bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physical and chemical changes in polystyrene during electron irradiation using EELS in the TEM: contribution of the dielectric function
Authors: Varlot  , Martin  , Quet  
Published: March 2003

We have performed electron energy‐loss spectroscopy analysis of polystyrene in the analytical transmission electron microscope in order to evaluate the possibility of obtaining both chemical and dielectric information on the polymer at the submicrometre scale. Irradiation has also been studied, particularly the influence of the specimen temperature on the kinetics of degradation.The main results show that polystyrene is resistant to electron beam with a critical dose of about 104 C m−2 at 127 K. Spectra could be acquired with doses less than this critical dose. We were thus able to propose an identification of the different chemical bonds of carbon (including the C–H bond), in agreement with previous X‐ray absorption near‐edge structure experiments. The chemical changes in polystyrene due to severe irradiation damage are also visible in the carbon K‐edge near‐edge structure.At the same time, we calculated the dielectric function from the low‐loss part of the spectra. Interestingly, this part of the spectrum is the most sensitive to irradiation, since great changes can be seen during exposure.Lastly, we propose a degradation process, in agreement with all these results.
Stereological analysis and modelling of gradient structures
Authors: Hahn  , Micheletti  , Pohlink  , Stoyan  , Wendrock  
Published: March 2003

Gradient structures are inhomogeneous along a particular gradient direction but homogeneous perpendicular to that direction. Consequently, structural parameters such as volume fraction or surface area density are local characteristics which depend on the ‘vertical’ coordinate with respect to the ‘vertical’ gradient axis.Analogously, models for gradient structures have model parameters depending on the vertical coordinate z. For example, a Voronoi tessellation with a gradient is generated by a gradient point process with a local intensity which is a function of z. Similarly, a gradient germ grain model is obtained from a gradient point process where the grain size distribution may also depend on z. For a gradient Boolean model, local volume fraction VV(z) and local surface area density SV(z) can be calculated from the model parameters.Stereological methods for gradient structures are based on vertical sections parallel to the gradient direction. Estimation of VV(z), SV(z) and local length density LV(z) is done by lineal analysis using horizontal test lines with vertical coordinate z. Similarly, lineal analysis is used to estimate local mean cell volume of gradient tessellations. For the estimation of local particle number density and size in the spirit of the Wicksell problem the use of kernel methods and distributional assumptions is required.
Structural and morphological anomalies in magnetosomes: possible biogenic origin for magnetite in ALH84001
Authors: Taylor A. P. , Barry J. C. , Webb R. I. 
Published: March 2003

We report biogenic magnetite whiskers, with axial ratios of 6 : 1, elongated in the [1 1 1], [1 1 2] and [1 0 0] directions, resembling the magnetite whiskers detected in the Martian meteorite ALH84001 by Bradley et al., and interpreted by those authors as evidence of vapour‐phase (abiogenic) growth. Magnetosomal whiskers with extended defects consistent with screw dislocations and magnetosomes resembling flattened twinned platelets, as well as other twinning phenomena and other structural defects, are also reported here. Magnetosomes with teardrop‐shaped, cuboidal, irregular and jagged structures similar to those detected in ALH84001 by McKay et al., coprecipitation of magnetite possibly with amorphous calcium carbonate, coprecipitation of magnetite possibly with amorphous silica, the incorporation of titanium in volutin inclusions and disoriented arrays of magnetosomes are also described. These observations demonstrate that the structures of the magnetite particles in ALH84001, their spatial arrangement and coprecipitation with carbonates and proximity to silicates are consistent with being biogenic.Electron‐beam‐induced flash‐melting of magnetosomes produced numerous screw dislocations in the {1 1 1}, {1 0 0} and {1 1 0} lattice planes and induced fusion of platelets. From this, the lack of screw dislocations reported in the magnetite particles in ALH84001 (McKay et al., and Bradley et al.) indicates that they have a low‐temperature origin.
Tissue shrinkage and unbiased stereological estimation of particle number and size*
Authors: Dorph‐Petersen K.‐A. , Nyengaard J. R. , Gundersen H. J. G. 
Published: March 2003

This paper is a review of the stereological problems related to the unbiased estimation of particle number and size when tissue deformation is present. The deformation may occur during the histological processing of the tissue. It is especially noted that the widely used optical disector may be biased by dimensional changes in the z‐axis, i.e. the direction perpendicular to the section plane. This is often the case when frozen sections or vibratome sections are used for the stereological measurements. The present paper introduces new estimators to be used in optical fractionator and optical disector designs; the first is, as usual, the simplest and most robust. Finally, it is stated that when tissue deformation only occurs in the z‐direction, unbiased estimation of particle size with several estimators is possible.
Near real time in vivo fibre optic confocal microscopy: sub‐cellular structure resolved
Authors: Sung K. B. , Liang C. , Descour M. , Collier T. , Follen M. , Malpica A. , Richards‐Kortum R. 
Published: March 2003

SummaryWe have built a fibre optic confocal reflectance microscope capable of imaging biological tissue in near real time. The measured lateral resolution is 3 µm and axial resolution is 6 µm. Images of epithelial cells, excised tissue biopsies, and the human lip in vivo have been obtained at 15 frames s−1. Both cell morphology and tissue architecture can be appreciated from images obtained with this microscope. This device has the potential to enable reflected light confocal imaging of internal organs for in situ detection of pathology.
Pre‐screening for antigen detectability in cells: a TEM‐based solid phase digital immunogold detection method utilizing ultra low volumes of reagents
Authors: Kaur R. , Dikshit K. L. , Raje M. 
Published: March 2003

SummaryRapid and sensitive pre‐screening for the presence of antigens in cell samples and confirmation of reactivity of antibodies, before proceeding with electron microscopy, is highly desirable. Most of the methods developed for this purpose are generally not very efficient and suitable for dealing with very small volumes of sample and reagents. In this work we present a simple, sensitive and rapid solid phase transmission electron microscope (TEM) based method for the detection of picogram (pg) levels of soluble antigens using as little as 10 µL of reagents. Protein was adsorbed onto grids coated with polystyrene films to form the solid phase. The presence of antigen was detected using immunogold labelling. Gold particles adhering to the film were visualized and counted in a TEM providing a digital signal. This method was 100‐fold more sensitive than dot blot in detection of rabbit IgG. We have demonstrated the utility of this technique by screening for Vitreoscilla haemoglobin (VHb) antigen in cell lysates and confirming the results directly with immunogold labelling transmission electron microscopy of cell sections.
Nonlinear bio‐photonic crystal effects revealed with multimodal nonlinear microscopy
Authors: Chu S.‐W. , Chen I.‐H. , Liu T.‐M. , Sun C.‐K. , Lee S.‐P. , Lin B.‐L. , Cheng P.‐C. , Kuo M.‐X. , Lin D.‐J. , Liu H.‐L. 
Published: March 2003

SummaryHighly optically active nonlinear bio‐photonic crystalline and semicrystalline structures in living cells were studied by a novel multimodal nonlinear microscopy. Numerous biological structures, including stacked membranes and aligned protein structures are highly organized on a nanoscale and have been found to exhibit strong optical activities through second‐harmonic generation (SHG) interactions, behaving similarly to man‐made nonlinear photonic crystals. The microscopic technology used in this study is based on a combination of different imaging modes including SHG, third‐harmonic generation, and multiphoton‐induced fluorescence. With no energy release during harmonic generation processes, the nonlinear‐photonic‐crystal‐like SHG activity is useful for investigating the dynamics of structure–function relationships at subcellular levels and is ideal for studying living cells, as minimal or no preparation is required.
X‐ray tomographic imaging of Ti/SiC composites
Authors: Mcdonald S. A. , Preuss M. , Maire E. , Buffiere J.‐Y. , Mummery P. M. , Withers P. J. 
Published: March 2003

SummaryIn this paper, high‐resolution tomographic synchrotron X‐ray imaging is applied to study the occurrence and evolution of damage in Ti‐6Al‐4V/SCS6 SiC fibre composite materials. Three composite morphologies of increasing complexity have been studied, namely single fibre, single‐ply and multi‐ply composites. The single fibre composite was strained to full fibre fragmentation and the progressive introduction of damage monitored. For the single‐ply composite, damage was introduced deliberately by laser drilling to establish the effect of damaged fibres on their neighbours, whereas for the multi‐ply composite the morphology of a fibre bridging fatigue crack was studied. In addition to traditional mode I fibre fractures, subsequent fibre wedge cracks were observed presumably nucleating from damage introduced into the fibre surface by the first fracture event. In addition to these crack morphologies, spiral defects were observed for the single ply during failure. Finally, for the multi‐ply composite, the matrix crack front showed a number of characteristic features, including advancement in fibre‐free regions, crack bifurcation near fibres and different crack plane heights either side of a fibre.
Photoperiod‐Dependent and ‐Independent Regulation of Melatonin Receptors in the Forebrain of Songbirds
Authors: Bentley G. E. , Ball G. F. 
Published: March 2003

AbstractMelatonin was recently identified as playing a role in fine‐tuning the effects of gonadal steroids in the regulation of seasonal neuroplasticity within the telencephalic song control system of European starlings. The present study investigated possible seasonal regulation of melatonin receptors (MelR) within the starling song control system, in the presence or absence of gonadal steroids. Brains were sampled from photosensitive starlings exposed to short days, photostimulated starlings exposed to long days and photorefractory starlings also exposed to long days. Each condition contained a group of gonad‐intact birds and a group of castrated birds. Melatonin receptor distribution was assessed in vitro by 125–iodomelatonin (IMEL) receptor autoradiography. In general, MelR distribution was similar to that described in other songbird species. However, there was a striking downregulation of MelR in the song control nucleus Area X of intact and castrated photostimulated birds on long days compared to their photorefractory counterparts on the same long days and to the short‐day groups. Downregulation of MelR occurred independently of gonadal steroids. Nevertheless, superimposed on this general pattern of MelR downregulation during photostimulation, IMEL binding was observed in a medial subdivision of Area X when gonadal steroids were present. Downregulation of MelR in Area X during the short breeding season has implications for seasonal regulation of the song control system. Subsequent upregulation of MelR as birds become photorefractory, in the absence of any change in photoperiod, gonadal steroids or melatonin signal is the first description of photoperiod‐independent regulation of MelR in adults of any vertebrate class.
Central Nervous System Structures Labelled from the Testis Using the Transsynaptic Viral Tracing Technique
Authors: Gerendai I. , Tóth I. E. , Boldogkői Z. , Medveczky I. , Halász B. 
Published: March 2003

AbstractIn the present study, the transneuronal transport of neurotrophic virus technique was used to identify cell groups of the spinal cord and the brain that are transsynaptically connected with the testis. Pseudorabies virus was injected into the testis and after survival times of 3–6 days, the spinal cord and brain were processed immunocytochemically using a polyclonal antibody against the virus. Virus‐infected perikarya were detected in the preganglionic neurones of the spinal cord (T10‐L1, L5–S1) and in certain cell groups and areas of the brain stem, the hypothalamus and the telencephalon. In the brain stem, the cell goups and areas in which labelled neurones were present included, among others, the nucleus of the solitary tract, the caudal raphe nuclei, the locus coeruleus and the periaqueductal grey of the mesencephalon. In the hypothalamus, virus infected perikarya were observed in the paraventricular nucleus and in certain other cell groups. Telencephalic structures containing labelled neurones included the preoptic area, the bed nucleus of the stria terminalis, the central amygdala and the insular cortex. These data identify a multisynaptic circuit of neurones in the spinal cord and in the brain which may be involved in the control of testicular functions.
The Effect of Leptin on Luteinizing Hormone Release Is Exerted in the Zona Incerta and Mediated by Melanin‐Concentrating Hormone
Authors: Murray J. F. , Mercer J. G. , Adan R. A. H. , Datta J. , Aldairy C. , Moar K. M. , Baker B. I. , Stock M. J. , Wilson C. A. 
Published: March 2003

AbstractThe adipose hormone, leptin, not only restrains appetite, but also influences energy expenditure. One such influence is to promote sexual maturation and fertility. The neuromodulatory circuits that mediate this effect are not well known but the present study suggests that one mediator could be melanin‐concentrating hormone (MCH). We show that the long‐form receptor (Ob‐Rb) is expressed in the zona incerta of the rat and that administration of leptin (both 0.5 µg and 1.0 µg/side) into this area of ovariectomized, oestrogen‐primed rats stimulated the release of luteinizing hormone (LH) within 1 h, the effect enduring for a further 1 h. Injections of leptin into the arcuate nucleus induced a smaller, transient rise in LH while injections into the paraventricular and ventromedial nuclei were without effect. MCH neurones are present in the zona incerta and administration of this hormone into the medial preoptic area (mPOA) stimulates LH release, therefore we investigated the possibility that MCH might mediate this effect of leptin. An injection of MCH antiserum into mPOA prevented the rise in LH normally induced by leptin injected into the zona incerta. In addition, melanocortin receptor antagonists ([D‐Arg8]ACTH(4‐10) and [Ala6]ACTH(4‐10)), previously shown to inhibit the stimulatory effect of MCH on LH release, also inhibited the effect of leptin. We propose that one route by which leptin may promote reproductive activity is by enhancing MCH release from fibres within the mPOA. Speculative mechanisms for the action of MCH include the following possibilities: MCH may be acting on the specific MCH receptor which in turn interacts with a melanocortin or melanocortin‐like receptor; MCH may bind directly to one of the melanocortin receptors; or melanocortin antagonists may interact with the MCH receptor.
Modulation of Pituitary Dopamine D1 or D2 Receptors and Secretion of Follicle Stimulating Hormone and Luteinizing Hormone During the Annual Reproductive Cycle of Female Rainbow Trout
Authors: Vacher C. , Mañanos E. L. , Breton B. , Marmignon M.‐H. , Saligaut C. 
Published: March 2003

AbstractThe two gonadotrophins follicle stimulating hormone (FSH) and luteinizing hormone (LH) have distinct temporal expression and release profiles in fish, but little is known regarding their neuroendocrine control, especially for FSH. The present experiments were performed on previtellogenic, mature and preovulatory female trout. The catecholamine synthesis inhibitor, α‐methyl‐p‐tyrosine, increased plasma LH and FSH concentrations of mature fish. The dopamine agonist apomorphine decreased and the dopamine antagonist domperidone increased plasma LH concentration of preovulatory fish and delayed ovulation, but did not modify plasma FSH concentration. The dopamine D2 agonist bromocryptine inhibited LH release in cultured gonadotrophs from mature and preovulatory fish, but not from previtellogenic fish. Bromocryptine also significantly inhibited basal and salmon gonadotrophin releasing‐hormone (sGnRH)‐induced FSH release from cultured gonadotrophs of mature fish, but not of preovulatory fish, and increased FSH release from gonadotrophs of previtellogenic fish. The dopamine D1 agonist SKF 38393 had no observed effect on the release of FSH and LH, at any reproductive stage studied. The D1 agonist SKF 38393, the D2 agonist bromocriptine and sGnRH had no observed effects on cell contents of FSH and LH. Taken together, these data suggest that, at the level of the pituitary, dopamine inhibits LH release as vitellogenesis proceeds, via activation of dopamine D2 receptors. We demonstrate for the first time in fish a control of FSH release (a dopamine control), especially in mature fish which have low circulating concentrations of FSH.
Insulin and Glucose Administration Stimulates Fos Expression in Neurones of the Paraventricular Nucleus That Project to Autonomic Preganglionic Structures
Authors: Carrasco M. , Portillo F. , Larsen P. J. , Vallo J. J. 
Published: March 2003

AbstractInsulin and glucose play a key role in the control of body energy homeostasis. However, the anatomical organization of the network of central insulin and glucose sensitive areas is still unclear. In the present study, we used a multiple‐labelling technique combining retrograde tracing and Fos‐like immunohistochemistry, to analyse the anatomical projections from hypothalamic neurones activated by the combined stimulus of insulin and glucose. After intraperitoneal injections of a bolus of insulin plus glucose, Fos‐like immunoreactive neurones were observed in the paraventricular nucleus (PVN), ventromedial and arcuate nuclei, as well as the lateral hypothalamic area. In addition, neurones projecting to the autonomic preganglionic levels in the brainstem and spinal cord potentially involved in the control of glucose metabolism were identified by injections of fluorochrome tracers. Thus, Fluorogold was injected into the intermediolateral cell column of the lower spinal cord and Fast Blue was injected into the dorsal motor nucleus of the vagus. Perikarya of descending neurones were detected chiefly in the dorsal, medial and lateral parvocellular subnuclei and also in the posterior magnocellular subnucleus of the PVN. In contrast, insulin‐glucose activated neurones in the PVN were observed mainly in the medial parvocellular and posterior magnocellular subnuclei. Fluorogold/Fos double‐labelled neurones were only observed in the ventral zone of the medial parvocellular subnucleus. These data indicate that, within the PVN, there could be neurones responding to insulin‐glucose administration, which are involved in the sympathetic control of the classical regulatory structures of body energy homeostasis, such as the liver and pancreas, and which could play a role in the output of the neuronal circuitry controlling food intake.
Prevention of Glucoprivic Stimulation of Corticosterone Secretion by Leptin Does Not Restore High Frequency Luteinizing Hormone Pulses in Rats
Authors: Nagatani S. , Thompson R. C. , Foster D. L. 
Published: March 2003

AbstractWe have previously determined that exogenous leptin prevents the inhibition of pulsatile luteinizing hormone (LH) release in the fasting rodent. The present study tested the hypothesis that the mechanism by which leptin facilitates high LH secretion is through an attenuation of the stress response produced by a deficit in energy. Because hypogonadotropism is associated with activation of the hypothalamic‐pituitary‐adrenal (HPA) axis during both metabolic stress and nonmetabolic stress, our approach included a comparison of whether exogenous leptin could prevent the rise in corticosterone produced by a nonmetabolic stress (immobilization for 2 h), as well as by a widely used metabolic stress (transient glucoprivation by 2‐deoxyglucose, 2DG; 400 mg/kg, b.w., i.v.). Each stressor was applied to well‐fed ovariectomized rats (n = 4–6 per group), 2 h after leptin (3 µg/g, b.w., i.p.) or vehicle administration. Blood samples were collected through an indwelling atrial cannula every 6 min for 1 h before and for 2 h after the stress treatment to measure LH, leptin and corticosterone. During metabolic stress (acute glucoprivation), circulating leptin decreased, corticosterone increased and LH decreased; leptin administration abolished the increase in corticosterone, but pulsatile LH secretion remained inhibited. In contrast, during nonmetabolic stress (immobilization), leptin secretion was unaffected, but circulating corticosterone increased and LH decreased; leptin treatment did not prevent either the increase in corticosterone or the decrease in LH secretion. An important overall finding is that leptin can differentially alter the HPA axis depending upon the type of stress. In addition, whether the pattern of leptin is altered depends upon the type of stress. Although a glucoprivic‐induced decrease in endogenous leptin can be a stressor responsible for the increase in corticosterone secretion, a nonmetabolic stress‐induced increase in corticosterone is not mediated by leptin. Moreover, our results reveal that the depression of LH secretion when leptin is low during reduced energy availability is not due to activation of the HPA axis. During an energy deficit, exogenous leptin could not restore high frequency LH secretion when HPA function was restored to normal. Finally, the inability of leptin to increase LH secretion in the face of 2DG supports the notion that the action of leptin is dependent upon the degree of glucose availability.
Changes in Preoptic and Hypothalamic Levels of Progesterone Receptor mRNA Across the Oestrous Cycle of the Ewe
Authors: Scott C. J. , Pereira A. M. , Tilbrook A. J. , Rawson J. A. , Clarke I. J. 
Published: March 2003

AbstractWe measured the levels of progesterone receptor (PR) mRNA in the hypothalamus and preoptic area (POA) of the ewe across the oestrous cycle. Perfusion‐fixed hypothalamic tissue was collected from sheep killed during the luteal and follicular phases and during behavioural oestrus. Blood samples taken at the time of tissue collection verified that the oestrous ewes were undergoing a preovulatory luteinizing hormone (LH) surge. Matched sections were taken from the POA, periventricular nucleus (PeVN), ventromedial nucleus (VMN) and arcuate nucleus of each animal. In situ hybridization was performed using a sheep specific, 35S‐labelled riboprobe for PR and semiquantitative image analysis was conducted on emulsion‐dipped slides. The number of silver grains per cell was greater in the VMN and arcuate nucleus of oestrous ewes than in luteal and follicular phase ewes; there was no cyclic variation in the level of PR mRNA expression in the cells of the POA and PeVN. The number of labelled cells per mm2 in the VMN was higher in the oestrous ewes than in luteal phase and follicular phase ewes. The number of labelled cells in the PeVN was also higher in the oestrous ewes than in follicular phase ewes, but there was no cyclic variation in the POA and arcuate nucleus. In the ewe, the onset of behavioural oestrus corresponds to the onset of the preovulatory LH surge and increased PR mRNA expression at this time is likely to be due to the high concentrations of circulating oestrogen that precede this period.