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Biomedical subjects

L Tian

Publications and source records attributed to L Tian.

At least 127 records · Page 7Linked to original sources
PubMed1995

Prejunctional actions of muscle relaxants: synaptic vesicles and transmitter mobilization as sites of action.

1. Nicotinic antagonists such as tubocurarine affect acetylcholine release from motor nerve terminals at the neuromuscular junction. 2. Electrophysiological studies comparing the prejunctional actions of tubocurarine to those of vesamicol and vecuronium have been used to provide an insight into the mechanisms involved in the prejunctional effects of tubocurarine-like compounds. 3. The observed prejunctional actions of tubocurarine can be accounted for by a model in which the compound has two separately identifiable effects on the nerve terminal. At low frequencies of nerve stimulation tubocurarine augments acetylcholine release while at high frequencies of nerve stimulation tubocurarine depresses acetylcholine release. 4. Both of the effects of tubocurarine on acetylcholine release are a consequence of a change in the number of quanta within the nerve terminal immediately available for release upon nerve stimulation. 5. On the basis of our experimental observations, we suggest that the two prejunctional effects of tubocurarine are mediated through two pharmacologically distinct prejunctional nAChRs.

Animals↗
PubMed1995

Effects of caloric restriction on age-related oxidative modifications of macromolecules and lymphocyte proliferation in rats.

Decreased immune function associated with aging has been demonstrated in both humans and animals. We hypothesize that reactive oxygen species (ROS)-mediated damage to biological macromolecules may contribute to compromised immune response during aging. In this study, we compared the levels of lipid peroxidation and oxidatively modified proteins in plasma and splenocytes, and the mitogen-induced T lymphocyte proliferation in ad lib-fed (AL) and caloric restricted (CR) Fischer 344 x BNF1 male rats at the ages of 5, 18, and 31 months. The results show that AL rats exhibit an age-related decrease in proliferative response of splenic lymphocytes to phytohemagglutinin (PHA) and concanavalin A (Con A). This functional decline in T-lymphocytes during aging is inversely correlated to the levels of both lipid peroxidation and protein carbonyl in the plasma and splenic lymphocytes. Caloric restriction, however, can partially reverse the age-dependent decrease in T lymphocyte proliferation and significantly reduce lipid peroxidation and protein carbonyl contents in plasma and splenocytes. The above observations support the hypothesis that the age-associated declines in immune function are related to the oxidative modification of biological macromolecules, which in turn may lead to enzyme inactivation, membrane disruption, and cell senescence. One of the mechanisms by which caloric restriction reverses declined immune function in aged rats is hypothesized to be through reduction in ROS production and thereby protection of cellular macromolecules against oxidative damage.

Aging↗
PubMed1995

The heterogeneity of vesicular acetylcholine storage in cholinergic nerve terminals.

The vesicular hypothesis of quantal acetylcholine release describes the process by which discrete packages (or quanta) of the transmitter are released from nerve terminals through the exocytosis of the content of synaptic vesicles. However, cholinergic synaptic vesicles can no longer be vaguely regarded as simple membrane bound 'sacks' of the transmitter. Modern molecular, biochemical, morphological and electrophysiological research has revealed them to be complex cellular structures with a heterogeneous mixture of functions. Thus, not all synaptic vesicle populations are formed under the same circumstances and there are variations in the releasability of synaptic vesicle populations. This review briefly outlines some of the experimental research that has lead to our current thinking on the heterogeneity of vesicular acetylcholine storage in cholinergic nerve terminals. In addition, a model for vesicular acetylcholine storage and release is presented that attempts to accommodate many of the modern ideas concerning cholinergic synaptic vesicle function and interaction.

Acetylcholine↗
PubMed1995

Establishment and characterization of three cell lines from Aedes triseriatus (Diptera: Culicidae).

Three cell lines (A.t. GRIP-1, 2, and 3) were established from Aedes triseriatus (Say) embryonated eggs or neonate larvae and their morphology, growth, karyotype, and isozyme pattern were studied. The isozyme alleles observed in the 3 cell lines also were found in adults of the original mosquito colony. Each cell line differed in enzymatic, morphological, and karyotypical patterns. La Crosse encephalitis (LAC) and snowshoe hare (SSH) viruses, members of the California encephalitis virus group, were able to replicate in these 3 cell lines. Furthermore, these cell lines, especially A.t. GRIP-1, were more sensitive than the Aedes aegypti (L.) (ATC 10) cell line for detection of small amounts of delta-endotoxin of Bacillus thuringiensis serovar. israelensis (de Barjac).

Aedes↗
PubMed1995

Neuromuscular blocking profile of the vecuronium analogue, Org-9487, in the rat isolated hemidiaphragm preparation.

1. The neuromuscular effects of the short-acting aminosteroid muscle relaxant Org-9487 have been studied in the in vitro rat phrenic nerve/hemidiaphragm preparation by use of twitch tension and electrophysiological recording techniques. 2. Org-9487 (5-100 microM) produced a concentration-dependent decrease in the amplitude of twitches (0.1 Hz) and tetanic contractions (50 Hz) evoked by motor nerve stimulation. The compound produced fade of force during both 50 Hz stimulation and train-of-four stimulation at 2 Hz, indicating a prejunctional component of action. 3. Anticholinesterases only partially reversed the effect of Org-9487 on twitch responses. This was possibly because, at the concentrations required to block twitches in the rat, Org-9487 itself was found to possess significant anticholinesterase activity. 4. Org-9487 (3 microM) increased the rundown of endplate current amplitudes during a 2 s train of 50 Hz nerve stimulation. This was because Org-9487 increased the quantal content of the first endplate current in the train without affecting acetylcholine release towards the latter part of the train. 5. Org-9487 (10 microM) produced a voltage-dependent decrease in the time constant of decay of endplate currents at 32 degrees C and 0.5 Hz, indicative of a block of endplate ion channels. The blocking rate constant increased with membrane hyperpolarization.

Acetylcholine↗
PubMed1995

Composite acupuncture treatment of mental retardation in children.

128 children of mental retardation were diagnosed in accordance with the diagnostic standards proposed by WHO in 1985. The patients were treated compositely with acupuncture, auriculo-acupoint pellet pressure and herbal plasters on acupoints, bringing about improved mental developments in intelligence quotient (IQ) and social adaptation behaviour (SAB), as evidenced by recognized intelligence tests for children.

Acupuncture Points↗
PubMed1994

Quinone-induced oxidative stress elevates glutathione and induces gamma-glutamylcysteine synthetase activity in rat lung epithelial L2 cells.

Glutathione (GSH) is one of the most important physiological antioxidants involved in detoxification of hydrogen peroxide and lipid hydroperoxide. Previous studies have shown that cells can maintain and even increase cellular GSH content in response to sublethal oxidative stress. We hypothesized that gamma-glutamylcysteine synthetase (gamma GCS), the rate-limiting enzyme in de novo GSH synthesis, could be induced by oxidative stress. Rat lung epithelial L2 cells were challenged with 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), generates O2.- and H2O2 continuously through redox cycling. Exposure of confluent L2 cells with sublethal doses of DMNQ caused sustained elevation of cellular GSH levels over a 24-h period (to 2.5-fold with 10 microM). DMNQ caused increases in gamma GCS activity (70% at 24 h with 10 microM), the gamma GCS catalytic heavy subunit (gamma GCS-HS) protein level, and gamma GCS-HS mRNA content (approximately 4-fold after 6 h with 10 microM). The elevation of gamma GCS-HS mRNA by DMNQ was eliminated by co-incubation with actinomycin D. Nuclear run-on experiments demonstrated that the transcriptional rate of the gamma GCS-HS gene was increased by 3- or 6-h exposure to 10 microM DMNQ. Our results suggested that the induction of de novo GSH synthesis by naphthoquinone-induced oxidative stress is associated with the transcriptional activation of the gamma GCS-HS gene and the subsequent elevation in gamma GCS activity. Unlike simpler quinones, DMNQ cannot form a GSH conjugate. Thus, the induction of gamma GCS-HS gene transcription does not require formation of an electrophile-glutathione conjugate.

Animals↗
PubMed1994

Rapamycin inhibits production of cytotoxic but not noncytotoxic antibodies and preferentially activates T helper 2 cells that mediate long-term survival of heart allografts in rats.

Rapamycin (RAPA) induces unresponsiveness toward heart allografts by at least two mechanisms: selective production of noncytotoxic IgG2c-blocking Ab and preferential activation of Th2 cells. RAPA (0.8 mg/kg/day) delivered via a 14-day osmotic pump to Wistar Furth (WF; RT-1u) recipients prolongs Buffalo (BUF; RT-1b) heart allograft survival from a mean survival time (MST) of 6.5 +/- 0.5 days to 75.0 +/- 18.9 days (n = 18; p < 0.001), with 6 of 18 grafts beating for more than 100 days. Recipient sera or their IgG but not IgM fraction, obtained after postgrafting day 40, passively transfer the unresponsive state to sublethally irradiated secondary recipients in a dose-dependent and immunologically-specific fashion. Sera obtained after untreated WF hosts rejected BUF hearts contained IgG moieties of all subclasses that bound to class I MHC BUF epitopes. In contrast, the unresponsive sera contained predominantly non-C'-fixing IgG2c and only marginal amounts of activated (C') fixing IgG1, IgG2a, and IgG2b Ab. The transcription of IL-2, IL-4, and IL-10 mRNAs was assessed using a PCR method. There were similar increases in the levels of IL-2, IL-4, and IL-10 mRNA in heart allografts from both untreated and RAPA-treated recipients on day 5 postgrafting. In contrast, on days 60 and 300 postgrafting heart allografts from RAPA-treated unresponsive recipients showed increased levels of IL-10 and IL-4 but not of IL-2 mRNA, suggesting preferential activation of Th2 cells. Thus, RAPA treatment selectively inhibits the synthesis of C'-binding of IgG subclasses, spares the non C-binding blocking IgG2c Ab, and preferentially activates Th2 cells.

Animals↗
PubMed1994

Nicotinic antagonist-produced frequency-dependent changes in acetylcholine release from rat motor nerve terminals.

1. The frequency (0.5-150 Hz) and calcium dependence (0.5-2.0 mM) of the effects of the nicotinic antagonist tubocurarine (0.2 microM) on acetylcholine (ACh) liberation from motor nerve terminals has been examined using binomial analysis of quantal transmitter release. 2. At an extracellular calcium ion concentration ([Ca2+]o) of 2.0 mM, tubocurarine produced a decrease in the endplate current (EPC) quantal content of approximately 30% at high frequencies of motor nerve stimulation (50-150 Hz). In contrast, at low frequencies of stimulation (0.5-1.0 Hz), tubocurarine enhanced the EPC quantal content by approximately 20%. 3. The enhancement of EPC quantal content produced by tubocurarine at low frequencies of motor nerve stimulation was [Ca2+]o dependent, being abolished when [Ca2+]o was lowered from 2.0 to 0.5 mM. In contrast, the decrease in quantal content produced by tubocurarine at high frequencies of motor nerve stimulation was independent of [Ca2+]o, being approximately 30% at all calcium ion concentrations studied. 4. In direct contrast to tubocurarine, the nicotinic antagonist vecuronium (1.0 microM) produced no increase in EPC quantal content at low frequencies of nerve stimulation. However, at high frequencies of nerve stimulation it decreased EPC quantal content to a similar extent to 0.2 microM tubocurarine. The frequency-dependent decrease in EPC quantal content produced by 1.0 microM vecuronium in 2.0 mM [Ca2+]o was very similar to that seen with 0.2 microM tubocurarine in 0.5 mM [Ca2+]o. 5. Binomial analysis revealed that all the changes in EPC quantal content associated with both nicotinic antagonists were due to changes in the size of the pool of quanta in the nerve terminal available for immediate release with no effect on the probability of release of an individual quantum. 6. The results are interpreted in terms of two separately identifiable prejunctional actions of the nicotinic antagonists, both involving an action at nicotinic ACh receptors situated on the motor nerve terminal. Thus, at high frequencies of motor nerve stimulation tubocurarine and vecuronium produce a [Ca2+]o-independent decrease in ACh release, probably through an inhibitory action on a positive-feedback prejunctional nicotinic autoreceptor closely related to the muscle-type nicotinic ACh autoreceptor. However, at low frequencies of motor nerve stimulation we suggest that tubocurarine, but not vecuronium, produces a [Ca2+]o-dependent increase in ACh release through an action at a negative-feedback prejunctional neuronal-type nicotinic ACh autoreceptor.

Acetylcholine↗
PubMed1994

Interferon gamma induces intercellular adhesion molecule-1 on murine midterm trophoblast and enhances susceptibility to specific lysis by paternally directed allo-immune cytotoxic T cells.

Expression and function of intercellular adhesion molecule-1 (ICAM-1) on murine trophoblast cells and its regulation by interferon gamma (IFN-gamma) were investigated. Flow cytometry was used to detect ICAM-1 and class I major histocompatibility complex (MHC) antigen expression, while a 51Cr release assay was used to investigate the role of ICAM-1 in cytotoxic T lymphocyte (CTL)-mediated lysis and the effect of anti-ICAM-1 antibody blockade on lysis. We found that murine trophoblasts cells from midterm pregnancy (Day 14 postcoitum) express low or undetectable ICAM-1 and MHC antigens but that these are readily inducible by IFN-gamma. Untreated cells resisted lysis by allospecific CTL however, after treatment with IFN-gamma for 72 h, these trophoblasts were readily susceptible to lysis by allospecific CTL. The lysis was significantly reduced by anti-ICAM-1 antibody blocking. This finding which indicates that ICAM-1 can take part in CTL-mediated lysis of midterm trophoblast, has potentially important implications in vivo for the immunological relationship between mother and fetus.

Adjuvants, Immunologic↗
PubMed1993

West Nile virus infection induces susceptibility of in vitro outgrown murine blastocysts to specific lysis by paternally directed allo-immune and virus-immune cytotoxic T cells.

Day 3 post-coitum BALB/c and (BALB/c x CBA/H)F1 blastocysts were isolated and hatched in replicate wells. Some were treated with interferon-gamma (IFN-gamma). Whilst others were infected with West Nile Virus (WNV) at 100 plaque-forming units per cell, for 18 h. Controls were mock-treated. Gamma-irradiated (2000 rads) CBA/H, (paternal) WNV-specific and allo(CBA/H)-specific cytotoxic T (Tc) cells were then added to replicates of infected, mock-infected or IFN-gamma-treated cultures for 20 h. [3H]Thymidine was then added for a further 8 h. [3H]Thymidine incorporation was inhibited by 40-50% in WNV-infected cultures exposed to WNV-paternal-specific Tc cells and by 30-40% in WNV-infected cultures exposed to allo-paternal-specific Tc cells compared to similarly exposed, uninfected, or unexposed, WNV-infected, or unexposed, uninfected cultures. No significant differences in [3H]thymidine incorporation were found between these controls and IFN-gamma-treated cultures exposed to allo-paternal-specific Tc cells or IFN-gamma-treated cultures not exposed to Tc cells. Parallel exposure of L929 fibroblasts to the same Tc cells irradiated with 500-8000 rads in doubling doses, showed that irradiation did not alter the efficacy or specificity of the Tc cells. Relevance to maternal anti-viral immune responses during implantation is discussed.

Animals↗
PubMed1993

[Quantitative study of diabetic retinopathy by computerized image analysis].

Composite fluorescein angiographic pictures of 66 eyes with diabetic retinopathy and nonperfusion areas were studied by computerized image analysis, and the ratio of the nonperfusion area to the disc area was calculated. There were 49 eyes with neovascularization (NV), in which the mean ratio +/- standard error was 46.33 +/- 7.01 (8.15 to 298.26), and the corresponding value in the other 17 eyes without NV was 6.90 +/- 1.31 (2.20 to 21.37), the difference being very significant. When the ratios were under 10, from 10 to 30, or over 30, the percentages of eyes manifesting NV were 13.3%, 81.8% and 100% respectively. In the 49 eyes with NV, the majority of the total 267 neovascular clusters were distributed 4-6 DD away from the optic disc, which itself was involved only in 18 eyes.

Adult↗