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Biomedical subjects

Xi Zhang

Publications and source records attributed to Xi Zhang.

At least 73 records · Page 4Linked to original sources

The sequential processing of visual feature conjunction mismatches in the human brain.

To clarify the brain mechanism for multifeature stimulus comparison, subjects matched the features of two serial visual stimuli in pairs. Stimulus pairs were of four categories: C-S-, color same, shape same (match); C-S+, color same, shape different (shape mismatch); C+S-, color different, shape same (color mismatch); C+S+, color different, shape different (conjunction mismatches). Subjects matched the stimuli in three different sessions according to different attention tasks: attending to color (Ac), attending to shape (As), or attending to both color and shape (Acs). A negative one-peak brain potential, N270, was elicited in all the mismatch conditions with amplitude enhanced in the task-relevant mismatch. Negative potential with two peaks, N270 and N400, appeared when attending to the conjunction mismatches concurrently. The two serial negativities in response to attended feature conjunctions might reflect the temporal different stages for processing conjunction mismatches or conflicts.

Adult↗

Safety and efficacy of dispase and plasmin in pharmacologic vitreolysis.

PURPOSE: To evaluate the safety and efficacy of dispase and plasmin when inducing posterior vitreous detachment (PVD) by intravitreous injection in rabbit eyes. METHODS: Forty-eight young pigmented rabbits were randomized into six groups. Groups 1 and 5 received 0.025 U dispase in test eyes; group 2, 0.1 U dispase; groups 3 and 6, 1 U plasmin; and group 4, 4 U plasmin. All groups received PBS in control eyes. Groups 5 and 6 were euthanatized 15 minutes after surgery for ocular histologic examination. The remaining groups (groups 1-4) received indirect ophthalmoscope and biomicroscopy 15 and 30 minutes; 1, 2, and 8 hours; and 1, 3, and 7 days after surgery. Ultrasonography and electroretinogram were performed 1 hour and 1 and 7 days after surgery. The eyes then were examined by scanning and transmission electron microscopy. RESULTS: Partial or complete PVDs were observed in the eyes that received dispase and plasmin, confirmed by the results of scanning electron microscopy. Light microscopy showed inflammation in both dispase- and plasmin-treated eyes of groups 5 and 6. However, whereas in plasmin-treated eyes the ERG and cell ultrastructure showed no significant changes, in dispase-treated eyes, the amplitudes of ERG showed a significant reduction from baseline and ultrastructural damage to the retina was detected by transmission electron microscopy. Cell damage, preretinal hemorrhage, and cataract were also observed in these eyes. No changes were observed in the control eyes. CONCLUSIONS: Intravitreal injection of dispase at 0.025 U or more can induce PVD, but it is not safe. Plasmin (1-4 U) is safer, except for the potential risk of inducing intraocular inflammation.

Animals↗

[Effects of leukemia bone marrow stromal cells on resistance of co-cultured HL-60 to idarubicin].

To study the role of hematopoietic microenvironment abnormality in development of minimal residual disease and its mechanism, the viability of HL-60 cells was investigated by means of bone marrow stromal cell culture system or co-culture system of bone marrow stromal cell with HL-60 cells and idarubicin (IDA), flow cytometry and ELISA. The results showed that viability of HL-60 cells gradually decreased along with the increase of IDA dose and prolongation of culture time. Amount of HL-60 cells co-cultured with leukemia bone marrow stramal cells was significantly increased as compared with that of the control (P < 0.05). Bone marrow stromal cells or stromal cell conditioned medium reduced the effect of IDA on HL-60 cells in culture. In conclusion, leukemia bone marrow stromal cells contribute to increasing resistance of HL-60 cells to chemotherapeutic agents, and play some role in developing minimal residual disease.

Bone Marrow Cells↗

Self-assembled monolayers of novel surface-bound dendrons: peripheral structure determines surface organization.

The synthetic and functional versatility of dendrimers and their well-defined shapes make them attractive molecules for surface modification. We synthesized six structurally very similar surface-bound dendrons and used them as building blocks for the preparation of self-assembled monolayers (SAMs) on a gold surface. We studied the effects of the surface-bound dendron's main structure, peripheral substituents, and the coadsorption process on its self-assembling behavior. Using scanning tunneling microscopy (STM), we observed nanostripes for SAMs of the surface-bound dendron consisting of symmetrical benzene rings. When we changed the symmetrical dendron's structure slightly, by increasing or decreasing the numbers of benzene rings at one wedge, we found no ordered structures were formed by the asymmetrical dendrons. We also introduced two kinds of substituents, heptane chains and oligo(ethylene oxide) chains, to the symmetrical dendron's periphery. Heptane chains appear to enhance the interaction between symmetrical backbones, leading to the formation of stripes, while oligo(ethylene oxide) chains appear to weaken the interaction between symmetrical backbones, resulting in a homogeneous structure. Dendrons with both heptane and oligo(ethylene oxide) chains exhibit nanophase separation in a confined state, leading to the formation of a honeycomb structure. Electrochemical studies provide additional evidence for understanding the resulting surface organizations: surface-bound dendrons with symmetrical structures form denser monolayers than their asymmetrical analogues; SAMs comprising peripherally substituted dendrons exhibit blocking effects proportionate to their hydrophilic fraction.

Journal Article↗

Stabilizing bolaform amphiphile interfacial assemblies by introducing mesogenic groups.

We describe the synthesis and characterization of the mesogen-bearing bolaform amphiphile 4,4'-dihydroxybiphenylbis(11-pyridinium-N-yl-undecanoic ester) dibromide (BP-10) and its solid/liquid interfacial self-assembly. Cylindrical micelles are directly observed by atomic force microscopy (AFM) at the interface between mica and the aqueous solution above the critical micelle concentration (cmc). In situ and ex situ AFM studies indicate that the cylindrical micelles are stable both at the mica/solution interface and in the dry state. The enhanced stability of the micellar structures enables a detailed investigation of their self-assembly behavior and supramolecular structures at the interface. The adsorption model proposed here is supported by the variation of the interfacial self-assemblies on changing the solution concentration and substrate temperature.

Journal Article↗

Neuromuscular block with vecuronium reduces the rapidly extracted auditory evoked potentials index during steady state anesthesia.

PURPOSE: During clinical monitoring, vecuronium appeared to reduce the rapidly extracted auditory evoked potentials index (A-line ARX index or AAI) to some extent. A prospective and randomized study was designed to analyze this phenomenon. METHODS: Forty adult patients undergoing elective surgery were studied. After tracheal intubation, anesthesia was maintained with an end-tidal isoflurane concentration (F(ET)ISO) of 1.0% for 20 min, then a 10-mL dose of either vecuronium 0.05 mg*kg(-1), 0.1 mg*kg(-1), 0.2 mg*kg(-1) or saline was administered in a randomized, double-blind design. The AAI and bispectral index (BI(hx)) were monitored throughout the study and analyzed off-line. RESULTS: BI(hx) was unaltered after the administration of saline or vecuronium. The mean of the averaged (per patient) AAI values recorded from two minutes to ten minutes after the administration of saline or vecuronium 0.05 mg*kg(-1) did not differ significantly from the corresponding mean recorded from 15 min to 20 min after F(ET)ISO maintained 1.0% (P = 0.678, 0.169), however after the administration of vecuronium 0.1 mg*kg(-1) or 0.2 mg*kg(-1), AAI was reduced from 18.3, 18.0 to 14.8, 13.4 (P = 0.016, 0.017). CONCLUSIONS: Neuromuscular block with vecuronium reduces AAI in patients during steady state anesthesia without surgical stimuli, while BI(hx) is unaltered. The cut-off values of AAI for events should be determined according to the level of neuromuscular blockade when monitoring the depth of anesthesia/sedation.

Adult↗

Event-related potential N270, a negative component to identification of conflicting information following memory retrieval.

OBJECTIVE: N270, an endogenous ERP component of conflict effect, was evoked in previous studies with S1-S2 paradigm. The present experiment is designed to confirm the speculation that this conflict-related negativity could also be elicited by stimulus probes having conflict with a memorized item in a visual post-retrieval comparison task. METHODS: A Sternberg probe-matching paradigm was modified in the present study. The stimuli consisted of a memory set of 3 different items (simple figures) and a retrieval set of 3 probe figures. Subjects matched each probe to its corresponding item in the memory set. The tasks were designed with different conflict loads of no-conflict, low-conflict and high-conflict in the probe retrieval test. RESULTS: Probes of no-conflict elicited a major positive going component, P300, with bilateral parietal distribution. Probes of low- and high-conflict evoked N270, while N430 was elicited only in high-conflict condition. N270 was more negative in high-conflict condition than in low-conflict condition. The N270 was right hemispheric prominent in the low-conflict task and remarkably distributed over the right prefrontal areas. On the other hand, both N270 and N430 were distributed bilaterally on the scalp in the high-conflict task. CONCLUSIONS: The present results demonstrate that the N270 is an index to the conflict identification, while the N430 of the high-conflict task reflects the processing for complex conflicts following probe retrieval. These negativities are related to the processing of conflicts.

Adult↗

[Vesicular stomatitis virus G-protein retrovector mediated a herpes simplex virus thymidine kinase gene transduction and expression in the human retinal pigment epithelial cells].

OBJECTIVE: The herpes simplex virus-thymidine kinase suicide gene (HSV-TK) was delivered to the human retinal pigment epithelial cell (RPE) by a new vesicular stomatitis virus G protein (VSV-G) retroviral vector. The growth inhibitory effects of ganciclovir on VSV-G/HSV-TK transfected RPE were studied. METHODS: A VSV-G retrovirus-packaging cell line 293GPG was transferred with retroviral vector plasmas bearing HSV-TK (G1NaCTK) or galactosidase (LacZ gene, G1BgSvNa) to produce a 293GPG/TK cell line or a 293GPG/LacZ cell line, respectively. LacZ activity was assessed following transduction of CRL2302 cells. HSV-TK transfected RPE and NIH3T3 cells (at different titer levels) were treated with ganciclovir. The growth inhibitory effects of ganciclovir on various cell lines were studied. RESULTS: The titer of VSV-G/HSV-TK concentration was 1.2 x 10(8) cfu/ml. At a high titer (MOI = 200), the efficiency of LacZ gene transfer in CRL2302 cells was 58%. Ganciclovir inhibited the growth of cells transfected by HSV-TK. The maximum inhibitory rate (45%) was obtained at cells with a high titer (MOI = 200). CONCLUSION: Our results suggested that VSV-G/LacZ and VSV-G/HSV-TK retroviral vectors are highly efficient for in vitro delivery and stable expression of genes in NIH3T3 cells and human RPE cells. The cells modified by HSV-TK gene are very sensitive to ganciclovir and the cell growth can be inhibited by ganciclovir.

Cells, Cultured↗

[Neuroprotection of nerve growth factor in experiment retinal detachment].

OBJECTIVE: To study the neuroprotection by nerve growth factor (NGF) in retina in experimental retinal detachment (RD). METHODS: Thirty one Sprague-Dawley rats were used as RD animal model by injected 0.1% sodium hyaluronate into the sub-neuroretina space. Those rats were divided into NGF experimental group, placebo group, normal control groups and pathologic control group. NGF 1 g/L/eye was injected into vitreous every 4 days in NGF experimental group and 5 micro l of PBS intravitreal injection was used as control after RD. On postoperative time 1/2 d, 1 d, 2 d, 4 d, 8 d, 16 d, 32 d, rats were sacrificed and eyes were enucleated. The effect of NGF on retina was assessed by electron, light microscopy and cell counters. RESULTS: Histology studies showed markedly changes in photoreceptor cells, bipolar cells and ganglion cells after RD, included depletion and shorten of inner and outer segments, disturbance and thinness of inner and outer nuclear layer and swelling of ganglion cells in NGF treated group and control. Changes in the microscopic examination in NGF group showed significantly less than that in control groups, especially in inner and outer segments of photoreceptor cells. In reattached retina, the tissue structure and cell morphology showed more close to normal in NGF group than that in RD control groups. Cell counters showed the cell numbers decreased both in NGF groups and RD control groups. When retina reattached, the cell number in experimental groups showed significantly lower than that in normal control group (P < 0.05). Nuclear number of outernuclear layer and ganglion cell layer in NGF groups was greater than that in RD control groups (P < 0.05). CONCLUSION: Intravitreal injection exogenous NGF partly protects retinal cells from degeneration in experimental RD and help recovery of retinal cells after retina reattached.

Animals↗

[Infective pathogens and drug resistance in burned patients].

OBJECTIVE: To find out the changes in the infective pathogens and their drug resistance in burned patients. METHODS: The patients were divided into two groups. The first group was from July 1991 to June 1996, and the second group was from July 1996 to June 2001. The bacteria of burned body surface and blood were cultured, and the bacteria and their drug sensitivity were analyzed. RESULTS: Gram-negative bacteria were the major bacteria in burn infection, among which Pseudomonas aeruginosa ranked the top. Staphylococcus aureous ranked the first among the Gram-positive bacteria, and the isolation rate of methicillin resistant Staphylococcus aureus increased; The isolation rate of Enterobacter cloacae (10.4%), Escherichia coli (8.3%), Klebsiella pneumoniae (7.3%), and fungus (4.2%) all rose. The antibiotic resistant strains of Pseudomonas aeruginosa and Staphylococcus aureous increased. CONCLUSION: The changes in pathogens of burn infection and bacterial drug resistance are related to the wide use of broad spectrum antibiotics such as cefazidime and imepenem, suggesting that dynamic observation of changes in pathogenic strains and sensitivity of bacteria to antibiotics are useful for clinical prevention and cure of burn infection.

Adolescent↗

[Experimental study of xenogeneic heart valve material].

OBJECTIVE: To explore the possibility of improving the performance of tissue engineering valve by means of preendothelialization with cultured human umbilical vein endothelial cell(hUVEC) and to develop a new xenogenic bioprosthesis valve material. METHODS: The porcine aortic valves treated by use of glutaraldehyde(GA), epoxychloropropane(EC), L-glutamic acid(L-GA) and cellular extraction(CE) respectively were divided into four groups; group 1(GA), group 2(EC), group 3(EC + L-GA), and group 4(EC + L-GA + CE). The cultured hUVECs were seeded onto the treated porcine aortic valve, then that stuff were examined by means of EC VIII factor staining, living cells counting and microscopy. RESULTS: The cultured hUVEC could adhere to culturing bottle wall an hour later, and propagated to two passages after seven days. The cells increased with serial passage at a 7-day interval. But the hUVEC grew slowly when seeded onto the treated valve material except group 4. The cells in group 4 covered the surface of valve completely seven days later, which could also be seen in group 3 but not completely. There was no cell growing in group 1, and only fewer in group 2. The living cell in groups 3 and 4 were significantly more than in groups 1 and 2 on the 3rd, 7th and 14th days (P < 0.01), meanwhile, the number of cells in group 4 were also significantly more than that in group 3 (P < 0.05). The covering area of cultured cell on the valve material in groups 3 and 4 was significantly larger than that in groups 1 and 2. The covering area of cell in group 4 was over 95%, and higher than that in group 3(60%-70%). The hUVEC of group 4 arranged in pattern of three dimension. So it could resist rising of foreign power from the cardiac cavity of high pressure and flowing volume. There was no cell on the leaflet surface in group 1, and only a few pinch of cells could be seen in group 2. CONCLUSION: The porcine aortic valve can be used to be an ideal xenogeneic valve scaffold; the scaffold of porcine aortic valve should be treated by use of epoxy-chloropropane, L-glutamic acid and cellular extraction, so that a best growing environment to the hUVEC would be given; the cultured hUVECs used to be source of seed living cell had a boundless prospects; the growing velocity of cultured hUVEC was controllable, which facilitated clinical application; and the endothelial cells of xenogeneic valve material which grew compactly onto the scaffold can resist rising of foreign power from the cardiac cavity itself.

Animals↗

[Effect and mechanism of removal of nitrogen in the mimic sewage using bio-zeolite system].

On the spot, the removal effect of pollutants such as NH3-N, N, NO3(-)-N, NO2-(-)N, TN and COD in the mimic sewage by bio-zeolite system was studied. The following results were obtained: it was obvious and stable for the removal of NH3-N by bio-zeolite with a removal efficiency over 95%, but the removal effect of NO3(-)-N was affected deeply by hydraulic retention time, according to the different removal mechanism; chemical adsorption and ion exchange were the main reasons for the removal of NH3-N as well as nitrification by microbe, while denitrification was the main reason for the removal of NO3(-)-N. Nitrification intensity of bio-zeolite was affected by the concentration of dissolved oxygen in the solution, so the nitrification intensity of bio-zeolite on the surface of the zeolite bed was two times of that in the middle in vertical direction. Denitrification intensity changed with different values of C/N in the study, and it could reach the maximum while COD/TN was 5; as for denitrification velocity, it was largest in the first six hour.

Adsorption↗

Event-related potentials evoked by multi-feature conflict under different attentive conditions.

Event-related potentials (ERPs) were recorded in subjects while they were performing a matching task. The focus of the present study was on the contributions made by ERP recording to revealing the time-course of multi-conflict information processing in the brain during visual attention. Participants were instructed to discriminate whether the attributes of the first stimulus (S1) were the same as those of the second one (S2) of a pair. Stimuli were defined by three features: color, global shape, and local shape. In condition 1, all attributes of the two stimuli of the pair were constant (no conflict); in condition 2, S2 was different from S1 in all attributes (conflict). The experiment comprised three tasks. In task 1, subjects attended to the color of the stimuli and ignored the other attributes. In task 2, they were asked to attend to both color and global shape of stimuli and disregard the local shape. In task 3, all attributes were attended to. An ERP component N270 was elicited by attending to the color conflict in session one. In task 2, attending to color and global shape induced two ERP effects in the conflict condition: N270 and N400. The results suggest that the attended different conflicts of the two visual attributes of the stimuli were processed in series. However, in task 3, only one apparent negative component, N270, was observed in the conflict condition. The difference between data from task 2 and 3 showed that more than one processing model exists in the human brain for processing multiple visual attribute conflicts.

Adult↗

Investigation on solvent casting films of surfactant-encapsulated clusters.

The surfactant-encapsulated cluster (SEC) composed of a hydrophobic dimethyl dioctadecyl ammonium (DODA) shell and an encapsulated hydrophilic polyoxoanion core can form casting films. The structure of the casting film is influenced by evaporation rates of organic solvent. When the casting films are prepared by slow evaporation of chloroform, the alkyl chains are considered to possess a partial interdigitation, and the interdigitated length is 1.6 nm. The casting film structure is characterized by scanning force microscopy (SFM), Fourier transformation infrared (FT-IR), wide-angle X-ray diffraction, and differential scanning calorimetry (DSC).

Journal Article↗

Early detection of cognitive impairment in patients with obstructive sleep apnea syndrome: an event-related potential study.

Event-related potentials (ERPs) were recorded to visual stimuli in a task that required matching the shape and serial position of the probes against previously memorized items. The effects of hypoxia on ERP were investigated in 24 patients with obstructive sleep apnea syndrome (OSAS) and a matched control group. N2b-late positive-going (LPC) components were elicited by probes that identically matched the memorized items (no-conflict condition). In contrast, N270-LPC and N270-N430-LPC components were elicited by probes having low-conflict and high-conflict with the memory set. Conflict ERP effect decreased in mild, while both no-conflict and conflict ERP effects decreased in amplitude in severe OSAS patients. Conflict ERPs associated with processing of conflicting information are more vulnerable than no-conflict ERPs to hypoxic cerebral damage.

Adult↗

Confined supramolecular nanostructures of mesogen-bearing amphiphiles.

Stable surface nanostructures with different morphology have been successfully constructed by modifying the chemical structure of synthetic amphiphiles; by introducing mesogenic groups into bolaform amphiphiles, stable spaghetti-like or stripe-like nanostructures can be obtained; it is believed that such a kind of surface structure could be used for templating synthesis and assembly.

Journal Article↗