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J Chan

Publications and source records attributed to J Chan.

At least 19 recordsLinked to original sources
PubMed1992

Ultrastructure of spared dopamine terminals in caudate-putamen nuclei of adult rats neonatally treated with intranigral 6-hydroxydopamine.

Residual dopamine terminals in the dorsal striatum, caudate-putamen nuclei (CPN), of adult rats neonatally lesioned with 6-hydroxydopamine (6-OHDA) sustain a relatively high level of dopamine release. We examined whether there were morphological differences in the spared dopamine terminals that might correlate with this increased efficacy. Postnatal male rat pups from 50 litters were pretreated with desmethylimipramine (DMI) to protect from non-specific monoamine damage, then given unilateral intranigral injections of 6-OHDA or vehicle. Coronal sections through the CPN and substantia nigra of the surviving adult animals from each litter were co-processed for immunoautoradiographic or immunoperoxidase localization of the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH). Quantitative ultrastructural analysis established that in animals showing maximal (greater than 90%) depletions in immunoautoradiographic labeling for TH, the number of TH-labeled axons in the CPN ipsilateral to the 6-OHDA injections was reduced to one third of the number seen in the contralateral, unlesioned hemisphere, or the CPN from vehicle-injected animals. The ultrastructural features of residual terminals ipsilateral to 6-OHDA lesions were morphologically similar to those of the contralateral side or in vehicle-injected animals. However, in comparison with controls, these TH-labeled terminals had significantly larger mean cross-sectional diameters. When subdivided into groups according to size, there were significantly fewer small (0.0-0.1 micron 2) and more large (0.41-0.50 micron 2) TH-immunoreactive profiles in lesioned versus unlesioned CPN. The remaining TH-labeled terminals ipsilateral to the 6-OHDA lesions also appeared to be more often in direct contact with unlabeled soma and proximal dendrites as opposed to dendritic spines in the unlesioned CPN. These results suggest that the enhanced activity of dopamine neurons innervating the CPN after nigral 6-OHDA lesions may contribute to changes in size and target of their terminals. Alternatively, the observed large size of remaining dopamine terminals may reflect selective vulnerability of smaller axons to 6-OHDA toxicity.

Aging↗
PubMed1992

A novel inhibitor of glutamate release reduces excitotoxic injury in vitro.

Excessive release of glutamate has been implicated in the pathogenesis of excitotoxic neurologic disorders, such as stroke. BW 1003C87, an inhibitor of glutamate release and a putative Na+ channel antagonist, reduced veratridine-stimulated, tetrodotoxin- and dizocilpine-sensitive toxicity (measured by lactate dehydrogenase efflux) in neuron-enriched cortical cultures (IC50 = 5 microM). In contrast, BW 1003C87 (300 microM) had no effect on toxicity induced by direct application of 1 mM glutamate or 1 mM N-methyl-D-aspartate, or by depolarization with 50 mM KCl. Glutamate release inhibitors such as BW 1003C87 may provide a novel approach to protection from excitotoxicity.

Animals↗
PubMed1992

Identification and characterization of two enhancers of the human albumin gene.

A 12.5-kilobase pair (kb) segment upstream of the human albumin gene was analyzed for transcription enhancing activity using transient transfection analysis, gel mobility shift assays, DNase I footprinting, and site-specific mutagenesis. Two enhancer regions were identified, one 1.7 kb upstream of the transcription initiation site (E1.7) and the other 6 kb upstream (E6). In E1.7, a nuclear protein from HuH-7 hepatoma cells binds to an AT-rich sequence, GTTACTAATTGAC. Competition gel mobility shift assays suggested that this protein is HNF-1, which regulates the promoter of the albumin gene and several other liver-specific genes. A 60-base pair E1.7 fragment carrying the AT-rich sequence stimulates a heterologous (alpha-fetoprotein) promoter in a dose-dependent manner. In E6, a HuH-7 nuclear protein binds to a GT-rich sequence, TGTTTGGC.A 27-base pair E6 fragment carrying this sequence is able to stimulate the SV40 promoter in an orientation-independent manner. An alteration of this sequence by site-specific mutagenesis resulted in the loss of transcriptional activity as well as binding to the HuH-7 nuclear protein. Competition gel mobility shift assays showed that homologous elements exist in the albumin promoter. These results show that the promoter and enhancer of the human albumin gene are regulated by two common transcription factors through two shared cis-acting elements, one AT-rich and the other GT-rich.

Albumins↗
PubMed1992

Comparative neurotoxic potential of glutamate, endothelins, and platelet-activating factor in cerebral cortical cultures.

The excitatory amino acid glutamate, the peptides endothelin-1 and -3, and the phospholipid platelet-activating factor have been implicated in ischemic injury to the nervous system. To determine if, like glutamate, endothelins and platelet-activating factor are directly toxic to neurons, we examined their effects on lactate dehydrogenase release and trypan blue dye exclusion in rat cerebral cortical cultures. Glutamate (1 mM) increased lactate dehydrogenase release by approximately 75% and reduced the number of cells excluding trypan blue dye by approximately 50%. In contrast, endothelins (0.5 and 100 nM) and platelet-activating factor (0.1 and 10 microM) had no effect on these indices of cell injury. Endothelins and platelet-activating factor appear more likely to act on blood vessels than on neurons or glia as mediators of ischemic injury.

Animals↗
PubMed1992

Cyclic GMP modulators and excitotoxic injury in cerebral cortical cultures.

N-Methyl-D-aspartate (NMDA) receptor activation generates nitric oxide (NO) and cyclic GMP (cGMP) and produces 'excitotoxic' neuronal injury. To examine the possible role of cGMP in excitotoxicity, we evaluated the effects of agents that stimulate or inhibit cGMP activity on the release of lactate dehydrogenase from neuron-enriched cortical cultures. cGMP analogs exhibited no toxicity, and inhibitors of guanylate cyclase or of cGMP-dependent enzymes failed to protect cultures from the toxic effects of NMDA or the NO donor sodium nitroprusside. These findings argue against a role for cGMP in the pathogenesis of excitotoxic neuronal injury.

Animals↗
PubMed1992

Killing of virulent Mycobacterium tuberculosis by reactive nitrogen intermediates produced by activated murine macrophages.

Tuberculosis remains one of the major infectious causes of morbidity and mortality in the world, yet the mechanisms by which macrophages defend against Mycobacterium tuberculosis have remained obscure. Results from this study show that murine macrophages, activated by interferon gamma, and lipopolysaccharide or tumor necrosis factor alpha, both growth inhibit and kill M. tuberculosis. This antimycobacterial effect, demonstrable both in murine macrophage cell lines and in peritoneal macrophages of BALB/c mice, is independent of the macrophage capacity to generate reactive oxygen intermediates (ROI). Both the ROI-deficient murine macrophage cell line D9, and its ROI-generating, parental line J774.16, expressed comparable antimycobacterial activity upon activation. In addition, the oxygen radical scavengers superoxide dismutase (SOD), catalase, mannitol, and diazabicyclooctane had no effect on the antimycobacterial activity of macrophages. These findings, together with the results showing the relative resistance of M. tuberculosis to enzymatically generated H2O2, suggest that ROI are unlikely to be significantly involved in killing M. tuberculosis. In contrast, the antimycobacterial activity of these macrophages strongly correlates with the induction of the L-arginine-dependent generation of reactive nitrogen intermediates (RNI). The effector molecule(s) that could participate in mediating this antimycobacterial function are toxic RNI, including NO, NO2, and HNO2, as demonstrated by the mycobacteriocidal effect of acidified NO2. The oxygen radical scavenger SOD adventitiously perturbs RNI production, and cannot be used to discriminate between cytocidal mechanisms involving ROI and RNI. Overall, our results provide support for the view that the L-arginine-dependent production of RNI is the principal effector mechanism in activated murine macrophages responsible for killing and growth inhibiting virulent M. tuberculosis.

Animals↗
PubMed1992

Ethanol inhibits excitotoxicity in cerebral cortical cultures.

Excitatory amino acid neurotransmitters have been implicated in the pathogenesis of cerebral ischemia and related forms of acute neuronal injury. Because ethanol inhibits cellular signaling mechanisms activated by excitatory amino acids, we examined its effect on excitatory amino acid-induced toxicity in neuron-enriched cultures prepared from rat cerebral cortex. Both glutamate and N-methyl-D-aspartate (NMDA) were toxic to cultured cortical cells, as demonstrated by a reduction in their ability to exclude trypan blue dye, and this toxicity was reversed by the NMDA antagonist MK-801. Ethanol (100 mM) provided partial protection from the excitotoxic effect of NMDA. Thus ethanol, like conventional excitatory amino acid antagonists, can attenuate excitotoxic neuronal injury in vitro.

Animals↗
PubMed1992

Cellular basis for interactions between catecholaminergic afferents and neurons containing Leu-enkephalin-like immunoreactivity in rat caudate-putamen nuclei.

Dopaminergic afferents to the dorsal striatum, caudate-putamen nuclei, are known to modulate the levels and synthesis of endogenous opiate peptides (Leu5 and Met5-enkephalins). We examined the dual immunocytochemical localization of antisera raised against Leu5-enkephalin and the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH), to determine the cellular substrates for these and/or other functional interactions. The antisera were identified by combined immunogold-silver and immunoperoxidase labeling in single coronal sections through the caudate-putamen nuclei of adult rats. These animals were given intraventricular injections of colchicine, and the brains were fixed by acrolein perfusion prior to immunocytochemical labeling. By light microscopy, perikarya and processes containing enkephalin-like immunoreactivity (ELI) were seen in close proximity to varicose processes immunoreactive for TH. Electron microscopy further demonstrated that the ELI was localized to perikarya, dendrites, and axon terminals, whereas the TH was exclusively in axons and terminals. The dendrites containing ELI were postsynaptic to terminals that were either (1) without detectable immunoreactivity, or (2) immunoreactive for TH or enkephalin. Nonsynaptic portions of the dendrites containing ELI were covered with astrocytic processes or were in direct apposition to unlabeled dendrites. Terminals containing ELI were densely immunoreactive and were in direct contact with (1) unlabeled and occasionally enkephalin-labeled proximal dendrites, and (2) TH-labeled and unlabeled terminals. In comparison with the opiate terminals, most catecholaminergic terminals were lightly immunoreactive for TH and usually contacted more distal unlabeled dendrites or spines and, more rarely, dendrites containing ELI. In a few favorable planes of section, the terminals containing ELI and those containing TH (1) converged on common unlabeled dendrites, or (2) formed dual contacts on two different labeled or unlabeled targets. Junctions formed by terminals containing ELI and TH were sometimes characterized by symmetric synaptic densities. However, numerous other dendritic and all axonal appositions were without recognized membrane densities. The findings of the study provide anatomical substrates for multilevel interactions between catecholamines, mostly dopamine, and enkephalin in rat dorsal striatum. These include (1) monosynaptic input from dopaminergic terminals to neurons containing enkephalin, (2) presynaptic modulation of transmitter release through axonal appositions, and (3) dual regulation of common targets through convergent input. In addition, the findings suggest that both enkephalin and dopamine may have similar modulatory roles in synchronizing the activity of dual targets postsynaptic to individual axon terminals. Alterations in any one of these multiple types of interactions could account for noted motor or sensory symptoms in neurological disorders characterized by depletion of dopamine or endogenous opiate peptides, or both.

Animals↗
PubMed1992

In vitro effects of 'designer' amphetamines on human peripheral blood mononuclear leukocytes proliferation and on natural killer cell activity.

Human peripheral blood mononuclear leukocytes (PBML) proliferation was measured in the presence or absence of amphetamines. Proliferation in response to T-cell mitogen PHA was suppressed from 22 to 34% by d- and dl-amphetamine, respectively, contrarily to 1-form which did not affect proliferation of PHA-stimulated PBML. The 'designer' amphetamines appeared to be more potent inhibitors of PBML proliferation induced by both PHA and PWM stimulation than those of the racemic and isomeric forms of amphetamine. A wide variation was seen in the suppressive actions of the 'designer' amphetamines, and the mean percentages of suppression varied from 12 to 45% compared with the control values. 4-Propoxy-amphetamine (4-PA) was found to be the most active among the 'designer' drugs. In vitro effects of d-, 1- and dl-amphetamine were also studied on natural killer (NK) cell activity. A marked increase in the NK cell activity was observed only in the presence of very low concentrations (10(-12) to 10(-10) M) of dl-amphetamine, however, the activity of the NK cell remained within the control limits in the presence of d- or 1-forms. The findings suggest that the abuse of amphetamines, especially the 'designer' drugs, may adversely affect the activity of immunoregulatory cells and might lead to a compromised immune system in amphetamine abusers.

Amphetamines↗
PubMed1992

Management of neonatal Graves disease with iopanoic acid.

An infant with thyrotoxicosis whose mother had Graves disease was treated with sodium iopanoate. Euthyroid status was achieved rapidly and maintained with minimal effort in comparison with the conventional multidrug regimen. There were no toxic effects, and hypothyroidism did not occur.

Graves Disease↗
PubMed1992

Ethanol and excitotoxicity in cultured cortical neurons: differential sensitivity of N-methyl-D-aspartate and sodium nitroprusside toxicity.

Neural injury due to ischemia and related insults is thought to involve the action of excitatory amino acids at N-methyl-D-aspartate receptors, which results in the influx of extracellular Ca2+ and the generation of nitric oxide. Because ethanol inhibits physiologic responses to excitatory amino acids, we examined its effect on toxicity induced by N-methyl-D-aspartate and by the nitric oxide donor sodium nitroprusside in neuron-enriched cultures prepared from rat cerebral cortex. Both N-methyl-D-aspartate and sodium nitroprusside were cytotoxic, as measured by the release of lactate dehydrogenase and by microfluorescent determination of cell viability. Ethanol (3-1,000 mM) protected cultures from N-methyl-D-aspartate but not sodium nitroprusside toxicity, and the ability of a series of n-alkanols to reproduce the effect of ethanol was related to carbon-chain length. Neuroprotection by ethanol was accompanied by a decrease in the N-methyl-D-aspartate-evoked elevation of free intracellular Ca2+ and did not appear to involve gamma-aminobutyric acid- or cyclic GMP-mediated mechanisms. These findings suggest that ethanol inhibits excitotoxicity at an early step in the N-methyl-D-aspartate signaling pathway, probably by reducing Ca2+ influx, and not by interfering with the action of nitric oxide.

Animals↗
PubMed1992

Identification of the thyroid hormone-responsive messenger RNA spot 11 as apolipoprotein-A1 messenger RNA and effects of the hormone on the promoter.

The induction of rat hepatic mRNA S11 by L-T3 (T3) is a useful model for studying the mechanisms of thyroid hormone action. Although numerous reports have examined the response of mRNA S11 to various physiological and hormonal manipulations, the role of S11 protein in cellular metabolism remains unknown. In this study we show that mRNA S11 is abundantly expressed and regulated by T3 only in liver and small intestine. High levels of the mRNA are present at birth, but drop sharply between 30-60 days of age. These and other features of the S11 gene product were similar to those of rat apolipoprotein-A1 (Apo-A1). The sequence of S11 cDNA was identical to a portion of the Apo-A1 mRNA, thus confirming identity of the S11 mRNA. To examine whether DNA sequences immediately adjacent to the transcription start site mediate the effects of thyroid hormone, we measured the activity of an Apo-A1 gene fragment, U-1 (-474 to -7) using a transient transfection assay. The activity of the full-length U-1 DNA in HuH-7 hepatoma cells was 2- to 2.5-fold higher in the presence of thyroid hormone. This finding closely matched previous results using the in vitro nuclear run-on assay. Internal deletion of a motif that resembles a thyroid hormone response element from U-1 DNA not only abolished the induction by T3, but suppressed promoter activity by 3- to 4-fold in response to the hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1992

Mirizzi syndrome with cholecystocholedochal fistula: preoperative diagnosis and management.

Gallstone obstruction of the cystic duct with resulting repeated attacks of inflammation and pressure necrosis leads to the formation of cholecystocholedochal fistulas (Mirizzi syndrome type II). Obstructive jaundice and cholangitis are the common presentations of the condition. These fistulas are often not recognized before operation and constitute a high risk of damage to the common duct during a formal cholecystectomy. A high index of suspicion is required to diagnose the condition. We report five patients with cholecystocholedochal fistulas diagnosed by endoscopic retrograde cholangiography that delineated the fistula and the obstructing stone. The plan of management was formulated before surgery, and persistent attempt to dissect the Calot's triangle was avoided. In three patients the common duct defect was closed with the use of a gallbladder flap. Hepaticojejunostomy was required for the two difficult cases with large common duct defects and inflamed tissue.

Aged↗
PubMed1991

SK&F 96365, a receptor-mediated calcium entry inhibitor, inhibits calcium responses to endothelin-1 in NG108-15 cells.

Endothelin-1 increases intracellular Ca2+ in NG108-15 cells by mobilizing Ca2+ from internal stores and by activating Ca2+ entry through dihydropyridine-sensitive, voltage-gated channels and another, unidentified route. Since SK&F 96365 has recently been reported to inhibit receptor-mediated Ca2+ entry in other systems, we examined its effect on intracellular Ca2+ responses to endothelin-1, measured with the fluorescent Ca2+ indicator fura-2, in NG108-15 cells. SK&F 96365 (30 microM) reduced both dihydropyridine-insensitive (peak) and dihydropyridine-sensitive (plateau) components of intracellular Ca2+ responses to 5 nM endothelin-1. In the presence of 100 nM nimodipine, which blocks dihydropyridine-sensitive channels, SK&F 96365 caused concentration-dependent inhibition of Ca2+ responses to 5 nM endothelin-1, with half-maximal inhibition at 16 microM. These findings support a role for receptor-mediated Ca2+ entry in neurocellular Ca2+ responses to endothelin-1.

Animals↗
PubMed1991

Relationship of Met-enkephalin-like immunoreactivity to vagal afferents and motor dendrites in the nucleus of the solitary tract: a light and electron microscopic dual labeling study.

Methionine (Met5)-enkephalin has been implicated in autonomic functions involving vagal reflexes within the nucleus of the solitary tract (NTS). We examined the light and electron microscopic relationships between neurons containing methionine (Met5)-enkephalin-like immunoreactivity (MELI) and vagal afferents and motor dendrites in the rat NTS. A polyclonal antibody raised against Met5-enkephalin and showing maximal cross-reactivity with this peptide was localized by immunoautoradiography. In the same sections, vagal afferents and motor neurons were identified by histochemical detection of anterogradely and retrogradely transported horseradish peroxidase (HRP). By light microscopy, the MELI was detected in perikarya distributed principally in the dorsomedial, intermediate and parasolitary subdivisions of the NTS. These subnuclei as well as medial and commissural divisions of the NTS also showed: (1) aggregates of silver grains thought to overlie terminals containing MELI, and (2) anterogradely transported HRP in varicose processes. Electron microscopic analysis of the dorsomedial NTS at the level of the area postrema established that MELI was detectable in perikarya, dendrites, and axon terminals. Most of the MELI was associated with large dense core vesicles (dcvs). These opioid terminals formed primarily symmetric synapses on proximal and asymmetric synapses on distal dendrites. Analysis of the dendritic targets of terminals containing MELI revealed that 13/222 were in synaptic contact with dendrites also containing MELI. The remainder of the terminals containing MELI either lacked recognized junctions or formed synapses with unlabeled dendrites. In comparison to the terminals containing MELI in the same series of sections, anterogradely labeled vagal terminals extensively formed asymmetric junctions with distal dendrites and spines. Of the observed anterogradely labeled terminals 6/84 formed synapses with dendrites containing MELI and 3/84 with dendrites containing retrogradely transported HRP. The remainder of the junctions were with dendrites lacking detectable immunoautoradiographic or HRP-labeling. The majority of the recognized synapses on labeled dendrites were at more proximal sites possibly reflecting more limited detection of both MELI and retrogradely transported HRP in smaller dendrites. However, the presence of even a few junctions at proximal sites on dendrites where synaptic transmission is known to be more effective suggests a potentially strong modulation of both opioid and vagal motor neurons by visceral afferents in the NTS. In addition to forming synapses on dendrites, both vagal afferents and terminals containing MELI showed frequent synaptic associations with unlabeled terminals, but not with each other. This finding suggests that the previously demonstrated opiate binding sites on vagal afferents is most likely attributed to other endogenous opiates.

Afferent Pathways↗