Biomedical subjects

Qi Yuan

Publications and source records attributed to Qi Yuan.

7 recordsLinked to original sources

PubMed2026

Marine air promotes structural compaction and coating growth of soot aerosols after long-range transport from East Asia.

Soot aerosol, a key global warming contributor, undergoes morphological and chemical transformations during atmospheric transport, particularly in humidified marine environments. This study investigates morphology, mixing state, and aging mechanisms of soot particles collected in the Bohai Sea and Yellow Sea. Transmission electron microscopy analyses reveal that coated soot particles dominate the marine atmosphere, accounting for over 98 % of soot-containing particles, with a mean mixing state index (χ) of 0.83. The fractal dimension (Df) of soot particles is 1.84 ± 0.05 in the Northern Yellow Sea, 1.90 ± 0.08 in the Bohai Sea, and 1.96 ± 0.07 in the Southern Yellow Sea, indicating structural compaction during long-range transport. Correspondingly, the average Dp/Dcore ratios (particle to core size ratio) are 5.3 in the Bohai Sea, 4.2 in the Northern Yellow Sea, and 3.9 in the Southern Yellow Sea. Notably, those ratios are higher in marine environments compared to those observed during continental regional transport from northern to southern China (3.54), suggesting enhanced coating growth in humid marine air. The results highlight the important role of marine atmospheres in accelerating soot aging, which in turn leads to significantly stronger light absorption compared to soot in continental air. Our results highlight the necessity of incorporating compact morphologies, uniform mixing states, and thick coatings into optical models for accurate radiative forcing simulations.

Aerosols↗

PubMed2005

Long-term depression at olfactory nerve synapses.

The synapses formed by the olfactory nerve (ON) convey sensory information to olfactory glomeruli, the first stage of central odor processing. Morphological and behavioral studies suggest that glomerular odor processing is plastic in neonate rodents. However, long-term synaptic plasticity, a cellular correlate of functional and structural plasticity, has not yet been demonstrated in this system. Here, we report that ON-->mitral cell (MC) synapses of 5- to 8-d-old mice express long-term depression (LTD) after brief low-frequency ON stimulation. Pharmacological techniques and imaging of presynaptic calcium signals demonstrate that ON-MC LTD is expressed presynaptically and requires the activation of metabotropic glutamate receptors but does not require fast synaptic transmission. LTD at the ON--> MC synapse is potentially relevant for the establishment, maintenance, and experience-dependent refinement of odor maps in the olfactory bulb.

Animals↗

PubMed2003

Early odor preference learning in the rat: bidirectional effects of cAMP response element-binding protein (CREB) and mutant CREB support a causal role for phosphorylated CREB.

Early odor preference learning in rats is associated with increases of phosphorylated CREB (pCREB) in mitral cells of the olfactory bulb. In the present study, herpes simplex virus expressing CREB (HSV-CREB) and dominant-negative mutant CREB (HSV-mCREB) have been injected into the bulb to assess a causal role for CREB and pCREB in this model. Odor paired with stroking or with the beta-adrenoceptor agonist isoproterenol produces odor approach 24 hr later. Isoproterenol-induced learning exhibits an inverted U curve dose-dependent learning relationship with both low and high doses failing to produce learning. pCREB increases have only been seen at the learning effective dose. In the present study, injection of an HSV vector expressing mutant CREB into the olfactory bulb prevented learning induced by stroking. Control HSV expressing LacZ was without effect. Expression of mutant CREB shifted the dose-learning curve for isoproterenol to the right such that a higher dose was required to induce learning. Expression of CREB shifted the dose-learning curve for isoproterenol to the left, with a lower dose now producing learning. As expected from this shift, CREB overexpression interfered with learning induced by stroking. When learning occurred, with either CREB or mutant CREB, pCREB was observed to be elevated relative to the nonlearning LacZ control groups. Unexpectedly, with odor plus stroking in the nonlearning CREB group, the level of pCREB was also higher than with odor plus stroking in LacZ controls that did learn. The data demonstrate a causal role for CREB and pCREB in early mammalian odor preference learning, reinforcing CREB as a "universal" memory molecule. They support evidence that CREB overexpression can be deleterious and suggest the hypothesis of an optimal pCREB window for learning.

Adrenergic beta-Agonists↗

PubMed2003

Dynamic impact stress analysis of a bileaflet mechanical heart valve.

BACKGROUND AND AIMS OF THE STUDY: Mechanical heart valves (MHV) are widely used to replace dysfunctional and failed heart valves. The bileaflet MHV is very popular due to its superior hemodynamics. At present, bileaflet MHVs account for about two-thirds of the prosthetic heart valve market. Since their introduction in 1977, the hemodynamics of bileaflet prostheses has been extensively studied. New technologies used to develop MHV include better design concepts, materials, manufacturing processes, and post-design verification. The study aim was to investigate the dynamic impact stress of a newly designed bileaflet MHV under normal physiological conditions. METHODS: Pro/Engineer was used to generate a 3-D model of the designed valve. ANSYS 5.5 and LS-DYNA were used to calculate stress and deformation of the valve. Due to symmetry, a one-half orifice and one leaflet were modeled using the eight-noded hexahedral elements. When valve leaflets are in the fully closed position, the static contact stress between leaflet and orifice was predicated under typical heart valve closing pressure of 80 mmHg. To study the dynamic effects of the closing valve, LS-DYNA was used to simulate leaflet motion. Typical physiological pressure waveform was employed to initiate this leaflet motion. Two types of valve were investigated: Test valve A (size 19, flat leaflet); and test valve B (size 19, tapered leaflet 1.5 degrees, with the same thickness at pivot as valve A). The non-invasive laser sweeping technique was used to measure leaflet closing velocity in a mock flow test rig. The closing velocity of test valve A was compared by experimental and computed results. The corresponding dynamic contact stress on the leaflet was obtained for different modes of loading, simulated under angular velocity, acceleration, and especially under representative pressure waveform. RESULTS: The experimental closing velocity of test valve A was 1.07 +/- 0.05 m/s; the computed value was 1.130 m/s. During full closure, the leaflets showed a slight rebound, and this was also seen experimentally. For test valve B, the computed closing velocity was 1.039 m/s. In the dynamic impact analysis, the physiological pressure waveform was obtained at a normal heart rate of 70 beats/min from the mock flow test rig. Dynamic stress and displacement of the model valve were calculated as the valve was closing. The time step of calculation was determined by the wave propagation velocity and element size. With an interhinge distance of 4.966 mm based on the geometric design of the valve, maximum dynamic von Mises stress appeared near the hinge of the leaflet (26.92 MPa for valve A; 22.36 MPa for valve B). By varying the position of the hinge/pivoting axis (+/- 10%), an optimized valve geometry could be obtained based on minimal impact stress on the valve leaflet. CONCLUSION: Based on closing velocity comparison of valve A, the calculated model and loading conditions were seen to be reasonable. Computational accuracy was satisfied. The tapering feature of the leaflet is designed especially for minimal impact stress at the leaflet contact areas upon impact with the inner walls of the BMHV. These points provide an optimum structure design for the Nanyang Technological University BMHV.

Finite Element Analysis↗

PubMed2002

Optical imaging of odor preference memory in the rat olfactory bulb.

Early olfactory preference learning in rat pups occurs when novel odors are paired with reinforcing tactile stimulation that activate the noradrenergic locus coeruleus. Pairing of odor and a noradrenergic agonist in the olfactory bulb is both necessary and sufficient for odor preference learning. This suggests the memory change occurs in the olfactory bulb. Previous electrophysiological experiments demonstrated that odor preference training induces an increase in the field excitatory postsynaptic potential to olfactory nerve input and an alteration, after training, in glomerular [14C]2- deoxyglucose uptake and in single-unit responses of principal cells. We investigate here whether, 24 h after olfactory preference training, there is an alteration in intrinsic optical signals at the glomerular level. Six-day-old rat pups were trained, as previously, for a peppermint odor preference. Trained pups and control littermates were subjected to imaging of odor-induced intrinsic optical signals 1 day after the training session. Trained pups exhibited significantly larger responses to the peppermint compared with untrained littermates previously exposed to the same odor. The response of trained pups to a control odor (amyl acetate) was, however, not significantly different from that of untrained littermates. These observations demonstrate that odor preference memory can be read-out by optical imaging techniques.

Animals↗

PubMedDate not supplied

Mitral cell beta1 and 5-HT2A receptor colocalization and cAMP coregulation: a new model of norepinephrine-induced learning in the olfactory bulb.

In the present study we assess a new model for classical conditioning of odor preference learning in rat pups. In preference learning beta(1)-adrenoceptors activated by the locus coeruleus mediate the unconditioned stimulus, whereas olfactory nerve input mediates the conditioned stimulus, odor. Serotonin (5-HT) depletion prevents odor learning, with 5-HT(2A/2C) agonists correcting the deficit. Our new model proposes that the interaction of noradrenergic and serotonergic input with odor occurs in the mitral cells of the olfactory bulb through activation of cyclic adenosine monophosphate (cAMP). Here, using selective antibodies and immunofluorescence examined with confocal microscopy, we demonstrate that beta(1)-adrenoceptors and 5-HT(2A) receptors colocalize primarily on mitral cells. Using a cAMP assay and cAMP immunocytochemistry, we find that beta-adrenoceptor activation by isoproterenol, at learning-effective and higher doses, significantly increases bulbar cAMP, as does stroking. As predicted by our model, the cAMP increases are localized to mitral cells. 5-HT depletion of the olfactory bulb does not affect basal levels of cAMP but prevents isoproterenol-induced cAMP elevation. These results support the model. We suggest the mitral-cell cAMP cascade converges with a Ca(2+) pathway activated by odor to recruit CREB phosphorylation and memory-associated changes in the olfactory bulb. The dose-related increase in cAMP with isoproterenol implies a critical cAMP window because the highest dose of isoproterenol does not produce learning.

Adrenergic beta-Agonists↗

PubMedDate not supplied

Calcium signaling in mitral cell dendrites of olfactory bulbs of neonatal rats and mice during olfactory nerve Stimulation and beta-adrenoceptor activation.

Synapses formed by the olfactory nerve (ON) provide the source of excitatory synaptic input onto mitral cells (MC) in the olfactory bulb. These synapses, which relay odor-specific inputs, are confined to the distally tufted single primary dendrites of MCs, the first stage of central olfactory processing. beta-adrenergic modulation of electrical and chemical signaling at these synapses may be involved in early odor preference learning. To investigate this possibility, we combined electrophysiological recordings with calcium imaging in olfactory bulb slices prepared from neonatal rats and mice. Activation of ON-MC synapses induced postsynaptic potentials, which were associated with large postsynaptic calcium transients. Neither electrical nor calcium responses were affected by beta-adrenergic agonists or antagonist. Immunocytochemical analysis of MCs and their tufted dendrites revealed clear immunoreactivity with antibodies against alpha1A (Cav2.1, P/Q-type) and alpha1B (Cav2.2, N-type), but not against alpha1C (Cav1.2, L-type) or alpha1D (Cav1.3, L-type) calcium channel subunits. Moreover, nimodipine, a blocker of L-type calcium channels, had no effect on either electrical or calcium signaling at ON-MC synapses. In contrast to previous evidence, we concluded that in neonatal rats and mice (P5-P8), mitral cells do not express significant amounts of L-type calcium channels, the calcium channel type that is often targeted by beta-adrenergic modulation. The absence of beta-adrenergic modulation on either electrical or calcium signaling at ON-MC synapses of neonatal rats and mice excludes the involvement of this mechanism in early odor preference learning.

Afferent Pathways↗