Studying 2D materials with advanced Raman spectroscopy: CARS, SRS and TERS

Raman spectroscopy has been established as a valuable tool to study and characterize two-dimensional (2D) systems, but it exhibits two drawbacks: a relatively weak signal response and a limited spatial resolution. Recently, advanced Raman spectroscopy techniques, such as coherent anti-Stokes spectroscopy (CARS), stimulated Raman scattering (SRS) and tip-enhanced Raman spectroscopy (TERS), have been shown to overcome these two limitations. In this article, we review how useful physical information can be retrieved from different 2D materials using these three advanced Raman spectroscopy and imaging techniques, discussing results on graphene, hexagonal boron-nitride, and transition metal di- and mono-chalcogenides, thus providing perspectives for future work in this early-stage field of research, including similar studies on unexplored 2D systems and open questions.

Antioxidant and orofacial anti-nociceptive activities of the stem bark aqueous extract of Anadenanthera colubrina (Velloso) Brenan (Fabaceae)

The anti-nociceptive and antioxidant activities of the Anadenantheracolubrina stem bark aqueous extract (AEAC) were investigated. AEAC (30 μg/mL) reduced 94.8% of 2,2-diphenyl-1-picrylhydrazyl radical and prevented 64% (200 μg/mL) of lipid peroxidation caused by 2,2'-azobis(2-methylpropionamidine) dihydrochloride-induced peroxyl radicals. AEAC treatment (200 and 400 mg/kg) significantly (p < 0.001) reduced mice orofacial nociception in the first (61.4% and 62.6%, respectively) and second (48.9% and 61.9%, respectively) phases of the formalin test. Nociception caused by glutamate was significantly (p < 0.001) reduced by up to 79% at 400 mg/kg, while 56-60% of the nociceptive behaviour induced by capsaicin was significantly inhibited by AEAC (100-400 mg/kg). Mice treated with AEAC did not show changes in motor performance in the Rota-rod apparatus. It appears that AEAC is of pharmacological importance in treating pain due to its anti-nociceptive effects, which were shown to be mediated by central and peripheral mechanisms.

Endothelial nitric oxide synthase gene variant modulates the relationship between serum cholesterol levels and blood pressure in the general population: New evidence for a direct effect of lipids in arterial blood pressure

BACKGROUND

A causal relationship between plasma cholesterol and blood pressure remains poorly understood. It has been postulated that the decrease in nitric oxide (NO) availability is a potential mechanism by which hypercholesterolemia may stimulate blood pressure elevation. However, evidence supporting the role of the L-arginine-NO pathway on the relationship between hypertension and hypercholesterolemia is still lacking.

METHODS AND RESULTS

We tested for an association of the expressed NO synthase (eNOS) Glu298Asp gene variant and plasma levels of lipids and lipoproteins in the determination of systolic blood pressure levels in a 1577 individuals randomly selected from the general population. Significant interactions could be disclosed either between the Glu298Asp gene variant and total-cholesterol (p = 0.02), log-transformed triglycerides (p = 0.004) or non-HDL-cholesterol (p = 0.003) in the determination of systolic blood pressure. In addition, although the presence of the AspAsp genotype did not significantly increase the risk of hypertension in individuals in the 50% lowest percentile of total-cholesterol, presence of this genotype significantly increased the risk of hypertension in individuals in the 50% highest percentile. Finally, in a multiple logistic regression model adjusting for age, sex, diabetes, ethnicity, smoking status and BMI, the AspAsp genotype significantly increased the risk of hypertension only in individuals with total-cholesterol above 209 mg/dL (p = 0.05, odds ratios (OR) = 2.0).

CONCLUSION

Taken together, these results provide evidence supporting the role of the eNOS Glu298Asp gene variant in modulating blood pressure through a relationship with lipid levels.

Racial differences in aortic stiffness in normotensive and hypertensive adults

OBJECTIVE

To investigate whether differences exist in the mechanical properties of large arteries between white and black subjects.

DESIGN

Eighty-two white (49 normotensive and 33 untreated hypertensive) and 38 black (24 normotensive and 14 untreated hypertensive) adult male volunteers were studied in a cross-sectional study.

METHODS

Carotid-femoral pulse wave velocity was measured as an index of arterial stiffness, using a recently developed non-invasive automatic device, and compared between white and black subjects before and after the adjustment for age. The slope of regressions for pulse wave velocity and systolic blood pressure were also compared between racial groups.

RESULTS

In the normotensive group, white subjects presented higher mean values of pulse wave velocity than blacks while the opposite behavior was found in the hypertensive group. After adjustment for age, significant differences in pulse wave velocity between whites and blacks became evident in the normotensive (whites 8.15 +/- 0.04 versus blacks 7.75 +/- 0.02 m/s; P < 0.001) and hypertensive (whites 8.88 +/- 0.02 versus blacks 9.30 +/- 0.17 m/s; P < 0.001) groups. Linear regression analysis for age-adjusted pulse wave velocity and systolic blood pressure showed that the slope was significantly greater in blacks than in whites (0.040 +/- 0.002 versus 0.019 +/- 0.001 m/s; P < 0.001).

CONCLUSION

These data indicate that there is a greater pressure-dependent increase in aortic stiffness in blacks than in whites. This finding points towards major differences in mechanical properties of large arteries between these racial groups.

Fibronectin expression and aortic wall elastic modulus in spontaneously hypertensive rats

Recent studies have shown that large-artery wall remodeling per se does not reduce distensibility in hypertension, indicating qualitative or quantitative changes in arterial components. The aim of the study was to determine in 1-year-old spontaneously hypertensive rats (SHRs) the changes in the elastic properties of large arteries, as assessed by the incremental elastic modulus (E(inc)), and the changes in the extracellular matrix, including fibronectin (FN) and alpha5beta1-integrin. The relationship between E(inc) and circumferential wall stress was calculated from in vivo pulsatile changes in blood pressure and arterial diameter by using a high-resolution echo-tracking system at the site of the abdominal aorta and in vitro medial cross-sectional area. E(inc)-stress curves and FN and integrin alpha5-subunit contents were determined for each animal. Mean stress and E(inc) were higher in SHRs than in Wistar rats. However, in a common range of stress, E(inc)-stress curves for SHRs were superimposable on those for Wistar rats, indicating that wall materials in both strains have equivalent mechanical behavior. Immunohistochemistry indicated that total FN, EIIIA FN isoform, and alpha5-integrin increased in the SHRs aortas without changes in elastin and collagen densities. Total FN was also increased in SHRs as determined by Western blot analysis. No differences in FN and alpha5-subunit mRNAs were detected between SHRs and Wistar rats. These results indicate that the aortic wall material of SHRs and Wistar rats have equivalent mechanical properties, although in SHRs it is subjected to a higher level of stress. By increasing cell-matrix attachment sites, FN may participate in the mechanical adaptation of both cellular and matrix components in SHRs.

Mechanical stress of the carotid artery at the early phase of spontaneous hypertension in rats

Common carotid artery (CCA) hypertrophy has long been recognized in the neonatal period of development in spontaneously hypertensive rats (SHR), but the mean circumferential and shear stresses acting on the arterial wall have never been investigated in vivo. We investigated intra-arterial blood pressure in conscious rats, CCA diameter (echotracking techniques), blood flow velocity (pulsed Doppler), wall thickness (histomorphometry), and ganglionic blockade (hexamethonium) in Wistar rats and SHR at 5 and 12 weeks of age. During this interval, weight gain was identical in the strains, whereas the increase in wall thickness and blood pressure was greater in SHR. CCA diameter was identical at week 5 and increased similarly at week 12 in both strains. During ganglionic blockade, a larger diameter was observed in SHR at week 5 for the same BP level, whereas equivalent values were observed at week 12. Blood flow velocity decreased with age but to a significantly greater extent in SHR. Mean circumferential stress and shear stress index were identical in both strains at week 12. However, from weeks 5 to 12, mean circumferential stress increased with age similarly in both strains, whereas the age-related decrease in mean shear stress index was much greater in SHR than Wistar rats. Thus, despite a higher blood pressure, SHR exhibit the same carotid diameter as Wistar rats during early development. Because the kinetics of shear stress are different in both strains, altered flow-dilatation mechanisms, and possibly resulting endothelial dysfunction, may be involved in the diameter changes.

Distension capacity of the carotid artery and ambulatory blood pressure monitoring. Effects of age and hypertension

In hypertension, the principal components of the mechanical stress acting on the arterial wall may be evaluated not only from the level of peak systolic and end-diastolic blood pressure but also by the level of pulse pressure and variability of blood pressure measured by ambulatory monitoring. The purpose of the present study was, in a population of 51 subjects with essential hypertension, to determine the influence of these parameters and of heart rate on the distension capacity of the common carotid artery, measured noninvasively by high-resolution echo-tracking techniques. The pulsatile change in diameter of the carotid artery diameter, estimated either in absolute or relative values, was shown to be significantly and independently correlated with four mechanical parameters deduced from daytime ambulatory blood pressure measurements: baseline diastolic blood pressure (the lower the diastolic blood pressure, the higher the distension capacity; r = -0.44; P < .001); pulse pressure (the higher the pulse pressure, the higher the distension capacity; r = 0.32; P < .024); variability of diastolic blood pressure (the higher the variability, the higher the distension capacity; r = 0.37; P < .008); and mean heart rate (the higher the heart rate, the more reduced the distension capacity; r = -0.28; P < .05). Multiple regression analysis indicated that mean diastolic blood pressure and its variability, mean heart rate, and pulse pressure acted independently on carotid artery distension, even after adjustment for age. The present study suggests for the first time that, in humans, hypertension may act on the arterial wall not only through the amplitude of peak systolic and end-diastolic blood pressure but also through several other mechanical factors involving the level of pulse pressure and heart rate and also blood pressure variability. Thus, in addition to the level of blood pressure, carotid artery distension is specifically influenced by two factors independently implicated in the epidemiologic cardiovascular risk: pulse pressure and heart rate.

Baroreceptor reflex function in rats submitted to chronic inhibition of nitric oxide synthesis

1. The chronic inhibition of nitric oxide synthesis by N omega-nitro-L-arginine-methyl ester (L-NAME) leads to arterial hypertension accompanied by a significant increase in cardiac sympathetic tone and an almost complete abolition of the vagal tone in conscious adult male Wistar rats. The main aim of the present study was to examine the baroreceptor heart rate reflex function in L-NAME-treated rats (N = 10). 2. Spontaneous daily oral intake of L-NAME (1 mg/ml for 6 days) caused marked hypertension and tachycardia (176 +/- 5 mmHg and 418 +/- 16 bpm), when compared to untreated rats (111 +/- 2 mmHg and 354 +/- 8 bpm). 3. Baroreflex gain was determined in conscious freely moving rats by sigmoidal curve fitting analysis using alternate intravenous injections of phenylephrine (0.2-10.0 micrograms/kg) and sodium nitroprusside (0.5-20.0 micrograms/kg) to produce pressor-induced bradycardia and depressor-induced tachycardia, respectively. The baroreflex gain (sensitivity) was significantly enhanced in L-NAME-treated rats compared to control rats (10.9 +/- 2.5 vs 4.5 +/- 0.3 bpm/mmHg, respectively) mainly due to exaggerated reflex bradycardia responses to increases in arterial hypertension. 4. The data indicate that chronic inhibition of nitric oxide synthesis enhances the bradycardic component of the baroreflex function.

Evidence that the autonomic nervous system plays a major role in the L-NAME-induced hypertension in conscious rats

The present study was designed to investigate the role of the autonomic nervous system in experimental hypertension induced by chronic administration of N-nitro-L-arginine methyl ester (L-NAME) in the drinking water (1 mg/mL) over 6 days. L-NAME ingestion caused a large rise in resting mean arterial pressure (MAP) (175 +/- 5 mm Hg) and heart rate (HR) (440 +/- 17 beats per minute) compared to nontreated control rats (resting MAP: 112 +/- 2 mm Hg and HR: 345 +/- 8 beats per minute). Ganglionic blockade induced by trimethaphan (5 mg/kg, intravenously) caused a significantly (P < .01) greater decrease in MAP (delta -86 +/- 7 mm Hg) compared to control rats MAP (delta -44 +/- 4 mm Hg). This strongly suggests that the level of central sympathetic tone in L-NAME-treated rats is much greater than in nontreated rats. Using atenolol and atropine alone and combined, the level of resting sympathetic drive to the heart was found to be significantly increased in L-NAME-treated rats compared to control rats. However, vagal tone to the heart was found to be virtually abolished in L-NAME-treated rats compared to control rats. These results indicate that an increase in central sympathetic drive plays an important role in the hypertension induced by chronic inhibition of nitric oxide synthesis with L-NAME.