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Biomedical subjects

H Q Zhang

Publications and source records attributed to H Q Zhang.

At least 19 recordsLinked to original sources
PubMed2005

Demonstration of bulk acceleration of ions in ultraintense laser interactions with low-density foams.

Ion acceleration inside low-density foams irradiated by ultraintense laser pulses has been studied experimentally and theoretically. It is found that the ion generation is closely correlated with the suppressed hot electron transport inside the foams. Particle-in-cell simulations suggest that localized electrostatic fields with multi peaks around the surfaces of lamellar layers inside the foams are induced. These fields inhibit hot electron transport and meanwhile accelerate ions inside the foams, forming a bulk acceleration in contrast to the surface acceleration at the front and rear sides of a thin solid target.

Journal Article↗
PubMed2003

Impulse propagation over tactile and kinaesthetic sensory axons to central target neurones of the cuneate nucleus in cat.

Paired, simultaneous recordings were made in anaesthetized cats from the peripheral and central axons of individual tactile and kinaesthetic sensory fibres. The aim was to determine whether failure of spike propagation occurred at any of the three major axonal branch points in the path to their cuneate target neurones, and whether propagation failure may contribute, along with synaptic transmission failures, to limitations in transmission security observed for the cuneate synaptic relay. No evidence for propagation failure was found at the two major axonal branch points prior to the cuneate nucleus, namely, the T-junction at the dorsal root ganglion, and the major branch point near the cord entry point, even for the highest impulse rates (approximately 400 impulses s(-1)) at which these fibres could be driven. However, at the highest impulse rates there was evidence at the central, intra-cuneate recording site of switching between two states in the terminal axonal spike configuration. This appears to reflect a sporadic propagation failure into one of the terminal branches of the sensory axon. In conclusion, it appears that central impulse propagation over group II sensory axons occurs with complete security through branch points within the dorsal root ganglion and at the spinal cord entry zone. However, at high rates of afferent drive, terminal axonal propagation failure may contribute to the observed decline in transmission security within the cuneate synaptic relay.

Action Potentials↗
PubMed2003

Inhibition of hypoxia/reoxygenation-induced oxidative stress in HGF-stimulated antiapoptotic signaling: role of PI3-K and Akt kinase upon rac1.

Rac1-regulated reactive oxygen species (ROS) production has been implicated in apoptosis. In contrast, pleiotropic protein kinase Akt protects against apoptosis. However, the pro- and antiapoptotic mechanisms of rac1 and Akt, respectively, and the intersection between these mechanisms are incompletely understood. In a model of oxidative stress and apoptosis induced by hypoxia/reoxygenation (H/R) in primary hepatocytes, activation of the PI3-K Akt axis by the prosurvival hepatocyte growth factor (HGF) inhibited H/R-stimulated rac1 activation and intracellular ROS production, and suppressed apoptosis. Suppression of PI3-K or Akt activity abrogated the inhibitory effect of HGF on rac1 activity and rac1-regulated oxidative stress. Furthermore, constitutive activation of Akt or PI3-K in the absence of HGF was sufficient to phosphorylate rac1, inhibit rac1 activation, and suppress rac1-regulated ROS production. These findings demonstrate that growth factor-stimulated activation of PI3-K-Akt is necessary and sufficient to suppress intracellular oxidative stress and apoptosis by inhibiting activation of pro-apoptotic, prooxidative rac1 GTPase.

Androstadienes↗
PubMed2002

Biological treatment characteristics of benzene and toluene in a biofilter packed with cylindrical activated carbon.

The biodegradation of toluene and benzene in a biofilter using cylindrical activated carbon as the filler materials was studied. Three gas low rates, i.e. 0.25, 0.50 and 0.75 m3/h, corresponding to empty bed gas residence of 75, 37.5 and 25 s, respectively, and total organic load lower than 400 g/m3 x h were tested. The biofilter proved to be highly efficient in biodegradation of toluene and benzene, and toluene was more easily degraded than benzene. When each inlet load was lower than 150 g/m3 x h, removal rate increased with inlet load and reached a maximum, which was 150 and 120 g/m(-3) x h for toluene and benzene, respectively. For inlet load higher than the maximum removal capacity conditions, the removal rate decreased with inlet load. Carbon dioxide concentration profile through the biofilter revealed that the mass ratios of carbon dioxide produced to the toluene and benzene removed were 2.15 g(CO2)/g(toluene) and 1.67 g(CO2)/g(benzene), which furthermore, confirmed the biodegradation performance in biofilter. The observation of biotic community demonstrated that the microbes consisted of bacillus, spore bacillus and fungi, of which the spore bacillus was dominant.

Adsorption↗
PubMed2001

The inhibitory effect of serotonin on the spontaneous discharge of suprachiasmatic neurons in hypothalamic slice is mediated by 5-HT(7) receptor.

The effects of serotonin (5-HT) receptor agonists and antagonists on the spontaneous discharge of suprachiasmatic nucleus (SCN) neurons were investigated using rat hypothalamic slice. It was found that: (1) the SCN neurons showed a persistent rhythm in the spontaneous discharge rate, which was higher during the light phase than during the dark phase; (2) the effects of 5-HT on SCN neurons was inhibitory in nature and the sensitivity of SCN neurons to 5-HT during the light phase was lower than that during the dark phase; (3) both 5-HT and 5-HT(1/7) receptor agonist, (+/-)-8-hydroxy-2-(DL-N-propylamino) tetralin hydrobromide, could inhibit the spontaneous discharge of SCN neurons. This inhibitory effect could be blocked by 5-HT(2/7) receptor antagonist ritanserin and putative 5-HT(7) receptor antagonists clozapine, but neither by selective 5-HT(2) receptor antagonist ketanserin, nor by 5-HT(1) receptor antagonist pindolol. It was suggested that the inhibitory effect of 5-HT on the spontaneous discharge of SCN neurons in rat hypothalamic slice is mediated by 5-HT(7) receptor subtype.

Animals↗
PubMed2001

Characterization of tactile afferent fibers in the hand of the marmoset monkey.

The marmoset monkey, Callithrix jacchus, has increasingly been the subject of experiments for the analysis of somatosensory system function in simian primates. However, as response properties of the mechanoreceptive afferent fibers supplying the skin have not been characterized for this primate, the present study was undertaken to classify fibers innervating the glabrous skin of the marmoset hand and determine whether they resembled those described for other mammalian species, including cat, macaque monkey, and human subjects. Forty-seven tactile afferent fibers with receptive fields (RFs) on the glabrous skin of the hand were isolated in fine median and ulnar nerve strands. Controlled tactile stimuli, including static indentation and skin vibration, were used to classify fibers. Twenty-six (55%) responded to static indentation in a sustained manner and were designated slowly adapting (SA) fibers, while 21 (45%) were selectively sensitive to the dynamic components of the stimulus. The SA fibers had well-defined boundaries to their RFs, lacked spontaneous activity in most cases (23/26 fibers), had an irregular pattern of discharge to static skin indentation, and displayed graded response levels as a function of indentation amplitude, attributes that were consistent with the properties of slowly adapting type I (SAI) fibers described in other species. The dynamically sensitive afferent fibers could be subdivided into two distinct functional classes, based on their responses to vibrotactile stimulation. The majority (15/21) responded best to lower frequency vibration (~10-50 Hz) and had small RFs, whereas the second class responded preferentially to higher frequency vibration (50-700 Hz) with maximal sensitivity at ~200-300 Hz. These two classes resembled, respectively, the rapidly adapting (RA) and Pacinian corpuscle-related (PC) fiber classes found in other species, and like them, responded to vibration with tightly phase-locked patterns of response over a wide range of frequencies. The results demonstrate that the functional classes of tactile afferent fibers that supply the glabrous skin in the marmoset monkey appear to correspond with those described previously for the cat and macaque monkey, and are similar to those supplying the human hand and fingers, although the SA fibers in the human hand appear to fall into two classes, the SAI and SAII fibers. With the increasing use of the marmoset monkey as a primate model for somatosensory system studies, these data now allow tactile neurons identified at central locations, such as the cerebral cortex and thalamus, to be classified in relation to inputs from the peripheral classes identified in the present study.

Afferent Pathways↗
PubMed2001

Functional characteristics of the parallel SI- and SII-projecting neurons of the thalamic ventral posterior nucleus in the marmoset.

The functional organization of the primate somatosensory system at thalamocortical levels has been a matter of controversy, in particular, over the extent to which the primary and secondary somatosensory cortical areas, SI and SII, are organized in parallel or serial neural networks for the processing of tactile information. This issue was investigated for the marmoset monkey by recording from 55 single tactile-sensitive neurons in the lateral division of the ventral posterior nucleus of the thalamus (VPL) with a projection to either SI or SII, identified with the use of the antidromic collision technique. Neurons activated from the hand and distal forearm were classified according to their peripheral source of input and characterized in terms of their functional capacities to determine whether the direct thalamic input can account for tactile processing in both SI and SII. Both the SI- and SII-projecting samples contained a slowly adapting (SA) class of neurons, sensitive to static skin displacement, and purely dynamically sensitive tactile neurons that could be subdivided into two classes. One was most sensitive to high-frequency (> or =100 Hz) cutaneous vibration whose input appeared to be derived from Pacinian sources, while the other was sensitive to lower frequency vibration (< or =100 Hz) or trains of rectangular mechanical pulse stimuli, that appeared to receive its input from rapidly adapting (RA) afferent fibers presumed to be associated with intradermal tactile receptors. There appeared to be no systematic differences in functional capacities between SI- and SII-projecting neurons of each of these three classes, based on receptive field characteristics, on the form of stimulus-response relations, and on measures derived from these relations. These measures included threshold and responsiveness values, bandwidths of vibrational sensitivity, and the capacity for responding to cutaneous vibrotactile stimuli with phase-locked, temporally patterned impulse activity. The analysis indicates that low-threshold, high-acuity tactile information is conveyed directly to both SI and SII from overlapping regions within the thalamic VP nucleus. This direct confirmation of a parallel functional projection to both SI and SII in the marmoset is consistent with our separate studies at the cortical level that demonstrate first, that tactile responsiveness in SII largely survives the SI inactivation and second, that SI responsiveness is largely independent of SII. It therefore reinforces the evidence that SI and SII occupy a hierarchically equivalent network for tactile processing.

Afferent Pathways↗
PubMed2001

Hierarchical equivalence of somatosensory areas I and II for tactile processing in the cerebral cortex of the marmoset monkey.

Responsiveness of the first somatosensory area (SI) of the cerebral cortex was investigated in the marmoset monkey (Callithrix jacchus) in association with cooling-induced, reversible inactivation of the second somatosensory area, SII. The aim was to determine whether SI responsiveness to peripheral tactile stimulation depends on SII and therefore whether SI and SII in the marmoset occupy hierarchically equivalent positions in a parallel organizational scheme for thalamocortical tactile processing as appears to be the case in nonprimate mammals. Inactivation of SII was achieved when the temperature over SII was lowered to < or =12 degrees C, as indicated by abolition of the SII-evoked potentials generated by brief tap stimuli to the hand or foot, and by abolition of tactile responses in single SII neurons located at the margin beneath the block. The effect of SII inactivation on SI-evoked potentials was examined in 16 experiments by simultaneous recording of the SI- and SII-evoked potentials. SI-evoked potentials were never abolished and remained unaffected in 11 cases. In three experiments there was a small reduction in amplitude and inconsistent effects in the remaining two. Responsiveness to controlled tactile stimuli was examined quantitatively in 31 individual SI neurons of different functional classes before, during, and after the inactivation of SII. Tactile responsiveness in individual SI neurons was never abolished by SII inactivation, remaining unchanged in 20 neurons (65%) while undergoing some reduction in the remaining 11 SI neurons (35%). This reduction of tactile responsiveness in one-third of SI neurons is most likely attributable to a removal of a facilitatory influence emanating from SII, based on the observation that background activity of the affected neurons was also reduced. Furthermore, phase locking of SI responses to vibrotactile stimulation was unchanged when SII was inactivated. The retention of responsiveness in SI neurons when SII was inactivated by cooling in the marmoset demonstrates that tactile inputs can reach SI without traversing an indirect, serially organized path through SII. The present results, together with our previous observations that responsiveness in the majority of SII neurons survived SI inactivation, demonstrate that there is a parallel organization of the SI and SII areas for tactile processing in the marmoset monkey and that SI and SII occupy hierarchically equivalent positions in a parallel processing network. There is therefore no longer justification for the view that there are fundamental differences in the organization of thalamocortical tactile processing for SI and SII between simian primates, in general, and other mammals.

Afferent Pathways↗
PubMed2001

Transmission security for single, hair follicle-related tactile afferent fibers and their target cuneate neurons in cat.

Transmission from single, identified hair follicle afferent (HFA) nerve fibers to their target neurons of the cuneate nucleus was examined in anesthetized cats by means of paired recording from individual cuneate neurons and from fine, intact fascicles of the lateral branch of the superficial radial nerve in which it is possible to identify and monitor the activity of each group II fiber. Selective activation of individual HFA fibers was achieved by means of focal vibrotactile skin stimulation. Forearm denervation precluded inputs from sources other than the monitored HFA sensory fiber. Transmission characteristics were analyzed for 21 HFA fiber-cuneate neuron pairs in which activity in the single HFA fiber of each pair reliably evoked spike output from the target neuron at a fixed latency. As the cuneate responses to each HFA impulse often consisted of 2 or 3 spikes, in particular at HFA input rates up to approximately 20 imp/s, the synaptic linkage displayed potent amplification and high-gain transmission, characteristics that were confirmed quantitatively in measures of transmission security and cuneate spike output measures. In response to vibrotactile stimuli, the tight phase locking in the responses of single HFA fibers was well retained in the cuneate responses for vibration frequencies up to approximately 200 Hz. On measures of vector strength, the phase locking declined across the synaptic linkage by no more than approximately 10% at frequencies up to 100 Hz. However, limitations on the impulse rates generated in both the HFA fibers their associated cuneate neurons meant that the impulse patterns could not directly signal information about the vibration frequency above 50-100 Hz. Although single HFA fibers are also known to have secure synaptic linkages with spinocervical tract neurons, it is probable that this linkage lacks the capacity of the HFA-cuneate synapse for conveying precise temporal information, in an impulse pattern code, about the frequency parameter of vibrotactile stimuli.

Animals↗
PubMed2001

Chemo- and radio-protective effects of polysaccharide of Spirulina platensis on hemopoietic system of mice and dogs.

AIM: To observe polysaccharide of Spirulina platensis (PSp) on the hematopoietic system of mouse and dogs which were damaged by injection of cyclophosphamide (CTX) and 60Co-gamma irradiation. METHODS: CTX and 60Co gamma ray were used to induce bone marrow damage, and the experimental animals were ig with different dose of PSp in vivo, after 12-d and 21-d administration, the whole blood cells and nucleated cells in bone marrow were measured, and the DNA in bone marrow were inspected by UV-spectrophotometer. RESULTS: CTX and 60Co-gamma irradiation induced hemopoietic system damage in mice and dogs, respectively. PSp 30, 60 mg/kg increased the level of the white cells in blood and nucleated cells and DNA in bone marrow in mice but had no effects on red cells and hemoglobins. PSp 12 mg/kg increased the level of red cells, white cells, and hemoglobins in blood and nucleated cells in bone marrow in dogs (P < 0.01), and the effects of PSp 60 mg/kg were better than that of berbamine hydrochloride 60 mg/kg. CONCLUSION: PSp has chemo-protective and radio-protective capability, and may be a potential adjunct to cancer therapy.

Animals↗
PubMed2000

Effect of Bcl-2 and caspase-3 on calcium distribution in apoptosis of HL-60 cells.

Apoptosis manifests in two major execution programs downstream of the death signal: the caspase pathway and organelle dysfunction. An important antiapoptosis factor, Bcl-2 protein, contributes in caspase pathway of apoptosis. Calcium, an important intracellular signal element in cells, is also observed to have changes during apoptosis, which maybe affected by Bcl-2 protein. We have previously reported that in Harringtonine (HT) induced apoptosis of HL-60 cells, there's a change of intracellular calcium distribution, moving from cytoplast especially Golgi's apparatus to nucleus and accumulating there with the highest concentration. We report here that caspase-3 becomes activated in HT-induced apoptosis of HL-60 cells, which can be inhibited by overexpression of Bcl-2 protein. No sign of apoptosis or intracellular calcium movement from Golgi's apparatus to nucleus in HL-60 cells overexpressing Bcl-2 or treated with Ac-DEVD-CHO, a specific inhibitor of caspase-3. The results indicate that activated caspase-3 can promote the movement of intracellular calcium from Golgi's apparatus to nucleus, and the process is inhibited by Ac-DEVD-CHO (inhibitor of caspase-3), and that Bcl-2 can inhibit the movement and accumulation of intracellular calcium in nucleus through its inhibition on caspase-3. Calcium relocalization in apoptosis seems to be irreversible, which is different from the intracellular calcium changes caused by growth factor.

Apoptosis↗
PubMed1999

Size effect in resin/glass composite flexure strengths.

The objective of this study was to test the hypothesis that composite restorative materials possess an elastic-brittle nature and therefore will exhibit a size effect for flexure strength data. The experimental material consisted of 20 wt% 60:40 BISGMA:TEGDMA, 10 wt% colloidal silica, and 70 wt% Sr glass and was cured by light irradiation. Two sizes of flexure specimens were fabricated: 3.2x1.6x35 mm, and 6.25x3.1x35 mm. Half of the specimens made were soaked to equilibrium weight gain in 50:50 ethanol:water. The fracture strengths were measured in four-point bending tests. The beams under load were modelled by the finite element package ABAQUS. A statistical fracture mechanics methodology embodied in a public domain computer program called CARES/LIFE, developed by NASA, utilized the ABAQUS input and the fracture strengths of the smaller specimens to predict the fracture strengths of the larger specimens. In making the computation it used an approach that combines a Weibull distribution of flaw size with Batdorf's fracture mechanical model for failure at a material flaw. Both the soaked and unsoaked specimens exhibited Weibull behaviour, with shape parameters ranging from 4.04 to 8.15. Soaking had a clearly detrimental effect on the strengths of specimens of both sizes, and produced a comparable percentage reduction in the estimated scale parameter of the fracture strength distribution. Both the soaked and unsoaked specimens also exhibited a clear and comparable size effect, i.e. the larger specimens had a fracture strength that was lower than that of the smaller specimens by roughly the same percentage. Moreover, the magnitude of the size effect was well predicted by the CARES/LIFE methodology for both the soaked and the dry specimens. The elastic-brittle character of both soaked and unsoaked composite specimens was validated by load-deflection data, the magnitude of the Weibull shape parameters of the observed fracture strength data (<10), and the observed effect of specimen size. The accuracy of CARES/LIFE in predicting the magnitude of the observed size effect in beams of two different sizes strongly suggests that CARES/LIFE will be useful for computation of failure probabilities for clinically relevant structures.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1999

Organization of somatosensory areas I and II in marsupial cerebral cortex: parallel processing in the possum sensory cortex.

Organization of somatosensory areas I and II in marsupial cerebral cortex: parallel processing in the possum sensory cortex. Controversy exists over the organization of mammalian thalamocortical somatosensory networks. An issue of particular contention is whether the primary and secondary somatosensory areas of cortex (SI and SII) are organized in a parallel or serial scheme for processing tactile information. The current experiments were conducted in the anesthetized brush-tail possum (Trichosurus vulpecula) to determine which organizational scheme operates in marsupials, which have taken a quite different evolutionary path from the placental species studied in this respect. The effect of rapid reversible inactivation of SI, achieved by localized cortical cooling, was examined on both evoked potential and single neuron responses in SII. SI inactivation was without effect on the amplitude, latency, and time course of SII-evoked potentials, indicating that the transient inputs responsible for the SII-evoked potential reach SII directly from the thalamus rather than traversing an indirect serial route via SI. Tactile responsiveness was examined quantitatively before, during, and after SI inactivation in 16 SII neurons. Fourteen were unchanged in their responsiveness, and two showed some reduction, an effect probably attributable to the loss of a facilitatory influence exerted by SI on a small proportion of SII neurons. The temporal precision and pattern of SII responses to dynamic forms of mechanical stimuli were unaffected, and temporal dispersion in the SII response bursts was unchanged in association with SI inactivation. In conclusion, the results establish that, within this marsupial species, tactile inputs can reach SII directly from the thalamus and are not dependent on a serially organized path through SI. A predominantly parallel organizational scheme for SI and SII operates in this representative of the marsupial order, as it does in a range of placental mammals including the cat and rabbit, the tree shrew and prosimian galago, and at least one primate representative, the marmoset monkey.

Animals↗
PubMed1999

[Clinical observation of one-visit root canal therapy by microwave instrument]

OBJECTIVE:To analysis post-treatmental reaction and long-term effect of one-visit root canal therapy by microwave instrument. METHODS:Applying heat effect and the other ones of microwave,the changes of dentine tissue of extracted teeth were observated by SEM examination.48hs and 1 year post-treatmental effect of 47 patients of periapical periodontitis treated by one-visit root canal therapy were observated and compared with the results of 54 cases treated with common method.RESULTS:In the cases of acute and chronic periapical periodontitis microwave applied in root canal therapy can close the openings of dentine,enhance the effects of sterilization and decrease times of treatment.CONCLUSION:Microwave applied in one-visit root canal therapy is competent.

Journal Article↗
PubMed1998

Signalling of static and dynamic features of muscle spindle input by cuneate neurones in the cat.

1. The capacity of cuneate neurones to signal information derived from muscle spindle afferent fibres about static stretch or vibration of forearm extensor muscles was examined electrophysiologically in anaesthetized cats. 2. Static stretch (>= 2 mm in amplitude) and sinusoidal vibration (at frequencies of 50-800 Hz) were applied longitudinally to individual muscle tendons by means of a feedback controlled mechanical stimulator, and responses were recorded from individual cuneate neurones and from individual spindle afferent fibres. 3. Cuneate neurones sampled were located caudal to the obex and displayed a sensitivity to both vibration and static stretch of forearm muscles that was consistent with their input arising from primary spindle endings. In response to static muscle stretch, they displayed graded and approximately linear stimulus-response relations, and a stability of response level at fixed lengths that was consistent with these neurones contributing discriminative information about static muscle stretch. 4. In response to sinusoidal muscle vibration the cuneate neurones also showed graded stimulus-response relations (in contrast to spindle afferents which at low vibration amplitudes attain a plateau response level corresponding to a discharge of 1 impulse on each vibration cycle). Lowest thresholds were at 100-300 Hz and bandwidths of vibration sensitivity extended up to approximately 800 Hz. 5. Temporal precision in cuneate responses to muscle vibration was assessed by constructing phase scatter and cycle histograms from which measures of vector strength could be calculated. Cuneate responses displayed somewhat poorer phase locking (and lower vector strengths) than spindle afferent responses to vibration (a reflection of uncertainties associated with synaptic transmission). Nevertheless, the remarkable feature of cuneate responses to muscle vibration is the preservation of tight phase locking at frequencies up to 400-500 Hz, which presumably enables these central neurones to contribute accurate temporal information for the kinaesthetic sense in a variety of circumstances involving dynamic perturbations to skeletal muscle.

Animals↗
PubMed1998

Involvement of interleukin-2 in analgesia produced by Coriolus versicolor polysaccharide peptides.

AIM: To study the role of interleukin-2 (IL-2) and mediobasal hypothalamus (MBH) in analgesia produced by Coriolus versicolor polysaccharide peptide (PSP). METHODS: The IL-2 antiserum was injected i.c.v. or i.p. and the MBH was destroyed electrolytically. RESULTS: PSP i.g. 1 g.kg-1.d-1 for 6 d increased the pain threshold in tail stimulation-vocalization test in rats. This PSP-produced analgesia was blocked by i.c.v., but not i.p., IL-2 antiserum and disappeared after electrolytic lesion of MBH. CONCLUSION: The analgesia produced by PSP is mediated by IL-2 which is activated by PSP and interacts with IL-2 receptors in the MBH.

Analgesics, Non-Narcotic↗