Measurement of Steroid Concentrations in Brain Tissue: Methodological Considerations

It is well recognized that steroids are synthesized de novo in the brain (neurosteroids). In addition, steroids circulating in the blood enter the brain. Steroids play numerous roles in the brain, such as influencing neural development, adult neuroplasticity, behavior, neuroinflammation, and neurodegenerative diseases such as Alzheimer’s disease. In order to understand the regulation and functions of steroids in the brain, it is important to directly measure steroid concentrations in brain tissue. In this brief review, we discuss methods for the detection and quantification of steroids in the brain. We concisely present the major advantages and disadvantages of different technical approaches at various experimental stages: euthanasia, tissue collection, steroid extraction, steroid separation, and steroid measurement. We discuss, among other topics, the potential effects of anesthesia and saline perfusion prior to tissue collection; microdissection via Palkovits punch; solid phase extraction; chromatographic separation of steroids; and immunoassays and mass spectrometry for steroid quantification, particularly the use of mass spectrometry for “steroid profiling.” Finally, we discuss the interpretation of local steroid concentrations, such as comparing steroid levels in brain tissue with those in the circulation (plasma vs. whole blood samples; total vs. free steroid levels). We also present reference values for a variety of steroids in different brain regions of adult rats. This brief review highlights some of the major methodological considerations at multiple experimental stages and provides a broad framework for designing studies that examine local steroid levels in the brain as well as other steroidogenic tissues, such as thymus, breast, and prostate

Raspodjela kapi tropskih kiša po veličini nad južnom Indijom

Drop size distributions (DSD) associated with tropical rainfall at Cuddalore in the south-eastern part of India have been measured by a Joss-Waldvogel disdrometer (RD–80 model) during September to November 2002. The rainfall data corrected for instrumental error, matches very well with rainfall rates measured by a self recording raingauge, at the same site. For further analysis of the DSD, the rainfall events were separated into convective and stratiform rainfall by an algorithm based on variation of DSD parameters. One rain event in the form of a squall line of 15 September 2002, was analysed in greater detail to investigate the validity of the classification scheme as well as to study the variation of the DSD parameters during the course of a rain event. It was observed that, the algorithm was robust and had quite good correspondence with other independent rainfall separation algorithms. During the rain event, at low rainrates, the convective phase of the rainfall event was marked by DSD spectra that have greater population of small droplets as compared to stratiform DSDs at the same rainrates. At higher rainrates, the convective regime is characterised by narrow spectra centred at higher diameters. At the transition region between convective and stratiform spectra, mixed large and small drop spectra are observed. Similar variation was also observed in the averaged drop spectra. In addition, the averaged spectra also reveal an equilibrium distribution of the drop population in DSDs at higher rainrates (>39 /hr) for diameter range (>1.91 mm) corresponding to nearly constant values of the slope of the distribution, the intercept and the mean mass diameter. The value of the shape parameter, which for small rainrates varies the same as the slope parameter, starts to increase with increasing rainrate as the other two parameters of the gamma distribution approach a constant value corresponding to equilibrium shape. The value of the intercept parameter is highest for low to moderate convective rainfall and decreases as the rainrate increases.Raspodjela kapi po veličini (RKV) koja je povezana s tropskim kišama u Cuddalore u jugoistočnom dijelu Indije, mjerena je Joss-Waldvogel disdrometrom (model RD-80) od rujna do studenog 2002. Mjerenja kiše su korigirana uvažavajući pogreške instrumenta te se vrlo dobro podudaraju s mjerenjima koja su dobivena automatskom kišomjernom postajom na istoj lokaciji. Radi daljnje analize RKV, količine oborine su podijeljene na konvektivnu i stratiformnu količinu oborine na temelju logaritma koji se zasniva na varijacijama RKV parametara. Jedan slučaj obilne kiše za vrijeme olujne pruge 15. rujna 2002. odabran je za detaljnu analizu radi ispitivanja valjanosti klasifikacijske sheme kao i za proučavanje promjena RKV parametara za vrijeme pomicanja olujne pruge. Pokazalo se da je algoritam robustan i da je imao dobro slaganje s drugim algoritmima za separaciju oborine. Tijekom ispitivanog slučaja, kod malih količina kiše, konvektivnu fazu oborine karakterizira izrazit RKV spektar koji ima veliki broj malih kapljica u odnosu na statiformnu RKV za istu količinu kiše. Za veće količine kiše, konvektivni režim karakterizira uzak spektar velikih kapljica. U području prijelaza između konvektivnog i stratiformnog spektra, uočeno je miješanje velikih i malih kapljica kiše. Slične promjene prisutne su i u spektru srednjih kapljica kiše. Srednji spektar također pokazuje ravnomjernu raspodjelu kapi RKV za veće količine kiše (>39/sat) promjera kapi (>1.91 mm) što odgovara skoro konstantnim vrijednostima nagiba distribucije, presjeka s ordinatnom osi i srednjeg promjera. Vrijednost parametra oblika, koji za male količine kiše varira isto kao i parametar nagiba, počinje se povećavati s povećanjem količine oborine kao i ostala dva parametra gama razdiobe dosežući konstantnu vrijednost koja odgovara ravnotežnom obliku. Vrijednost presjeka s ordinatnom osi je najviša za male ili umjerene konvektivne količine oborine i smanjuje se s povećanjem količine kiše

A method to quantitatively evaluate Hamaker constant using the jump-into-contact effect in Atomic Force microscopy

We find that the jump-into-contact of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the jump-into-contact distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the jump-into-contact using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with natural oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the jump-into-contact is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.Comment: 11 pages, 4 figures, 1 tabl

Viscous instabilities in flowing foams: A Cellular Potts Model approach

The Cellular Potts Model (CPM) succesfully simulates drainage and shear in foams. Here we use the CPM to investigate instabilities due to the flow of a single large bubble in a dry, monodisperse two-dimensional flowing foam. As in experiments in a Hele-Shaw cell, above a threshold velocity the large bubble moves faster than the mean flow. Our simulations reproduce analytical and experimental predictions for the velocity threshold and the relative velocity of the large bubble, demonstrating the utility of the CPM in foam rheology studies.Comment: 10 pages, 3 figures. Replaced with revised version accepted for publication in JSTA