Correlation of mineral density and elastic modulus of natural enamel white spot lesions using X-ray microtomography and nanoindentation

Our objectives were to correlate the mineral density (MD) and elastic modulus (E) of natural white spot lesions (WSLs) and compare them with analytical and numerical models. Five natural WSLs from four extracted sound premolar teeth were scanned at a voxel size of 7.6 μm using a desktop X-ray microtomography (XRMT) system. Five hydroxyapatite phantoms with densities ranging from 1.52 to 3.14 g cm^?3 were used as calibration standards for each scan. MD throughout the WSLs was quantified using an MD calibration equation derived from hydroxyapatite phantoms. Subsequently, teeth were cross-sectioned and the E modulus was measured systematically across the WSLs at intervals of 25 and 50 μm using nanoindentation. The MD and E modulus of WSLs correlated well. The relationship may be expressed as E = E₀ exp^?bP (R² = 0.952) with E₀ the elastic modulus of the fully dense material, P the porosity and b a constant. The results for sound enamel were compared with Spears model. The limitation of Spears model to the WSLs is discussed and an alternative model developed by Rice for porous materials is proposed. Clinical implications of this work for quantifying de-/remineralization of teeth are pointed out. We conclude that XRMT can be utilized to extrapolate the E modulus of WSLs. This provides a basis for non-destructive, longitudinal analysis of WSLs in de-/remineralization studies of enamel.     

Antioxidant treatment restores prejunctional regulation of purinergic transmission in mesenteric arteries of deoxycorticosterone acetate-salt hypertensive rats

Norepinephrine (NE) and ATP are co-released by periarterial sympathetic nerves. In mesenteric arteries (MA) from deoxycorticosterone-acetate (DOCA)-salt hypertensive rats, ATP, but not norepinephrine, release is impaired suggesting that their release may be regulated differently. We tested the hypothesis that different calcium channels contribute to ATP and norepinephrine release from sympathetic nerves in vitro in MA from normotensive and DOCA-salt hypertensive rats and that oxidative stress disrupts prejunctional regulation of co-transmission. Excitatory junction potentials (EJPs) were used to measure ATP release. Norepinephrine release was measured amperometrically with carbon-fiber microelectrodes. CdCl₂ (30 μM) inhibited norepinephrine release in sham and DOCA-salt arteries by 78% and 85%, respectively. The N-type calcium channel antagonist, ω-conotoxin GVIA (CTX, 0.1 μM) inhibited norepinephrine release by 50% and 67% in normotensive and DOCA-salt arteries, respectively while CTX blocked EJPs. The P/Q-type calcium channel antagonist ω-agatoxin IVA (ATX; 0.03 μM) reduced norepinephrine release in sham but not DOCA-salt arteries and increased EJPs in sham but not DOCA-salt arteries. ATX did not increase EJPs in sham arteries in the presence of the α₂-adrenergic receptor antagonist, yohimbine (1 μM). α₂-Autoreceptor-sensitive EJP facilitation is impaired in DOCA-salt hypertension but this response is restored in DOCA-salt rats treated chronically with the antioxidant, apocynin. Apocynin restored α₂-autoreceptor regulation of norepinephrine release. We conclude that ATP released from periarterial sympathetic nerves is controlled directly by N-type calcium channels. Norepinephrine release is controlled by N and P/Q type calcium channels. Norepinephrine release controlled by P/Q channels acts at α₂-adrenergic receptors to inhibit norepinephrine release suggesting that there may be multiple pools of norepinephrine in periarterial sympathetic nerves. Regulation of norepinephrine release by α₂-autoreceptors and P/Q-type channels is impaired in DOCA-salt hypertension and α₂-autoreceptor function is disrupted by oxidative stress.     

Dynamic particle image velocimetry flow analysis of the flow field immediately downstream of bileaflet mechanical mitral prostheses

New dynamic particle image velocimetry (PIV) technology was applied to the study of the flow field associated with prosthetic heart valves. Four bileaflet prostheses, the St. Jude Medical (SJM) valve, the On-X valve with straight leaflets, the Jyros (JR) valve, and the Edwards MIRA (MIRA) valve with curved leaflets, were tested in the mitral position under pulsatile flow conditions to find the effect of the leaflet shape and overall valve design on the flow field, particularly in terms of the turbulent stress distribution, which may influence hemolysis, platelet activation, and thrombus formation. Comparison of the time-resolved flow fields associated with the opening, accelerating, peak, and closing phases of the diastolic flow revealed the effects of the leaflet shape and overall valve design on the flow field. Anatomically and antianatomically oriented bileaflet valves were also compared in the mitral position to study the effects of the orientation on the downstream flow field. The experimental program used a dynamic PIV system utilizing a high-speed, high-resolution video camera to map the true time-resolved velocity field inside the simulated ventricle. Based on the experimental data, the following general conclusions can be made. High-resolution dynamic PIV can capture true chronological changes in the velocity and turbulence fields. In the vertical measuring plane that passes the centers of both the aortic and mitral valves (A-A section), bileaflet valves show clear and simple circulatory flow patterns when the valve is installed in the antianatomical orientation. The SJM, the On-X, and the MIRA valves maintain a relatively high velocity through the central orifice. The curved leaflets of the JR valve generate higher velocities with a divergent flow during the accelerating and peak flow phases when the valve is installed in the anatomical orientation. In the velocity field directly below the mitral valve and normal to the previous measuring plane (B-B section), where characteristic differences in valve design on the three-dimensional flow should be visible, the symmetrical divergent nature of the flow generated by the two inclined half-disks installed in the antianatomical orientation was evident. The SJM valve, with a central downward flow near the valve, is contrasted with the JR valve, which has a peripherally strong downward circulation with higher turbulent stresses. The On-X valve has a strong central downward flow attributable to its large opening angle and flared inlet shape. The MIRA valve also has a relatively strong downward central flow. The MIRA valve, however, diverts the flow three-dimensionally due to its peripherally curved leaflets.     

CD4+ T-cell memory: generation and multi-faceted roles for CD4+ T cells in protective immunity to influenza

Summary: We have outlined the carefully orchestrated process of CD4⁺ T‐cell differentiation from naïve to effector and from effector to memory cells with a focus on how these processes can be studied in vivo in responses to pathogen infection. We emphasize that the regulatory factors that determine the quality and quantity of the effector and memory cells generated include (i) the antigen dose during the initial T‐cell interaction with antigen‐presenting cells; (ii) the dose and duration of repeated interactions; and (iii) the milieu of inflammatory and growth cytokines that responding CD4⁺ T cells encounter. We suggest that heterogeneity in these regulatory factors leads to the generation of a spectrum of effectors with different functional attributes. Furthermore, we suggest that it is the presence of effectors at different stages along a pathway of progressive linear differentiation that leads to a related spectrum of memory cells. Our studies particularly highlight the multifaceted roles of CD4⁺ effector and memory T cells in protective responses to influenza infection and support the concept that efficient priming of CD4⁺ T cells that react to shared influenza proteins could contribute greatly to vaccine strategies for influenza.     

The effector to memory transition of CD4 T cells

The small number of antigen-specific memory CD4 T cells surviving long-term after antigen or pathogen challenge are often characterized by a surprising degree of phenotypic and functional heterogeneity. We here propose that the immune system has evolved to express this diversity in memory T-cell populations, in order to provide flexibility in recall responses, via a rapid transition from heterogeneous effector cells into correspondingly heterogeneous memory cells. Little attention has been paid to another important transition—from resting memory cell to re-activated effector. We would suggest that superior functional attributes of secondary effectors arising from memory CD4 T cells, as compared to primary effectors arising from naïve precursors, play an important and underappreciated role in protective secondary immune responses.     

Pretraining enhances recovery from visuospatial deficit following cerebellar dentate nucleus lesion

Following bilateral lesions targeting lateral deep cerebellar nuclei, rats were subjected to a bridge test as a measure of visuomotor coordination and were trained on the Morris water maze (MWM) as a measure of visuospatial processing. Lesioned rats were significantly impaired in visuospatial processing, but not visuomotor coordination, relative to sham rats. In a 2nd experiment, rats were pretrained on a delayed spatial alternation task (T maze) before MWM training. Pretraining reversed the visuospatial deficit caused by the lesions as compared with nonpretrained rats. Results suggest that lateral deep cerebellar nuclei contribute to visuospatial processing with a negligible contribution to visuomotor skills and that visuospatial deficits resulting from lateral nuclei damage can be reversed with pretraining on aspatial working memory task.     

Alcohol and Sexual Risk Behavior among Migrant Female Sex Workers and Male Workers in Districts with High In-Migration from Four High HIV Prevalence States in India

This paper examines the association between alcohol use and sexual risk in two critical migrant populations living within the same geographical areas—migrant men and female sex-workers (FSWs). Data are drawn from two independent surveys of migrant FSWs and male workers in 14 districts of four high HIV prevalent Indian states. In the paper we have examined the independent effects of degree of mobility and alcohol use prior to sex on HIV risk behaviors. Nearly two-thirds of FSWs and a similar proportion of male migrant workers, as well as nine out of ten clients of FSWs consume alcohol. More than half of the FSWs and their clients consumed alcohol prior to sex. The practice of alcohol use prior to sex among both FSWs and their clients has a significant association with inconsistent condom use during paid as well as unpaid sex, and these effects are independent of degree of mobility. The results suggest a need for developing an in-depth understanding of the role of alcohol in accentuating HIV risk particularly among migrant populations who move frequently from one place another.     

Time-resolved particle image velocimetry and laser doppler anemometry study of the turbulent flow field of bileaflet mechanical mitral prostheses

Dynamic particle image velocimetry (PIV) was applied to the study of the flow field associated with prosthetic heart valves. The results were compared with those of laser Doppler anemometry (LDA). Anatomically and antianatomically oriented Jyros (JR) and St. Jude Medical (SJM) valves were compared in the mitral position to study the effects of valve design on the downstream flow field. The experimental program used a dynamic PIV system utilizing high-speed, high-resolution video to map the true time-resolved velocity field inside the simulated ventricle. This system was complemented by a study using the more traditional LDA system for comparison. Based on the experimental data, the following general conclusions can be made. High-resolution dynamic PIV can capture true chronological changes in the velocity and turbulence fields. It also produces very detailed velocity and turbulence information comparable to the LDA results. In the vertical measuring plane that passes both the center of the aortic and mitral valves (A-A section), the two valves (the SJM and the JR) show distinct circulatory flow patterns when the valve is installed in the antianatomical orientation. Small differences in valve design can generate noticeable differences, particularly during the accelerating flow phase. The SJM valve maintains a relatively high velocity through the central orifice; the curved leaflets of the JR valve generate higher velocities with a divergent flow during the accelerating and peak flow phases. In the velocity field directly below the mitral valve and normal to the previous measuring plane (B-B section), where characteristic differences in valve design will be visible, symmetrical twin circulations were observed because of the divergent nature of the flow generated by the two inclined half-disks installed in the antianatomical orientation. The SJM valve, with a central downward flow near the valve, is contrasted with the JR valve, which has a peripheral downward circulation with higher, turbulent stresses.     

Neither neutrophils nor reactive oxygen species contribute to tissue damage during Pneumocystis pneumonia in mice

Neutrophils are implicated in the damage of lung tissue in many disease states, including infectious diseases and environmental insults. These effects may be due to oxidative or nonoxidative functions of the neutrophil or both. We examined the role of neutrophils in pulmonary damage during infection with the opportunistic fungal pathogen Pneumocystis sp. in four mouse models of neutrophil dysfunction. These were (i) a knockout of the gp91(phox) component of NADPH oxidase, in which reactive oxygen species (ROS) production is greatly reduced; (ii) a double knockout of gp91(phox) and inducible nitric oxide synthase, in which ROS and nitric oxide production is greatly decreased; (iii) a knockout of the chemokine receptor CXCR2, in which accumulation of intra-alveolar neutrophils is severely diminished; and (iv) antibody depletion of circulating neutrophils in wild-type mice with the monoclonal antibody RB6. Surprisingly, in each case, indicators of pulmonary damage (respiratory rates, arterial oxygen partial pressures, and intra-alveolar albumin concentrations) were the same in knockout mice and comparable wild-type mice. Therefore, whereas neutrophils are a valid correlative marker of lung damage during Pneumocystis infection, neither neutrophils nor ROS appear to be the causative agent of tissue damage. We also show that there is no difference in Pneumocystis burdens between wild-type and knockout mice, which supports the idea that neutrophils do not have a major role in the clearance of this organism.