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R Xu

Publications and source records attributed to R Xu.

At least 145 records · Page 8Linked to original sources
PubMed1999

Anatomic relationship of the cervical nerves to the lateral masses.

Eight cervical specimens were transversely sectioned with slices approximately 2 mm to 3 mm in thickness to evaluate the anatomic relationship of the spinal nerves to the lateral masses. Results showed that the spinal nerve either does not appear or, when it does, is situated anteromedially to the superior facet on the cross sections through the upper portion of the superior facet. The anterolateral aspect of the superior facet is free from the spinal nerve. Cross sections through the lower pedicle of the vertebra showed that the spinal nerve rested on the transverse process anterolateral to the lateral mass. The mean distances between the posterior midline of the lateral mass and the posterior border of the spinal nerve measured 15 degrees in the lateral direction were 16.1+/-1.7 mm for C3, 16.5+/-1.8 mm for CA, 16.8+/-1.2 mm for C5, 16.3+/-2.0 mm for C6, and 8.5+/-0.9 mm for C7. This study suggests that the anterolateral corner of the superior facet and the anterior aspect of the lateral mass lateral to the origin of the transverse process would be safer zones for screw exit. Attention should therefore be paid to the screw orientation for the Magerl technique and to the screw length for the Roy-Camille technique. Care should be taken to insert the screw into the C7 lateral mass.

Aged↗
PubMed1999

RSD1000: a novel antiarrhythmic agent with increased potency under acidic and high-potassium conditions.

This study reports the use of a novel agent, RSD1000 [(+/-)-trans-[2-(4-morpholinyl)cyclohexyl]naphthalene-1-acetate mono hydrochloride], to test the hypothesis that a drug with pKa close to the pH found in ischemic tissue may have selective antiarrhythmic actions against ischemia-induced arrhythmias. The antiarrhythmic ED50 for RSD1000 against ischemic arrhythmias was 2.5 +/- 0.1 micromol/kg/min in rats. This value was significantly lower than doses that suppressed electrically induced arrhythmias. In isolated rat hearts, RSD1000 was approximately 40 times more potent in producing ECG changes (i.e., P-R and QRS prolongation) in acid (pHo = 6.4) and high [K+]o (10.8 mM) buffer than in normal buffer (pHo = 7.4; [K+]o = 3.4 mM). In patch-clamped, whole-cell rat cardiac myocytes, inhibition of sodium (INa) currents by RSD1000 was pH- and use-dependent. The IC50 for INa blockade was lower (P <.05) in acid (0.8 +/- 0.1 microM) than in pH 7.3 (2.9 +/- 0.3 microM), respectively, whereas the IC50 for blockade of transient outward potassium current (ITO) at pH = 6.4 and 7.3 was 3.3 +/- 0.4 and 2.8 +/- 0.1 microM, respectively. Mixed ion channel block in ischemic myocardium with minimal effects on normal cardiac tissue, as governed by the low pKa of RSD1000, may account for its antiarrhythmic activity against ischemia-induced arrhythmias.

Animals↗
PubMed1999

Thoracic pedicle screw placement guided by computed tomographic measurements.

Cadaveric pedicle screw placement guided by the measurements from axial computed tomography (CT) scans in the thoracic spine was assessed in this study. Axial CT scans were performed on four cadaveric thoracic spines, and the measurements included the pedicle transverse angle, inner pedicle width, and distance between the midline of the vertebra and the pedicle axis on the dorsal aspect of the lamina. With utilization of the data from CT scans, screws were directly placed into the thoracic pedicle from T1 to T10. Screw penetration of the pedicle was determined by gross examination. The results showed that the largest pedicle transverse angle was found at the levels of T1-2, and the smallest occurred at the T3 through T8 levels. The value of the pedicle inner width was quite different between specimens with a minimum of 3.0 mm at T4 and a maximum of 9.2 mm at T10. Gross examination of the pedicle showed that 13 (16.3%) of 80 screws penetrated the pedicle wall, with a Grade I penetration in 11 pedicles and a Grade II penetration in 2 pedicles. Screw penetration of the medial wall was found in four pedicles and penetration of the lateral wall was noted in nine pedicles. No screw penetration of the superior and inferior walls of the pedicle was identified in any of the four specimens. Thoracic pedicle screw placement guided by the measurements from axial CT scans significantly reduced the incidence of pedicle penetration. Axial CT measurements of the pedicle inner diameter and transverse angle as well as the starting point for screw insertion are recommended if pedicle screw fixation is intended in the thoracic spine.

Aged↗
PubMed1999

Fenretinide activates caspases and induces apoptosis in gliomas.

The synthetic retinoid fenretinide (N-[4-hydroxyphenyl] retinamide or 4HPR) has been shown to not only inhibit cell growth but also to induce apoptosis in a variety of malignant cell lines. It is being tested presently for its potential as a chemopreventive agent against several cancers. A related retinoid, 13-cis-retinoic acid (cRA), has been shown to have activity against gliomas in vitro as well as in a recent clinical study. The present study aimed at assessing the activity of fenretinide against glioma cells in vitro and comparing it with that of cRA at pharmacologically relevant doses. We hypothesized that the ability of fenretinide to induce apoptosis would make it more potent against gliomas than cRA. Four glioma cell lines (D54, U251, U87MG, and EFC-2) were treated with fenretinide (1-100 microM) and showed dose- and time-dependent induction of cell death. At pharmacologically relevant doses, fenretinide was more active against glioma cells than cRA because of its ability to induce apoptosis. Flow cytometric studies using D54 cells demonstrated no significant changes in the cell cycle distribution compared with untreated control, but a sub-G1 fraction consistent with apoptosis was detected. Terminal deoxynucleotidyl transferase-mediated nick end labeling assay indicated that the apoptotic fraction was cell cycle nonspecific. Fenretinide treatment resulted in cleavage of poly ADP-ribose polymerase, indicating an activation of the caspase 3. Immunofluorescence studies using the nuclear stain 4',6-diamidine-2'-phenylindole dihydrochloride showed nuclear condensation and an apoptotic morphology. Hence, this study demonstrates that, at clinically relevant doses, fenretinide is a potent inducer of apoptosis in gliomas acting via the caspase pathway. We also show that at clinically achievable doses, fenretinide has more activity against gliomas than comparable doses of cRA. The favorable side effect profile seen in previous clinical studies and the in vitro activity against gliomas demonstrated in this study suggest that fenretinide could be a promising therapeutic agent against gliomas.

Antineoplastic Agents↗
PubMed1999

CREB phosphorylation promotes nerve cell survival.

The cyclic AMP-responsive element binding protein (CREB) is a posttranslationally activated transcription factor that has been implicated in numerous brain functions including cell survival. In this study we investigated whether CREB overexpression using transient transfection of a pAAV/CMV-CREB plasmid altered neuronal cells' susceptibility to apoptosis. We found that elevated CREB protein inhibited apoptosis induced by okadaic acid. At least part of this effect is critically dependent on prolonged Ser133 phosphorylation, as a directed mutation at this site decreased CREB-induced protection. These results suggest that CREB is a survival factor for neuronal cells and that treatments aimed at augmenting CREB phosphorylation in the brain may be neuroprotective.

Animals↗
PubMed1999

Evaluation of the upper sacrum by three-dimensional computed tomography.

Axial and sagittal computed tomographic (CT) scans of 40 sacrum specimens were obtained. The measurements of the upper sacral canal and S1-2 and S2-3 anterior sacral foramina were performed on axial scans, and the evaluation of the upper sacral pedicle was based on sagittal scans. The results showed that there were statistically significant differences between male and female specimens in 3 of 29 measurements. In general, the measurements of male specimens were slightly larger than those of the female specimens, and the linear dimensions of the sacral canal, anterior foramina, and pedicle decreased from the S1 to S3. This study indicated that the critical area of the sacral pedicle for screw insertion lies in the junction between the pedicle and vertebral body. CT scans provide more accurate information about the essential sacral anatomy.

Female↗
PubMed1999

Inhibition of DNA synthesis in isolated human endometrial cells by a levonorgestrel-releasing intrauterine device.

OBJECTIVE: To estimate the effect of an intrauterine device (IUD) releasing 20 micrograms levonorgestrel (LNG) per 24 hours on DNA synthesis in human endometrial cells before and after 12 months of use. STUDY DESIGN: Endometrial specimens were collected from the anterior or posterior wall of the miduterus from 6 females on cycle day 10-12 before insertion of the IUD and after 12 months of use. RESULTS: Previous results from our group did not reveal any influence on endometrial DNA cell content when a levonorgestrel IUD releasing 2 micrograms/24 h was used for 12 months in a group of fertile females. In this study, the IUD release rate, 20 micrograms LNG/24 h, was statistically significantly different from the results in the previous studies. The effect of the levonorgestrel IUD on endometrial proliferation was dose dependent, and a significant correlation could be found between continuous exposure to LNG and inhibition of DNA synthesis in endometrial cells. CONCLUSION: Inhibition of proliferative activity in endometrial cells seems to be reflected by a decrease in DNA synthesis per cell nucleus and contributes to the clinical performance of the LNG-releasing IUD.

Adult↗
PubMed1999

Anatomy of the cervicothoracic junction: a study of cadaveric dissection, cryomicrotomy, and magnetic resonance imaging.

The morphologic characteristics of the cervicothoracic junction from C6 to T2 were examined. Gross dissection and cryomicrotomy was performed on 13 fresh cadavers. Four healthy volunteers underwent magnetic resonance imaging. Results indicated that vertebral body dimensions do not change appreciably, except for vertebral body heights and medial pedicular angulation, both of which increase from C6 to T2. Based on the findings of gross dissection and cryomicrotomy, the mediolateral width of the spinal canal was largest at C6 to accommodate the larger spinal cord at C6. The cross-sectional area ratios of the spinal cord to spinal canal were 1:2.3 at C6, 1:3.7 at C7, 1:4 at T1, and 1:3.7 at T2. The foraminal height and width were greater at C7-T1 and T1-T2 than at C6-C7. The thinnest lamina was at C7. The anatomy of the pedicles showed that the outer mediolateral diameter averaged 6.78 mm at C6, 7.5 mm at C7, 9.23 mm at T1, and 7.9 mm at T2. The superior-inferior diameter of the pedicle increased from 7.58 mm at C6 to 12.43 mm at T2. Medial angulations decreased from 44.5 at C6 to 23.35 at T2. The coronal angulation of the exiting nerve was 64.83 for C7, 79.83 for C8, and 90.33 for T1 nerve roots based on coronal magnetic resonance imaging. Finally, gross dissection during the anterior approach to the cervicothoracic junction revealed that this approach was extensible, allowing access to the anterior aspect of the cervicothoracic spine. Associated vital structures must be protected, such as the arch of aorta, common carotid artery, innominate vein, thoracic duct, recurrent laryngeal nerve, stellate ganglion, trachea, and esophagus.

Adult↗
PubMed1999

[Inhibition of hematopoiesis by sera from patients with myelodysplastic syndromes].

OBJECTIVE: To explore the inhibitory effect of sera from patients with myelodysplastic syndromes (MDS) on the growth of normal hematopoietic progenitor cells. METHODS: The inhibitory activity to the growth of BFU-E and CFU-GM was analysed by in vitro methylcellulose culture. Hematopoietic cell apoptosis was assayed with a programmed cell death assay kit and flow cytometry. RESULTS: In the 23 MDS patients studied, a potent inhibitory activity to CFU-GM and BFU-E was demonstrated in 3 and 4 patients, respectively. The inhibitory activity to BFU-E of sera from 3 patients was almost entirely neutralized by anti-TNF alpha McAb. Sera from two MDS patients induced apoptosis of normal hematopoietic progenitor cells. CONCLUSION: Inhibitors of hematopoietic progenitor cells are present in sera from some MDS patients. One of the inhibitors might be TNF alpha, which can induce apoptosis, resulting in ineffective hematopoiesis in MDS.

Adult↗
PubMed1999

[Microelectrode-guided posteroventral medial pallidotomy for Parkinson's disease].

OBJECTIVE: To introduce the methods and effects of microelectrode-guided posteroventral pallidotomy (PVP) for Parkinson's disease. METHODS: 109 patients underwent PVP by microelectrode electrophysiological recording for intraoperative target localization. 45 patients underwent unilateral PVP, 21 patients simultaneous bilateral PVP, 43 patients combined thalamotomy and PVP. Modified Webster Scale was used for objective assessments before and after operation. Postoperative CT scan or MRI was performed to localise lesions. RESULTS: Microelectrode recording usually led to a final pallidotomy lesion position that deviated from the CT stereotactically defined target point. The change rate of targets was 84.7%. PVP significantly and immediately improved all Parkinsonian motor signs and reduced drug-induced motor fluctuations and dyskinesia. The mean Webster Scale was improved by (72.7 +/- 11.3)% in the "on"" state, and (89.3 +/- 8.1)% in the "off" state. No patient showed permanent complications. CONCLUSIONS: Microelectrode-guided PVP was proved to be safe and effective. Bilateral PVP and combined PVP can significantly and immediately abolish all Parkinsonian motor signs. Physiological methods of microelectrode recording can significantly improve the safety and efficacy of PVP, and decrease the rate of complication.

Adult↗
PubMed1999

[Effects of growth factors and estrogen on the proliferation and prolactin gene expression in anterior pituitary cells of rats].

OBJECTIVE: Detect the effects of exogenous 17 beta-estradiol (E2), epidermal growth factor (EGF), and transforming growth factor beta 1 (TGF beta 1) on the proliferation and prolactin (PRL) gene expression in primary serum-free cultured anterior pituitary cells in vitro. METHODS: Laser scanning confocal microscopy (LSCM) and in situ hybridization in primary serum-free cultures of rat anterior pituitary cells were employed. RESULTS: After 36 hours incubation of the monolayer with E2(10(-8) mol/L) and EGF(10(-8) mol/L), DNA and PRL mRNA contents in the cells were increased significantly (P < 0.001); and when cells were co-incubated with E2 and EGF at the same time, the levels of DNA and PRL mRNA were higher than those treated with E2 or EGF alone (P < 0.01), respectively. TGF beta 1(2 ng/ml) treatment decreased the DNA and PRL mRNA contents significantly (P < 0.001). Its inhibitory effect was reduced at the presence of E2, the DNA and PRL mRNA levels in the cells were higher than those treated with TGF beta 1 alone (P < 0.001), but still lower than E2 alone treatment (P < 0.001). CONCLUSIONS: The results indicate that EGF and TGF beta 1 exerte stimulatory inhibitory effects, on cell proliferation and PRL gene expression in anterior pituitary cells of rats in both basal and E2-induced conditions. EGF and TGF beta 1 may be involoved in the regulation of proliferation and PRL gene expression in anterior pituitary cells in vivo; and also may be correlated with prolactin-secreting tumors formation induced by E2.

Animals↗
PubMed1999

[Analysis of Cu-O bond stretching vibration in CuO2 plane of Bi-system high temperature superconductor].

Infrared absorption spectra of Bi-system high zero resistance temperature (Tc) superconductors were measured. The relation between Cu-O bond stretching vibration in CuO2 plane and superconducting properties of Bi-system high Tc superconductors were analysed and discussed. The result of analysis indicated that the change of absorption peak strength of Cu-O bond stretching vibration was similar to the change of Tc. The reason was related to the coupling between the phonon and free carrier. And according to the theory of molecule vibration, the frequencies of Cu-O bond stretching vibration in CuO2 plane were calculated on the base of simplified model.

English Abstract↗
PubMed1998

The vertebral body depths of the cervical spine and its relation to anterior plate-screw fixation.

STUDY DESIGN: A study was performed to measure the vertebral body depths in different locations from C2 to C7. OBJECTIVES: To measure the vertebral body depths in 10 linear dimension from C2 to C7. SUMMARY OF BACKGROUND DATA: Anterior plate-screw fixation of the cervical spine has been the common surgical procedure for management of multilevel degenerative disc disease and fracture dislocation. However, injury to the spinal cord during drill or screw placement is the most feared complication of this procedure. It is beneficial for one to have a knowledge of the vertebral body depths in different locations of the vertebral body before anterior cervical plating. METHODS: Twenty-seven cervical spines from C2 to C7 were evaluated directly for this study. Anatomic evaluation of the vertebral body included the anteroposterior midline sagittal depth and the anteroposterior parasagittal depth 5 mm lateral to midline on the superior and inferior endplates, as well as on the middle body. Measurements also were made of anteroposterior parasagittal vertebral depth with both medial and lateral inclination of 10 degrees, with respect to the parasagittal plane of the vertebral body. RESULTS: In general, the measurements of male specimens were larger than those of female specimens. Significant differences were noted at 21 measurements over C3 through C7. The mean depths of the superior endplate for all male and female specimens increased consistently from C3 to C7. The mean depths of the inferior endplate varied but generally increased from C2 to C6, then decreased to C7. The mean sagittal and parasagittal middle vertebral body depths were both 14 mm. CONCLUSIONS: This information, in conjunction with preoperative computed tomographic evaluation, may be helpful in determining proper screw length during anterior plating of the cervical spine.

Aged↗
PubMed1998

The reliability of the lateral radiograph in determination of the optimal transarticular C1-C2 screw length.

STUDY DESIGN: This study assessed the value of using lateral radiographs in evaluating the optimal screw length in transarticular C1-C2 screw fixation. OBJECTIVES: To assess the reliability of the lateral radiograph in determining the optimal transarticular C1-C2 screw length. SUMMARY OF BACKGROUND DATA: Transarticular C1-C2 screw placement is usually performed using anatomic landmarks and fluoroscopy. A lateral fluoroscopic image is valuable when directing screws in the sagittal plane, but its exact role in determining screw length has not been investigated. METHODS: Eight cervical spine specimens were used in this study. Screw placements were performed in each specimen, fixed in the exact lateral position and under direct visualization. After each placement, a lateral radiograph was taken. The odontoid process was divided into three equal portions. Another portion anterior to the odontoid process was called the anterior tubercle region. The number of screw tips appearing in each portion on the radiograph was then recorded for each placement. In addition, 30 C1 specimens were measured to evaluate the anterior part of C1. RESULTS: The results showed that 12.5% of the screws placed 2 mm short of reaching the ventral cortex and 0 mm overpenetrating the ventral cortex of the lateral mass of C1 projected in the radiograph on the anterior tubercle region, 37.5% on the anterior region of the odontoid process, and 50% on the middle region of the odontoid process. Twenty-five percent of the screws that were placed to overpenetrate, by 2 or 4 mm, the ventral cortex of the lateral mass of C1 were projected on the anterior tubercle region in the radiograph, and 50% and 62.5% were projected on the anterior region of the odontoid process, respectively. The mean vertical distance between the anteriormost point of the anterior tubercle of the anterior ring and the middle of the ventral cortex of the lateral in all specimens was 5.6 +/- 1 mm, and the mean transverse angle of the anterior ring relative to the frontal plane was 21.1 +/- 3.5 degrees. CONCLUSIONS: This results in this study indicate that a lateral radiograph may not be reliable in determining the optimal screw length, although it is valuable in directing accurate screw angle in the sagittal plane. Preoperative computed tomographic evaluation of the C1-C2 region may be helpful in estimating the location of the screw tip on the lateral radiograph during surgery.

Adult↗
PubMed1998

The anatomic location of the dorsal ramus of the cervical nerve and its relation to the superior articular process of the lateral mass.

STUDY DESIGN: This study analyzed the anatomic relation of the dorsal ramus of the cervical spinal nerve to the lateral mass. OBJECTIVES: To determine the location of the dorsal rami of the cervical spinal nerves from C3 to C7 in relation to the superior articular processes of the lateral masses. SUMMARY OF BACKGROUND DATA: The anatomic study of the cervical spinal nerve and its relations to adjacent bony structures have been addressed. No previous anatomic study with regard to the location of its dorsal ramus relative to the lateral mass has been reported. METHODS: Twelve specimens were obtained for study of the dorsal rami of the cervical spinal nerves. All soft tissues surrounding the cervical spinal nerves from C3 to C7 were dissected from the intervertebral foramens until the dorsal rami were clearly exposed. The facet joints in the corresponding levels were then opened by removal of the capsules. Three measurements, including the height of the dorsal ramus, the distance between the dorsal ramus and the tip of the superior articular facet, and the angle of the dorsal ramus relative to the superior articular surface, were taken for each ramus. RESULTS: The results showed that the mean height of the dorsal ramus for both sides decreased progressively from C3 (2.2 +/- 0.6 mm) to C7 (1.2 +/- 0.2 mm). The mean distance between the dorsal ramus and the tip of the superior facet showed an inconsistent change, with the maximum value seen at C5 (7.4 +/- 1.6 mm) and the minimum at C7 (5.5 +/- 2.9 mm). The mean angle of the dorsal ramus relative to the superior articular facet ranged from 23.3 degrees +/- 14.3 degrees to 29.8 degrees +/- 11.2 degrees. CONCLUSIONS: The dorsal ramus of the cervical spinal nerve is closer to the anterolateral corner of the base of the superior articular processes. Lateral mass screws directed to the anterolateral corner of the base of the superior articular process should be avoided.

Aged↗
PubMed1998

Safe lateral-mass screw lengths in the Roy-Camille and Magerl techniques. An anatomic study.

STUDY DESIGN: Investigation of the mean safe lateral-mass screw lengths in the Roy-Camille and Magerl screw techniques in cadaveric cervical specimens. OBJECTIVES: To report the mean screw path length and to evaluate the relation of the screw trajectory to the nerve root in the Roy-Camille and Magerl screw techniques. SUMMARY OF BACKGROUND DATA: Potential injury to the cervical nerve root caused by too long a screw remains a major concern. Few studies regarding proper screw length and its relation to the adjacent nerve root are available. METHODS: Fourteen cervical spines were used for this study. Each lateral mass from C3 to C7 was drilled according to the techniques described by Roy-Camille (right side) and Magerl (left side). The cervical spines were harvested from the cadavers, and the anterior aspect of the lateral mass and spinal nerve were exposed. The screw path length between the dorsal and ventral cortices of the lateral mass were measured. An additional measurement was taken from the ventral aspect of the lateral mass to the nerve root along the screw path. RESULTS: The mean screw path length in the Roy-Camille technique decreased consistently from C3 (15.7 +/- 1.7 mm) to C7 (11.3 +/- 0.8 mm). The mean distance from the ventral cortex to the nerve root ranged from 1.2 to 2.3 mm, and the smallest value was at C7. The mean screw path length in the Magerl technique also decreased from cephelad to caudal, with a range of 15-16 mm at C3-C6 and a mean value of 13.8 mm at C7. CONCLUSIONS: A safe screw length is 14-15 mm in the Roy-Camille technique and 15-16 mm in the Magerl technique at C3-C6. A short screw may be used at C7 if desired.

Bone Plates↗
PubMed1998

Synthesis and pharmacological characterization of O-alkynyloximes of tropinone and N-methylpiperidinone as muscarinic agonists.

A number of O-alkynyloximes of tropinone and N-methyl-4-piperidinone have been synthesized and evaluated for muscarinic activity. The affinities of these oximes were tested in homogenates of cerebral cortex, heart, and submandibulary glands from rats using [3H]pirenzepine and [3H]-N-methylscopolamine as radioligands. The oximes bind to the cortical muscarinic receptors with pKi values varying from 3 to 7. Higher binding affinities were observed for the O-alkynyl tropinone oximes than the corresponding piperidinone analogues. Binding to the muscarinic sites in the heart and submandibulary glands was also observed but with lower affinities. Good M1 subtype selectivity (10-fold or greater) was observed with some oximes (26a, 28a, 32a) at the cortical sites. These oximes also attenuated scopolamine-induced impairment of the water mask task in mice. Functional assays for M3 activity on the rat aorta showed that all oximes possessed M3 agonist action but M2 agonist activity was not observed at the endothelium-denuded rabbit aorta. Analysis of the quantitative structure-activity relationship (QSAR) indicated that the Connolly surface area is an important determinant of activity, accounting for 70% of the variation in cortical binding affinity among the oximes.

Animals↗