PubMed Health⌕ Search

Biomedical subjects

J X Shen

Publications and source records attributed to J X Shen.

18 recordsLinked to original sources
PubMed2005

Vertebroplasty by use of a strontium-containing bioactive bone cement.

STUDY DESIGN: A review of the laboratory and clinical data for a new strontium-containing hydroxyapatite bioactive bone cement. OBJECTIVES: To compare the properties of the strontium-containing bioactive bone cement with those of polymethyl methacrylate (PMMA) and hydroxyapatite (HA) bone cements. SUMMARY OF BACKGROUND DATA: Vertebroplasty and kyphoplasty using conventional PMMA bone cements have been effectively used to treat osteoporotic spine fractures with good short- and medium-term results. However, PMMA has some undesirable properties, including its high setting temperature, lack of osseointegration, and large stiffness mismatch with osteoporotic bone. These properties are responsible for some postoperative complications. METHODS: Strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement consists of a filler blend of strontium-containing hydroxyapatite, fumed silica and benzoyl peroxide; and a resin blend of bisphenol A diglycidylether methacrylate, triethylene glycol dimethacrylate, poly(ethylene glycol) methacrylate, and N, N-dimethyl-p-toluidine. Its properties, including mechanical strength, setting temperature, biocompatibility, and osseoinduction, were compared with other cements in vitro and in vivo. Early clinical results are presented. RESULTS: The Sr-HA cement has a setting time of 15 to 18 minutes, a maximum setting temperature of 58 degrees C, a compressive strength of 40.9 MPa, bending strength of 31.3 MPa, and a bending modulus of 1,408 MPa. The bending strength and modulus are closer to human cancellous bone. Sr-HA cement promotes osteoblast attachment and mineralization in vitro and bone growth and osseointegration in vivo. In a pilot study, 23 cases of osteoporotic fractures treated with this cement with a mean follow-up of 18 months suggest that it is as effective as PMMA in relieving pain. DISCUSSIONS: Oral strontium has been shown to induce new bone formation and is effective in reducing fracture risk in osteoporosis. Our data suggest that strontium delivered locally has the same effect; thus, the combination of strontium with HA in a cement with a low setting temperature, adequate stiffness, and low viscosity makes this a good bioactive cement for vertebroplasty and kyphoplasty.

Animals↗
PubMed2004

Microfracture and changes in energy absorption to fracture of young vertebral cancellous bone following physiological fatigue loading.

STUDY DESIGN: Fifty-five human thoracolumbar vertebrae were randomly fatigue loaded and analyzed. OBJECTIVES: The purpose of this study was to explore the relationship between fatigue loading, trabecular microfracture, and energy absorption to fracture in human cadaveric thoracolumbar vertebrae. BACKGROUND: Although trabecular microfractures are found in vivo and have been produced by fatigue loading in vitro, the effect of the level of physiologic fatigue loading on microfracture and energy absorption has not been investigated. METHODS: Fifty-five human thoracolumbar vertebrae (T11-L4) were randomly divided into 5 groups: 1) control (no loading, n = 6); 2) axial compression to yield (n = 7); and 3-5) 20,000 cycles of fatigue loading at 2 Hz (each n = 14). The level of fatigue loading was determined as a proportion of the yield load of Group 2 as follows: 10% (Group 3), 20% (Group 4), and 30% (Group 5). Half of the specimens in groups 3 to 5 were used for radiographic and histomorphometric analysis to determine microfracture density and distribution, whereas the other half were tested to determine the energy absorption to yield failure. RESULTS: No radiographic evidence of gross fracture was found in any of the groups following fatigue loading. A mean 7.5% increase in stiffness was found in specimens subject to cyclic loading at 10% of yield stress (Group 3). Fatigue at 20% (Group 4) and 30% of yield stress (Group 5) caused significantly higher (P < 0.05) increases in mean stiffness of 23.6% and 24.2%, respectively. Microfracture density increased from 0.46/mm in Group 3 to 0.66/mm in Group 4 and 0.94/mm in Group 5 (P < 0.05). The energy absorbed to failure decreased from 21.9 J in Group 3 to 18.1 J and 19.6 J in Groups 4 and 5, respectively (P < 0.05). CONCLUSIONS: Fatigue loading at physiologic levels produced microfractures that are not detectable by radiography. Increased fatigue load results in an increase in microfracture density and decrease energy absorbed to fracture, indicating a reduced resistance to further fatigue loading.

Absorptiometry, Photon↗
PubMed2001

[Application of diapason instrumentation for treatment of unstable lumbosacral spinal stenosis].

OBJECTIVE: To observe the preliminary clinical outcome of using a new instrumentation Diapason system and to introduce the characterization and surgical technique of this new system for treatment of unstable lumbar spinal stenosis. METHODS: 16 patients with unstable spinal stenosis who were treated by decompression, posterolateral intertransverse arthrodesis and transpedicle instrumentation of Diapason system, were analyzed retrospectively. RESULTS: Lower back pain (LBP) of 16 patients were significantly alleviated after surgery (scores of LBP before operation: 47.5 +/- 0.8; scores of LBP after operation: 31.9 +/- 2.3, P < 0.001). There was no implant failure, no early or later infection and no neurological complications in 16 patients at an average of 6.2-month follow-ups. No pseudoarthrosis was observed on roentgenography. CONCLUSION: Our short-term follow-up and limited cases study showed satisfactory preliminary result of treating unstable lumbar spinal stenosis with Diapason internal fixation.

Adult↗
PubMed2000

Neural representation of sound duration in the inferior colliculus of the mouse.

In this study we examined the neuronal responses of single units to different sound durations in the inferior colliculus (IC) of the mouse. One hundred and one recorded units were classified into onset (58%), sustained (9%) on-sustained (22%), pauser (9%) and chopper (2%) response patterns. Thirty-four percent of the recorded units showing stronger responses to long stimulus durations were defined as long-duration-selective neurons. Twenty-five percent of the units preferred a narrow range of sound durations and were classified as band-pass neurons. Ten percent of the units responded preferentially to short stimulus durations and thus displayed short-duration selectivity. Twelve percent of the units that responded with nearly constant spike counts to stimuli of varying duration were classified as all-pass neurons. In contrast to the result of no short-duration-selective neurons found in chinchilla IC, we observed that some of the onset units in the IC of the mouse displayed a short duration preference. The best duration range of the duration-selective neurons in the present study corresponds to the duration range of mouse calls. We suggest that an inhibitory mechanism contributes to the duration selectivity observed in the present study.

Animals↗
PubMed2000

Speech evaluation of partially implantable piezoelectric middle ear implants in vivo.

OBJECTIVE: Cochlear microphonic responses (CMs) were measured in a rabbit model in the intact ear (CM1) and in ears with a partially implantable piezoelectric middle ear implant (P-MEI) (CM2) to investigate the characteristics of speech transmission of the P-MEI in vivo. DESIGN: The spectra of pure tones, voices, and elicited CM1 and CM2 obtained from the round window before and after the implantation of a P-MEI device were calculated by using fast Fourier transform. Frequency response functions of CM1 and CM2 were used to demonstrate the functional similarity between the implanted P-MEI and the normal ossicular chain. The coherence functions between the voices and CM1 and between CM1 and CM2 were evaluated to characterize speech transmission of the P-MEI in vivo. Ten rabbit ears were used in this study. Pure tones, six Chinese vowels, and six Chinese characters were the acoustic stimuli. The CMs elicited by a list of bisyllabic words were tape-recorded and then recognized by subjects with normal hearing. RESULTS: Using pure tones at the same intensity of 90 dB SPL, frequency response functions of the CMs between the two states (the intact ear with normal hearing and ears with a P-MEI device at the medium volume) were calculated showing great resemblance in shape. Compared with that at 1 kHz, gain factors were 10 and 20 dB, respectively, at higher frequencies. The correlation and spectral analyses of the vocalizations, CM1 and CM2, demonstrated that the harmonics of CM1 were approximately identical as those of the voices between 0.5 and 5.0 kHz with coherence functions of about 0.7 to approximately 1 at the formants' frequencies, whereas the harmonics of CM2 between 0.5 and 2.5 kHz were enhanced with the coherences near to unity at the formants' frequencies, and others <0.5 kHz and >2.5 kHz were attenuated. The recognition score of the CMs elicited by a list of bisyllabic words was >90% using subjects with normal hearing. CONCLUSIONS: Data from this study suggest that cochlear microphonic potentials can be used as an important tool to evaluate objectively whether the implantation of a P-MEI device is successful and whether the quality in speech transmission of the P-MEI is satisfactory. Thus, the method would be of significance to clinically ascertain the performance of the device in vivo.

Animals↗
PubMed1999

Evidence for columnar organization in the auditory cortex of the mouse.

Single cortical auditory neurons sequentially isolated within orthogonal electrode penetrations in the mouse were studied using tonal stimulation. They had common functional properties, such as firing pattern, best frequency, minimum threshold, sharpness of frequency tuning and onset latency. The finding suggests that there is columnar organization in the cortex.

Animals↗
PubMed1999

[A quantitative study on the synaptic ultrastructural alterations in visual cortex in the maintenance of LTP].

The ultrastructure of synapses three hours after formation of long-term potentiation (LTP) was examined in the local microslices of visual cortical brain slices of 18-20 d rats. Slices without potentiating stimulation which were similarly incubated served as controls. The following structural changes were examined using a graph analyzer: (1) synaptic cleft width; (2) thickness of the postsynaptic densities(PSD); (3) length of the active zones; and (4) curvature of the synaptic interface. The number of synapses of different types in layer II/III of visual cortex was quantified by double-blind scoring procedures. The various counts were converted to the number of synapses per unit volume using stereological quantitation method. Analysis of variance was used for statistical evaluation. Our results suggest that field potentials reached their peak values at about one and a half hours after tetanus and could be maintained as long as three hours without decay. In comparison with the control groups, synaptic cleft width, thickness of PSD, surface density per unit volume(Sv) of the active zones, curvature of the synaptic interface, numeric density per unit volume (Nv) of all synapses, spine synapses and the Nv of perforated synapses were all increased significantly. These data suggest that the increase of Sv of active zones and the increase of the curvature of synaptic interface may be the morphological feature characterizing the maintenance of LTP, in addition to the formation of perforated synapses.

Animals↗
PubMed1997

Binaural and frequency representation in the primary auditory cortex of the big brown bat, Eptesicus fuscus.

This study examines the binaural and frequency representation in the primary auditory cortex (AC) of the big brown bat, Eptesicus fuscus, by using an ear-phone stimulation system. All 306 cortical neurons studied were excited by contralateral sound stimulation but they were either excited, inhibited or not affected by ipsilateral sound stimulation. These cortical neurons were columnarly organized according to their binaural and frequency-tuning properties. The excitation-excitation columns which occupy about 15% of the AC are mainly aggregated within an oval-shaped area of the central AC. The excitation-inhibition neurons and binaural neurons with mixed properties are distributed in the remaining 85% of the surrounding primary AC. Although the best frequency (BF) of these neurons shows a tendency to decrease from high to low along the anteroposterior axis of the primary AC, systematic variation in BF is not always consistent across the entire mapping area. In particular, BFs of cortical neurons isolated in the anterior AC vary quite unsystematically such that neurons with similar BFs are aggregated in isolated patches. Isofrequency and binaural columns are segregated into bands that intersect each other.

Acoustic Stimulation↗
PubMed1997

Cytoarchitecture and sound activated responses in the auditory cortex of the big brown bat, Eptesicus fuscus.

Under free field and closed-system stimulation conditions, we studied the frequency threshold curves, auditory spatial sensitivity and binaurality of neurons in the primary auditory cortex (AC) of the big brown bat, Eptesicus fuscus. All 298 recorded AC neurons discharged phasically. They were recorded at depths less than 1,000 microns with response latencies of 7-25 ms, best frequencies (BFs) of 28-97 kHz and minimum thresholds (MTs) of 8-90 dB SPL. They received excitatory inputs from the contralateral ear and either excitatory (EE) or inhibitory (EI) inputs from the ipsilateral ear. These cortical neurons were tonotopically organized along the anteroposterior axis of the AC. High best frequency neurons were located anteriorly and low best frequency neurons posteriorly. They were most sensitive to sounds delivered from a restricted region of the contralateral frontal auditory space (0 degree-50 degrees in azimuth and 2 degrees up, 15 degrees down in elevation). Frontal auditory space representation appears to be systematically arranged according to the tonotopic axis such that the lateral space is represented posteriorly and the middle space anteriorly. Cortical neurons sequentially isolated from an orthogonally penetrated electrode had similar frequency threshold curves, BFs, MTs, points of maximal auditory spatial sensitivity and binaurality. The EE and EI columns are organized concentrically such that the small number of centrally located EE columns were surrounded by an overwhelming number of EI columns. Using Nissl and Golgi stains as well as c-fos immunocytochemistry, we studied the cytoarchitecture, cell types and sound elicited Fos-like immunoreactivity in the primary AC of this bat species. The primary AC of this bat species can be described into molecular (137 microns), external granular (55 microns), external pyramidal (95 microns), internal granular (102 microns), internal pyramidal (191 microns) and multiform (120 microns) layers. The main type of cells distributed among these six layers are the small, medium and large pyramidal cells. Others include the stellate, horizontal, granular, fusiform, basket, and Martinotii cells. When stimulated with 30 kHz and 79 dB SPL sounds under natural conditions, bilaterally and symmetrically distributed Fos-like immunoreactive neurons were observed in about 20% of neurons in each AC. When stimulated under monaurally plugged conditions, 39-48% more of Fos-like immunoreactive neurons were observed in the ipsilateral AC. This finding supports the fact that the primary AC receives auditory inputs mainly from the contralateral ear.

Acoustic Stimulation↗
PubMed1996

Use of infrared multiphoton photodissociation with SWIFT for electrospray ionization and laser desorption applications in a quadrupole ion trap mass spectrometer.

Infrared multiphoton photodissociation (IRMPD) is combined with stored wave form inverse Fourier transforms (SWIFT) to effect dissociation and ion ejection in a quadrupole ion trap mass spectrometer. The application of IRMPD to the structural characterization of biochemical ions generated by chemical ionization and electrospray ionization and the feasibility of utilizing infrared photons for the activation of laser-desorbed metal ion-crown ether complexes was examined. The effect of helium pressure on the dissociation efficiency and relative dissociation rate constants for systems with well-known thermochemistry was evaluated. The helium pressure is not detrimental to the IRMPD experiment when nominal pressures lower than 2 x 10(-5) Torr are used. At pressures close to nominally 8 x 10(-5) Torr of helium, collisonal deactivation dominates. Results show conventional CAD is a more selective dissociation technique; however, the amount of fragment ion information generated depends highly on the qz value. IRMPD, on the other hand, is independent of the value of qz such that low rf storage values can be utilized during the irradiation period. Thus, under these conditions, informative lower mass fragment ions are trapped and detected. A larger number of structurally informative fragments is generated upon irradiation with infrared photons relative to the CAD method because of the further excitation of primary fragment ions upon photoabsorption. SWIFT wave forms are successfully utilized to determine the extent of excitation of primary fragment ions as well as prove/disprove dissociation pathways of a variety of ions such as macrolide antibiotics and hydrogen-bonded complexes.

Lasers↗
PubMed1993

[Studies on the basophil histamine releasability in allergic rhinitis].

Observing the basophil releasability of 17 patients with allergic rhinitis and 14 nonatopic subjects stimulated with house dust mite and concanavalin A (ConA), we found that the histamine release was much higher in patients with allergic rhinitis than in normal controls and that no positive correlation was found between the histamine release rate and the serum total IgE. This result suggests that the enhanced basophil releasability might be an important factor in allergic disorders, and might contribute to a means for the differentiation between allergic and non-allergic disorders.

Adult↗
PubMed1993

Morphology and physiology of auditory interneurons of the bushcricket Gampsocleis gratiosa.

Seven types of auditory interneurons were characterized from the prothoracic ganglion of the bushcricket. They are sensitive in the range of 7-18 kHz and fire with distinct discharge patterns. They encode sound intensity and temporal parameters in various way. They show significant directional sensitivity, dependent on sound frequency. The acoustic tracheal system can partly account for the directional hearing of the bushcricket.

Acoustic Stimulation↗
PubMed1989

[The synthesis and pharmacological activities of analogs of erycibe alkaloid II].

The C2 deoxy and C6 electron isosteric analogs of a new antiglaucoma agent, erycibe alkaloid II, were designed and synthesized. The main pharmacological results were as follows: 1. The C2-OH in erycibe alkaloid II was one of the key groups for its myotic activity; 2. It was worth noting that compounds 2 and 4 showed cholinergic and anticholinergic activities, respectively. This phenomenon in tropane alkaloids was not reported before; 3. The C6 electron isosteric compounds 16 and 17 showed neither anticholinergic nor cholinergic activities.

Animals↗
PubMed1988

Interaction of 2-halogenated dATP analogs (F, Cl, and Br) with human DNA polymerases, DNA primase, and ribonucleotide reductase.

Recently, 2-halogenated deoxyadenosine analogs (F, Cl, and Br) have been shown to have antitumor activity. These analogs are phosphorylated by cells and are believed to exert their cytotoxic action at the nucleoside triphosphate level. In this work the interaction of these nucleoside triphosphate analogs with potential targets, such as DNA polymerase alpha, beta, and gamma, DNA primase, and ribonucleotide reductase was examined in detail. All of these compounds competitively inhibited the incorporation of dAMP into DNA by DNA polymerase alpha, beta, or gamma. F-dATP was able to completely substitute for dATP using DNA polymerase alpha and gamma, but not with DNA polymerase beta. Cl-dATP and Br-dATP substituted poorly for dATP using DNA polymerase alpha and beta. Extension of a 32P-labeled primer by DNA polymerase alpha, beta, or gamma on a single-stranded M13 template showed that these compounds were incorporated into the 3' end of the growing DNA chain and that elongation beyond the incorporated analogs was significantly retarded for Cl-dATP and Br-dATP using either DNA polymerase alpha or beta. DNA primase using poly(dC) as template was inhibited by these compounds at a concentration 4 to 5 times greater than that required for 2-F-araATP. The 2-halogenated dATP analogs were potent inhibitors of ADP reduction by ribonucleotide reductase. In conclusion, the cytotoxic action of 2-Cl-deoxyadenosine and 2-Br-deoxyadenosine may partially be mediated through the mechanism of "self-potentiation," by depression of the deoxynucleoside triphosphate pools due to inhibition of ribonucleotide reductase, which would facilitate their incorporation into DNA and result in the inhibition of DNA synthesis.

Antineoplastic Agents↗