Biomedical subjects

R H Liu

Publications and source records attributed to R H Liu.

At least 55 records · Page 3Linked to original sources

PubMed1994

Anatomical evidence for the presence of glutamate or enkephalin in noradrenergic projection neurons of the locus coeruleus.

This paper reviews the anatomical evidence for the presence of glutamate (GLU) in noradrenergic neurons of the nucleus locus coeruleus (LC) and adjacent nuclei in the dorsolateral pontine tegmentum (DLPT) that project to the spinal cord, cerebellum, or cerebral cortex. Additionally, the evidence for the existence of methionine-enkephalin (ENK) in noradrenergic neurons of the DLPT that project to the spinal cord of the cat is reviewed. In these studies, we have combined the retrograde transport of either Fast Blue (FB), rhodamine labeled latex microspheres (MS), or rhodamine labeled dextran and indirect immunofluorescence histochemistry to determine whether the neurons that contain tyrosine hydroxylase (TH) and project to these terminal fields also contain GLU or ENK. The neurons of the cat that project to the spinal cord, cerebellum, and neocortex were observed in the nucleus LC and Kölliker-Fuse (KF) nucleus. They were also present, to a lesser extent, in the nucleus subcoeruleus (SC) and nuclei parabrachialis medialis (PBM) and lateralis (PBL). In the rat the majority of the neurons that project to the neocortex and hippocampus were located in the nucleus LC. Our data revealed a major proportion of these neurons to be immunostained for both GLU and TH (cat, rat), or ENK and TH (cat). Functional implications of such colocalized neurochemicals within individual LC projection neurons are discussed.

Animals↗

PubMed1994

Characterization and immortalization of woodchuck hepatocytes isolated from normal and hepadnavirus-infected woodchucks (Marmota monax).

Primary woodchuck (Marmota monax) hepatocytes from normal woodchucks and woodchucks with chronic woodchuck hepatitis virus (WHV) infection were cultured in either a conventional serum-containing medium or a serum-free medium. The de novo synthesis of the plasma proteins albumin, transferrin, fibrinogen, and complement C3 were identical under both conditions. However, expression of the WHV and the synthesis of nitric oxide were diminished under serum-free conditions. Primary woodchuck hepatocytes cultured in conventional, serum-containing medium were immortalized utilizing the simian virus 40 T antigen oncogene. Immortalized hepatic cell lines retained differentiated functions of nitric oxide synthesis and expression of complement C3. The woodchuck hepatocyte culture model will supplement current experimental methods, allowing investigation of hepadnaviral pathogenesis, including hepatocarcinogenesis in vitro.

Albumins↗

PubMed1994

Cotransmitter-mediated locus coeruleus action on motoneurons.

This article reviews evidence for a direct noradrenergic projection from the dorsolateral pontine tegmentum (DLPT) to spinal motoneurons. The existence of this direct pathway was first inferred by the observation that antidromically evoked responses occur in single cells in the locus coeruleus (LC), a region within the DLPT, following electrical stimulation of the ventral horn of the lumbar spinal cord of the cat. We subsequently confirmed that there is a direct noradrenergic pathway from the LC and adjacent regions of the DLPT to the lumbar ventral horn using anatomical studies that combined retrograde tracing with immunohistochemical identification of neurotransmitters. These anatomical studies further revealed that many of the noradrenergic neurons in the LC and adjacent regions of the DLPT of the cat that send projections to the spinal cord ventral horn also contain colocalized glutamate (Glu) or enkephalin (ENK). Recent studies from our laboratory suggest that Glu and ENK may function as cotransmitters with norepinephrine (NE) in the descending pathway from the DLPT. Electrical stimulation of the LC evokes a depolarizing response in spinal motoneurons that is only partially blocked by alpha 1 adrenergic antagonists. In addition, NE mimicks only the slowly developing and not the fast component of LC-evoked depolarization. Furthermore, the depolarization evoked by LC stimulation is accompanied by a decrease in membrane resistance, whereas that evoked by NE is accompanied by an increased resistance. That Glu may be a second neurotransmitter involved in LC excitation of motoneurons is supported by our observation that the excitatory response evoked in spinal cord ventral roots by electrical stimulation of the LC is attenuated by a non-N-methyl-D-aspartate glutamatergic antagonist. ENK may participate as a cotransmitter with NE to mediate LC effects on lumbar monosynaptic reflex (MSR) amplitude. Electrical stimulation of the LC has a biphasic effect on MSR amplitude, facilitation followed by inhibition. Adrenergic antagonists block only the facilitator effect of LC stimulation on MSR amplitude, whereas the ENK antagonist naloxone reverses the inhibition. The chemical heterogeneity of the cat DLPT system and the differential responses of motoneurons to the individual cotransmitters help to explain the diversity of postsynaptic potentials that occur following LC stimuli.

Animals↗

PubMed1994

Hippocampal beta-amyloid reduces locus coeruleus glutamate and tyrosine hydroxylase.

The effects of intrahippocampally injected beta-amyloid protein (beta-AP) on glutamate- (Glu) and tyrosine hydroxylase (TH)-like immunoreactivities in the neurons of the locus coeruleus (LC) were studied in rats. A synthetic peptide or the vehicle alone was injected into the hippocampus as controls. All injections were made once a week (two or three injections; 3 nmol in 2 microliters of distilled water). Fluorescent microspheres (either alone or with one of the peptides) were also injected into the hippocampus to identify coeruleo-hippocampal neurons. The results revealed cell loss in the hippocampus at the site near beta-AP or control peptide deposition. Furthermore, in beta-AP/microsphere injected animals, only 22.4% and 49.6% of hippocampal projection neurons contained Glu and TH, respectively, compared to 88.4% and 85.3% in the animals that received control peptide with microspheres. Our results suggest that beta-AP has an effect on noradrenergic cells whose axons project to the hippocampus. These effects may contribute to the TH cell loss in the LC of Alzheimer's brains.

Amyloid beta-Peptides↗

PubMed1994

Existence of glutamate in noradrenergic locus coeruleus neurons of rodents.

This study distinguished three types of immunolabeled neurons in nucleus locus coeruleus (LC) of the rat and mouse: cells single labeled either for tyrosine hydroxylase-like immunoreactivity (TH-LI) or glutamate (Glu)-LI, and those double labeled for both antigens. Although the double labeled neurons tend to be located in the middle and ventral thirds of the rat LC nucleus, throughout its rostrocaudal extent, such feature was not apparent in the mouse. Quantitatively a majority of neurons cocontaining TH- and Glu-LI were commonly observed in the rat (62%) and mouse (77%) LC. Additional studies utilizing the combined retrograde and immunohistochemical labeling revealed that such a high incidence of coexistence of the TH- and Glu-LI was also represented by coeruleocortical neurons in the rat (69% and 75% of all ipsilateral and contralateral projection cells, respectively). A possible role of coeruleocortical neurons involvement in Glu- and norepinephrine-mediated target neuron dysfunction is discussed.

Animals↗

PubMed1994

Woodchuck hepatitis virus surface antigen induces nitric oxide synthesis in hepatocytes: possible role in hepatocarcinogenesis.

Woodchuck hepatitis virus surface antigen (WHsAg) stimulated hepatocytes in culture to produce nitric oxide (NO.), as evidenced by the accumulation of nitrite in the medium. NO. synthesis by hepatocytes was positively correlated with WHsAg concentration. WHsAg-induced NO. synthesis was inhibited by NG-monomethyl-L-arginine and anti-WHsAg antibody. To our knowledge, this is the first demonstration of an increase in NO. formation by a viral antigen. These data, when considered in the light of the known genotoxicity of NO., raise the possibility that viral hepatitis increases the risk of liver cancer by increasing the production of NO.. Long-term elevated production of NO. free radicals due to stimulation by WHsAg in chronic hepatitis may directly cause reactions with cellular DNA leading to mutagenesis, as well as the formation of hepatocarcinogenic N-nitroso compounds. This provides a new mechanism by which hepatitis B virus infection might hypothetically increase the risk of liver cancer.

Animals↗

PubMed1994

Bulbospinal neurons of the cat that co-contain serotonin and methionine enkephalin.

The present study utilizes a combined retrograde transport of Fast Blue (or rhodamine-labeled latex microspheres) and simultaneous immunofluorescence technique to demonstrate directly the coexistence of serotonin and methionine enkephalin in bulbospinal neurons of the cat. The bulbospinal neurons that immunostained for both serotonin and enkephalin were observed, without any distinct somatotopic organization, in the nuclei raphe pallidus, obscurus and magnus. They were also observed in the nucleus reticularis magnocellularis and the ventrolateral medulla (cell group B1/3). Among the bulbospinal neurons encountered within individual 5-HT-rich medullary nuclei, high proportions of these neurons co-containing serotonin and methionine enkephalin were evidenced in the nucleus raphe obscurus (64%) and nucleus raphe pallidus (56%), less so in cell group B1/3 (41%), nucleus raphe magnus (39%), and the nucleus reticularis magnocellularis (29%). Physiological significance of such a morphological substrate is discussed.

Amidines↗

PubMed1994

Improved gas chromatography/mass spectrometry analysis of barbiturates in urine using centrifuge-based solid-phase extraction, methylation, with d5-pentobarbital as internal standard.

Effective solid-phase extraction, derivatization, and GC/MS procedures are developed for the simultaneous determinations of butalbital, amobarbital, pentobarbital, and secobarbital, using a deuterated pentobarbital (d5-pentobarbital) as the internal standard. Buffered (pH 7) urine samples were extracted with Bond Elute Certify II cartridge. Iodomethane/tetramethylammonium hydroxide in dimethylsulfoxide was used for methylation, while a HP 5970 MSD equipped with a 13 m J & W DB-5 column (5% phenyl polysiloxane phase) and the Thru-Put Target software package were used for GC/MS analysis and data processing. This protocol was found to be superior, in both chromatographic performance characteristics and quantitation results, over a liquid-liquid extraction procedure without derivatization using hexobarbital as the internal standard. Extraction recoveries observed from control samples containing four barbiturates range from 80% to 90%. Good one-point calibration data are obtained for all four barbiturates in the 50 to 3200 ng/mL range. Interestingly, the one-point calibration data for pentobarbital are inferior to the other three barbiturates--due to interference from the internal standard (d5-pentobarbital). The calibration data of pentobarbital are best described by a hyperbolic curve regression model. Precision data (% CV) for GC/MS analysis, over-all procedure, and day-to-day performance are approximately 2.0%, 6.0%, and 8.0%, respectively. With the use of a 2 mL sample size, the attainable detection limit is approximately 20 ng/mL.

Amobarbital↗

PubMed1993

Immunohistochemical localization of glutamate-containing neurons in the lateral reticular nucleus projecting to the cerebellar vermis in the kitten.

The lateral reticular nucleus (LRN) and afferents to the cerebellum are known to contain glutamate-like immunoreactive (Glu-LI) neurons and axons, respectively. However, such a direct link between the Glu-LI LRN neurons and the cerebellar vermal cortex has not been identified. In this study we have combined the retrograde transport of rhodamine labeled latex microspheres and immunofluorescence histochemistry to determine the locations of Glu-LI neurons of the kitten reticulocerebellar system. Following microsphere injections into the cerebellar vermis (lobules V-VII), retrogradely labeled neurons were encountered throughout the rostrocaudal extent of the LRN. More than 60% (n = 3 kittens) of these retrogradely labeled neurons were immunostained for Glu-like immunoreactivity. Our observations of the Glu-like immunoreactivity in a majority of the reticulocerebellar neurons suggest that Glu in these neurons may participate in LRN's control of target neuron activities in the cerebellar vermis of kittens.

Animals↗

PubMed1993

Effect of systemic morphine on neurons in the lateral reticular nucleus area of the rat.

The present study is undertaken to investigate the effect of systemic morphine on neurons in the lateral reticular nucleus (LRN) using extracellular recording techniques. The spontaneous activities of 64 neurons in the LRN area were tested with morphine (3-5 mg/kg, IV). Morphine excited 23 and inhibited 28 neurons tested, and 13 neurons were not affected. Of the 28 neurons inhibited, 20 were identified as nociceptive and the remaining 6 were nonnociceptive. Of the 23 neurons excited by morphine, 18 were nociceptive and 5 were nonociceptive. Systemic naloxone (0.3-0.5 mg/kg) significantly reversed the morphine effect in 15 out of 19 neurons excited and 19 out of 20 neurons inhibited by morphine. Thirteen out of 64 neurons were further identified as reticulospinal neurons, of which four were excited and four were inhibited by morphine. The remaining five were not affected. The results demonstrate that a similar proportion of neurons in the LRN area were either excited or inhibited by systemic morphine, and the majority of them are nociceptive neurons. It is suggested that different types of neurons in the LRN area may have different functions in morphine analgesia.

Animals↗

PubMed1993

Synthesis of nitric oxide and nitrosamine by immortalized woodchuck hepatocytes.

Woodchuck (Marmota monax) hepatic cells, which were immortalized by the simian virus 40 large T antigen (SV40 Tag) produced nitric oxide (NO; measured as nitrite) in vitro from L-arginine (L-Arg) after lipopolysaccharide (LPS) treatment. NO synthesis was related to L-Arg and LPS concentration and plateaued at 1.0 mM L-Arg and 1.0 microgram/ml LPS. LPS-stimulated cells nitrosated morpholine to form N-nitrosomorpholine (NMOR) in the presence of L-Arg at pH 7.4. NMOR production increased 7-fold in LPS stimulated cells compared to unstimulated hepatocytes. N-nitrosodimethylamine (NDMA) was detected in the cell culture medium in the presence of LPS and L-Arg but without added dimethylamine. NG-monomethyl-L-arginine, a selective inhibitor of nitric oxide synthase, inhibited formation of NO and NMOR, indicating that NO and nitrosating agents were formed via the L-Arg-nitric oxide pathway. These data are the first to report NO and N-nitrosamine production by immortalized hepatocytes and confirm earlier work showing that primary hepatocytes form NO in culture. This suggests that hepatic formation of N-nitroso compounds and/or NO could be an etiologic factor in hepatocellular carcinoma. Immortalized woodchuck hepatic cells may be useful as in vitro models to study the L-Arg-nitric oxide pathway and its possible role in liver carcinogenesis.

Animals↗

PubMed1993

Evaluation of enzyme immunoassay performance characteristics--phencyclidine example.

Four reagent formulations (three provided by a manufacturer; one prepared in-house by mixing equal volumes of two commercial reagents) are used for the assay of phencyclidine (PCP) in urine samples. Performance characteristics evaluated included assay precision and sensitivity at and near the assay cutoff concentration. Data resulting from the reagent prepared in-house are better than those using then commercially available formulations, and are comparable with those obtained using the recently available new commercial formulation.

Enzyme Multiplied Immunoassay Technique↗

PubMed1992

Selective blockade by yohimbine of descending spinal inhibition from lateral reticular nucleus but not from locus coeruleus in rats.

The present study was undertaken to compare the effects of the alpha 2-adrenoceptor antagonist yohimbine on inhibition of C-fiber-evoked responses of dorsal horn neurons produced by electrical stimulation of the lateral reticular nucleus (LRN) and the Locus coeruleus (LC) in the rat. In the majority of neurons, C-fiber-evoked responses were significantly inhibited by 53.84 +/- 5.02% and 57.63 +/- 5.79% of control by LRN and LC stimulation, respectively, whereas in less than half of the neurons, A-fiber-evoked responses were reduced by 20.99 +/- 6.06% and 21.78 +/- 4.48% of control, respectively. After systemic or spinal administration of yohimbine, LC-induced inhibition of C-fiber-evoked responses was not affected. In contrast, LRN-induced inhibition was markedly attenuated by yohimbine. The results suggest that alpha 2-adrenoceptors may be involved in mediation of inhibition of spinal nociception induced by stimulation of LRN but not by LC.

Administration, Topical↗

PubMed1992

Nitrite and nitrosamine synthesis by hepatocytes isolated from normal woodchucks (Marmota monax) and woodchucks chronically infected with woodchuck hepatitis virus.

Hepatocytes isolated from woodchucks (Marmota monax) were shown to produce nitrite in vitro from L-arginine after stimulation with lipopolysaccharide (LPS). Hepatocytes isolated from woodchucks that were chronic carriers of woodchuck hepatitis virus formed twice as much nitrite as hepatocytes from noninfected animals. Nitrite synthesis by hepatocytes was directly related to L-arginine and LPS concentrations in the tissue culture medium and reached a plateau at 0.5 mM L-arginine and 1.0 micrograms/ml LPS. LPS-stimulated hepatocytes nitrosated morpholine to form N-nitrosomorpholine in the presence of L-arginine at a physiological pH of 7.4. There was a 10-fold increase in N-nitrosomorpholine production when hepatocytes were stimulated with LPS compared to unstimulated hepatocytes under similar conditions when both nitrite and morpholine were directly added to the medium. NG-monomethyl-L-arginine, a selective inhibitor of nitric oxide synthase, inhibited formation of both nitrite and N-nitrosomorpholine. These results demonstrate that nitrosating agents are formed in hepatocytes via the L-arginine-nitric oxide pathway. This suggests that endogenous formation of carcinogenic N-nitroso compounds could influence the process of hepatocarcinogenesis in woodchucks with chronic woodchuck hepatitis virus infection.

Animals↗

PubMed1992

Left ventricular opacification after peripheral venous injection of a modified albumin solution.

The usefulness of a modified albumin solution was assessed in 8 dogs after peripheral venous and inferior vena cava injections. The contrast agent is a mixed solution made of glucose, albumin and glycerin, with sonicated microbubble diameter of 5.0 +/- 2.3 microns. Multiple injections (8 ml each) of this contrast agent (total 80 injections) into peripheral vein and inferior cava were performed. The blood pressure from femoral artery was measured before, during and after injections. Two-dimensional echocardiograms were recorded in a modified long axis view on videotapes for play back analysis. The pulmonary transit time and left ventricular contrast persistent time was determined for each injection. The videodensity of the region of interest (ROI) at the center of right ventricle and left ventricle was measured. The background videodensity of both ventricles was evaluated. The videodensity over the ROI of both ventricles with peak contrast enhancement was measured in all frames for 3 consecutive cardiac cycles. The peak videodensity of right and left ventricle subtracting the background videodensity of each ventricles was further calculated respectively. The injections caused no change in blood pressure or heart rate. All injections produced right ventricular contrast echo. As much as 85% of peripheral venous and 82.5% of inferior vena cava injections resulted in left ventricular contrast which was 0.68 and 0.65 as bright as that produced in the right ventricle. Pulmonary transit time and left ventricle contrast persistent time of peripheral venous injection was 4.05 +/- 0.53 and 13.67 +/- 4.28 seconds respectively. No difference of these data (3.93 +/- 0.47 and 11.65 +/- 4.66 seconds) from those produced by inferior vena cava injections were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗

PubMed1991

Elevated formation of nitrate and N-nitrosodimethylamine in woodchucks (Marmota monax) associated with chronic woodchuck hepatitis virus infection.

Nitrate balance and N-nitrosodimethylamine (NDMA) excretion were studied in woodchucks chronically infected with woodchuck hepatitis virus (WHV). Twenty-four-h urinary recovery of a bolus dose of [15N]nitrate was 54 +/- 12% in woodchucks. WHV-infected animals formed 3-fold more nitrate endogenously than did control animals (P less than 0.01). Treatment of WHV-infected animals with Escherichia coli lipopolysaccharide increased nitrate excretion 15-fold, while uninfected animals increased nitrate excretion 4-fold. The endogenous formation of NDMA was higher in WHV-infected woodchucks than in uninfected controls. After administration of L-[15N2]arginine, [15N]nitrate, and [15N]NDMA were detected in urine indicating that arginine is a precursor of biosynthesized nitrate and the hepatocarcinogen NDMA. NDMA probably results from the formation of nitrosating agents during the oxidation of arginine to oxides of nitrogen and citrulline. Woodchucks chronically infected with WHV develop hepatocellular carcinomas with high frequency. Our observations suggest an additional mechanism that may be involved in the pathogenesis of hepatocellular carcinoma associated with chronic WHV infection.

Animals↗

PubMed1991

Termination of digitalis-induced ventricular tachycardias by clonidine involves central alpha 2-adrenoceptors in cats.

1. Effects of intravenous (i.v.) and intravertebral arterial (i.a.) administration of the alpha 2-adrenoceptor agonist, clonidine (Clon) and its antagonist, yohimbine (Yoh, 0.5 mg kg-1, i.v.; 0.05 mg kg-1, i.a.), on ventricular tachycardia (VT) induced by intravenous acetylstrophanthidin (AS) were studied in cats anaesthetized with intraperitoneal chloralose. 2. AS dose-dependently produced cardiac arrhythmias including complete atrioventricular conduction block (118 +/- 14 micrograms kg-1, i.v.), junctional tachycardia (128 +/- 20 micrograms kg-1, i.v.), multiform ventricular premature beats (157 +/- 21 micrograms kg-1, i.v.) and sustained VT (220 +/- 23 micrograms kg-1, i.v.). 3. Doses of Clon (i.v.) required for termination of VT following i.v. Yoh (62.9 +/- 5.2 micrograms kg-1) or i.a. Yoh (88.5 +/- 16.3 micrograms kg-1) were higher than those for termination of VT without Yoh administration (28.3 +/- 6.2 micrograms kg-1). Doses of Clon (i.a.) required for termination of VT without or with i.a. Yoh administration were 5.8 +/- 1.0 or 14.8 +/- 3.7 micrograms kg-1, respectively, and they were significantly different. 4. These experiments demonstrate that either i.v. or i.a. Yoh antagonizes the antiarrhythmic effect of Clon on AS-induced VT. Since small doses of Clon administered i.a. act predominantly on the central nervous system, we suggest that its antiarrhythmic effect is likely to be on central alpha 2-adrenoceptors in the central nervous system.

Animals↗

PubMed1991

Detection of acute myocardial infarction by evaluation of ultrasonic gray levels in dogs.

The study tested whether an experimental myocardial infarction can be detected from two-dimensional echocardiograms (2DE) by analysis of regional gray levels. The mid-left anterior descending coronary artery was ligated for 3 hours in 14 dogs (group 1) and for 5 hours in 6 dogs (group 2). 2DE were performed before, and after 3 and 5 hours of coronary artery ligation. The ultrasonic amplitude of the control and infarcted regions were obtained from digitized 2DE in the short axis view, at the mid-papillary muscle level. The mean gray levels (+/- SD) of the control and infarcted regions were compared during end-diastolic stop frames. After sacrifice, the hearts were cut into 1 cm thick slices and stained with 1% triphenyl tetrazolium chloride (TTC) solution. The myocardium was then studied by light microscopy. Computerized tomographic scans were also obtained in vitro from 3 hearts of both groups. There was no difference in mean gray levels of the control region during the experiments. However, in the region of wall motion abnormality (area of infarction), the mean gray levels increased from 49.9 +/- 3.5 (before ligation) to 62.0 +/- 7.4 (after 3 hours of ligation, p less than 0.005) in 10 group 1 dogs, but no differences were seen in mean gray levels (49.6 +/- 3.8 vs 50.4 +/- 4.0) in those without a myocardial infarction in 4 group 1 dogs; gray levels also increased from 50.4 +/- 2.9 (before ligation) to 58.6 +/- 6.1 (after 3 hours of ligation, p less than 0.05) and to 65.0 +/- 4.2 (after 5 hours of ligation, p less than 0.005) in group 2 dogs. The area of left ventricular asynergy corresponded precisely to the area of myocardial infarction, determined by both TTC staining and the computerized tomographic scans. The light microscopy of the infarcted area also demonstrated interstitial edema and polymorphonuclear cell infiltration.

Animals↗