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Biomedical subjects

J Chan

Publications and source records attributed to J Chan.

At least 235 records · Page 13Linked to original sources
PubMed1991

Effects of glucose on calcium channels in neural cells.

Hyperglycemia has been reported to alter outcome following experimental and clinical cerebral ischemia, but the mechanisms involved are incompletely understood. Since glucose influences the function of dihydropyridine-sensitive, voltage-gated Ca2+ channels in some non-neural cells, and since cellular Ca2+ overload has been implicated in the pathogenesis of ischemic neuronal injury, we examined whether glucose regulates Ca2+ channel function in a cultured neural cell line. Physiologic concentrations of glucose had no effect on free intracellular Ca2+ levels in PC12 cells, but 4-fold elevation of glucose above physiologic levels reduced the dihydropyridine-sensitive, depolarization-induced increase in Ca2+. This effect would not account for exacerbation of ischemic brain injury by hyperglycemia, but may contribute to attenuation of ischemic injury by glucose in certain settings.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Serologic evidence of Campylobacter jejuni/coli enteritis in patients with Guillain-Barré syndrome.

We performed serologic testing for Campylobacter jejuni in 17 consecutive patients with acute Guillain-Barré syndrome from the Boston, Mass area to compare the frequency of this preceding infection with the high rates reported from other areas of the world. The rate of seropositivity, 18%, was considerable, but it was lower than that reported in Australia. Moreover, all of our patients with definite serologic evidence of infection had severe enteritis before Guillain-Barré syndrome, usually with the organism cultured from stool samples. Campylobacter enteritis is an important antecedent illness for Guillain-Barré syndrome but did not precipitate the disease without enteritis.

Antibodies, Bacterial↗
PubMed1991

Idiopathic cervical dystonia: clinical characteristics.

We reviewed detailed clinical features of 266 patients with idiopathic cervical dystonia, commonly called spasmodic torticollis. Mean age at onset (41 years), female-to-male ratio (1.9:1), clustering of onset between ages 30 and 59 (70%), familial history of dystonia (12%), and remissions (9.8%) were similar to those found in previous studies. In contrast to the single prior large clinical study of this disorder, no predominance of right-handers or significant thyroid disease was found. Pain, which occurred in 75% of patients and contributed to disability score (p less than 0.01), distinguishes this syndrome from all other focal dystonias. Pain was also strongly associated with constant (vs. intermittent) head turning, severity of head turning, and presence of spasm. Eighty-three percent of patients had deviation of the head of greater than 75% of the time when sitting with the head unsupported (constant head deviation at rest). Of the 97% who had head turning, 81% also had head tilting in various combinations. The 23% with hand tremor had an older age at onset (mean, 46 vs. 41 years; p less than 0.05). An earlier age at onset (p less than 0.05) was seen in patients with a family history of dystonia (mean, 36 years), with trauma shortly preceding symptoms (mean, 36 years), with a change in the direction of head turning (mean, 30 years), and with remissions (mean, 33 years). Jerky movements or forced transient spasms of the head occurred in 62% of the patients, and these patients would be the ones for whom the designation "spasmodic torticollis" could logically apply.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Plasmalemmal appositions between cholinergic and non-cholinergic neurons in rat caudate-putamen nuclei.

We have observed that in rat caudate-putamen nuclei, neurons immunolabeled for choline acetyltransferase were sometimes in direct apposition to unlabeled perikarya and dendrites [Pickel V. M. and Chan J. (1990) J. Neurosci. Res. 25, 263-280]. Similar juxtapositions between plasmalemmas of nerve cells each receiving input from one common terminal have been associated with activation of certain central neurons [Theodosis D. T. and Poulain D. A. (1989) Brain Res. 484, 361-366]. Thus, we sought to determine the relative abundance and ultrastructure of the appositions and the frequencies of shared synapses between choline acetyltransferase-labeled and unlabeled neurons in the rat striatum. A monoclonal antibody raised against choline acetyltransferase was localized in semi-adjacent ultrathin sections through 24 neurons in the dorsolateral caudate-putamen nuclei. Five of these choline acetyltransferase-labeled perikarya showed direct somatic appositions with unlabeled neurons. The remaining 19 of the choline acetyltransferase-labeled perikarya did not show somatic appositions with unlabeled perikarya; however, when traced through multiple (20-100) semi-adjacent sections their dendrites always showed extensive plasmalemmal juxtapositions with one or more unlabeled perikarya. The apposed perikarya had round nuclei and other characteristics of medium, spiny neurons. The majority of the apposed cholinergic and non-cholinergic neurons were postsynaptic to at least one common unlabeled terminal. These terminals usually formed symmetric junctions. At sites of appositions, the plasmalemmas of choline acetyltransferase-immunoreactive soma or dendrites and unlabeled neurons were closely spaced without intervening astrocytic processes. The appositions lacked the ultrastructural features typical of gap-junctions, but did occasionally show parallel arrays of thin (1-2 nm) electron-dense bands. In both labeled and unlabeled perikarya, the nuclei were separated from the appositional zones by narrow (0.7-3.3 microns) rims of cytoplasm. This cytoplasmic rim contained subsurface cisternae and other less specialized smooth and rough endoplasmic reticulum, and vesicular structures. The findings suggest that in the caudate-putamen nuclei (1) the tonically active cholinergic neurons [Wilson C. J. et al. (1990) J. Neurosci. 10, 508-519] may modulate or be modulated by non-cholinergic spiny neurons through non-synaptic somatic or dendritic appositions, and (2) that both neurons may be simultaneously inhibited by shared afferent input. Activation of this system could facilitate coordinated movements through synchronization of cholinergic interneurons and spiny projection neurons containing GABA or other transmitters.

Animals↗
PubMed1991

One-step isolation of alpha 1-acid glycoprotein.

alpha 1-Acid glycoprotein could be isolated by a one-step extraction method from human sera and plasma. Protein recovered in the water phase after extraction with phenol at 70 degrees C for 20 min was verified as human alpha 1-acid glycoprotein when it was compared with the reference standard human alpha 1-acid glycoprotein by Ouchterlony double immunodiffusion, sodium dodecylsulfate-polyacrylamide gel electrophoresis, Western blot analysis, and periodic acid-Schiff stain. The present isolation procedure is simple and fast, and can extract about 81% of the total alpha 1-acid glycoprotein in the sera and plasma, as determined by radial immunodiffusion.

Blotting, Western↗
PubMed1991

Lipoarabinomannan, a possible virulence factor involved in persistence of Mycobacterium tuberculosis within macrophages.

Mycobacterium tuberculosis and Mycobacterium leprae, the causative agents of tuberculosis and leprosy, respectively, produce large quantities of lipoarabinomannan (LAM), a highly immunogenic, cell wall-associated glycolipid. This molecule has been previously reported to be a potent inhibitor of gamma interferon-mediated activation of murine macrophages. Studies of the mechanism by which this mycobacterial glycolipid down-regulates macrophage effector functions provide evidence that LAM acts at several levels and that it can (i) scavenge potentially cytotoxic oxygen free radicals, (ii) inhibit protein kinase C activity, and (iii) block the transcriptional activation of gamma interferon-inducible genes in human macrophage-like cell lines. These results suggest that LAM can inhibit macrophage activation and triggering and cytocidal activity and that it may represent a chemically defined virulence factor contributing to the persistence of mycobacteria within mononuclear phagocytes.

Cells, Cultured↗
PubMed1991

A position-dependent silencer plays a major role in repressing alpha-fetoprotein expression in human hepatoma.

A large percentage of human hepatomas produce alpha-fetoprotein (AFP), but the levels of AFP expression vary greatly among hepatomas. To understand the molecular basis for this variation, we analyzed transcriptional regulatory activities associated with the 5'-flanking region of the AFP gene in two human hepatoma cell lines, HuH-7 and huH-1/cl-2, which produce a high and a low level of AFP, respectively. We found that the low level of AFP production in huH-1/cl-2 is due to the action of at least two silencer regions located between the enhancer and the promoter of the AFP gene. In contrast, no silencer activity is expressed in HuH-7. We identified 5'-CTTCATAACTAATACTT-3' to be a core sequence responsible for the negative regulatory activity. This sequence is repeated four times in a strong, distal silencer region, Sd, whereas one copy is present in a weak, proximal silencer region, Sp. The silencer reduces transcriptional initiation by blocking enhancer activation of the AFP promoter in a position-dependent manner. The silencer functions in the presence of positive transcription factors and may play a key role in developmental repression as well as variable expression of the AFP gene in hepatomas.

Albumins↗
PubMed1991

Increasing incidence of hypertrophic pyloric stenosis.

The incidence of pyloric stenosis in the Mersey region rose from 1.54/1000 births in 1976-8 to 2.22/1000 births in 1986-8. Reliance on ultrasonography for diagnosis in the 1980s resulted in fewer 'tumours' being felt; diagnostic delay was not shortened overall but serial ultrasonography showed evolving lesions in six patients. Clinical examination and selective use of ultrasonography is advocated.

England↗
PubMed1991

eek and erk, new members of the eph subclass of receptor protein-tyrosine kinases.

We have identified human and rat DNAs encoding two novel members of the eph subclass of putative receptor protein-tyrosine kinases. Rat cDNA clones encoding eek (eph- and elk-related kinase) were isolated from a brain cDNA library probed with DNA encoding the kinase region of the insulin receptor-related receptor. The predicted eek protein contains all the amino acid residues conserved in the catalytic domains of protein-tyrosine kinases and is most similar to two putative receptor protein-tyrosine kinases of the eph subclass, elk (69%) and eph (57%). Human genomic DNAs encoding part of eek (EEK) as well as another putative protein-tyrosine kinase most similar to elk (90%), ERK (elk-related kinase), were isolated and partially characterized. The novel identity of these two eph-family genes was further supported by Southern blot analyses and localization to human chromosome 1. In Northern blot analysis of rat RNA, DNAs encoding rat eek and human ERK hybridized to transcripts most abundant in brain and lung, respectively. These two new members of the eph subclass of receptor protein-tyrosine kinases, eek and erk, may therefore have tissue-specific functions distinct from those of other eph family members.

Amino Acid Sequence↗
PubMed1991

Endothelin and calcium signaling in NG108-15 neuroblastoma x glioma cells.

Endothelin (ET)-mediated Ca++ signaling in NG108-15 neuroblastoma x glioma cells was studied by measuring free intracellular Ca++ (Ca++i) levels with the fluorescent Ca++ indicator, fura-2. ET-1 produced biphasic increases in Ca++i consisting of a transient peak elevation followed by a sustained plateau phase. Both peak and plateau Ca++i responses to 5 nM ET-1 were reduced by depletion of extracellular Ca++. Peak responses were also attenuated by inhibitors of inositol phosphate metabolism, whereas plateau responses were affected by dihydropyridine Ca++ channel agonists and antagonists and by differentiation. These results suggest that peak Ca++i responses to ET-1 involve mobilization of Ca++ from inositol phosphate-sensitive intracellular stores and influx of extracellular Ca++ through nonclassical Ca++ channels, whereas plateau responses are mediated by Ca++ influx through dihydropyridine-sensitive, voltage-gated channels.

Animals↗
PubMed1990

Infectious measles virus from cloned cDNA.

The study of measles virus (MV) and of negative strand RNA viruses in general has been hampered by the lack of an experimental system for genetic manipulation. Here we describe a procedure for generating infectious MV from cloned MV cDNA. First we assembled a genetically marked DNA copy of the MV genome in plasmids, under the control of phage T3 or T7 promoters, allowing production of transcripts almost identical to the MV genome or antigenome. Incubation of these linearized plasmid DNAs with the appropriate phage polymerase and only two ribonucleoside triphosphates yielded committed transcription complexes. Microinjection of these complexes into the cytoplasm of helper cells which provide the proteins necessary for MV genome encapsidation and transcription/replication, reproducibly give rise to lytic MVs. The transcripts of one of these viruses were analysed by sequencing after reverse transcription followed by DNA amplification, and found to contain the genetic tags. The described procedure permits the analysis of a negative strand RNA virus with the same genetic tools previously applicable only to positive strand RNA viruses and retroviruses.

Base Sequence↗
PubMed1990

Spiny neurons lacking choline acetyltransferase immunoreactivity are major targets of cholinergic and catecholaminergic terminals in rat striatum.

The ultrastructural substrate for functional interactions between intrinsic cholinergic neurons and catecholaminergic afferents to the caudate-putamen nucleus and nucleus accumbens septi (NAS) was investigated immunocytochemically. Single sections of glutaraldehyde-fixed rat brain were processed 1) for the immunoperoxidase labeling of a rat monoclonal antibody against the acetylcholine-synthesizing enzyme choline acetyltransferase (CAT) and 2) for the immunoautoradiographic localization of a rabbit polyclonal antiserum against the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). The ultrastructural morphology and cellular associations did not significantly differ in the caudate-putamen versus NAS. Immunoperoxidase reaction for CAT versus NAS. Immunoperoxidase reaction for CAT was seen in perikarya, dendrites, and terminals, whereas immunoautoradiography for TH was in terminals. The perikarya and dendrites immunolabeled for CAT were large, sparsely spiny, and postsynaptic mainly to unlabeled axon terminals. Only 2-3% of the CAT-labeled terminals (n = 136) and less than 1% of the TH-labeled terminals (n = 86) were apposed to, or formed synapses with, perikarya or dendrites immunoreactive for CAT. Most unlabeled and all labeled terminals formed symmetric synapses. In the same sample, 18% of the CAT and 16% of the TH-labeled terminals were directly apposed to each other. Unlabeled dendritic shafts received the major (40% for CAT versus 23% for TH) synaptic input from cholinergic terminals, while unlabeled spines received the major (47% for TH versus 23% for CAT) synaptic input from catecholaminergic terminals. Neither the unlabeled dendrites or spines received detectable convergent input from CAT and TH-labeled terminals. Thirteen percent of the CAT-labeled and 14% of TH-labeled terminals were in apposition to unlabeled terminals forming asymmetric, presumably excitatory, synapses with unlabeled dendritic spines. We conclude that in both the caudate-putamen and NAS cholinergic and catecholaminergic terminals 1) form symmetric, most likely inhibitory, synapses primarily with non-cholinergic neurons, 2) differentially synapse on shafts or spines of separate dendrites, and 3) have axonal appositions suggesting the possibility of presynaptic physiological interactions. These results support the hypothesis that the cholinergic-dopaminergic balance in striatal function may be mediated through inhibition of separate sets of spiny projection neurons with opposing excitatory and inhibitory functions.

Adrenergic Fibers↗
PubMed1990

Optimization of differential immunogold-silver and peroxidase labeling with maintenance of ultrastructure in brain sections before plastic embedding.

The limited success of immunogold labeling for pre-embedding immunocytochemistry of neuronal antigens is largely attributed to poor penetration of large (5-20 nm) colloidal gold particles. We examined the applicability of using silver intensification of 1 nm colloidal gold particles non-covalently bound to goat anti-rabbit immunoglobulin (1) for single labeling of a rabbit antiserum against the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH), and (2) for immunogold localization of rabbit anti-TH simultaneously with immunoperoxidase labeling of a mouse monoclonal antibody against the opiate peptide, leucine-enkephalin (LE). Vibratome sections were collected from acrolein fixed brains of adult rats. These sections were immunolabeled without use of freeze-thawing or other methods that enhance penetration, but damage ultrastructure. By light microscopy, incubations in the silver intensifier (Intense M, Janssen) for less than 10 min at room temperature resulted in a brownish-red reaction product for TH. This product was virtually indistinguishable from that seen using diaminobenzidine reaction for detection of peroxidase immunoreactivity. Longer incubations produced intense black silver deposits that were more clearly distinguishable from the brown immunoperoxidase labeling. However, by light microscopy, the gold particles seen by electron microscopy were most readily distinguished from peroxidase reaction product with shorter silver intensification periods. The smaller size of gold particles with shorter periods of silver intensification also facilitated evaluation of labeling with respect to subcellular organelles. Detection of the silver product did not appear to be appreciably changed by duration of post-fixation in osmium tetroxide. In dual-labeled sections, perikarya and terminals exhibiting immunogold-silver labeling for TH were distinct from those containing immunoperoxidase labeling for LE. These results (1) define the conditions needed for optimal immunogold-silver labeling of antigens while maintaining the ultrastructural morphology in brain, and (2) establish the necessity for controlled silver intensification for light or electron microscopic differentiation of immunogold-silver and peroxidase reaction products and for optimal subcellular resolution.

Animals↗
PubMed1990

Bronchodilatation induced by deep breaths in relation to transpulmonary pressure and lung volume.

Induced bronchoconstriction in normal subjects can be transiently reversed by a deep breath (airway hysteresis). The mechanisms of airway hysteresis are not fully understood. The aim of these studies was to determine whether the nature of the deep breath (slow or fast inspiration, five or 10 second breath hold) affects the resultant bronchodilatation. Bronchoconstriction was induced in 10 normal subjects by inhalation of histamine until specific airway conductance (sGaw) was halved (mean (SEM) post-histamine sGaw 0.099* (0.009) s-1 cm H2O-1). A subsequent deep breath to total lung capacity (TLC) increased sGaw by 57% (13%) and neither the rate of inspiration to TLC nor periods of breath holding at TLC produced a significantly different degree of bronchodilation. Reducing the volume of the deep breath produced progressively less bronchodilatation and this was no longer significant after a breath to 68% (2%) TLC. To determine whether the volume of the deep breath or the accompanying increase in transpulmonary pressure (PstL) was responsible for the effect on sGaw, subjects were studied with an oesophageal balloon in place with and without their chest strapped. Subjects took a deep breath to a PstL of 20 cm H2O after bronchoconstriction had been induced by histamine. The degree of bronchodilatation (mean (SEM) %) was not significantly different (strap on 25 (6), strap off 36 (5)) even though significantly larger lung volumes (as % TLC) were reached with the strap off (strap on 57 (2), strap off 78 (3)). These results suggest that PstL rather than lung volume during a deep breath determines airway hysteresis.

Adult↗