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Biomedical subjects

T H Chiu

Publications and source records attributed to T H Chiu.

At least 109 records · Page 6Linked to original sources
PubMed1986

Displaceable binding of [3H]l-glutamic acid to non-receptor materials.

[3H]L-glutamic acid binding to microfuge tubes and glass was investigated in four buffers. Background binding to these materials was negligible, but was increased by centrifugation or suction in Tris-HCl and Tris-citrate buffer. This binding was much less or eliminated when HEPES-KOH, or Tris-acetate buffer was used instead. [3H]L-glutamate binding to microfuge tubes was inhibited by L- but not D-isomers of glutamate and aspartate. DL-2-amino-7-phosphonoheptanoic acid also did not inhibit the binding. Other compounds which showed low to moderate inhibition were: N-methyl-D-aspartate, quisqualate, L-glutamic acid diethyl ester, N-methyl-L-aspartate, kainate, and 2-amino-4-phosphonobutyrate. Binding was inhibited by denatured rat brain membranes. A protein-dependent [3H]glutamate binding was obtained with a repeatedly frozen-thawed membrane preparation when binding was done in Tris-acetate buffer. It is recommended that Tris-acetate or HEPES-KOH buffer should be used in the glutamate binding assay. If Tris-HCl or Tris-citrate buffer is used, appropriate control experiment should be done to correct for binding to microfuge tubes or glass fiber filters.

Animals↗
PubMed1986

An improved preparation of phosphatidylglycerophosphate.

Phosphatidylglycerophosphate is not normally accumulated in the reaction mixture. It was found that octyl-beta-D-glucopyranoside greatly stimulated the synthesis and inhibited the degradation of phosphatidylglycerophosphate. The phenomenon could be used for the preparation of phosphatidylglycerophosphate from CDPdiacylglycerol and the sn-glycero-3-phosphate with the crude membrane enzyme preparation. The optimal concentration of octyl-beta-D-glucopyranoside to be used for such a purpose was 24.5 mM.

Chemical Phenomena↗
PubMed1986

Adenosine inhibits locus coeruleus neurons: an intracellular study in a rat brain slice preparation.

Intracellular recording was used to study the effect of adenosine (3-100 microM) on rat locus coeruleus (LC) neurons in a brain slice preparation. Bath application of adenosine (100 microM) reduced the rate of spontaneous firing in 88% of LC neurons. In some LC neurons adenosine also caused membrane hyperpolarization (2-10 mV) and reductions in input resistance of 9-24%. Adenosine effects were dose-dependent and antagonized by the adenosine receptor antagonist theophylline.

Adenosine↗
PubMed1986

Effects of pentylenetetrazol on GABA-A/benzodiazepine/picrotoxinin receptor complexes in rat brain regions.

The effects of acute convulsive doses of pentylenetetrazol (PTZ) on [35S]t-butyl-bicyclophosphorothionate (TBPS), [3H]flunitrazepam (FNP), [3H]muscimol, and [3H]gamma-aminobutyric acid (GABA) binding sites were examined in well-washed homogenates of various brain regions of rat. Except for a significant increase in the number of striatal [35S]TBPS binding sites, no significant change in [35S]TBPS, [3H]FNP, [3H]muscimol, and [3H]GABA binding was found in various brain regions 30 min after subcutaneous injection of PTZ at 90 or 100 mg/kg. Similarly, there were no significant changes in [35S]TBPS and [3H]FNP binding to unwashed P2 membranes of cerebral cortices 30 min following administration of convulsive doses of PTZ. These experiments failed to demonstrate acute modulation of GABA-A/benzodiazepine/picrotoxinin receptor complex by PTZ in the various brain regions examined except striatum. The significance of the increased [35S]TBPS binding in striatum caused by PTZ remains unclear.

Animals↗
PubMed1986

Target-specific nerve regeneration through a nerve guide in the rat.

Nerve regeneration across a gap in peripheral nerve has been achieved through various nonneural nerve guides in both lower and primate species. This technique can only be useful if the regenerated nerve cable grows specifically to and reinnervates the appropriate distal target. In this study, the proximal peroneal fascicle of rat sciatic nerve was inserted into the proximal limb of a Y-shaped nerve guide. Distal peroneal and tibial fascicles were placed within the two distal limbs of the same Y. The proximal peroneal nerve grew preferentially by a 2:1 ratio to the appropriate distal peroneal fascicle suggesting that target-specific reinnervation is possible through a nerve guide.

Animals↗
PubMed1986

Autoradiographic localization of benzodiazepine receptor downregulation.

Regional differences in downregulation of brain benzodiazepine receptors were studied using a quantitative autoradiographic method. Rats were given a 4-week flurazepam treatment known to cause tolerance and receptor downregulation. A second group of rats was given a similar treatment, but for only 1 week. A third group was given a single acute dose of diazepam to produce a brain benzodiazepine-like activity equivalent to that found after the chronic treatment. Areas studied included hippocampal formation, cerebral cortex, superior colliculus, substantia nigra, dorsal geniculate nucleus, lateral amygdala and lateral hypothalamus. There was a regional variation in the degree of downregulation after 1 week of flurazepam treatment, ranging from 12% to 25%. Extending the flurazepam treatment to 4 weeks caused little further downregulation in those areas studied, except for the pars reticulata of the substantia nigra, which showed a 13% reduction in [3H]flunitrazepam binding after 1 week and a 40% reduction after 4 weeks of treatment. In a few areas, such as the lateral hypothalamus, no significant change in binding was found after 4 weeks. Acute diazepam treatment caused no change in binding. This latter finding as well as results obtained during the development of the methodology show that downregulation was not an artifact due to residual drug content of brain slices. The regional variations in degree and rate of downregulation suggest areas that may be most important for benzodiazepine tolerance and dependence and may be related to the varying time courses for tolerance to different benzodiazepine actions.

Animals↗
PubMed1985

An in vivo model to quantify motor and sensory peripheral nerve regeneration using bioresorbable nerve guide tubes.

An in vivo preparation is presented to study the rate and time course of motor and sensory axonal regeneration. The cut ends of a transected sciatic nerve were inserted into each end of a 5-6 mm non-toxic and bioresorbable nerve guide tube to create a 4 mm nerve gap in adult mice. Subsequently, cell bodies in the ventral spinal cord and L3-L5 dorsal root ganglia that had regenerated axons across the gap were retrogradely labeled with horseradish peroxidase (HRP). The HRP was applied 3 mm distal to the nerve guide and was accessible only to axons that had regenerated through the nerve guide. Labeled cells were counted in 40 micron serial sections at 2, 4 and 6 weeks after initial nerve transection. The results indicate a significant increase in the number of labeled motor and sensory cell bodies over time. By 6 weeks after transection, approximately two thirds as many ventral horn motor cells and one third as many dorsal root ganglion sensory cells were labeled as in control non-transected animals. These data serve as a baseline to compare differential effects of additives to the nerve guide lumen in terms of sensory and motor neuron response.

Animals↗
PubMed1985

Phosphatidyl glycerolphosphate serves as glycerolphosphate donor in polymer synthesis.

Phosphatidyl glycerolphosphate was found to serve as the glycerolphosphate donor for polymer synthesis. When CDP-diglyceride and radiolabeled glycerolphosphate were incubated with the membrane enzyme prepared from Streptococcus sanguis, active syntheses of radiolabeled lipids and polymers were observed. The synthesis of polymer was not inhibited by low concentration of unlabeled phosphatidylglycerol. When [3H, 32P]glycerolphosphate was used, the polymer synthesized contained both 3H and 32P. The lipids formed were characterized as phosphatidylglycerol and phosphatidyl glycerolphosphate. The polymers formed from the latter were characterized as lipoteichoic acid like compounds by sodium dodecylsulfate-polyacrylamide gel electrophoresis.

Chromatography, Paper↗
PubMed1985

Blood pressure response to Ro15-1788, a benzodiazepine antagonist.

The effects of Ro15-1788, a benzodiazepine antagonist, on heart rate and blood pressure were studied in chloralose anesthetized cats. In previously untreated controls, Ro15-1788 lowered both systolic and diastolic arterial pressure about 15 mm Hg, and slightly decreased heart rate. In cats that had been given a single acute dose of diazepam or flurazepam, Ro15-1788 increased blood pressure about 40 mm Hg. A similar increase was measured in cats that were tolerant and physically dependent after 5 weeks of chronic flurazepam treatment. High spinal (C-1) section abolished all Ro15-1788 effects. It is suggested that the observed drug actions occur within the CNS rather than in the periphery, and that it might be useful to study further the cardiovascular actions of benzodiazepine agonists and antagonists.

Animals↗
PubMed1985

Increased rate of peripheral nerve regeneration using bioresorbable nerve guides and a laminin-containing gel.

The sciatic nerve of adult mice was transected and proximal and distal nerve stumps were sutured into a nontoxic bioresorbable nerve guide. Nerve guide lumens were either empty or filled with a gel containing 80% laminin and additional extracellular matrix components. Two weeks later cells in the L3 through L5 dorsal root ganglia and the ventral horn of the spinal cord were retrogradely filled with horseradish peroxidase. All animals with the laminin-containing gel but none with empty nerve guides displayed labeled cells. This suggests that the laminin-containing gel significantly hastened axonal regeneration in vivo.

Absorption↗
PubMed1985

Nerve regeneration through biodegradable polyester tubes.

One approach to repair of transected nerves is to attempt extrinsic guidance of axons across the gaps. We inserted the proximal and distal stumps of severed mouse sciatic nerves into opposite ends of biodegradable polyester tubes. The nerves and ensheathing tubes were examined after postoperative survival times of as long as 2 years. Myelinated fiber number in each successfully regenerated nerve was measured and correlated with the tube's residual lumen size. In selected regenerated nerves axonal sizes and myelin sheath widths were sampled and compared with control values. Swelling and deformation of tube walls occurred in nearly all tubes. Successful regeneration was obtained through more than half of the implants, and was more probable in tubes with larger initial lumens. Myelinated fiber number in regenerated nerves ranged from 231 to 3561 (normally 3900 to 4200); larger values again were found in tubes with larger initial lumens. Mean axonal areas in regenerated nerves were roughly half of normal, though myelin sheaths became appropriately thick. We concluded that the more biodegradable a tube, the more likely it was to incur distortion and luminal narrowing. Tube composition per se seemed of importance mainly as it related to maintenance of adequate luminal size over the length of the degrading tubes; luminal adequacy, not tube composition, seemed paramount in determining the extent of nerve regeneration.

Animals↗
PubMed1985

Tolerance to the anticonvulsant action of benzodiazepines. Relationship to decreased receptor density.

Tolerance to the anticonvulsant action of benzodiazepines was studied in rats that had been treated for 4 weeks with 100-150 mg/kg per day of flurazepam. Previous studies had shown that this treatment produced tolerance to motor impairment induced by benzodiazepines and also down-regulation of benzodiazepine receptors in brain, which was seen as a reduced number of binding sites with no change in binding affinity. In the present study, seizures were produced using pentylenetetrazol (PTZ). In rats that had been chronically treated with flurazepam, pretreatment with diazepam was significantly less effective in blocking pentylenetetrazol-induced seizures, thus indicating tolerance. This tolerance could not be explained by a change in sensitivity to pentylenetetrazol resulting from chronic treatment, nor by any differences in levels of active drug in the brain following doses of diazepam. Residual amounts of flurazepam and its active metabolites may have artifactually reduced the apparent degree of tolerance measured 12 hr after the end of chronic treatment, but not at later times. Tolerance to the antipentylenetetrazol action of diazepam was evident up to the fourth day following chronic treatment with flurazepam, but tolerance had largely disappeared a week after chronic treatment. The duration of tolerance was much longer than that reported for tolerance to motor impairment induced by benzodiazepines, and for down-regulation of receptors. These results suggest that different mechanisms or different neural systems must mediate tolerance to these different actions of benzodiazepines. Furthermore, an adaptive reduction in the number of benzodiazepine receptors does not seem to be a likely mechanism for tolerance to the anticonvulsant action of these drugs.

Animals↗
PubMed1985

Time course for development of benzodiazepine tolerance and physical dependence.

Chronic benzodiazepine treatment elicits adaptive responses in the CNS, seen behaviorally as functional tolerance and physical dependence. Experiments are described in which a radioreceptor assay is used to follow benzodiazepine activity in CSF samples during daily flurazepam treatment of cats. Tolerance is evident even after the second dose, despite increasing CSF drug activity, showing a large and rapidly developing functional tolerance. Other studies are discussed which also show tolerance within 24 hours of initiating benzodiazepine treatment. In contrast, a spontaneous withdrawal syndrome is usually seen only after prolonged treatment with high doses. However, physical dependence can also be studied by precipitating abstinence with a benzodiazepine antagonist, such as Ro15-1788. Cats were treated daily with flurazepam, then Ro15-1788 was given and abstinence signs were recorded. Abstinence could be precipitated 24 hours after beginning treatment, and dependence was nearly maximal after 7 days. Dependence developed during treatment with as little as 0.5 mg/kg flurazepam, which is near threshold for any behavioral response. Chronic diazepam caused the same dependence as flurazepam. Thus, the development of tolerance and physical dependence both show a remarkably rapid adaptation of the CNS in response to benzodiazepines.

Animals↗
PubMed1985

Electromechanical effects of caffeine in isolated human atrial fibres.

Effects of caffeine on the action potential and contractile force of human atrial fibres obtained at cardiac surgery were studied with standard microelectrode technique. In 4 mmol . litre-1 [K]o, the only significant action produced by 0.3 to 3 mmol . litre-1 caffeine on the electro-mechanical activity of relatively normal atrial fibres was a slight shortening of the action potential duration at 50% repolarisation. When the fibres were depolarised in 27 mmol . litre-1 [K]o or in atrial fibres showing slow responses in 4 mmol . litre-1 [K]o, however, caffeine could increase the upstroke of slow response and the force. In 18% of atrial fibres showing slow responses in 4 mmol . litre-1 [K]o, caffeine induced spontaneous discharges and potentiated afterdepolarisations. The positive inotropic and the arrhythmogenic effects of caffeine could be diminished by pretreating the fibres with propranolol or Ca antagonists (diltiazem and verapamil). In fibres beating spontaneously in normal [K]o, caffeine accelerated spontaneous rhythms initially and then depressed them. Propranolol potentiated the later depression but did not block the initial acceleration. The results suggest that caffeine increases the transmembrane Ca influx and enhances the release of Ca from the intracellular stores in human atrial fibres. As a consequence, caffeine could induce arrhythmias in atria from certain individuals.

Action Potentials↗
PubMed1985

Allosteric modulation of flunitrazepam binding to rat brain benzodiazepine receptors by methyl beta-carboline-3-carboxylate.

The inhibition of flunitrazepam (FNP) binding to rat brain benzodiazepine (BZ) receptors by methyl beta-carboline-3-carboxylate (MCC) was studied. Biphasic dissociation was observed for [3H]FNP and [3H]MCC in cerebral cortex, cerebellum, and hippocampus, although the dissociation of [3H]MCC was much faster. The dissociation rate of [3H]FNP was increased by MCC in the cerebellum, but was not altered in cerebral cortex or hippocampus. [3H]FNP binding stimulated by gamma-aminobutyric acid was enhanced in the presence of MCC in all three regions examined. These results indicate that MCC exerts these effects by interacting with allosteric sites that are different from the FNP recognition sites on the BZ receptors.

Animals↗
PubMed1985

Pre- versus postsynaptic localization of benzodiazepine and beta-carboline binding sites.

[3H]Flunitrazepam (FNP) and [3H]methyl beta-carboline-3-carboxylate (MCC) binding was examined in soluble and particulate fractions from membranes solubilized with Triton X-100 or in subfractions of synaptosomal membranes obtained by a physical separation technique. Results using both methods demonstrate that benzodiazepine and beta-carboline sites reside on both pre- and postsynaptic membranes. Further, subfractionation experiments indicate that the binding sites for both ligands are unequally distributed within the synapse and among brain regions. For example, in cerebral cortical presynaptic membranes there are twice as many FNP as MCC sites whereas in postsynaptic membranes this ratio is reversed. The number of FNP and MCC sites are equal in the presynaptic fraction from cerebellum. The postsynaptic membranes derived from cerebellum have three times the number of FNP compared to MCC sites. In hippocampus this ratio varies between 1.5 and 2.8 in each subfraction. These results support the idea that benzodiazepine and beta-carboline binding sites represent different recognition sites.

Animals↗