phase and cation-exchange HPLC purifications. A purified bioactive substance showed a single peak on the reversed-phase HPLC and was further subjected to amino acid sequence analysis and molecular weight presumption. The substance was identified as avian galanin, which was previously isolated from chicken intestine. The synthetic peptide enhanced contractions of both the vagina and the uterus in a manner similar to the native peptide, and the threshold concentrations were 10(-9) - 10(-8) M in the vagina and 10(-10) - 10(-9) M in the uterus. An intraperitoneal injection of the synthetic peptide significantly evoked quail oviposition during 5 min after injection. Immunohistochemical analysis with the anti-galanin serum revealed that abundant immunoreactive fibers were distributed in muscle layers of the vagina and the uterus. The immunoreaction examined in these regions was completely inhibited by preincubation of the antibody with synthetic peptide. These results suggest that avian galanin in the oviduct evokes oviposition through mechanisms of the induction of uterine and vaginal contractions. This peptide may contribute as a neurotransmitter or a neuromodulator to avian oviposition.

Amino Acid Sequence↗
PubMed1996

[Changes of brain potentials related to visual attention during simulated weightlessness].

To study the possible effect of simulated weightlessness on brain function state, the brain event-related potentials (ERPs) during a simple visual selective response task were compared between head down tilt (HDT) and head up tilt (HUT) in 9 normal subjects. The results were: both the target (T) and non-target (NT) flash signals induced significant slow positive potentials which were supposed to be related to the attention activity; the amplitude of the positive potentials in the frontal regions decreased significantly especially for NT-ERPs during HDT as compared with that during HUT. The data provide new evidence indicating that the ability of brain response declined during simulated weightlessness and more attention should be paid to the study of brain function during space flight.

Attention↗