Search PubMed⌕ Search

Biomedical subjects

K C Chen

Publications and source records attributed to K C Chen.

At least 55 records · Page 3Linked to original sources
PubMed1998

The global turning probability density function for motile bacteria and its applications.

The angular turning probability density distribution for motile bacteria is usually measured in local coordinates and is therefore inconvenient for global analyses of the chemotactic bacterial migration. In this paper we present analytical derivations that convert the local angular turning probability density distribution into a global one. The explicit expression of a reduced global turning probability density function for motile bacteria was derived and its relevant properties were investigated. Depending on the angle variable being intergrated and the integration range, three types of cosine moments were separately defined and studied. Some statistical indices and parameters such as the directional persistence, persistence number, and one-dimensional reversal probability were found to be embedded in the various moments of the reduced global turning probability density function. Applications of the reduced global turning probability and its integrated moments to a three-dimensional cell balance equation in an axisymmetric system were also discussed.

Bacterial Physiological Phenomena↗
PubMed1998

Simultaneous measurement of blood and brain microdialysates of granisetron in rat by high-performance liquid chromatography with fluorescence detection.

Simultaneous microdialysis probes in the blood and brain and sensitive high-performance liquid chromatography with fluorescence detection were used to examine the granisetron concentration in the jugular vein and frontal cortex of rats after drug administration. Two microdialysis probes were inserted into the right jugular vein and frontal cortex of male Sprague-Dawley rats to which granisetron (6 mg/kg, i.v.) had been administered. Dialysates were automatically collected using a microfraction collector. Samples were eluted with a mobile phase containing 25 mM acetate buffer (pH 4.8)-acetonitrile (72:28, v/v). Excitation and emission wavelengths were set at 305 and 360 nm, respectively, on a scanning fluorescence detector. The limit of quantification for granisetron was 0.5 ng/ml. The in vitro recovery of granisetron was 29.7+/-1.2% (n=6) for the jugular vein microdialysis probe and 6.1+/-0.5% (n=6) for the frontal cortex microdialysis probe. The increasing brain/blood concentration ratio of granisetron suggests that granisetron penetrates the blood-brain barrier.

Animals↗
PubMed1998

Ultrasonography for inguinal hernias in boys.

BACKGROUND/PURPOSE: History taking and physical examination alone no longer meet the surgeon's need in the diagnosis of inguinal hernia. Ultrasonography (US) provides a good and safe diagnostic tool for inguinal hernias in boys. METHODS: From 1995 to 1997, 244 boys with inguinal hernias (41 bilateral and 203 unilateral), received preoperative US on both groins to confirm the diagnosis. Those with positive US findings, such as viscera or fluid in inguinal canal or widening of the internal inguinal ring, underwent surgery. RESULTS: The accuracy of diagnosis with US and clinical assessment were 97.9% and 84%, respectively. More than 95% of widening of internal inguinal rings (>4 mm) proved to be hernias. There were two direct inguinal hernias and two femoral hernias, which were misdiagnosed by clinical examination, but proved to be diagnosed correctly by US. CONCLUSIONS: US serves as a noninvasive and highly accurate diagnostic tool for inguinal hernias in boys. Using 4 mm as the upper limit of the normal diameter of the internal inguinal ring, an occult inguinal hernia can be easily detected before surgery.

Adolescent↗
PubMed1998

Temporal and spatial expression of erbB4 in ectodermal and mesenchymal cells during primary palatogenesis in noncleft and cleft strains of mice.

Primary palatogenesis in mice is similar to that in humans, and spontaneous cleft lip appears to be multifactorially determined in both. Binding of a ligand to erbB4 has been shown to stimulate the receptor's protein kinase activity, which subsequently stimulates a signal-transduction cascade leading to cell growth and differentiation, and to morphogenesis during development. In this study, an immunohistochemical technique was used to investigate the temporal and spatial expression of erbB4 in the primary palate of cleft (A/WySn) and noncleft strains of mice (BALB/cBy). Positive staining of erbB4 was found in ectodermal and mesenchymal cells of facial prominences before the primary palate formation stage (day 10, hour 20) in both strains. During the primary palate formation stage (day 11, hour 20), positive staining of erbB4 was found in the ectodermal and mesenchymal cells of the facial prominences of the noncleft strain, but not in those of the cleft strain. These results suggest erbB4 expression may be associated with normal primary palatogenesis of mice and, conversely, cleft lip may be associated with a deficiency of erbB4 expression during primary palate formation in mice.

Animals↗
PubMed1998

Perinatal outcome of oligohydramnios without associated premature rupture of membranes and fetal anomalies.

To investigate the perinatal outcome of patients with oligohydramnios (amniotic fluid index < or = 5 cm), but without premature rupture of membranes and fetal congenital anomalies, data from 245 singleton pregnancies were analyzed and compared to those with normal amniotic fluid volumes (5 < amniotic fluid index < 24 cm, n=27,261). Significantly higher incidences of primiparity, pregnancy-induced hypertension, premature separation of placenta, past history of intrauterine fetal death, past history of preterm delivery, postterm pregnancy, and advanced maternal age were noted to be associated with the occurrence of oligohydramnios. Pregnancies complicated by a markedly diminished amniotic fluid volume assessed antenatally by ultrasound were significantly more frequently associated with adverse perinatal outcomes such as preterm delivery, low or very low birth weight, low Apgar scores, intrauterine fetal death, small-for-gestational-age newborns, meconium staining, cesarean delivery, neonatal intensive care, and neonatal death.

Cohort Studies↗
PubMed1997

Calcium channel density and hippocampal cell death with age in long-term culture.

The expression of voltage-gated calcium (Ca2+) channel activity in brain cells is known to be important for several aspects of neuronal development. In addition, excessive Ca2+ influx has been linked clearly to neurotoxicity both in vivo and in vitro; however, the temporal relationship between the development of Ca2+ channel activity and neuronal survival is not understood. Over a period spanning 28 d in vitro, progressive increases in high voltage-activated whole-cell Ca2+ current and L-type Ca2+ channel activity were observed in cultured hippocampal neurons. On the basis of single-channel analyses, these increases seem to arise in part from a greater density of functionally available L-type Ca2+ channels. An increase in mRNA for the alpha1 subunit of L-type Ca2+ channels occurred over a similar time course, which suggests that a change in gene expression may underlie the increased channel density. Parallel studies showed that hippocampal neuronal survival over 28 d was inversely related to increasing Ca2+ current density. Chronic treatment of hippocampal neurons with the L-type Ca2+ channel antagonist nimodipine significantly enhanced survival. Together, these results suggest that age-dependent increases in the density of Ca2+ channels might contribute significantly to declining viability of hippocampal neurons. The results also are analogous to patterns seen in neurons of aged animals and therefore raise the possibility that long-term primary neuronal culture could serve as a model for some aspects of aging changes in hippocampal Ca2+ channel function.

Animals↗
PubMed1997

Functional connectivity of the transected brachial plexus after intercostal neurotization in monkeys.

Microsurgical reconstructions of brachial plexuses were performed on twelve monkeys by using ipsilateral intercostal nerves (T3-9). Reinnervation in individual nerves was evaluated monthly by observations of neuromuscular and electromyographic improvements. The electromyographic studies revealed reappearance of motor unit potentials. According to a motor scale ranging from 0 to 4, the mean muscle power 6 months after operation improved to 2.75 in the deltoid muscles, 2 in the biceps muscles, 1.22 in the triceps muscles, 1.13 in the flexor carpi radialis muscles, and 1.6 in the intrinsic muscles of the hands. Retrograde transport of horseradish peroxidase (HRP) from the neuromuscular junctions of the reconstructed musculocutaneous nerves 6 months after complete brachial plexus lesion in four animals demonstrated HRP-labeled neurons in the anterior horns, spinal ganglia and sympathetic ganglia of the thoracic spinal cords. It suggested that the regenerated afferent and efferent circuits in the thoracic cords innervating the transected brachial plexuses were able to generate the movements in the paralyzed upper limbs. However, as evidenced by the behavior patterns and the fact that retrograde-labeled neurons were all found in the thoracic cords, the novel movements observed in the reconstructed brachial plexuses were in synchrony with respiration. These results suggested that the plasticity of central neural networks is limited between two widely separated areas, such as between the midcervical and midthoracic motor cortical areas in the present studies, and therefore, the efforts to reconstruct neural networks, both centrally and peripherally, should aim at rebuilding situations as nearly to the original status as possible.

Animals↗
PubMed1997

The importance of determination of jaw position in orthodontic diagnosis and treatment planning for adult patients.

The basic data needed for orthodontic diagnosis and treatment planning include color prints of soft tissue facial profile, intraoral dental arches, and occlusion; cephalometric and panoramic radiographs; and dental casts. Hand-wrist and TMJ radiographs are also necessary in some circumstances. If orthodontic diagnosis and treatment plans are made only from the dental alignments and occlusion from the static or hand-assembled dental casts, the diagnosis and treatment planning made may be wrong in some cases. Clinically, it is necessary to find the centric relation of the lower jaw and to transfer the jaw relationship to the articulator. Correct diagnosis and orthodontic treatment planning may then be made from the findings of the occlusal relationship from the articulator accompanied with the information on skeletal age and craniofacial characteristics from the hand-wrist and cephalometric radiographs. Four clinical cases have been presented to demonstrate the importance of determination of jaw position in orthodontic diagnosis and treatment planning in adult patients.

Adult↗
PubMed1997

Effects of glucose on placental hormones in the human term placenta in vitro.

Glucose intake during pregnancy results in a decrease in endogenous insulin-like growth factor binding protein-1 (IGFBP-1). However, the exact role of glucose on placental secretion of IGFBP-1 is unclear. This study was designed to investigate the direct effects of glucose on the production of IGFBP-1 and other placental hormones, using an isolated placental preparation. Using the dual recirculating perfusion system for an isolated human placenta lobule, a total of 43 experiments were performed over a duration of 6 hours. Twenty placentae were perfused with a medium containing 141 +/- 10 mg/dL (7.83 +/- 0.56 mmol/L) glucose (group I) and 23 placentae with 242 +/- 12 mg/dL (13.43 +/- 0.67 mmol/L) glucose (group II). Levels of insulin, glucose, lactate, insulin-like growth factor (IGF-I), IGFBP-1, human placental lactogen (hPL) and beta-human chorionic gonadotropin (beta-hCG) were measured at 30 minute intervals during perfusion. Insulin and IGF-I were barely detectable in the perfusates and their levels were not modulated by glucose. IGFBP-1 was predominantly detected in the maternal rather than the fetal compartment of the placental circulation. Glucose increased the levels of IGFBP-1 in the maternal circulation in groups I and II during the first two hours of perfusion (188 +/- 58% and 193 +/- 31%, respectively). However, during the subsequent 4 hour period, the increase in IGFBP-1 concentration was significantly higher in group II (926 +/- 427%) than in group I (428 +/- 216%) (p < 0.05). There was no difference in the levels of hPL or beta-hCG between the two groups in the maternal circulation. Thus, glucose stimulates the production of IGFBP-1 in the maternal circulation of a placenta in vitro. This increase in IGFBP-1 by glucose in vitro, as opposed to the decrease of IGFBP-1 in vivo, may be due to a lack of circulatory maternal insulin in the isolated placental preparation. These results also suggest that there may be a functional barrier within the placenta that prevents an increase in the level of IGFBP-1 in the fetal circulation.

Chorionic Gonadotropin, beta Subunit, Human↗
PubMed1996

Determination of acetylcholine by on-line microdialysis coupled with pre- and post-microbore column enzyme reactors with electrochemical detection.

A sensitive procedure consisting of a pre- and post-microbore column reactor sequence of a LC-electrochemical detection system coupled with on-line microdialysis system is described in the present study to measure endogenous acetylcholine concentration in freely moving rats. The pre-column packed, with immobilized choline oxidase and catalase, was used to remove choline, whereas the post-column, packed with immobilized acetylcholine oxidase and choline oxidase, was used to measure acetylcholine selectively. The detection limit of acetylcholine oxidase and choline oxidase, was used to measure acetylcholine selectively. The detection limit of acetylcholine was found to be 5 fmol/microliter (50 fmol/10 microliters). The usefulness of the described methodology was evaluated by examining the change in the striatal acetylcholine concentration of freely moving rats after physostigmine (0.5 mg/kg, s.c.) administration.

Acetylcholine↗
PubMed1996

Cytotoxic effects of anthrax lethal toxin on macrophage-like cell line J774A.1.

The cytotoxic effects of anthrax lethal toxin purified from an avirulent strain were examined on mouse macrophage-like J774A.1 cells. Cell death induced by high concentration of purified lethal toxin had the characteristics of necrosis. At lower concentrations, the toxin caused no morphological change and most of the cells were viable. Interestingly, apoptotic cells were observed when the cells were preincubated with a serine/threonine phosphatase inhibitor, calyculin A, and then exposed to a toxin concentration of 0.1 microg/ml. This is the first report that lethal toxin of the anthrax bacillus can induce both necrosis and apoptosis and that protein phosphatases are implicated in the regulation of bacterial toxin-induced apoptosis.

Animals↗
PubMed1996

[Sequence analyses of Epstein-Barr virus (EBV) Bam HI F DNA fragment in EBV associated diseases].

In order to compare nucleotide differences of Epstein-Barr virus (EBV) Bam HI F DNA fragment from various EBV associated diseases, polymerase chain reactions (PCR) were used to amplify a subfragment (nucleotides 55,381-56,020) of the F fragment from different tissue DNAs, including 20 NPCs, 2 B-cell lymphomas, 2 T-cell lymphomas, 3 infectious mononucleosis (IM), and 3 normal controls. DNA sequences were determined by PCR direct sequencing or sequencing after DNA cloning. The PCR products were cloned into pGEM-3Z vector, then the resulting recombinant plasmids were used to transform DH5 alpha competent cells. Plasmid DNAs from the correct transformants were prepared for DNA sequencing. The results showed that the proportion of the f variant in NPCs, B-cell lymphomas, T-cell lymphomas, IMs, and normals were 40%, 0%, 0%, 33%, and 33%, respectively. Because the f variant was not specifically more prevalent in NPC tissues compared to the non-tumor tissues, we speculate that there is no strong association between the f variant and NPC. These results were different from other reports. Coinfection of the F strain and the f variant was found both in some NPC patients and normal individuals. Analyses of Bam HI F subfragments of 35 EBV isolates from the 30 tissue DNAs revealed that there were changes at four corresponding positions of the B95-8 strain. They were nucleotide T at 55,473 replaced by G, an insertion of TGT after nucleotide 55,543, nucleotide A at 55,564 replaced by G, and nucleotide T at 55,958 replaced by C. These 4 nucleotide changes may confer a character of Taiwan strains. The nucleotides of the F strain at coordinates 55,519, 55,596, 55,680, 55,703, and 55,895 were T, T, A, A, and C, and those for the f variant were C, C, C, C, and T. These two patterns were not correlated with types A and B of EBV.

Base Sequence↗
PubMed1996

Hyperglycemia induced activation of type-1 protein phosphatase activator (kinase FA) in perfused human placenta.

We report the identification of type-1 protein phosphatase activating factor (kinase FA), a unique biologic mediator for both insulin and epidermal growth factors in the human placenta. The activity of kinase F, was found to be extremely labile in the unperfused placenta. Fresh term placentas lost more than 50% of the total kinase FA activity within 6 hours when exposed to air of incubated in medium but not perfused. In contrast, the activity of kinase FA was stable when the human term placenta was dually perfused. This indicates that placental dual perfusion is a useful method for studying protein phosphorylation-dephosphorylation involved in signal transduction. When fresh placentas were perfused with media containing glucose at 141 +/- 10, 242 +/- 12 and 436 +/- 20 mg/dL, kinase FA activity was stimulated several-fold in a glucose concentration-dependent manner when compared with control levels at delivery. The results suggest that hyperglycemia-mediated activation may represent a previously unknown control mechanisms for the regulation of protein kinase FA. The results also suggest that human placental perfusion is a good in vitro system for studying signal transduction mechanisms involved in hormonal actions and metabolic regulation.

Analysis of Variance↗
PubMed1996

High maternal serum free beta-hCG levels in Down syndrome pregnancies: a preliminary report.

To investigate the serum free beta-human chorionic gonadotropin (beta-hCG) value in women carrying Down syndrome fetus, we have retrospectively studied 11 Down syndrome pregnancies and 200 singleton unaffected pregnancies between 15 and 22 weeks' gestation. Each affected pregnancy was assigned at least 15 control cases matched with maternal age and gestational age. The median value of free beta-hCG in Down syndrome pregnancies and unaffected pregnancies was 2.56 multiples of the median (MoM) and 1.06 MoM, respectively. The mean free beta-hCG value after log transformation in Down syndrome pregnancies was 2.01 MoM that was significantly different from that of unaffected pregnancies (1.05 MoM, P = 0.024). There were 54.6% (6/11) of Down syndrome pregnancies and 5% (10/200) of unaffected pregnancies with free beta-hCG levels greater than 2.5 MoM. It is suggested that free beta-hCG may be a potentially useful and superior marker in the detection of Down syndrome pregnancies in our population.

Adult↗
PubMed1996

[The phagetype and detection of drug-resistance of Salmonella typhi-muriun in Fujian province].

Salmonella typhimurium has accounted for 29.43% of total Salmonella according to the surveillance in Fujian province since 1975. Seven common phagetypes of S. typhimurium were found. The principal phagetype was 7774, which accounted for 46.6% of all phagetypes. S. typhimurium was significantly more resistant to antibiotics in early 1990's than in the 1980's. 57%-72% of the S. typhimurium strains were resistant to aminoglycosides (except amikacin), about 70% were strains resistant to first generation penicillins and tetracyclins while a high proportion of S. typhimurium strains have rapidly become resistant to new broad-spectrum penicillins. The strains of S. typhimurium which are resistant to the first and the second generation of cephalothins become sensitive only to the third generation of cephalo thins. There has been 20% of S. typhimurium strains resistant to some types of quinolones. All S. typhimurium were sensitive to norfloxacin, ofloxacin and ciprofloxacin. In the early 1980's resistant strains to 2-3 kinds of antibiotics accounted for 97%, and nostrains was resistant to more then 6 kinds of antibiotics. In the early 1990's, the strain resistant to 2-3 kinds of antibiotics were less than 20%; while strains resistant to more than 10 kinds of antibiotics were 66%. The increasing rate of resistant strains to antibiotics with widening of drug resistant pattern and the extensive appearance of multiresistant strains have become serious problems to be solved.

Aminoglycosides↗