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K Chen

Publications and source records attributed to K Chen.

At least 181 records · Page 10Linked to original sources
PubMed1999

Reduced spontaneous activity in the dorsal cochlear nucleus of Scn8a mutant mice.

Spontaneous activity was recorded in the dorsal cochlear nucleus of brain slices from mice homozygous for the med-J and jolting mutations in the neuronal sodium channel alpha-subunit Scn8a. Densities of spontaneously active neurons in slices from both mutants were significantly lower than in control slices. Spontaneous firing patterns with bursts of action potentials were recorded from approximately 50% of the neurons in control slices, but the typical bursting patterns were not observed in neurons of med-J and jolting mouse slices. The results suggest that this voltage-gated sodium channel is essential for the spontaneous bursting firing of cochlear nucleus cartwheel neurons. This mutant animal model may be useful for the study of the functional roles of cochlear nucleus neurons.

Action Potentials↗
PubMed1999

In Azotobacter vinelandii, the E1 subunit of the pyruvate dehydrogenase complex binds fpr promoter region DNA and ferredoxin I.

In Azotobacter vinelandii, deletion of the fdxA gene that encodes a well characterized seven-iron ferredoxin (FdI) is known to lead to overexpression of the FdI redox partner, NADPH:ferredoxin reductase (FPR). Previous studies have established that this is an oxidative stress response in which the fpr gene is transcriptionally activated to the same extent in response to either addition of the superoxide propagator paraquat to the cells or to fdxA deletion. In both cases, the activation occurs through a specific DNA sequence located upstream of the fpr gene. Here, we report the identification of the A. vinelandii protein that binds specifically to the paraquat activatable fpr promoter region as the E1 subunit of the pyruvate dehydrogenase complex (PDHE1), a central enzyme in aerobic respiration. Sequence analysis shows that PDHE1, which was not previously suspected to be a DNA-binding protein, has a helix-turn-helix motif. The data presented here further show that FdI binds specifically to the DNA-bound PDHE1.

Amino Acid Sequence↗
PubMed1999

Chicken macrophage stimulating protein is a ligand of the receptor protein-tyrosine kinase Sea.

Affinity chromatography, employing the extracellular domain of the Sea receptor, was used to enrich Sea-binding proteins from chicken serum. One isolated protein bound both a Sea-immunoglobulin fusion protein and an antisera raised against murine macrophage stimulating protein. Amino-terminal sequencing of the dual-reactive protein yielded sequences which were identical to the predicted alpha and beta subunits of chicken macrophage stimulating protein. The partially purified chicken macrophage stimulating protein caused autophosphorylation of the Sea receptor. Previous work showed that recombinant expression of fully activatible human or mouse macrophage stimulating protein required a specific Cys to Ala substitution (Wahl, R. C., Costigan, V. J., Batac, J. P., Chen, K., Cam, L., Courchesne, P. L., Patterson, S. D. Zhang, K., and Pacifici, R. E. (1997) J. Biol. Chem. 272, 1-4). Therefore, we expressed both the wild type and the specific Cys to Ala form of chicken macrophage stimulating protein as recombinant proteins. After proteolytic activation, only conditioned media from COS cells transfected with the C665A chicken macrophage stimulating protein, but not from wild type chicken macrophage-stimulating protein, or control vector, was detected by the Sea-immunoglobulin fusion protein in Western blotting experiments. Conditioned media containing the C665A chicken macrophage-stimulating protein readily caused Sea phosphorylation, while conditioned media containing the wild type chicken macrophage-stimulating protein was only effective at inducing receptor phosphorylation at high concentrations. In addition to receptor phosphorylation, the C665A chicken macrophage-stimulating protein induced phosphorylation of Shc, Erk1, and Erk 2. We conclude that macrophage-stimulating protein is a ligand of the Sea receptor protein-tyrosine kinase.

Animals↗
PubMed1999

Flt3 ligand antitumor activity in a murine breast cancer model: a comparison with granulocyte-macrophage colony-stimulating factor and a potential mechanism of action.

We have shown that Flk2/Flt3 ligand (Flt3L)-transduced tumor vaccine induces transferable T cell protection against a murine breast cancer cell line, but a direct comparison with the potent effector GM-CSF, the activity against preestablished tumors, and the mechanism of antitumor response in this breast cancer model are not known. We compared vaccination with C3L5 cells expressing Flt3L (C3Lt-Flt3L) and GM-CSF (C3L5-GMCSF) by injecting 1 x 10(4) cells subcutaneously into the chest wall and then, after 4 weeks, challenging the contralateral chest of tumor-free mice with parental C3L5 cells. C3L5-Flt3L and C3L5-GMCSF had reduced in vivo growth rates (25% tumor formation each) compared with 100% tumor formation of C3L5 cells expressing only neomycin phosphotransferase (C3L5-G1N). However, when tumor-free animals were challenged with parental C3L5 cells, C3L5-Flt3L vaccination was significantly better at preventing tumor growth (p < 0.05) than C3L5-GMCSF vaccination (33% of C3L5-Flt3L-vaccinated animals developed tumor compared with 77% of C3L5-GMCSF-vaccinated animals). Adoptive transfer of immunity for both vaccines was demonstrated; splenic T cells from tumor-free mice protected naive mice from parental tumor challenge. To simulate minimal disease, parental C3L5 cells at two concentrations (high, 5 x 10(3) cells; or low, 1 x 10(3) cells) were injected into the contralateral chest wall 4 days prior to treatment with C3L5-G1N or C3L5-Flt3L. C3L5-Flt3L treatment decreased contralateral parental tumor formation (high, 67% tumor free; low, 90% tumor free) compared with C3L5-G1N treatment (high and low, 0% tumor free). Immunodepletion of activated natural killer cells with anti-asialo-GM1 blocked C3L5-Flt3L- and C3L5 plus soluble Flt3L-mediated antitumor activity. Thus, Flt3L-transduced tumor cells manifest potent antitumor activity, apparently mediated, at least partially, by natural killer cells.

Animals↗
PubMed1999

The maximal affinity of ligands.

We explore the question of what are the best ligands for macromolecular targets. A survey of experimental data on a large number of the strongest-binding ligands indicates that the free energy of binding increases with the number of nonhydrogen atoms with an initial slope of approximately -1.5 kcal/mol (1 cal = 4.18 J) per atom. For ligands that contain more than 15 nonhydrogen atoms, the free energy of binding increases very little with relative molecular mass. This nonlinearity is largely ascribed to nonthermodynamic factors. An analysis of the dominant interactions suggests that van der Waals interactions and hydrophobic effects provide a reasonable basis for understanding binding affinities across the entire set of ligands. Interesting outliers that bind unusually strongly on a per atom basis include metal ions, covalently attached ligands, and a few well known complexes such as biotin-avidin.

Binding Sites↗
PubMed1999

Ketanserin and tetrabenazine abolish aggression in mice lacking monoamine oxidase A.

Mice deficient in monoamine oxidase A (MAO A) have elevated brain levels of 5-HT and manifest enhanced aggression. We used these mice as a model to study the role of 5-HT in aggression. Our results show that ketanserin and tetrabenazine (TBZ) strikingly abolished the aggressive behavior of MAO A-deficient mice. The anti-aggressive effect of ketanserin may be primarily mediated by 5-HT(2A) receptors. Another specific 5-HT(2A) antagonist, [R-(+)-a-(2, 3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine-methan ol (MDL 100907), also blocks the aggression of mutant mice but was less dramatic. Ketanserin and TBZ are both antagonists of the vesicular monoamine transporter (VMAT2). The anti-aggressive effect of TBZ and part of the effect of ketanserin may be mediated by the VMAT2. Using radioligand binding and autoradiography, we also showed that the numbers of VMAT2, 5-HT(1A), 5-HT(2A) and 5-HT(2C) sites are decreased in brains of mutant mice, which may reflect down-regulation by excess 5-HT. This study suggests that ketanserin and TBZ may be developed as novel anti-aggressive agents.

Adrenergic Uptake Inhibitors↗
PubMed1999

Dopamine transporter loss and clinical changes in MPTP-lesioned primates.

Single photon emission computed tomography (SPECT) and the dopamine (DA) transporter tracer, 2 beta-carboxymethoxy-3 beta-(4-iodophenyl)tropane ([123I]beta-CIT), were used to determine DA transporter density in 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-lesioned monkeys with varying degrees of parkinsonism. The clinical stage of parkinsonism corresponded to SPECT measures of striatal DA transporter density suggesting that more severe parkinsonism was associated with a greater degree of dopaminergic terminal degeneration. These findings are similar to those reported earlier using positron emission tomography (PET) and the DA metabolism tracer, 6-[18F]fluoro-L-m-tyrosine (FMT), indicating that both are good methods for evaluating nigrostriatal degeneration in MPTP primate models.

Animals↗
PubMed1999

Oligodendrocyte-specific protein peptides induce experimental autoimmune encephalomyelitis in SJL/J mice.

Oligodendrocyte-specific protein (OSP) is a recently isolated and cloned, 207-aa, hydrophobic, four-transmembrane protein found in CNS myelin. It represents approximately 7% of total myelin protein. The OSP cDNA sequence has no significant homology with previously reported genes, but the predicted protein structure suggests that OSP is a CNS homologue of peripheral myelin protein-22. We previously reported the presence of anti-OSP Abs in the cerebrospinal fluid of relapsing-remitting multiple sclerosis (MS) patients, but not control patient groups. In this study, we tested the ability of a panel of 20-mer peptides with 10-aa overlaps, representing the sequence of murine OSP, to induce experimental autoimmune encephalomyelitis (EAE), an animal model for MS. SJL mice challenged with murine OSP peptides 52-71, 82-101, 102-121, 142-161, 182-201, and 192-207 exhibited clinical EAE. OSP:52-71 elicited severe relapsing-remitting EAE in some individuals. All other encephalitogenic peptides elicited, at most, a loss of tail tonicity from which the mice most often completely recovered. Mononuclear cell infiltrates and focal demyelination characteristic of EAE were evident. T cell proliferative responses were seen with all encephalitogenic peptides except 142-161 and 182-201. OSP peptides 72-91 and 132-151 did not cause clinical EAE, but did elicit robust proliferative responses. B10.PL and PL/J mice challenged with the same OSP peptide doses as SJL mice did not exhibit clinical EAE. These results in the SJL EAE model, together with the results from MS patient clinical samples, make OSP a promising candidate for autoantigenic involvement in MS.

Amino Acid Sequence↗
PubMed1999

Neuroanatomical correlates of hunger and satiation in humans using positron emission tomography.

The central role of the hypothalamus in the origination and/or processing of feeding-related stimuli may be modulated by the activity of other functional areas of the brain including the insular cortex (involved in enteroceptive monitoring) and the prefrontal cortex (involved in the inhibition of inappropriate response tendencies). Regional cerebral blood flow (rCBF), a marker of neuronal activity, was measured in 11 healthy, normal-weight men by using positron emission tomography in a state of hunger (after 36-h fast) and a state of satiation (after a liquid meal). Hunger was associated with significantly increased rCBF in the vicinity of the hypothalamus and insular cortex and in additional paralimbic and limbic areas (orbitofrontal cortex, anterior cingulate cortex, and parahippocampal and hippocampal formation), thalamus, caudate, precuneus, putamen, and cerebellum. Satiation was associated with increased rCBF in the vicinity of the ventromedial prefrontal cortex, dorsolateral prefrontal cortex, and inferior parietal lobule. Changes in plasma insulin concentrations in response to the meal were negatively correlated with changes in rCBF in the insular and orbitofrontal cortex. Changes in plasma free fatty acid concentrations in response to the meal were negatively correlated with changes in rCBF in the anterior cingulate and positively correlated with changes in rCBF in the dorsolateral prefrontal cortex. In conclusion, these findings raise the possibility that several regions of the brain participate in the regulation of hunger and satiation and that insulin and free fatty acids may be metabolic modulators of postprandial brain neuronal events. Although exploratory, the present study provides a foundation for investigating the human brain regions and cognitive operations that respond to nutritional stimuli.

Adult↗
PubMed1999

Cerebral cortical blood flow maps are reorganized in MAOB-deficient mice.

Cerebral cortical blood flow (CBF) was measured autoradiographically in conscious mice without the monoamine oxidase B (MAOB) gene (KO, n=11) and the corresponding wild-type animals (WILD, n=11). Subgroups of animals of each genotype received a continuous intravenous infusion over 30 min of phenylethylamine (PEA), an endogenous substrate of MAOB, (8 nmol g-1 min-1 in normal saline at a volume rate of 0.11 microl g-1 min-1) or saline at the same volume rate. Maps of relative CBF distribution showed predominance of midline motor and sensory area CBF in KO mice over WILD mice that received saline. PEA enhanced CBF in lateral frontal and piriform cortex in both KO and WILD mice. These changes may reflect a differential activation due to chronic and acute PEA elevations on motor and olfactory function, as well as on the anxiogenic effects of this amine. In addition to its effects on regional CBF distribution, PEA decreased CBF globally in KO mice (range -31% to -41% decrease from control levels) with a lesser effect in WILD mice. It is concluded that MAOB may normally regulate CBF distribution and its response to blood PEA.

Animals↗
PubMed1999

Lack of protection from ischemic injury of monoamine oxidase B-deficient mice following middle cerebral artery occlusion.

Adult male wild-type mice received intraperitoneal (i.p.) administration of saline (n = 9) or 10 mg/kg L-deprenyl (n = 9) three times a week for 3 weeks. Mice with targeted inactivation of the monoamine oxidase B (MAO-B) gene received i.p. administration of saline (n = 8). Animals underwent ligation of the left common and external carotid arteries, followed by cauterization of the ipsilateral middle cerebral artery. Twenty-four hours post-surgery, all groups showed right torsion of the torso but no evidence of limb weakness, lateral instability, or circling. Ischemic changes were assessed from digitized video-images of serial sections of the brain stained with Hematoxylin/Eosin. No significant group differences were detected in infarct volume (14-18% of ipsilateral cortex) or in the extent of brain edema (4-7% increase in ipsilateral hemispheric swelling with respect to contralateral side). Our results suggest that absence of the MAO-B gene or inhibition of the enzyme with L-deprenyl are not protective or detrimental in an animal model of acute cortical infarction.

Animals↗
PubMed1999

Medial temporal lobe activation during episodic encoding and retrieval: a PET study.

Recent neuroimaging studies have obtained evidence of activation in the medial temporal lobe (MTL) during episodic encoding and retrieval. On the basis of a meta-analysis of MTL activations in studies that used positron emission tomography (PET), Lepage et al. (Hippocampus 1998;8:313-322) suggested that episodic encoding tends to involve the anterior MTL, whereas episodic retrieval tends to involve the posterior MTL. In a meta-analysis of studies that used PET and functional magnetic resonance imaging, Schacter and Wagner (Hippocampus 1999;9:7-24) reported weaker evidence for such a rostrocaudal distribution of encoding and retrieval activations. However, these meta-analyses were based largely on studies that examined encoding or retrieval separately. Here, we report a direct, within-subjects comparison of MTL activation during episodic encoding and retrieval by using PET. Results indicated that both encoding and retrieval were associated with blood flow increases in similar MTL regions with little indication that encoding and retrieval are preferentially associated with activity in the anterior versus the posterior MTL. Direct comparisons revealed greater blood flow increases in posterior MTL during encoding than retrieval.

Adult↗
PubMed1999

cis-Dihydroxylation of Olefins by a Non-Heme Iron Catalyst: A Functional Model for Rieske Dioxygenases.

The first iron complex capable of olefin cis-dihydroxylation in combination with H(2)O(2) provides a functional model for Rieske dioxygenases. Mechanistic studies on the model reaction suggest the participation of an Fe(III)(eta(2)-OOH) intermediate, with the oxygen atoms coming exclusively from H(2)O(2) (see reaction scheme; L denotes a tris(6-methyl-2-pyridylmethyl)amine ligand, Solv=solvent). The similarities between the model and the enzymes strengthen the proposal that an Fe(III)-peroxo intermediate is involved in the enzymatic reactions.

Journal Article↗
PubMed1999

Movement and reaction times and fine coordination tasks following pallidotomy.

The effect of a unilateral, microelectrode-guided lesion in the globus pallidum internum (GPi) was evaluated in 41 patients (21 women) with moderately advanced Parkinson's disease (PD). The mean age was 60.3+/-9.0 years (range, 40-74) and the mean symptom duration was 14.7+/-5.3 years (range, 4-25). In addition to clinical ratings, movement time (MT) and reaction time (RT) tests were performed at baseline and 3 months after surgery during the "practically defined off" state (more than 12 hours after the last dose of levodopa). Improvement occurred bilaterally with more robust and statistically significant improvement on the contralateral side in all RT tests. Simple reaction time (SRT) improved by 14.5% (p<0.001) and the choice reaction time (CRT) by 12.2% (p<0.001) when the arm contralateral to the pallidotomy side was tested. There was a trend toward improvement in the ipsilateral arm. The MT, determined by repetitive movement between two adjacent targets, improved by 24% contralaterally (p<0.0001) and by 12% ipsilaterally (p<0.005). In addition, the Purdue Pegboard (PP) test scores, used to evaluate hand dexterity, improved on the contralateral side by 35.5% (p<0.0002) but there was no statistically significant ipsilateral improvement. To the extent that MT and RT are quantitative measures of bradykinesia, our study provides evidence that this parkinsonian feature improves after pallidotomy.

Adult↗
PubMed1999

Visceral adipose tissue is not increased in Pima Indians compared with equally obese Caucasians and is not related to insulin action or secretion.

Pima Indians are insulin resistant and hyperinsulinaemic compared with Caucasians. We investigated whether abdominal fat distribution was different between Pimas and Caucasians and whether differences in the amount of visceral fat explained metabolic differences between the groups. Total body fat (absorptiometry) and abdominal fat distribution at L4-L5 (magnetic resonance imaging) were compared in 20 Pima Indians (10 men/10 women) and 20 age-, sex- and BMI-matched Caucasians. Insulin action was measured as glucose disposal during a two-step hyperinsulinaemic-euglycaemic glucose clamp and insulin secretion was assessed in response to oral and intravenous glucose tolerance tests. By design, percent body fat was similar in Pimas and Caucasians. Abdominal visceral and subcutaneous adipose tissue areas were also similar in the two groups (151+/-16 vs 139+/-15 cm2 and 489+/-61 vs 441+/-7 cm2 respectively). Plasma insulin concentrations were higher in Pimas than Caucasians in the fasting state (27+/-6 vs 11+/-2 mU/ml; p < 0.01) and after a 75-g oral glucose load (area under the curve 19975+/-2626 vs 9293+/-1847 mU x l(-1) x 180 min(-1); p < 0.005). Glucose disposal was lower in Pimas than Caucasians during both steps of the clamp and negatively correlated (after adjustment for percent body fat and sex) with visceral adipose tissue in Caucasians (partial r = -0.51, p = 0.03), but not in Pima Indians (r = -0.03, p = 0.92). Insulin secretion was not related to visceral fat independently of percent body fat in either group. We conclude that a relative increase in visceral fat does not explain insulin resistance and hyperinsulinaemia in Pima Indians.

Adipose Tissue↗
PubMed1999

Alteration in brain proteins following occlusion of the middle cerebral artery in rat.

The effects of permanent focal ischemia on specific proteins of the cerebral hemisphere were studied by unilateral occlusion of the middle cerebral artery (MCAO) in rat. Brain proteins were prepared 72 h after the occlusion and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The proteins were identified by their interaction with rabbit antibodies against rat serum proteins and anti-transferrin antibodies. SDS-PAGE analysis of the proteins prepared from ischemic tissue showed significant increase in the 66 and 80 kDa components; where a marked decrease in the 260 kDa protein occurred in the ischemic and para-ischemic tissues. The 66 kDa and 80 kDa proteins stained intensely with anti-serum protein antibodies, indicating that they are related to plasma components. Moreover, the 66 kDa band had the same electrophoretic mobility as bovine serum albumin used as a standard molecular size marker. The 80 kDa band was identified as transferrin by staining with the specific antibody. Transferrin was immunolocalized in the penumbra of cerebral cortex, hippocampal CA1 region and dentate gyrus of the ischemic cerebral hemisphere. The present results suggest that alteration in the brain content of 66 kDa (albumin), 80 kDa (transferrin) and 260 kDa (unidentified) proteins may reflect early effects of focal ischemia.

Albumins↗
PubMed1999

Lack of protection of monoamine oxidase B-deficient mice from age-related spatial learning deficits in the Morris water maze.

Monoamine oxidase B (MAO-B) increases in brain in response to aging and neurodegeneration. Whether such increases represent a risk factor to further neuronal damage or simply represent epiphenomena remains unclear. L-deprenyl, an inhibitor of MAO-B, has been shown to improve learning in aged rodents. However, recent data suggests this may occur through mechanisms independent of its enzymatic inhibition. This study investigates visualspatial learning of MAO-B deficient mice and examines what effects absence of MAO-B has on age-related cognitive decline. Learning was tested in the Morris Water Maze in male transgenic MAO-B knockout mice (KO) ages 2 months (n = 9), 7 months (n = 7), and 17 months (n = 8). Performance was compared to that of wild type (WT) littermates. Animals were given four 60 second trials per day with the submerged platform in the "North" position. Animals received 7 days of learning in which they were introduced into the pool facing the wall, alternating between the "East" and "West" positions. A single probe trial followed on day 8, followed by continuation of the original learning paradigm on days 9 and 10. Subsequently, the platform position was changed to the diagonally opposite quadrant and learning continued on days 11-13, followed by a cue phase in which the platform was made visible. Total distance traveled and latency to the platform was increased in 7- and 17- month old mice, most significantly at the beginning of the acquisition phase. This effect reappeared again in 17- month old mice during the reversal phase. No predominant genotypic differences in latency or distance were observed during any phase of the experiment. Our results show that presence or absence of MAO-B does not appear to alter performance in the Morris water maze. Furthermore, presence or absence of MAO-B does not provide protection from the age-dependent deficits in spatial learning.

Aging↗