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Biomedical subjects

L Guo

Publications and source records attributed to L Guo.

At least 307 records · Page 17Linked to original sources
PubMed1993

Release of endogenous GABA in the posterior hypothalamus of the conscious rat; effects of drugs and experimentally induced blood pressure changes.

Push-pull superfusion was used to investigate the release of endogenous GABA in the posterior hypothalamus of the conscious, freely moving rat at basal conditions and in response to centrally applied drugs or to peripherally induced blood pressure changes. After an initial, exponential decline, the release rate of GABA remained fairly constant for many hours. Fluctuations in the release rate of GABA point to the existence of an ultradian rhythm with an approximate frequency of 1 cycle/65 min. Hypothalamic superfusion with a potassium-rich (50 or 90 mmol/l) artificial cerebrospinal fluid led to a concentration-dependent increase in the GABA release. The release of GABA was also enhanced by veratridine (1 or 10 mumol/l) in a concentration-dependent way. Hypothalamic superfusion with the neutrotoxin tetrodotoxin (1 mumol/l) led to a long-lasting decrease in the GABA release. The rise in blood pressure (45 mmHg) elicited by an intravenous infusion of noradrenaline was associated with an increased release rate of GABA in the hypothalamus. Hypotension produced by nitroprusside (25 mmHg) led to a counteracting decrease in hypothalamic GABA outflow. The findings suggest that approximately 45% of the basal outflow of GABA found in the superfusate are released from GABA-ergic neurons of the posterior hypothalamus. The release rate of GABA fluctuates according to an ultradian rhythm. The modified release of GABA in response to experimentally induced blood pressure changes suggests that, in the posterior hypothalamus of the conscious rat, GABAergic neurons are involved in cardiovascular control and possess a hypotensive function.

Animals↗
PubMed1993

Can visual perception be used to estimate body part angles?

For two decades, observational methods have been used to measure postural loads in industry. These methods depend on the analyst's judgment to characterize correctly the working postures. The errors associated with estimating the body part's angular deviation from the neutral position are not known. Recently, videotaping of a work situation, followed by examination of the tape to assess postural position has become more commonly practised. This study was conducted to determine the error which accompanies the judging (without tools) of postural angles. In the present study, a method was used whereby 20 subjects were asked to report the perceived angles which closely matched the actual shoulder flexion angle displayed on the TV screen. The results showed no significant differences among the three angular ranges ('low', 1-60 degrees; 'medium', 61-120 degrees; and 'high', 121-180 degrees) of shoulder flexion, in terms of algebraic and absolute errors. Subjects tended to slightly overestimate the true angle in the low range and to slightly underestimate the true angle in the medium and high angle ranges. This study suggests that visual perception can be used to estimate shoulder flexion angles displayed on a VDT.

Adult↗
PubMed1993

[Synthesis of protected active peptide analogues of cholecystokinin and study of their biological activities].

A number of protected active peptide analogues of Cholecystokinin were prepared in solution by N-end stretching method with active esters. In the synthesis t-butoxycarbonyl (Boc-) and benzyloxycarbonyl (Z-) were applied as protecting groups. Six oligopeptides which contained protecting groups have not yet been reported in literature. Their structures were identified by amino acid analysis, opticity, IR and FAB-MS. The results of preliminary pharmacological tests show all the samples have biological activities in various degrees.

Amino Acid Sequence↗
PubMed1993

[Production of transgenic rabbits by micro injection].

The feasibility of using whole animal instead of bioreactor in genetic engineering has been investigated with transgenic domestic rabbits. The gene chosen is the surface gene (S gene) of hepatitis B virus. Two plasmids were specifically constructed for this purpose, pHBV3.0 contains the promoter pre S gene and a part of c gene of the virus; while MT-SA, the S gene and mouse MT promotor. These plasmids were made linear by suitable restriction endonuclease before they were transferred into maleprounclei by means of microinjection. From 757 microinjected and transplanted fertilized eggs 101 rabbits were obtained. 57% of these animals were found with integrated microinjected genes. 28 of the transgenic animals were tested for the presence of the surface antigen of the virus in the serum by ELISA method. 8 animals were found positive, approximately 30% of the tested transgenic animals. The second generation transgenics were obtained either by first generation ransgenics crossed with non-trans-genics or transgenics. Among them 73% contained the transgene and 15% had the surface antigen in the serum. Some experiments were also carried out with human growth hormone gene.

Animals↗
PubMed1992

Observations of synaptic efficacy and paired-pulse facilitation in area CA1 of hippocampal slices from coriaria lactone-kindled rats.

The changes of population spike(PS)/population excitatory postsynaptic potential (EPSP) slope relationship and paired-pulse facilitation (PPF) were primarily investigated with extracellular recording in stratum pyramidale to stimulation of Schaffer collaterals in CA1 region of hippocampal slices from coriaria lactone (CL)-kindled and control rats. The results were as follows: (1) neither spontaneous nor evoked epileptiform bursts were found in all hippocampal slices from CL-kindled and control rats; (2) the synaptic efficacy, expressed by the ratio of PS/EPSP slope, at low stimulation intensity ranging from 10-30% of its maximum was significantly increased on CL-kindled rats (P less than 0.05); and (3) although PPF was found in all slices, the PPF strength only at stimulation intensity of 10 and 20% of maximum was augmented remarkably in CL-kindled rats (P less than 0.002 and 0.024, respectively). According to the results from our previous work, we suggested that the increment of PS/EPSP slope ratio and PPF strength at low stimulation intensity may result from the potentiation of excitatory synaptic activity or/and the change of intrinsic excitability of pyramidal neurons.

Action Potentials↗
PubMed1992

Physical training: a tool for increasing work tolerance limits of employees engaged in manual handling tasks.

The lack of physical fitness is a contributing factor to the etiology of musculoskeletal disorders resulting from the manual handling of material in industry. Thus the major objectives of this paper were (1) to discuss the role of physical fitness in the control of occupational injuries; (2) to review techniques available in the exercise physiology literature for increasing human physical capacity in industry; and (3) to review and evaluate studies on the effects of physical training on individuals engaged in manual handling tasks.

Humans↗
PubMed1992

Effects of job-simulated flexibility and strength-flexibility training protocols on maintenance employees engaged in manual handling operations.

This study examined the effects of four flexibility and strength-flexibility training protocols on the dynamic strength, endurance time, and truncal flexibility of 24 maintenance employees engaged in manual material handling operations. The study was conducted over an 8-week period. Significant improvement in physical capacity was obtained through flexibility training either by a progressive increase in the holding time with fixed exercise repetition or a progressive increase repetition with fixed holding time. The flexibility and strength-flexibility training protocols exhibited similar effects on physical capacity. It was suggested that a follow-up flexibility protocol should be performed on a daily basis in order to maintain the gains obtained in flexibility during the intensive/short training programme.

Adult↗
PubMed1992

Purification and characterization of 1-aminocyclopropane-1-carboxylate N-malonyltransferase from etiolated mung bean hypocotyls.

1-Aminocyclopropane-1-carboxylate (ACC) N-malonyltransferase converts ACC, an immediate precursor of ethylene, to the presumably inactive product malonyl-ACC (MACC). This enzyme plays a role in ethylene production by reducing the level of free ACC in plant tissue. In this study, ACC N-malonyltransferase was purified 3660-fold from etiolated mung bean (Vigna radiata) hypocotyls, with a 6% overall recovery. The final specific activity was about 83,000 nmol of MACC formed mg(-1) protein h(-1). The five-step purification protocol consisted of polyethylene glycol fractionation, Cibacron blue 3GA-agarose chromatography using salt gradient elution, Sephadex G-100 gel filtration, MonoQ anion-exchange chromatography, and Cibacron blue 3GA-agarose chromatography using malonyl-CoA plus ACC for elution. The molecular mass of the native enzyme determined by Sephadex G-100 chromatography was 50 +/- 3 kD. Protein from the final purification step showed one major band at 55 kD after sodium dodecyl sulfate polyacrylamide gel electrophoresis, indicating that ACC N-malonyltransferase is a monomer. The mung bean ACC N-malonyltransferase has a pH optimum of 8.0, an apparent K(m) of 0.5 mm for ACC and 0.2 mm for malonyl-coenzyme A, and an Arrhenius activation energy of 70.29 kJ mol(-1) degree(-1).

Journal Article↗
PubMed1992

Mechanisms of adrenaline-induced antinociception in mice.

Infusion of adrenaline into the upper lumbar subarachnoid space in lightly anesthetized mice produced a significant elevation of the nociceptive threshold as quantitated by tail flick test. The antinociceptive effect of adrenaline was dose-dependent and antagonized equally by pretreatment with either alpha-1 selective antagonist prazosin or alpha-2 selective antagonist yohimbine at a dose of 0.05 microgram/5 microliter/mouse. This antinociceptive effect of adrenaline was also blocked by pretreatment with beta antagonist propranolol or opiate antagonist naloxone at higher doses, i.e., 0.5 microgram and 1.0 microgram/5 microliter/mouse, respectively. These results suggest that the antinociceptive mechanisms of adrenaline at the lumbar spinal level in the mouse seem to be mediated not only through alpha- and beta-adrenergic pathways but also through opiate system.

Analgesics↗
PubMed1992

[Observation of paired-pulse depression in CA1 region of hippocampal slices from coriaria lactone-kindled rats].

Paired-pulse depression (PPD) technique was used to investigate the potency of recurrent synaptic inhibition mediated by GABA in area CA1 of 54 hippocampal slices from coriaria lactone (CL)-kindled and control rats. When paired stimuli were sent to the axon of CA1 pyramidal cell and Schaffer collaterals, the effect of population spike PPD lasted about 40-60ms; no significant change was observed on PPD potency between kindled and control groups (P = 0.06, 2-way ANOVA). The results indicate that the GABA-ergic synaptic inhibition seemed not to play a key role in the maintenance of the chemical kindling induced by CL.

Animals↗
PubMed1992

Volatile N-nitrosamines in salted fish samples from high- and low-risk areas for NPC in China.

Four carcinogenic volatile nitrosamines (N-dimethylnitrosamine, NDMA; N-diethylnitrosamine, NDEA; N-nitrosopyrroline, NPYR; and N-nirosopiperilidine, NPIP) were screened in twenty specimens of salted fish collected from areas in China with different nasopharyngeal carcinoma (NPC) mortality rates. The highest NDMA, NDEA and total N-nitrosamine contents (322.92, 50.27 and 373.19 micrograms/kg, respectively) were found in the samples from Sihui, one of the areas with highest NPC mortality. The lowest contents (12.64, 7.65 and 20.29 micrograms/kg, respectively) were seen in the samples from Shanghai, the area with the lowest mortality from NPC in the study. These results confirm that there are appreciable levels of nitrosamines in the salted fishes consumed by residents in high-risk areas of NPC in China.

Animals↗
PubMed1991

Posttranslational modifications within the HIV-1 envelope glycoprotein which restrict virus assembly and CD4-dependent infection.

Alterations in two highly conserved N-linked glycosylation sites within the gp120 envelope glycoprotein of human immunodeficiency virus type I (HIV-1) implicated in the phenotype of a noncytopathic HIV-1 variant were introduced independently and in combination into a cytopathic, infectious HIV-1 clone by site-specific mutagenesis. Neither mutation affected the synthesis of HIV-1 envelope glycoproteins. However, one of the mutations restricted the ability of HIV-1 envelope to localize on the cell membrane and thus markedly impaired virus assembly. The HIV-1 assembly defect could be overcome in trans if site-specific mutants were packaged in HeLa cells constitutively producing wild-type HIV-1 envelope glycoprotein. In addition to inefficient virus assembly, this mutation impaired the ability of the virus to infect CD4+ T cells, but did not affect CD4-independent infection of muscle cells. These results suggest additional functions of posttranslational modification in virus replication (i.e., envelope glycoprotein transport). Given that such modifications can restrict CD4-mediated uptake without affecting CD4-independent uptake, variations in posttranslational env processing between different HIV-1 genotypes may affect virus tropism in vivo.

Amino Acid Sequence↗
PubMed1991

Further investigation on nuclear transplantation in different orders of teleost: the combination of the nucleus of Tilapia (Oreochromis nilotica) and the cytoplasm of Loach (Paramisgurnus dabryanus).

The nucleus of a blastula cell from Tilapia (Oreochromis nilotica, family Cichlidae, order Perciformes) was transplanted into an enucleated egg of Loach (Paramisgurnus dabryanus, family Cobitidae, order Cypriniformes). From among 3747 nucleo-cytoplasmic hybrid (NCH) eggs two NCH larval fish (0.05%) were obtained; one died on the 6th day and the other died on the 12th day after the operation. Morphological examinations showed that both NCH larval fish had developed normally with an opened mouth except they could not take food after complete utilization of their egg yolk on the 5th day of development. The possible mechanisms for obtaining such inter-order NCH larval fish are discussed. This is the first report indicating that inter-order NCH larval fish can be obtained in spite of their evolutionary divergence.

Animals↗
PubMed1990

[Coriaria lactone-induced epileptiform activity in the hippocampal slices of rat].

Coriaria lactone (CL) is an active constituent of a medicinal herb used as psychosolytic in traditional Chinese medicine. Recently it has been found that CL appears to act as a convulsant agent. Subsequently both acute and chronic epilepsy models caused by CL have been established successfully. In order to observe further the epileptogenic effects of CL in vitro, the hippocampal slice technique was used in experiments with 36 slices. The results are as follows: Addition of CL to the perfusion bathing the slices of rat hippocampus increased evoked-response in body layer of CA1 in a dose-dependent manner, and induced epileptiform burst. CL augmented population spike of CA1 pyramidal neurons triggered by either orthodromic stimulus (through synapses) or antidromic stimulus (direct effect on the axon of CA1 pyramidal cells) without alteration of presynaptic fiber volley and field-EPSP, and there was no significant change in latency of burst. Finally GABA had a weak effect on CL-induced epileptiform activity. These observations suggest that CL probably has a direct effect on the soma of pyramidal neurons, CL-induced epileptiform burst may be a result of altering the innate capacity of burst and increasing the intrinsic excitability of pyramidal cell membranes.

Animals↗
PubMed1979

Isolation and partial characterization of a guinea pig serum apolipoprotein comigrating with apo-E on sodium dodecyl sulfate-polyacrylamide electropherograms.

Study of guinea pig plasma lipoproteins has shown that they contain a polypeptide that comigrates with the arginine-rich polypeptide (apo-E) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This comigrating polypeptide differs from apo-E in its amino acid composition, immunological cross-reactivities, electrophoretic mobility in urea polyacrylamide gel, and elution volume from Sephadex gel columns. It is present in very low density lipoproteins and low density lipoproteins from both control and cholesterol-fed guinea pigs.

Amino Acids↗
PubMedDate not supplied

Expression of leukemia-inhibitory factor as an autocrinal growth factor in human medulloblastomas.

Medulloblastoma is the most frequent pediatric brain tumor, with the capacities of rapid proliferation and intracranial dissemination. However, the factor(s) regulating medulloblastoma growth has not yet been well characterized. Leukemia-inhibitory factor (LIF) and interleukin-6 (IL-6) play different roles in the formation/progression of various embryonic and pediatric tumors, but their biological effects on medulloblastoma cells are less well known. Therefore, in vivo and in vitro expression of LIF, IL-6 and their signal transducer genes encoding LIF receptor (LIFR), IL-6 receptor (IL-6R) and gp130 in human medulloblastoma cells were investigated by multiple cellular and molecular biology approaches. The results revealed that LIF expression could be found in 26 out of 28 tumors/cell line and over 90% of the samples expressed LIFR, IL-6R and gp130. In contrast, none of the samples showed IL-6 expression. An established medulloblastoma cell line, Med-3, was used to evaluate the potential effects of LIF and IL-6 on the proliferation of medulloblastoma cells. The growth of Med-3 cells was efficiently inhibited either by anti-LIF antibody or by antisense LIF oligonucleotide. Addition of exogenous human recombinant IL-6 could dramatically enhance Med-3 cell outgrowth. Our data thus for the first time demonstrated the important role of LIF as an autocrinal and IL-6 as a paracrinal growth factor in the proliferation of medulloblastoma cells.

Blotting, Southern↗