Search PubMed⌕ Search

Biomedical subjects

K Chung

Publications and source records attributed to K Chung.

At least 109 records · Page 6Linked to original sources
PubMed1996

Degradation of Fenamiphos Sulfoxide and Fenamiphos Sulfone in Soil with a History of Continuous Applications of Fenamiphos

Mineralization rates of fenamiphos sulfoxide (FSO), total-toxic-residue [TTR, FSO+fenamiphos sulfone (FSO2)] disappearance rates for FSO, disappearance rates of FSO2, and metabolites in surface and subsurface soil samples collected from a turfgrass site (fairway) were determined. This site had been treated with fenamiphos annually or biannually for 20 years, and enhanced degradation of fenamiphos TTR was observed. Both the mineralization of FSO and the disappearance of FSO TTR, as well as the disappearance of FSO2 in soil samples collected from the fairway were much more rapid than in soil samples collected from a nearby site (rough) that had no previous history of fenamiphos application. Both FSO and FSO2 were degraded more rapidly in surface soil samples than in subsurface samples. The degradation pathway of FSO in the fairway soil samples was different from the rough samples. Hydrolysis to FSO phenol (FSO-OH) was the initial route of degradation of FSO in the fairway samples, whereas hydrolysis to FSO-OH and oxidation to FSO2 were the initial routes of degradation in the rough samples.

Journal Article↗
PubMed1996

Properties of glass--ceramic materials for fixed partial denture construction.

In order to determine the feasibility of constructing fixed partial dentures using glass-ceramic materials, the flexural strength and marginal fit of three experimental glass ceramic materials, and DICOR as control, were studied. The flexural strength ranged from 105.8 MPa to 129.5 MPa. Ceramic and alumina addition provided significant strength as tested by ANOVA and multiple range tests (P < 0.05). The range for the cemented bridge margins was from 48.9 microns to 80.4 microns. The tested ceramics had no statistically significant differences in margin openings for the same sites (P < 0.05). However, the openings on the mesial side of the premolar abutment and the distal end of the molar abutment of the fixed partial denture did have statistically significant differences (P < 0.01). Appropriate addition of alumina led to an increase in bending strength. The alumina stabilizes and strengthens the glass-ceramic material by incorporation into the silicone network.

Aluminum Oxide↗
PubMed1994

Immunohistochemical evidence for sprouting of ventral root afferents after neonatal sciatic neurectomy in the rat.

The present study demonstrates that afferent fibers in the rat ventral root sprout after transection of the neonatal sciatic nerve. The key data are that the number of unmyelinated fibers increased dramatically in the L5 ventral roots and about half of these unmyelinated fibers were labeled with antibody to growth associated phosphoprotein (GAP-43), suggesting that they are regenerating axons. Furthermore, these fibers survived in the distal stump of the acutely cut ventral root, suggesting that they are afferent fibers. The results provide direct evidence for sprouting of afferent fibers in the ventral root induced by a neonatal peripheral nerve lesion.

Animals↗
PubMed1994

Androgen resistance and deficiency have different effects on the growing skeleton of the rat.

Mature male, female, and androgen-resistant testicular feminized (Tfm) male rats of the same strain were sacrificed at the age of 120 days. Young male and Tfm rats were orchidectomized (orch) at 1 month of age and sacrificed at 120 days. The right femora were dissected, cleaned, defatted, and scanned with the Hologic QDR-1000. Orch and Tfm rats had similar body weights that were intermediate between body weights of their normal male and female littermates. Serum IGF-I concentrations were lowest in Tfm rats; IGF-1 concentrations in orch rats were not lower than in males. Dual-energy X-ray absorptiometry yielded the following results: Total femoral mass and area were lower in female, Tfm rats and in both orch groups compared with intact male rats. Femoral bone density was, however, only decreased in orch rats. Bone density measured in an area containing only cortical bone was not different between groups. However, the density was lower in orch rats in an area containing both cancellous and cortical bone. This finding is consistent with a +/- 50% decrease of cancellous bone volume in orch rats compared with all other groups at the proximal tibial metaphysis (an area containing mainly cancellous bone). These data show that Tfm rats, despite having lower IGF-I levels in serum, low body weight, and decreased femoral areas, manage--in contrast with orchidectomized rats--to maintain similar trabecular bone densities and volumes during growth. We conclude that trabecular bone densities can be preserved in androgen-resistant male rats independent of bone or body growth velocity or IGF-I secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1993

Neonatal sciatic nerve lesion triggers the sprouting of fibers in the contralateral ventral root of the rat.

We explored the possibility that unilateral neurectomy of the sciatic nerve of the rat at the neonatal stage triggers sprouting of afferent fibers in the contralateral ventral root. 3 months after neonatal sciatic neurectomy, the numbers of both myelinated and unmyelinated fibers in the L5 and L3 ventral roots were counted on electron micrographic montages. Age-matched littermates were used as unoperated controls. To identify regenerating axons, electron microscopic immunohistochemistry was done on the ventral roots using antibody against growth-associated phosphoprotein (GAP-43). Neonatal sciatic neurectomy resulted in: (1) about a three-fold increase in the number of unmyelinated fibers in the contralateral L5 ventral root as compared with the unoperated control; (2) about a 25-fold increase in the number of unmyelinated fibers in the ipsilateral L5 ventral root as compared with the control; (3) approximately 25% of the unmyelinated fibers in the contralateral L5 ventral root expressing GAP-43; and (4) no significant change in the number of unmyelinated fibers in the L3 ventral root of either side as compared with the control. The data suggest that a neonatal sciatic neurectomy of the rat triggers sprouting of unmyelinated afferent fibers in the ventral root of the contralateral as well as the ipsilateral side. The sprouting is restricted, however, to spinal segments which receive inputs from the sciatic nerve.

Animals↗
PubMed1993

Genomic structure of rat liver aryl sulfotransferase IV-encoding gene.

This report contains the first description of the genomic structure for a sulfotransferase (ST). The gene (ASTIV) encodes rat hepatic aryl ST IV, also known as tyrosine-ester ST (EC 2.8.2.9). A phage genomic clone containing 70% of the 3' AST gene coding sequence was isolated after screening a rat genomic library with an ASTIV cDNA. The remaining 5' sequence was determined from a PCR product obtained from rat genomic DNA and ASTIV cDNA-specific primers. ASTIV spans 3.5 kb and contains eight exons and seven introns. The fourth intron of this gene contains sequences homologous to rodent B1 repetitive elements and an Alu repeat found in rat. An alignment of the primary structures of ten different ST revealed several conserved regions, as well as a putative binding site for the cofactor for enzymatic sulfation reactions, 3'-phosphoadenosine-5'-phosphosulfate.

Amino Acid Sequence↗
PubMed1993

Abnormalities of sympathetic innervation in the area of an injured peripheral nerve in a rat model of neuropathic pain.

Using the rat model that we have developed, a potential underlying mechanism for sympathetically maintained neuropathic pain (SMP) was explored. In rats showing neuropathic pain behaviors after a tight ligation of the L5 spinal nerve, putative sympathetic postganglionic fibers were examined in the injured spinal nerve and the dorsal root ganglion (DRG), using immunohistochemical staining with antibody against tyrosine hydroxylase (TH). In the neuropathic rats, there was an increase in the number of TH-immunolabeled fibers in the spinal nerve, and some DRG cells were surrounded by the labeled fibers. These abnormalities of sympathetic postganglionic innervation of the injured spinal nerve or the DRG may be a part of the mechanisms underlying the development of SMP.

Animals↗
PubMed1993

Spinal projections of pelvic visceral afferents of the rat: a calcitonin gene-related peptide (CGRP) immunohistochemical study.

Little information is available concerning the pelvic visceral afferent system, in view of its terminal location in the spinal cord and its associated transmitter substances in the rat. By utilizing an immunostaining method to examine the transneuronal neurotransmitter depletion resulting from peripheral sensory nerve injury, the spinal projections of primary afferent fibers containing calcitonin gene-related peptide (CGRP) and originating from pelvic viscera were studied in the lumbosacral spinal cord of the rat. After unilateral or bilateral pelvic nerve section, CGRP immunoreactivity in the lumbosacral spinal cord was decreased greatly in the sacral parasympathetic nucleus (SPN), the dorsolateral fasiculus, the medial border of the dorsal horn, the dorsal gray commissure (DGC), and the intermediate gray connecting the SPN and DGC. Fine structural analysis showed that the CGRP-immunoreactive terminals made synaptic contact with dendrites and, rarely, with somata. Although there was some incidence of a synaptic contact between a CGRP-IR terminal and a vesicle-containing profile, definite evidence of axo-axonal synapse has not been confirmed. These data indicate that CGRP-containing pelvic visceral primary afferent fibers project to autonomic areas of the lumbosacral spinal cord by way of the pelvic nerve and make synaptic contact with dendrites and somata.

Animals↗
PubMed1993

Bone and mineral metabolism in the androgen-resistant (testicular feminized) male rat.

Androgens have important effects on bone in vivo, possibly by direct activation of the androgen receptors in osteoblasts. To test this hypothesis, calcium homeostasis, bone mass, and bone turnover were evaluated in mature (4-month-old) androgen-resistant (testicular feminized, TFM) male rats. Data were compared with data from both female and male littermates of the same age and strain. Compared to normal males, TFM had similar serum testosterone, twofold higher estradiol and estrone, and sixfold higher androstenedione concentrations. Compared to normal females, TFM rats showed lower estradiol but also elevated concentrations of androstenedione and estrone. Despite similar free 1,25-(OH)2D3 concentrations, both TFM and male rats maintained higher serum calcium and phosphate concentrations than their female littermates. Serum IGF-I concentrations in TFM rats were decreased compared to male rats (-12%) or female rats (-27%). Serum osteocalcin concentrations, however, were twofold higher in TFM rats than in females but not significantly different from males. Femoral length, diameter, and cortical thickness were intermediate between those of males and females. The cancellous bone density of the femur and cancellous bone volume of the proximal metaphysis of the tibia, however, were not significantly different between groups. The ash weight of the tibia was also not significantly different, and the ash weight of the four distal lumbar vertebrae ranged between male and female values. Bone mechanical properties as measured by torsional strength and energy absorption of the femur were lower in TFM than in females but not different from males.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgen-Insensitivity Syndrome↗
PubMed1993

Chronic effects of topical application of capsaicin to the sciatic nerve on responses of primate spinothalamic neurons.

The responses of 144 spinothalamic tract (STT) cells were recorded in 15 anesthetized macaque monkeys (Macaca fascicularis). Three to 4 weeks prior to the acute experiment, the sciatic nerve was surgically exposed on one or both sides so that capsaicin or vehicle could be applied. Responses of STT cells recorded in 3 experimental groups were compared: untreated (21 cells), vehicle-treated (40 cells), and capsaicin-treated (83 cells). The background activity of cells in the vehicle- and capsaicin-treated groups was the same as in the untreated group (that is, cells on the side contralateral to surgery). Responses to innocuous (BRUSH) and noxious (PINCH) mechanical stimuli were unchanged by vehicle or by capsaicin treatment. However, responses to other noxious (PRESSURE and SQUEEZE) mechanical stimuli were significantly increased in the vehicle-treated group. Compared with a large reference population, all experimental groups showed a significant increase in overall responsiveness to mechanical stimuli (as determined by cluster analysis), greatest in the vehicle-treated group. Responses to noxious heat stimuli were significantly reduced in the capsaicin-treated group for 45 degrees C and 47 degrees C stimuli. Volleys in A fibers, probably A delta fibers, evoked prolonged responses in many STT cells of all treatment groups. Electron microscopic counts of axons in the sciatic nerves of animals treated with capsaicin showed a reduced number of C fibers but no appreciable loss of myelinated axons. This loss of unmyelinated sensory fibers was presumably responsible for the reduction in the responses of the STT cells to noxious heat stimuli. Increased responses to some noxious mechanical stimuli and to A fiber volleys may have been the consequence of several factors, including surgical manipulation, a chemical action of vehicle and a contralateral action of capsaicin treatment.

Administration, Topical↗
PubMed1993

Technique of intraluminal biliary ultrasonography during laparoscopic cholecystectomy.

Intraluminal ultrasonography of the common duct was performed in nine patients undergoing laparoscopic cholecystectomy, using a system comprising a 20-MHz crystal in a 95-cm, blunt-tipped 6F sheath, mechanically rotated at 1,800 rpm. The probe was introduced through an incision in the cystic duct and passed into the duodenum. When the catheter was withdrawn, excellent visualization of the common and cystic ducts and lower end of the common hepatic duct was achieved. In seven patients, the biliary tree was normal. A small calculus was discovered in the common duct in one patient. This stone was not seen on a subsequent cholangiogram and was subsequently retrieved. An additional patient had mucus or sludge noted in the duct, which cast no acoustic shadow and thus was distinguished from calculi. The technique was fast, efficient, and easy to perform in this small group of patients and holds promise for screening the common duct pathology during laparoscopic cholecystectomy.

Adult↗
PubMed1993

Exogenous neuropeptide Y blocks myoelectric activity in the upper gastrointestinal tract of starved dogs. Brain neuropeptide Y converts a fasting pattern of myoelectric activity to a fed pattern.

The effect of intracerebroventricular (ICV) neuropeptide Y (NPY) on the migrating motor complex (MMC) was examined in five starved dogs. Myoelectric activity was recorded using gastric, duodenal, and jejunal electrodes. Intragastric pressure was monitored via a gastric fistula, and ICV injections were given through a cerebroventricular guide. Recordings were made with no ICV injection and before and after 250-microliters bolus injections of vehicle as control (0.1% dog serum albumin in saline) or 500 pmol/kg NPY. The mean interval between MMCs was 98 +/- 10 min without ICV injection and 96 +/- 7 min after control solution. After ICV injection of NPY no further MMCs were recorded in any dog, even though the study was continued for a minimum of 3.5 h. Instead, the myoelectric pattern became indistinguishable from that in fed dogs. We conclude that central NPY plays a role in modulation of upper gastrointestinal myoelectric activity. This may reflect a central regulatory role for NPY in the coordination of feeding.

Animals↗
PubMed1992

Numbers and proportions of unmyelinated axons at cervical levels in the fasciculus gracilis of monkey and cat.

The present study is a quantitative analysis of the unmyelinated fiber population in the fasciculus gracilis of the second cervical segment of cat and monkey. We find that unmyelinated fibers represent 13.7% of the total fiber population in this pathway in the cat and 18.9% in the monkey (Macaca fascicularis). The existence of such large numbers of these axons suggests that there may be a sizeable ascending fine primary afferent pathway in the fasciculus gracilis in cat and monkey whose destination is presumably the dorsal column nuclei. These findings are of interest in regard to classic ideas that the afferent fibers in the dorsal columns are large myelinated fibers that convey fine discriminative information to the dorsal column nuclei.

Animals↗
PubMed1992

Effects of palladium addition on properties of dental amalgams.

Palladium-containing amalgam alloys were developed utilizing the atomization method. Single-compositional type alloys were fabricated and palladium was substituted for silver in concentrations up to 5 w/o. Alloy powder with a particle size of less than 45 microns was collected and triturated with mercury. Creep, compressive strength and dimensional change tests were performed according to ADA Specification No. 1 along with controls of Tytin, Valiant and Valiant-Ph.D. Values for creep decreased and compressive strength increased markedly with additions of palladium. Current densities of the experimental amalgams containing palladium were determined to be an order of magnitude less than the original amalgams in the electrochemical test. A trend of positive relationships between properties and palladium additions was indicated.

Corrosion↗
PubMed1992

Peripheral gangrene associated with Kawasaki disease.

Three American infants with Kawasaki disease (KD) complicated by peripheral extremity gangrene are reported. Eight such patients (only 1 from Japan) have been reported previously. These 11 patients, infants less than 7 months old at onset of KD, are predominantly non-Asian. At least nine had associated giant coronary aneurysms, and eight had associated peripheral arterial aneurysms. In eight infants the diagnosis of KD was not established and therapy was not instituted until greater than or equal to 14 days after onset. Peripheral ischemia initially was noted 15-31 days after onset. Although the pathogenesis of this complication is not well understood, it likely includes some combination of local peripheral arteritis, arteriospasm, thrombosis peripherally and/or more proximally (e.g., in an axillary artery aneurysm), and cardiogenic shock. Treatment may include use of antiinflammatory agents such as salicylates and intravenous gamma globulin, vasodilative agents and/or methods, and thrombolytic and/or anticoagulant agents in an attempt to prevent the potentially devastating consequences of progressive gangrene.

Aneurysm↗
PubMed1991

Unmyelinated primary afferent fiber stimulation depletes dynorphin A (1-8) immunoreactivity in rat ventral horn.

The present study demonstrates many dynorphin (DYN)-immunoreactive fibers and presumed presynaptic terminals in rat lumbar ventral horn. The fibers and terminals seem to arise largely from DYN-containing intrinsic neurons in the dorsal horn. The majority of the presumed terminals closely surround a subpopulation of motoneurons that tend to be located in flexor motoneuron columns. Acute C fiber, but not A fiber, primary afferent stimulation depletes the ventral horn DYN immunostaining. We interpret these findings to indicate that the spinal DYN neurons are well positioned to serve both as modulators of nociceptive input and as interneurons in motor reflexes. We further hypothesize that the depletion of DYN-immunoreactivity that follows either acute C fiber stimulation or intense nociceptive stimuli may be the trigger for the upregulation in spinal cord DYN that occurs in models of chronic pain states.

Afferent Pathways↗