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Biomedical subjects

L Dong

Publications and source records attributed to L Dong.

At least 91 records · Page 5Linked to original sources
PubMed1998

A pencil-beam photon dose algorithm for stereotactic radiosurgery using a miniature multileaf collimator.

A computer-controlled miniature multileaf collimator (MMLC) with 4 mm leaf width and a maximum field size of 6 cm X 6 cm has been designed as a tertiary beam-shaping device for linac-based stereotactic radiosurgery. The purpose of this study is to develop an accurate and efficient dose calculation model for use with the MMLC. A pencil-beam based algorithm using a sum of three Gaussian kernels was developed to model the off-axis ratio of MMLC fields. Because the kernel integration over a rectangular field can be solved in closed form, dose to any point from an arbitrary MMLC field can be calculated efficiently by summing dose contribution from a set of rectangular apertures and transmission blocks that model individual leaf openings or leaf transmissions. The model uses an effective rectangular field and equivalent square method for determination of depth dose and dose output. Results showed that the calculated percentage depth dose was within 1% and output factor was within 1.5% of measured data. The parameters of the pencil beam kernels were extracted by fitting measured off-axis profiles for a few field sizes at a few depths. The accuracy of the calculated off-axis ratio was tested by comparison with measured data for a number of MMLC fields. The algorithm was shown to be accurate to within 1.5% or 1 mm for off-axis ratios. The algorithm computes at a speed of 34,600 data points per second on a DEC Alpha server model 2000/433 (Digital Equipment Corp., Maynard, MA), which is about 15 times faster than a Clarkson-type summation method.

Algorithms↗
PubMed1998

[Relationship between risk-taking behavior and knowledge for HIV infection among young men in Longchuan, Yunnan of China].

OBJECTIVE: To study the relationship between characteristics of risk-taking behavior and knowledge level of HIV infection/AIDS and risk perception of HIV infection among young men in an AIDS epidemic area. METHODS: A cross-sectional survey was carried out among young men aged 18-29 years in 82 villages in Longchuan, Yunnan, China in 1994. Their demographic and behavioral information and knowledge level of AIDS were collected by interviewer administered anonymous questionnaire. RESULTS: A total of 1,548 subjects were interviewed and 433 were drug abusers, including 192 intravenous users with 73% of them sharing syringes with others. Drug abusers were four times more likely to have pre-/extra-marital sex than non-users. More than half of the interviewees scored zero in HIV/AIDS knowledge. CONCLUSION: Factors predisposing spread of HIV infection were common in the local young men. It is recommended that intervention be implemented as soon as possible to prevent HIV infection and AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1998

[Aberrant expression of immunoglobulin germline gene C mu in leukemias].

OBJECTIVE: To investigate the significance of immunoglobulin germline gene C mu expression in leukemias. METHODS: Immunoglobulin germline gene C mu transcripts in 63 bone marrow samples from 59 leukemia patients were examined by RT-PCR. RESULTS: Germline C mu transcripts could be identified in 17 of 26 AML, 9 of 12 ALL, 4 CML-BC and 2 CLL patients. HLA-DR was expressed in 80% C mu(+) patients and in 92.9% C mu(+) AML patients. In 10 normal bone marrow or peripheral blood samples C mu transcripts were undetectable. CONCLUSION: Leukemogenesis in most acute leukemia may originate from the common progenitors of early B-lymphoid and myeloid cells.

Acute Disease↗
PubMed1998

[Effect of ligustrazine on CD34 antigen expression of bone marrow cells in immune-mediated aplastic anemia mice].

OBJECTIVE: To explore the effect of ligustrazine on CD34 antigen expression of bone marrow cells in immune-mediated aplastic anemia (AA) mice. METHODS: The model of immune aplastic anemia mice was induced by means of 6.0 Gy60Co gamma-ray irradiation and lymphocyte infusion through tail vein. The mice were divided into 3 groups: the normal group, the AA control group and the ligustrazine group. Mice of the ligustrazine group were fed by 4 mg of ligustrazine injection twice a day by gastrogavage. On the 10th day, CD34 antigen expression intensity of bone marrow cell membrane was measured by flow cytometer analysis system. RESULTS: CD34 antigen expression intensity of ligustrazine group was 77.6 +/- 6.5, with no statistic difference from that in the normal group (80.0 +/- 2.6), while that of the control group was much higher (68.6 +/- 4.5, P < 0.05). CONCLUSIONS: Ligustrazine could promote proliferation of stem and progenitor cell of AA mice through influencing on bone marrow micro-environment so as to increase the CD34 antigen expression of bone marrow cells.

Anemia, Aplastic↗
PubMed1998

[Treatment of arteriovenous malformation by linear accelerator radiosurgery].

OBJECTIVE: To summarize the effectiveness of radiosurgery for cerebral arteriovenous malformations (AVMs). METHOD: We treated with linear accelerator radiosurgery 17 patients harboring AVMs in the brain. 15 AVMs were located supratentorially and others infratentorially. All the patients were treated with single fraction. The doses at AVM margin were 15 to 30 Gy. RESULT: AVMs disappeared in 13 of the 17 patients, reduced in 3 and unchanged in only 1 at 2 year follow up. Vasogenic edema observed in 2 patients, their neurologic deficits were all improved with steroid. CONCLUSION: Linear accelerator radiosurgery is effective in dealing with cerebral AVMs. It provides with a new means of treatment for AVMs which can't be effectively treated with microsurgery and embolization.

Adolescent↗
PubMed1998

Ultrastructural observation on spermatocytogenesis in Taeniid cestodes.

AIM: To study the spermatocytogenesis of taeniid cestodes at the ultrastructural leaves. METHODS: Transmission electron microscopy. RESULTS: The ultrastructural observation on spermatocytogenesis in Taenia solium, T. saginata and T. pisiformis were made by TEM. Two types of spermatogonia; type A and B, as well as the supporting cells surrounding the peripheral of spermatogonia are recognized. The type A spermatogonia are stem cells and the type B are mother cells which produce 16 primary spermatocytes by mitosis for 4 times with the cells unseparated. The primary spermatocytes are characterized by the ribosome masses in the cytoplasm. 32 secondary spermatocytes arranged in roselike were produced by reductive division of primary spermatocytes. The secondary spermatocytes become the spermatid quickly by short time development. CONCLUSION: The dividing mode of spermatogonia in Taeniid cestodes is mitosis with cells unseparated.

Animals↗
PubMed1998

Ultrastructural observation on the transformation of the spermatozoon in spermatogenesis of Taeniid cestodes.

AIM: To study the transformation of taeniid spermatozoon during spermatogenesis on the ultrastructure level. METHODS: Transmission electronmicroscopy. RESULTS: This paper was the second part of the ultrastructural observations on the spermatogenesis in Taeniid cestodes: The transformation of the spermatozoon. The 64-spermatid-plasmodium was generated from the secondary meiosis of the 32 rose-like secondary spermatocytes. The transformation of the spermatozoon was a complex process. Firstly, both the cytoplasm and nucleus of the spermatid elongated while the cytoplasm increased and connected to the cytoplasmic mass (cytophore). Secondly, the chromatins of nucleus polymerized to a thread-bundle-like structure. Finally, it detached from the cytoplasm mass and became a mature spermatozoon. The mature spermatozoon was a thread-like structure, about 16.2-18.6 microns in length and 0.35-0.45 micron in diameter. There were two structurally distinct parts: the part with the nucleus was the head and the part without the nucleus was the tail. The head measured about 5-6 microns in length, 1/3 of the total body length and contained an elongated nucleus which twined around the axoneme without mitochondria. The tail was about 11.2-16.6 microns in length. Throughout the core of the tail was an axoneme with typical "9 + 1" structure. The anterior of the tail, just behind the head, were some mitochondria, about 1.6-1.7 microns in total length which twined around the axoneme. The posterior of the tail contained only an axoneme. In cross-section of the spermatozoon, about 46 microtubules were beneath the plasma membrane. CONCLUSION: The transformation of the spermatozoon is a very complex process.

Animals↗
PubMed1998

[The observations of plasma of AC operation in the CT-6B Tokamak by Ha emissions].

The spatial distribution and temporal evolution of plasma of AC operation in the CT-6B Tokamak has been observed through Ha emissions by an optical multichannel diagnostic system for the first time. The results show the plasma density is not completely lost during current reversal, therefore, there were no need for second breakdown after the current reversal. The spatial and temporal evolution of plasma is dependent on the current wave forms.

English Abstract↗
PubMed1998

Transformation-sensitive changes in expression, localization, and phosphorylation of adducins in renal proximal tubule epithelial cells.

Adducins are cytoskeletal proteins that facilitate interactions between spectrin and actin to form the subcortical membrane skeleton. We recently determined that alpha- and gamma-adducins are among a group of PKC substrates that we have designated "STICKS" (substrates that interact with C-kinase). To study the role of adducins and their regulation by protein kinase C (PKC) in carcinogenesis, we compared the content, localization, and phosphorylation of alpha- and gamma-adducins in primary renal proximal tubule epithelial (RPTE) cells and oncogene-altered derivative lines. RPTE cells expressing adenovirus E1A are immortalized but not transformed, whereas RPTE cells expressing SV40 large T antigen are transformed. Phosphorylation of adducins was monitored with a phosphorylation state-specific antibody directed toward the PKC phosphorylation site on adducins. Basal levels of phospho-alpha-adducin were relatively low in growing and confluent primary RPTE cells; however, basal levels of phosphoadducins relative to total adducins were increased in E1A-RPTE and SV40-RPTE cells. Phorbol esters stimulated alpha-adducin phosphorylation to a greater extent in primary cells than in oncogene-altered cells, possibly because of the already high basal levels of phosphorylation in those cells. Phosphorylated adducins were preferentially recovered in the soluble fraction, indicating that PKC phosphorylation either directly or indirectly influences the subcellular location and functions of adducins in regulating membrane skeleton structure. Thus, these studies provide evidence for increased endogenous PKC activity in oncogene-altered cells and suggest that the increased activity directly influences cytoskeletal organization by phosphorylating regulatory proteins, such as the adducins.

Animals↗
PubMed1997

Down-regulation of major histocompatibility complex Q1b gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

We analyzed mouse hepatoma cells using differential display to discover new genes that respond to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We identified a class I major histocompatibility complex (MHC) gene, which we designated as MHC Q1b, whose expression decreases in the presence of TCDD. TCDD-induced down-regulation of MHC Q1b requires both the aromatic hydrocarbon receptor and the aromatic hydrocarbon receptor nuclear translocator, transcription factors that up-regulate other genes in response to TCDD. Down-regulation of MHC Q1b by TCDD appears to involve both transcriptional and post-transcriptional regulatory events; the post-transcriptional destabilization of MHC Q1b mRNA is probably a secondary response to TCDD. Our findings reveal new mechanistic aspects of gene regulation by TCDD. In addition, our observations suggest a mechanism that might account for some of TCDD's immunotoxic effects.

Amino Acid Sequence↗
PubMed1997

Inflammatory damage to skin by prolonged contact with 1,2-dichlorobenzene and chloropentafluorobenzene.

Skin samples from Fischer-344 rats and Hartley guinea pigs exposed dermally to 1,2-dichlorobenzene (DCB) and chloropentafluorobenzene (CPFB) for up to 4 h were examined for chemical-induced damage. Samples were stained with hematoxylin and eosin and scored for polymorphonuclear cell (PMN) margination, dermal inflammation, and epidermal necrosis by light microscopy. Ultrastructural evaluation of samples fixed with 2% glutaraldehyde and postfixed with 1% osmium tetroxide was used to visualize margination of PMNs. Guinea pigs exhibited postexposure inflammatory changes following an exposure of about an hour-and-a-half shorter duration than rats. DCB-induced inflammation and PMN margination occurred following an exposure about a half hour shorter in both species compared to CPFB. In contrast, epidermal necrosis was more severe with CPFB than with DCB. These changes may account for decreases in chemical penetration rates which have been observed in previous studies with DCB and CPFB in rats and guinea pigs.

Animals↗
PubMed1997

Matching Ca efflux and influx to maintain steady-state levels in cultured cardiac cells. Flux control in the subsarcolemmal cleft.

The study examines the feed-back mechanism by which Ca efflux via Na/Ca exchange adjusts to match Ca influx via Ca channels-the condition which must obtain if cellular steady-state Ca level is to be maintained. It is proposed that variation in Ca channel influx produces changes in sarcoplasmic reticulum content which, in turn, through interaction within the subsarcolemmal cleft space, sets the level of Na/Ca exchange-mediated efflux. We measured Ca channel influx with whole-cell voltage-clamp, Ca efflux specifically via Na/Ca exchange by high resolution, non-perfusion-limited 45Ca wash-out technique and sarcoplasmic reticulum (SR) Ca content by combination of the latter with measurement of sarcolemmal Ca-binding by use of instantaneous "gas-dissected" sarcolemmal membrane isolation. Ca channel influx was varied by Bay K 8644 or nifedipine. Ca influx via Ca channels was increased by 37.8% with Bay K and decreased by 68% with nifedipine. The SR contribution to Na/Ca exchange-mediated efflux was increased by 36.7% with Bay K and reduced by 66.8% by nifedipine-virtually identical changes. Application of the cleft space model to determine beat-to-beat efflux via Na/Ca exchange predicted values which closely matched beat-to-beat channel influx.

Animals↗
PubMed1997

Study on oxygen supply and protection of bone marrow in acute radiation injured mice.

After irradiated by 8 Gy 60Co gamma-ray, mice were intraperitoneally injected immediately with 0.2 ml 100% compound blood-activating soup twice a day for 10 days. The in situ ulnar bone marrow partial pressure of oxygen (PbO2) was determined in vivo before, during and after irradiation respectively. The bone marrow sections in the same part were observed. Our results showed that the normal murine ulnar PbO2 was 12.72 +/- 1.05 kPa. During irradiation, the level of PbO2 decreased to 10.78 +/- 1.17 kPa (P < 0.001). And 3 days after irradiation, PbO2 decreased to 9.75 +/- 0.52 kPa, suggesting that the commonly used "blood-activating and stasis-eliminating" Chinese drugs could promote the rehabilitation and proliferation of bone marrow microvessels in the acute radiation injured mice, expand their areas, increase the oxygen supply of bone marrow microenvironment, thereby leading to PbO2 much higher increase than that of control group. It is also helpful in the proliferation and rehabilitation of hematopoietic cells.

Animals↗
PubMed1997

Aggregation of mutant Cu/Zn superoxide dismutase proteins in a culture model of ALS.

Mutations in the Cu/Zn-superoxide dismutase (SOD-1) gene underlie some familial cases of amyotrophic lateral sclerosis (FALS), a neurodegenerative disorder characterized by loss of cortical, brainstem, and spinal motor neurons. To investigate the mechanisms responsible for the toxicity of mutant enzyme, SOD-1 cDNAs bearing mutations found in FALS patients (mSOD) were expressed in cultured spinal motor neurons, dorsal root ganglion (DRG) and hippocampal neurons. Many features of motor neuron disease seen in humans with FALS and in transgenic mouse models were reproduced, including preferential susceptibility of motor neurons to toxicity of mSOD. Abnormal cytoplasmic aggregation of mSOD protein was observed in mSOD-expressing motor neurons, but never in neurons expressing SODwt enzyme, and was followed by evidence of apoptotic cell death. Such aggregates were not observed in nonvulnerable neuronal populations expressing mSOD (DRG or hippocampal neurons). Aggregation of SOD-1 may contribute significantly to the death of motor neurons expressing mutations associated with FALS-1 and the mechanisms leading to aggregation may pertain to the specific vulnerability of motor neurons in this disease.

Amyotrophic Lateral Sclerosis↗
PubMed1997

Verification of radiosurgery target point alignment with an electronic portal imaging device (EPID).

A procedure has been developed using an electronic portal imaging device (EPID) to verify that the center of a patient's lesion is aligned with the center of a treatment cone prior to treatment in a linac-based stereotactic radiosurgery procedure. The coordinates of the lesion center are set on the Brown-Roberts-Wells phantom base using a target simulator. A 3 mm tungsten ball, mounted on the target simulator, is used as the reference point for the planned isocenter. The target simulator is then attached to an adapter mounted on the linac couch, and an EPID image of the simulated target is acquired. The center of the circular-shaped radiation field is calculated from the centroid of the segmented EPID image, and the center of the tungsten ball is identified by an automated computer search algorithm. A summation filter is used to find the position of the lowest radiation intensity coincident with the center of the ball. The alignment error is defined as the difference between the center of the radiation field and the center of the ball. The accuracy of this method was tested and found to be within 0.2 mm. The advantage of the EPID-based procedure is that it can give quantitative offset values quickly for immediate readjustment. We have found that the method is also a convenient tool for testing room laser alignment and the accuracy of the treatment cones.

Algorithms↗
PubMed1997

[Relationship between reaction of membrane potential and size of glomus cells in rat carotid body during hypoxia].

The membrane potentials (Em) of 85 cultured isolated glomus cells were measured by intracellular recording. The shapes of glomus cells were recorded by microscopic photograph and the cell diameter was measured by micrometer enlarger. The glomus cells with different diameters exhibited two distinct responses to hypoxia. The glomus cells with diameter shorter than 10 microns were depolarized in response to hypoxia, while the cells with diameter over 10 microns were hyperpolarized during hypoxia. Thus, it is sugested that glomus cells may be divided into two functionally different subtypes. Although the smaller glomus cells depolarized more seriously under extreme hypoxia, the degree of hypoxia could not change the original response pattern of glomus cells to hypoxia.

Animals↗