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A C Chen

Publications and source records attributed to A C Chen.

At least 19 recordsLinked to original sources
PubMed1998

Effect of static compression on proteoglycan biosynthesis by chondrocytes transplanted to articular cartilage in vitro.

Transplantation of chondrocytes by injection or within carrier matrices has shown promise for augmenting the repair of articular cartilage defects. In vivo, transplanted chondrocytes are exposed to mechanical forces. This in vitro study examined the effect of a step application of compressive load to chondrocytes after the cells had been seeded onto a cartilage surface. Bovine chondrocytes were transplanted onto bovine cartilage disks, allowed to attach for 1 hour or 4 days, and subjected to compression through overlying cartilage disks in a confined compression configuration. Before use, the disks were lyophilized to lyse the endogenous chondrocytes and thereby allow assessment of the metabolic activity of the transplanted cells. During a 16-hour application of compressive stress of 0.24-0.72 MPa, proteoglycan synthesis, assessed as [35S]sulfate incorporation into macromolecules, was inhibited by approximately 68% after the 1-hour attachment and by approximately 45% after the 4-day attachment. Cell retention after the application of load was assessed by use of [3H]thymidine-tagged chondrocytes and quantitation of the displacement of radioactivity. After the 1-hour seeding period, loading induced a dose-dependent dislodgment of [3H]radioactivity (as much as 35%) from the tissue bilayer. In contrast, after the 4-day seeding period, there was no detectable effect of loading on chondrocyte dislodgment with an 8-12% release of radioactivity. The inhibitory effect of a 16-hour compression of 0.48 MPa applied after the 4-day seeding period was studied further. This protocol did not appear to have an irreversible effect on chondrocyte metabolism; at 2 days after the release of load, proteoglycan synthesis by the loaded cells was stimulated by 41% compared with transplanted cells that were not subjected to loading. These results suggest that the application of static compressive stress to chondrocytes at a cartilage surface may affect biosynthesis by these cells and thus subsequent integrative cartilage repair. Such an effect may have implications for optimization of the tightness of the press fit of a cell-laden cartilaginous construct into an articular defect.

Animals↗
PubMed1998

Gene expression studies of mRNAs encoding the NMDA receptor subunits NMDAR1, NMDAR2A, NMDAR2B, NMDAR2C, and NMDAR2D following long-term treatment with cis-and trans-flupenthixol as a model for understanding the mode of action of schizophrenia drug treatment.

It has been hypothesized that glutamate receptor function is important in both the aetiology and treatment of schizophrenia. In order to understand how specific glutamate receptor genes are involved in the treatment of schizophrenia we have used a multiprobe oligonucleotide solution hybridization (MOSH) technique to examine the regulation of gene express of the NMDAR1, 2A, 2B, 2C, 2D receptor subunits in the left rat brain following treatment with the optical isomers of flupenthixol. cis- and trans-flupenthixol are both present in the commonly used oral and depot treatments for schizophrenia and a controlled trial showed that cis-flupenthixol had a significantly superior ability to ameliorate the positive symptoms of schizophrenia compared to its trans-isomer. At a dose of 0.2 mg/kg/day over a period of 1, 2, 4, 8, 12 and 24 weeks, we found that both isomers down regulated the expression of NMDAR1 mRNA in most regions of the brain. NMDAR2A, 2B and 2C receptor subunits showed a significantly decreased expression from 12 to 24 weeks but after 2 weeks NMDAR2B, 2C, 2D expression was increased in several brain regions. The NMDAR1 receptor subunit immunoreactivity in the right brain following 4 and 24 weeks of drug treatment was also examined by Western blotting. Both trans- and cis-flupenthixol significantly decreased the NR1 immunoreactivity in the right cerebellum after 24 weeks of treatment. These results suggest that NMDA receptor subunits may have a role in the action of antipsychotic drugs. If we assume that the NMDA receptor expression changes reflect a beneficial and significant mechanism in the treatment of schizophrenia, it could be argued that NMDA receptor changes are more related to the negative or non-specific symptoms of schizophrenia.

Administration, Oral↗
PubMed1998

Topology of EEG coherence changes may reflect differential neural network activation in cold and pain perception.

Pain perception in the brain can be analyzed by neuroimaging (PET, fMRI) and electrophysiological parameter mapping (EEG, ERP/MEG, MEF). These studies have generally been focused on the localization of cerebral activation. Whether pain can be conceptualized as localized function or best be understood by distributed function is important to the theory of human pain processing in the brain. Here, we report that cold and pain perception in the brain is characterized by webs of EEG coherence changes which may reflect coupling or de-coupling of different cortical areas during cold and pain processing. EEG was recorded during cold and pain perception (right hand immersion in 15 degrees C cool-water vs. 0.3 degrees C ice-water for 3 min.) with eyes opened. Subjects rated the cold perception at 2.3 (cool to cold, but no pain) and the pain perception at 6.7 (moderate-strong pain) in a 1-10 scale. The obtained EEG spectral parameters were compared with the corresponding parameters of the resting baseline using paired Wilcoxon tests in the sense of statistical filters to depict those differences which differ clearly from changes by chance. The results were presented in probability maps. The EEG results indicated highly differential coherence networks between cold and pain perception. The cold perception was characterized as decreased coherence in the theta band mainly between frontal electrodes and increased interhemispheric coherence in the alpha range mainly between central and frontal positions. During pain perception almost no coherence changes in the theta band were observed, but great coherence increase in the delta band between central, parietal and frontal electrodes. The network of coherence changes in the alpha band showed strong involvement of electrode C3 concerning coherence increases with frontal positions. In the beta-1 band coherence increase within the left hemisphere was much more pronounced during pain than during cold. The differential characteristics of EEG coherence changes based on neural networks and their spatial organization in the neocortex indicate the distributed brain processing between cold and pain perception in man. This study may contribute to our understanding of the large scale neural networks in cognition based on neurophysiological binding hypothesis and network connections of neural ensembles.

Adult↗
PubMed1998

Comparison of genomic DNA in various strains of Boophilus microplus (Acari: Ixodidae).

The conventional method of identifying acaricide resistance in a suspect tick population by the United Nations Food and Agriculture Organization packet assay is a laborious and time-consuming process. DNA probes have been demonstrated as rapid and accurate tools for detecting pesticide resistance in insect species. Random-amplified polymorphic DNA (RAPD) has been used by other groups to differentiate species of mosquitoes and populations within a mosquito species. By using different arbitrary oligonucleotides as primers with RAPD, we have demonstrated that various strains of Boophilus microplus (Canestrini) show different patterns of DNA fragments on agarose gel electrophoresis. The unique DNA fragments may be useful for developing probes that can detect acaricide resistance in field pest populations.

Animals↗
PubMed1998

Experiences with functional magnetic resonance imaging at 1 tesla.

Functional magnetic resonance imaging (fMRI) has been performed on a standard 1 T system using a pulse sequence developed to utilize blood oxygen level dependent (BOLD) contrast and an off-line analysis routine using correlation techniques. The sequence and the data analysis routine have been validated by reproducing the conventional hand movement paradigm studies reported by numerous other workers. Our work has then been extended to investigate cerebral foci for a tonic pain stimulus and the cortical representation of oesophageal stimulation. Both these studies relate to paradigms where the expected BOLD signal is significantly less than that encountered for motor or visual cortex paradigms. The results show good agreement with other modalities (positron emission tomography, magnetoencephalography and cortical evoked potentials). Performing fMRI at 1 T is slightly controversial. However, our successful study of demanding paradigms, using a standard clinical 1 T imaging system, has important implications for many other users operating at this field strength.

Brain↗
PubMed1997

Human breast cancer cells and normal mammary epithelial cells: retinol metabolism and growth inhibition by the retinol metabolite 4-oxoretinol.

To understand the signaling and growth-inhibitory effects of retinoids, we have examined the metabolism of [3H]retinol in a number of estrogen receptor-positive (ER+) and estrogen receptor-negative (ER-) human breast cancer cell lines. We have also assayed the metabolism of [3H]retinol in normal human mammary epithelial cells. The ER+ breast cancer cell lines MCF-7 and T47D produce [3H]4-oxoretinol from [3H]retinol; the production of [3H]4-oxoretinol is increased by initial culture in the presence of nonradiolabeled retinoic acid (RA) or N-(4-hydroxyphenyl)retinamide, indicating that these drugs enhance [3H]retinol metabolism to [3H]4-oxoretinol. No metabolism of [3H]retinol to [3H]RA in these ER+ tumor lines was detected. ER- breast cancer lines MDA-MB-231, MDA-MB-468, and BT20 do not metabolize [3H]retinol to [3H]4-oxoretinol. In the ER- tumor lines, most of the [3H]retinol remains unmetabolized during the 24-h culture period; MDA-MB-468 and BT20 metabolize some [3H]retinol to [3H]RA. Unlike the majority of the tumor lines, the normal human breast epithelial cell strains AD074 and MCF10A rapidly metabolize [3H]retinol to [3H]retinyl esters. No detectable [3H]RA is produced from [3H]retinol in AD074 and MCF10A cells. Thus, the normal breast epithelial strains, the ER+ tumor lines and the ER- tumor lines differ greatly in their pathways of [3H]retinol metabolism. The levels of cellular retinol binding protein-I mRNA expression are not correlated with the levels or types of various retinol metabolites. Whereas the normal breast epithelial cells and the ER+ tumor lines are growth inhibited by RA, N-(4-hydroxyphenyl)retinamide, and 4-oxoretinol, only the 4-oxoretinol is growth inhibitory in the ER- tumor lines. The cellular retinoic acid-binding protein II mRNA levels are not correlated with the growth inhibition by RA or 4-oxoretinol in the normal and tumor lines.

Breast↗
PubMed1997

Exclusion of linkage between schizophrenia and the gene encoding a neutral amino acid glutamate/aspartate transporter, SLC1A5.

An abnormality in glutamatergic function has been hypothesized as being of etiological importance in schizophrenia. Twenty-three multiplex English and Icelandic schizophrenia families were genotyped with a polymorphic dinucleotide repeat sequence in the 3'-untranslated region of the glutamate/aspartate transporter gene called SLC1A5. Using the lod and a model-free method of linkage analysis (MFLINK), no evidence of linkage between SLC1A5 and schizophrenia was found. Our results do not support the hypothesis that SLC1A5 gene mutations or allelic variants provide a major gene contribution to the etiology of schizophrenia. However, because of the likelihood of heterogeneity of linkage in schizophrenia, there is a case for testing other pedigrees for linkage to the SLC1A5 locus. The SLC1A5 locus is one of a complex family of genes encoding neutral amino acid transporter proteins and the genetic relation between these other loci and schizophrenia has not yet been established.

Alleles↗
PubMed1997

Physical properties of rabbit articular cartilage after transection of the anterior cruciate ligament.

The effect of unilateral transection of the anterior cruciate ligament on the confined compression and swelling properties of the distal femoral articular cartilage of skeletally mature rabbits at 9 weeks after surgery was determined. Gross morphological grading of the transected and contralateral control distal femora stained with India ink confirmed that cartilage degeneration had been induced by ligament transection. Osteochondral cores, 1.8 mm in diameter, were harvested from the medial femoral condyles. The modulus, permeability, and electrokinetic (streaming potential) coefficient of the articular cartilage of the osteochondral cores were assessed by confined compression creep experiments. The properties (mean +/- SD) of control cartilage were: confined compression modulus, 0.75 +/- 0.28 MPa; hydraulic permeability, 0.63 +/- 0.28 x 10(-15) m2/Pa*sec; and electrokinetic coefficient, 0.16 +/- 0.31 x 10(-9) V/Pa. In transected knees, the modulus was reduced by 18% (p = 0.04), while the permeability and electrokinetic coefficient were not detectably altered. The change in modulus was accompanied by a trend (p = 0.07) toward a decrease (-11%) in the glycosaminoglycan density within the tissue, a significant increase (p < 0.001) in the water content of the cartilage after equilibration in 1 x phosphate buffered saline from 70.3 +/- 4.1% in control knees to 75.2 +/- 4.0% in transected knees, and little further swelling after tissue equilibration in hypotonic saline. The compressive modulus of the cartilage from both control and transected knees was positively correlated with the density of tissue glycosaminoglycan. The alterations in the physical properties of the articular cartilage after transection of the anterior cruciate ligament in the rabbit show trends similar to those observed in human and other animal models of osteoarthritis and provide further support for the use of this model in the study of cartilage degeneration.

Animals↗
PubMed1997

Depth-dependent confined compression modulus of full-thickness bovine articular cartilage.

The objective of this study was to determine the equilibrium confined compression modulus of bovine articular cartilage as it varies with depth from the articular surface. Osteochondral samples were compressed by 8, 16, 24, and 32% of the cartilage thickness and allowed to equilibrate. Intratissue displacement within the cartilage was measured with use of fluorescently labeled chondrocyte nuclei as intrinsic, fiducial markers. Axial strain was then calculated in nine sequential 125 microns thick cartilage layers comprising the superficial 1,125 microns and in a 250 microns thick layer of cartilage adjacent to the cartilage-bone interface. Adjacent osteochondral cores were also tested in confined compression to determine the equilibrium stresses required to achieve the same levels of compression. Stress-strain data for each layer of each sample were fit to a finite deformation stress-strain relation to determine the equilibrium confined compression modulus in each tissue layer. The compressive modulus increased significantly with depth from the articular surface and ranged from 0.079 +/- 0.039 MPa in the superficial layer to 1.14 +/- 0.44 MPa in the ninth layer. The deepest layer 250 microns thick, had a modulus of 2.10 +/- 2.69 MPa. These moduli were markedly different from the apparent "homogeneous" modulus for full-thickness cartilage (0.38 +/- 0.12 MPa) and ranged from 21 to 560% of that value. The relatively low moduli and the compression-induced stiffening of the superficial layers suggest that these layers greatly affect the biomechanical behavior of cartilage, such as during confined compression testing. The delineation of the depth-dependent modulus provides a basis for detailed study of the relationship between the composition, structure, and function of cartilage in such processes as aging, repair, and degeneration.

Animals↗
PubMed1997

Chondrocyte transplantation to articular cartilage explants in vitro.

The transplantation of chondrocytes has shown promise for augmenting the repair of defects in articular cartilage. This in vitro study examined the efficiency of the transplantation of bovine chondrocytes onto articular cartilage disks and the ability of the transplanted chondrocytes to subsequently synthesize and deposit proteoglycan. The radiolabeling of chondrocyte cultures with [3H]thymidine, followed by 4 days of chase incubation, resulted in the incorporation of 98% of the radiolabel into DNA (as assessed by susceptibility to DNase). At the end of the culture period, the [3H]DNA was stable, with a half-life of radioactivity loss into the medium of 73 days. With use of radiolabeled chondrocytes for quantitation, the efficiency of transplantation onto a cartilage substrate was 93 +/- 4% for seeding densities of as much as 650,000 cells per cm2 and a seeding duration of 1 hour. These findings were confirmed both by tracking cells stained with 5-chlormethylfluorescein diacetate and by quantitating DNA. During the 16 hours after seeding onto a cartilage substrate (in which the endogenous cells had been lysed by lyophilization), the transplanted cells synthesized sulfated proteoglycan in direct proportion to the number of cells seeded. Most (83%) of the newly synthesized proteoglycan was released into the medium rather than retained within the layer of transplanted cells and the recipient cartilage substrate. Comparative studies with lyophilized-rehydrated or live cartilage as the recipient substrate indicated a similar efficiency of chondrocyte seeding and proteoglycan synthesis by the seeded chondrocytes. The transplanted cells retained the chondrocyte phenotype, as judged by a high proportion of the [35S]macromolecules being in the form of aggrecan that was capable of aggregating with hyaluronan and link protein, as well as by immunostaining within and around the transplanted cells for type-II, but not type-I, collagen. These results indicate that the number of chondrocytes transplanted onto a cut cartilage surface greatly affects the level of matrix synthesis; this in turn may affect repair.

Animals↗
PubMed1997

Brain asymmetry and facial attractiveness: facial beauty is not simply in the eye of the beholder.

We recently reported finding asymmetry in the appearance of beauty on the face [Zaidel et al., Neuropsychologia, Vol. 33, pp. 649-655, 1995]. Here, we investigated whether facial beauty is a stable characteristic (on the owner's very face) or is in the perceptual space of the observer. We call the question 'the owner vs observer hypothesis'. We compared identity judgements and attractiveness ratings of observers. Subjects viewed left-left and right-right composites of faces and decided which most resembled the normal face (Experiment 1). Identity judgements (resemblance) are known to be associated with perceptual factors in the observer. Another group viewed the same normal faces and rated them on attractiveness (Experiment 2). In each experiment, there were two separate viewing conditions, original and reversed (mirror-image). Lateral reversal did affect the results of Experiment 1 (confirming previous findings [Bennett et al., Neuropsychologia, Vol. 25, pp. 681-687, 1987; Gilbert and Bakan, Journal of Anatomy, Vol. 183, pp. 593-600, 1993]) but did not affect the results of Experiment 2. The fact that lateral reversal did not affect the results of Experiment 2 suggests that facial attractiveness is more dependent on physiognomy (of the owner) and less dependent on an asymmetrical perceptual process (in the observer) than is facial identity. The results are discussed in the context of beauty's biological significance and facial processing in the brain.

Adolescent↗
PubMed1997

Involvement of nitric oxide and N-methyl-D-aspartate in acute hypoxic altitude convulsion in mice.

BACKGROUND: Altitude convulsion is a rather specific form of experimental convulsion which is induced by acute exposure to a hypobaric hypoxic condition. Several neurotransmitters have been shown to be involved in the mechanisms of altitude convulsions. However, their roles and interaction were not clear. HYPOTHESIS: The novel neurotransmitter nitric oxide (NO) may be involved in the mechanisms of altitude convulsion through its neuronal signalling roles in relation to the NMDA receptor. METHODS: There were 177 mice intraperitoneally administrated (i.p.) with several drugs. The altitude convulsion threshold (ACT) was used as an index to evaluate the acute hypoxic tolerance. RESULTS: NO synthesis precursor, L-arginine (20, 40, 200, 800 mg/kg), resulted in a dose-dependent decrease in the ACT in mice, while the NO synthase (NOS) inhibitor, NG-nitro-L-arginine-methyl ester (L-NAME, 1.25, 2.50, 5.00 mg/kg, i.p.) increased the ACT. Pretreatment with L-NAME (5.0 mg/kg) prior to L-arginine (200 mg/kg) administration prevented the effect of decreasing ACT caused by L-arginine. Similarly, N-methyl-D-aspartate (NMDA, 2.5, 10.0, 20.0 mg/kg, i.p.) yielded a decrease in the ACT in mice and this decrease in hypoxic tolerance caused by NMDA can be prevented by pretreatment with either NMDA receptor antagonist 2-amino-5-phosphovalerate (AP-5, 20.0 mg/kg, i.p.) or NOS inhibitor L-NAME (5.0 mg/kg, i.p.). CONCLUSIONS: These findings suggest an important signalling role for nitric oxide and NMDA in the development of altitude convulsion and further support the hypothesized relationship between NMDA-receptor mediated neurotoxicity and nitric oxide.

Acute Disease↗
PubMed1996

An analysis of retinoic acid-induced gene expression and metabolism in AB1 embryonic stem cells.

Murine embryonic stem cells such as the AB1 cell line undergo differentiation in the presence of retinoic acid (RA) into an extraembryonic epithelial cell type. This results in the activation of genes such as Hoxa-1, Hoxb-1, laminin, collagen IV(alpha1), tissue plasminogen activator, RARbeta, and CRABPII. The CRABPI gene is regulated in an unusual fashion; CRABPI message and protein levels are induced at low concentrations of RA, but induction is diminished at higher concentrations. AB1 cells take up RA rapidly from the medium, and the addition of low, exogenous concentrations of RA to the culture medium results in very high intracellular RA concentrations. For example, AB1 stem cells cultured in 5 nM [3H]RA have an internal [3H]RA concentration of 1-2 microM within the first hour. AB1 cells also metabolize [3H]RA to more polar RA derivatives. The half-life of RA in AB1 cells not previously exposed to RA is about 2-2.5 h versus 40-45 min in cells cultured for 2-3 days in 1 microM exogenous RA. Thus, the enzyme(s) which metabolize RA are induced or activated by RA. Furthermore, the local concentration of RA required to elicit some biological responses may be higher than previously thought.

Actins↗
PubMed1996

Direct isolation of ultra-late (C-fibre) evoked brain potentials by CO2 laser stimulation of tiny cutaneous surface areas in man.

In this study, it is reported that CO2 laser heat stimulation of tiny skin surface area (0.15 mm2) provides a unique method to directly and selectively activate C-fibre as assessed by the ultra-late brain potentials (peak latencies: N810, P996) evoked consistently across a set of stimulus energy levels. On a larger surface area (15.5 mm2), low energy stimulation also resulted in minute ultra-late potential, while higher intensities induced only late potentials related to A-delta fibre activity (peak latencies: N247, P394). The selective activation of C afferent sensory terminals in the skin by stimulation of tiny surface area is explained by their relative high density and lower activation threshold.

Adult↗
PubMed1996

Activation of cells of cochlear nucleus by electrical stimulation of lateral hypothalamus.

Effects of electrical stimulation of the lateral hypothalamus (HS) were examined in 67 cells of the dorsal or ventral cochlear nucleus. Both short latency activity in the 10-20 ms post-stimulus period and late activity in the > 20 ms post-stimulus period were elicited in response to HS. A greater percentage of units exhibited the short latency response in dorsal (89%) than ventral (68%) cochlear nucleus. It was not previously recognized that stimulation of the hypothalamus could elicit increases in spike activity in this auditory relay nucleus. The hypothalamus is known to play a role in visceral-emotional functions, including feeding, fleeing, fighting and reproductive behavior. These results suggest a means by which neural activities supporting these functions could influence acoustic relay transmissions.

Animals↗
PubMed1996

Lack of evidence for close linkage of the glutamate GluR6 receptor gene with schizophrenia.

OBJECTIVE: Previous research has consistently implicated genetic factors in the pathogenesis of schizophrenia. It has been hypothesized that an abnormality in glutamatergic function is of etiologic importance in schizophrenia, and therefore the glutamate receptor family of genes are potential susceptibility loci for schizophrenia. To test this hypothesis the authors sought to detect linkage between the GluR6 glutamate receptor gene and schizophrenia. METHOD: Twenty-three English and Icelandic families containing multiple cases of schizophrenia were genotyped with a microsatellite trinucleotide repeat polymorphism localized at the GluR6 glutamate receptor locus. Lod scores, model-free linkage analysis, and extended relative pair analysis were used to test for linkage. RESULTS: No statistically significant evidence of linkage between GluR6 and schizophrenia was found. CONCLUSIONS: The results do not support the hypothesis that GluR6 allelic variants provide a major gene contribution to the etiology of schizophrenia in a large proportion of these pedigrees.

Alleles↗
PubMed1996

Pregnancy following in vitro fertilization and embryo transfer by microsurgical epididymal sperm aspiration from a patient with congenital absence of the vas deferens: a case report.

Congenital absence of the vas deferens (CAVD) has been considered a virtually untreatable cause of male infertility. Men with this condition have been shown on testicular biopsy to have adequate spermatogenesis, and are theoretically producing sperm capable of fertilizing an oocyte. Yet epididymal transit was thought to be essential for the maturation of spermatozoa and development of their fertilizing ability since the characteristics of sperm motility improve as the sperm passes through the cauda. However recent studies in man have shown that spermatozoa aspirated from the obstructed caput epididymis and ductuli efferentia are, in fact, capable of fertilization in vitro. Microsurgical epididymal sperm aspiration (MESA) from the proximal region (caput) of the epididymis, obtained 0.5 x 10(6) sperm per ml, following washing and direct swim-up. Twelve oocytes were inseminated and three embryos were generated for transfer. The patient conceived and delivered a healthy female baby weighting 2838 gm, on March 3, 1994. This is the first documentation in Taiwan of live birth resulting from MESA from a patient with CAVD combined with in vitro fertilization and embryo transfer.

Adult↗