Search PubMed⌕ Search

Biomedical subjects

J Dai

Publications and source records attributed to J Dai.

At least 127 records · Page 7Linked to original sources
PubMed1999

[Study on laser flash spectroscopy of laser-induced interaction of DNA and polynucleotides with SO4*-].

The interactions of DNA and polynucleotides (poly[G],poly[A] and poly[C]) with SO4*- were investigated by 248 nm laser flash photolysis. The results show that, the reactions of poly[G] or poly[A] with SO4*- yield predominantly the corresponding one-electron-oxidated base radicals. With poly[C], it is suggested that SO4*- radical reacts predominantly by addition to the base moiety to produce C5-yl and C6-yl sulphate radical adducts,and subsequently H-abstraction yields C2'-sugar radical. The predominant species resulting from the reaction of DNA with SO4*- is DNA guanyl radical.

DNA↗
PubMed1999

[The study of castor oil sulphate synthesis process by infrared spectroscopy].

The castor oil sulphate synthesis process was studied by infrared spectroscopy. Based on the determination of iodone value the reaction mechanism was discussed. Both the duplicated bond and the hydroxide ion in castor oil took part in sulphate reaction and a hydrolysis also took place in the castor acid.

Castor Oil↗
PubMed1998

Postmortem anterograde tracing of intrahypothalamic projections of the human dorsomedial nucleus of the hypothalamus.

Together with the paraventricular nucleus (PVN), the dorsomedial nucleus of the hypothalamus (DMH) acts as one of the hypothalamic centers that integrate autonomic and central information. The DMH in the rat brain has extensive intrahypothalamic connections and is implicated in a wide variety of functions. Up until now, no knowledge has been available to indicate that the human DMH might have functions similar to those of the rat DMH. In the present study, intrahypothalamic efferent projections of the human DMH were revealed by a recently developed in vitro postmortem tracing method. It was found that the most densely innervated areas are the PVN, the ventromedial nucleus of the hypothalamus, and the area below the PVN. Other significant terminal fields include the periventricular nucleus, the lateral hypothalamic area, and the medial part of the anteroventral hypothalamic area. Scarce fibers project to the suprachiasmatic nucleus, infundibular nucleus, posterior hypothalamic nucleus, and posterior part of the bed nucleus of the stria terminals. The projections of the ventral and dorsal part of the DMH show some differences. The dorsal part of the DMH has denser projections to the dorsal part of the PVN than to the ventral part of the PVN. In contrast, the ventral part of the DMH has denser projections to the ventral part of the PVN. Labeled fibers in the PVN from ventral and dorsal DMH appear to run near many vasopressin and oxytocin neurons of different sizes, and also near some corticotropin- releasing hormone neurons, suggesting that the DMH neurons may directly affect the functioning of these PVN neurons. In many aspects, the observed projections of the human DMH resemble those of the rat, indicating that the organization of DMH intrahypothalamic projections of human is similar to that of rat. The functional significance of DMH intrahypothalamic connections is discussed.

Brain Mapping↗
PubMed1998

Postmortem tracing reveals the organization of hypothalamic projections of the suprachiasmatic nucleus in the human brain.

The suprachiasmatic nucleus (SCN) is a small structure considered to be the site of the major circadian pacemaker of the mammalian brain. Disturbances in human biological clock function may occur in several diseases, such as Alzheimer's disease, sleep problems, and seasonal depression. Since basic knowledge of the anatomical connections of the human SCN is limited due to the lack of suitable neuroanatomical tracing methods, the understanding of physiological mechanisms of human SCN function has obviously been hampered. In the present study, the hypothalamic connections of the human SCN were revealed for the first time with a newly developed in vitro postmortem anterograde tracing method. The human SCN was found to be connected with nuclei in the hypothalamus that are involved in hormone secretion, cardiovascular regulation, and behavior activity. These human SCN projections appear to follow the same general patterns as those in the rodent brain. This homology may indicate an evolutionary conservation of the SCN projections from rodent to human. Through these connections, the human SCN may transmit its circadian information to regulate hormone secretion, body temperature, and behavioral functions as it does in animal species. In addition, the postmortem tracing technique may be a valuable tool that will contribute to our understanding of anatomical connections in the human brain, and may have other applications in the research on the physiology and pathology of the human brain.

Animals↗
PubMed1998

Membrane tension in swelling and shrinking molluscan neurons.

When neurons undergo dramatic shape and volume changes, how is surface area adjusted appropriately? The membrane tension hypothesis-namely that high tensions favor recruitment of membrane to the surface whereas low tensions favor retrieval-provides a simple conceptual framework for surface area homeostasis. With membrane tension and area in a feedback loop, tension extremes may be averted even during excessive mechanical load variations. We tested this by measuring apparent membrane tension of swelling and shrinking Lymnaea neurons. With hypotonic medium (50%), tension that was calculated from membrane tether forces increased from 0.04 to as much as 0.4 mN/m, although at steady state, swollen-cell tension (0. 12 mN/m) exceeded controls only threefold. On reshrinking in isotonic medium, tension reduced to 0.02 mN/m, and at the substratum, membrane invaginated, creating transient vacuole-like dilations. Swelling increased membrane tension with or without BAPTA chelating cytoplasmic Ca2+, but with BAPTA, unmeasurably large (although not lytic) tension surges occurred in approximately two-thirds of neurons. Furthermore, in unarborized neurons voltage-clamped by perforated-patch in 50% medium, membrane capacitance increased 8%, which is indicative of increasing membrane area. The relatively damped swelling-tension responses of Lymnaea neurons (no BAPTA) were consistent with feedback regulation. BAPTA did not alter resting membrane tension, but the large surges during swelling of BAPTA-loaded neurons demonstrated that 50% medium was inherently treacherous and that tension regulation was impaired by subnormal cytoplasmic [Ca2+]. However, neurons did survive tension surges in the absence of Ca2+ signaling. The mechanism to avoid high-tension rupture may be the direct tension-driven recruitment of membrane stores.

Animals↗
PubMed1998

Human retinohypothalamic tract as revealed by in vitro postmortem tracing.

Animal experimental studies have shown that the retinohypothalamic tract (RHT) is an anatomical and functionally distinct retinofugal pathway mediating photic entrainment of circadian rhythms. In the present study, RHT projections were studied in the human brain by our recently developed postmortem tracing technique with neurobiotin as a tracer. Similar patterns of labeling were observed in brains of one control subject without neurological or mental disorders and five patients with Alzheimer's disease. The topography of RHT projections has several characteristics. (1) RHT fibers leave the optic chiasm and enter the hypothalamus medially and laterally at the anterior level of the suprachiasmatic nucleus (SCN). (2) The medial fibers enter the ventral part of the SCN and innervate the ventral SCN over its entire length, but the density decreases gradually from anterior to posterior. Labeled RHT fibers in the SCN make contact mainly with immunocytochemically positive neurotensin or vasoactive intestinal polypeptide neurons and only occasionally with vasopressin-positive neurons located in the ventral part of the SCN. (3) Only few projections to the dorsal part of the SCN and the anteroventral part of the hypothalamus were found. (4) Lateral projections reach the ventral part of the ventromedial SON and the area lateral to the SCN. No projections were observed to other hypothalamic areas. The presence of an RHT in humans suggests that the RHT may serve a function in humans similar to that demonstrated in animals.

Aged↗
PubMed1998

Effect of antipsychotic drugs on extracellular serotonin levels in rat medial prefrontal cortex and nucleus accumbens.

Amperozide, clozapine, olanzapine and risperidone are more potent serotonin (5-hydroxytryptamine, 5-HT)2A receptor antagonists than dopamine D2-like receptor antagonists. Haloperidol and S(-)-sulpiride are potent or selective dopamine D2-like receptor antagonists and lack 5-HT2A receptor antagonist properties. We studied the effect of these five proven antipsychotic drugs and one putative (amperozide) antipsychotic drug on extracellular 5-HT levels in the medial prefrontal cortex and the nucleus accumbens of awake, freely-moving rats, using in vivo microdialysis with dual probe implantation. Risperidone (1 mg/kg) and clozapine (20 mg/kg) significantly increased extracellular 5-HT levels in the medial prefrontal cortex and the nucleus accumbens, respectively. Amperozide (2 and 10 mg/kg) significantly increased extracellular 5-HT levels in both regions. Olanzapine (1 and 10 mg/kg), S(-)-sulpiride (10 and 25 mg/kg), haloperidol (0.1 and 1 mg/kg) and the selective 5-HT2A receptor antagonist MDL-100,907 (1 mg/kg) had no significant effect on extracellular 5-HT levels in either region. Thus, the ability to increase extracellular 5-HT levels in the medial prefrontal cortex and the nucleus accumbens by these antipsychotic drugs is not directly related to their affinity for 5-HT2A receptors since olanzapine and MDL-100,907 had no significant effect on extracellular 5-HT levels. A variety of mechanisms other than those involving 5-HT2A receptors, e.g., reuptake inhibition (amperozide) and blockade of alpha2-adrenoceptors (clozapine), may contribute to the ability to increase extracellular 5-HT levels in the brain. The increase in extracellular 5-HT levels in the medial prefrontal cortex or nucleus accumbens following amperozide, clozapine, or risperidone administration may not be related to the effect on psychotic symptoms but could be related to effects on other types of psychopathology such as depression, negative symptoms, or cognition.

Animals↗
PubMed1998

Effect of the RF cavity temperature on low-energy injection at HLS.

The resonant frequency shift caused by the temperature of the RF cavity at the Hefei Light Source has been measured and the results analysed. The effect of this frequency shift on low-energy injection with a low cavity voltage is discussed, and a new injection mode is proposed.

Journal Article↗
PubMed1998

A role for Dictyostelium racE in cortical tension and cleavage furrow progression.

The small GTPase racE is essential for cytokinesis in Dictyostelium. We found that this requirement is restricted to cells grown in suspension. When attached to a substrate, racE null cells form an actomyosin contractile ring and complete cytokinesis normally. Nonetheless, racE null cells fail completely in cytokinesis when in suspension. To understand this conditional requirement for racE, we developed a method to observe cytokinesis in suspension. Using this approach, we found that racE null cells attempt cytokinesis in suspension by forming a contractile ring and cleavage furrow. However, the cells form multiple blebs and fail in cytokinesis by regression of the cleavage furrow. We believe this phenotype is caused by the extremely low level of cortical tension found in racE null cells compared to wild-type cells. The reduced cortical tension of racE null cells is not caused by a decrease in their content of F-actin. Instead, mitotic racE null cells contain abnormal F-actin aggregates. These results suggest that racE is essential for the organization of the cortical cytoskeleton to maintain proper cortical integrity. This function of racE is independent of attachment to a substrate, but can be bypassed by other signaling pathways induced by adhesion to a substrate.

Actins↗
PubMed1998

Expression of the mouse metallothionein-I gene conferring cadmium resistance in a transgenic cyanobacterium.

This paper reports the construction of a transgenic strain of cyanobacterium aimed at removing heavy metal pollution in waters. The mouse metallothionein-I (mMT-I) gene was inserted in the vector pRL-439 downstream of the strong psbA promoter. The resulting plasmid pRL-MT was ligated at the EcoRI site of the shuttle vector pKT-210 to generate the shuttle expression vector pKT-MT. This recombinant plasmid was introduced into Anabaena sp. PCC 7120 by triparental conjugative transfer. After selection on streptomycin, a stable transgenic Anabaena strain was obtained. The presence of the mMT-I gene was confirmed by DNA/DNA hybridization and its expression was demonstrated by immunodetection with specific antibodies. A metal tolerance experiment showed that this transgenic Anabaena strain had acquired higher metal resistance.

Anabaena↗
PubMed1998

Phospholipase A2-mediated activation of phospholipase D in rat heart sarcolemma.

The effect of phospholipase A2 (PLA2)-dependent release of unsaturated fatty acids (FA) on phospholipase D (PLD) function was examined in purified sarcolemmal (SL) membranes isolated from rat heart. PLD hydrolytic activity was determined by measuring either [14C] phosphatidic acid formation from exogenous [14C] phosphatidylcholine (PtdCho) or [3H] choline release from prelabelled SL Ptd[3H]choline. SL membranes with endogenous [3H] PtdCho that were prelabelled with [3H] myristic acid were used for testing PLD transphosphatidylation activity. Exogenous cis-unsaturated FA, arachidonate and oleate, significantly enhanced the [3H] choline formation at 50 and 100 microM, respectively; their effect was maximal at 250 microM and declined at higher concentrations. Use of melittin (which stimulates membrane-bound PLA2, thus releasing FA) or exogenous PLA2 reproduced the stimulatory effect of added arachidonate and oleate. Under melittin, PLA2-dependent FA release was strongly correlated (r = 0.99) to the PLD-dependent phosphatidic acid formation. Arachidonate- or melittin-enhanced PLD transphosphatidylation activity confirmed the augmented catalytic rate of PLD by these agents. Melittin-evoked PLD activation was completely blocked by 1 microM E-6-(bromomethylene) tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one, a selective inhibitor of Ca(2+)-independent v Ca(2-)-dependent PLA2, thus indicating that PLD stimulation under melittin occurred via PLA2. Activity measurement and Western blotting studies revealed the presence of a Ca(2+)-independent, high molecular weight (110 kDa) PLA2 in the SL membrane, and its immunoprecipitation by monoclonal antibodies significantly reduced the melittin-related PLD stimulation. These results suggest that Ca(2+)-independent PLA2 and subsequent endogenous mobilization of sn-2 unsaturated FA modulate PLD activity in heart SL membranes. This event may occur in physiological conditions via hormonal stimulation of membranal PLA2 as well as in heart diseases characterized by PLA2 pathological dysfunction.

Animals↗
PubMed1998

Determination and estimation of water solubilities and octanol/water partition coefficients for derivates of benzanilides.

A shake-flask method was used to determine the water solubilities (Sw) and the octanol/water partition coefficients(Kow) of 14 derivates of benzanilides. The results showed that the octanol/water partition coefficients were correlated (r=-0.93) with Sw. The linear solvation energy relationship(LSER) and molecular connectivity methods have been used to establish correlation equation successfully. The LSER method was used to predict these partitioning properties more accurately. The estimated values were well fitted with observed ones.

Benzamides↗
PubMed1998

Garlic prevents hypoxic pulmonary hypertension in rats.

Hypoxic pulmonary vasoconstriction underlies the development of high-altitude pulmonary edema. Anecdotal observations suggest a beneficial effect of garlic in preventing high-altitude symptoms. To determine whether garlic influences pulmonary vasoconstriction, we assessed the effect of garlic on pulmonary pressures in rats subjected to alveolar hypoxia and on vasoconstriction in isolated pulmonary arterial rings. Garlic gavage (100 mg/kg body wt) for 5 days resulted in complete inhibition of acute hypoxic pulmonary vasoconstriction compared with the control group. No difference in mean arterial pressure or heart rate response to hypoxia was seen between the groups. Garlic solution resulted in a significant dose-dependent vasorelaxation in both endothelium-intact and mechanically endothelium-disrupted pulmonary arterial rings. The administration of NG-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor) inhibited the vasodilatory effect of garlic by 80%. These studies document that garlic blocks hypoxic pulmonary hypertension in vivo and demonstrate a combination of endothelium-dependent and -independent mechanisms for the effect in pulmonary arterial rings.

Acetylcholine↗
PubMed1998

Effect of desialylation on binding, affinity, and specificity of 56 monoclonal antibodies against MUC1 mucin.

We evaluated 56 monoclonal antibodies (MAbs), submitted to the ISOBM TD-4 Workshop, for changes in binding following desialylation of the MUC1 molecule and for epitope specificity. Antibody binding of MAbs was assayed by an ELISA method using microtiter plates coated with the MUC1 mucin obtained from supernatants of the ZR75-1 cell line. The MUC1 mucin was desialylated directly on the plate by treatment with neuraminidase. For each MAb, binding to untreated mucin was compared over a range of antibody concentrations. The concentration at which binding was half-maximal (K50) was determined for all antibodies whose binding reached saturation in the assay. Results showed that K50 values for MAb binding to untreated MUC1 mucin varied from 10(-10) to 10(-6) M. These data suggest that MAbs to MUC1 mucin bind with a broad range of intrinsic affinities. Desialylation was found to have variable effects on antibody binding, in that binding was either increased, decreased, or unchanged. No relationship was found between the apparent affinities for untreated mucin and changes in binding following desialylation. Among the 56 Workshop MAbs, 33 were found reactive with synthetic peptides which mimic the MUC1 tandem repeat. We determined the epitope specificity of the 33 MAbs by competitive binding using 10 amino acid peptides corresponding to various regions of the 20-amino acid tandem repeat domain of MUC1. All antibodies which recognized epitopes in the 1-10 amino acid region of the tandem repeat showed increased binding to desialylated mucin. Antibodies to other peptide epitopes showed no consistent pattern of change in binding following desialylation. Our results suggest that sialic acid residues on the MUC1 mucin may contribute either positively or negatively to antibody binding. In addition, our results suggest that improved antibody selection methods could provide MAbs with improved selectivity for cancer-derived mucin compared with mucin from normal tissues. This could form the basis of improved biomarker assays for breast cancer.

Amino Acid Sequence↗
PubMed1998

Mineral dusts directly induce epithelial and interstitial fibrogenic mediators and matrix components in the airway wall.

Exposure to mineral dusts is associated with the development of chronic airflow obstruction, probably mediated in part by dust-induced fibrosis of the small airways. To investigate the mechanism of fibrosis, we exposed rat tracheal explants to amosite asbestos, iron oxide, or titanium dioxide. Explants were then maintained in air organ culture, and the expression of genes encoding for various mediators and matrix components assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). At 7 d, all dusts produced significant increases in platelet-derived growth factor-A (PDGF-A) and transforming growth factor-beta1 (TGF-beta1) gene expression compared with control; asbestos and titanium dioxide produced increases in PDGF-B, and titanium dioxide increased TGF-alpha expression. Only asbestos caused increases in procollagen expression. No dust increased expression of tumor necrosis factor-alpha (TNF-alpha), fibronectin, or tropoelastin. Elevations in these factors coincided temporally with transport of particles into the epithelium and then to the subepithelial space. By in situ hybridization, TGF-beta gene expression was found in both the epithelium and subepithelial (interstitial) space, and PDGF-B and procollagen gene expression in the subepithelial space. Chemical analysis showed a small increase in hydroxyproline, a measure of collagen content, in asbestos-treated explants. We conclude that mineral dusts can induce airway wall fibrosis by directly upregulating proliferative and fibrogenic mediators as well as matrix components in the airway epithelium and interstitium, and that neither airspace nor circulating inflammatory cells are required for these effects. Different mineral dusts produce different patterns of reaction.

Airway Obstruction↗
PubMed1998

[Clinical observation on benign osteolytic bone defects treated with natural non-organic bone].

It is extremely necessary to find an ideal filling material for the treatment of benign bone defect, particularly those benign osteolytic defect in children with a comparatively large cavity. From July, 1995 to December, 1996, 10 cases of benign osteolytic bone defects were treated, in which 5 cases of benign osteolytic defects, 3 cases of bone cysts, 1 case of fibrous dysplasia of bone and 1 case of non-ossifying fibroma. After through curettage of the cavity, the natural non-organic bone in cube-shaped was used to fill the prepared cavity. The results showed that the activities of the patients resumed normal in 3 to 6 months after operation. The roentgenographic examination after operation showed that the lucent spaces between NNB cubes disappeared with obvious new bone formation and the bony cavity was obliterated with newly-formed bone. There was no recurrence of the lesion during a follow-up of 7 to 24 months. It was concluded that to treat the osteolytic defect of bone with NNB was a method of choice. The new bone formation appeared early in large amount and increased rapidly.

Adolescent↗