Beamline simulations using monochromators with high d-spacing crystals

Monochromators for synchrotron radiation beamlines typically use perfect crystals for the hard X-ray regime and gratings for soft X-rays. There is an intermediate range, typically 1-3 keV (tender X-rays), which common perfect crystals have difficulties covering and gratings have low efficiency, although some less common crystals with high d-spacing could be suitable. To evaluate the suitability of these crystals for a particular beamline, it is useful to evaluate the crystals' performance using tools such as ray-tracing. However, simulations for double-crystal monochromators are only available for the most used crystals such as Si, Ge or diamond. Here, an upgrade of the SHADOW ray-tracing code and complementary tools in the OASYS suite are presented to simulate high d-spacing crystals with arbitrary, and sometimes complex, structures such as beryl, YB₆₆, muscovite, etc. Isotropic and anisotropic temperature factors are also considered. The YB₆₆ crystal with 1936 atomic sites in the unit cell is simulated, and its applicability for tender X-ray monochromators is discussed in the context of new low-emittance storage rings.

A new scheme for stigmatic x-ray imaging with large magnification

This paper describes a new x-ray scheme for stigmatic imaging. The scheme consists of one convex spherically bent crystal and one concave spherically bent crystal. The radii of curvature and Bragg reflecting lattice planes of the two crystals are properly matched to eliminate the astigmatism, so that the conditions for stigmatic imaging are met for a particular wavelength. The magnification is adjustable and solely a function of the two Bragg angles or angles of incidence. Although the choice of Bragg angles is constrained by the availability of crystals, this is not a severe limitation for the imaging of plasmas, since a particular wavelength can be selected from the bremsstrahlung continuum. The working principle of this imaging scheme has been verified with visible light. Further tests with x rays are planned for the near future.

Application of spatially resolved high resolution crystal spectrometry to inertial confinement fusion plasmas

High resolution (λ∕Δλ ∼ 10 000) 1D imaging x-ray spectroscopy using a spherically bent crystal and a 2D hybrid pixel array detector is used world wide for Doppler measurements of ion-temperature and plasma flow-velocity profiles in magnetic confinement fusion plasmas. Meter sized plasmas are diagnosed with cm spatial resolution and 10 ms time resolution. This concept can also be used as a diagnostic of small sources, such as inertial confinement fusion plasmas and targets on x-ray light source beam lines, with spatial resolution of micrometers, as demonstrated by laboratory experiments using a 250-μm (55)Fe source, and by ray-tracing calculations. Throughput calculations agree with measurements, and predict detector counts in the range 10(-8)-10(-6) times source x-rays, depending on crystal reflectivity and spectrometer geometry. Results of the lab demonstrations, application of the technique to the National Ignition Facility (NIF), and predictions of performance on NIF will be presented.

A novel zirconium Kα imager for high energy density physics research

We report on the development and characterization of a zirconium Kα imager for high energy density physics research. The imager consists of a spherically bent quartz crystal operating at 15.7 keV photon energy. We compare the performance of the imager in terms of integrated reflectivity (R(int)) and temperature dependent collection efficiency (η(Te)) to that of the widely used Cu Kα imager. Our collisional-radiative simulations show that the new imager can be reliably used up to 250 eV plasma temperature. Monte Carlo simulations show that for a 25 μm thick tracer layer of zirconium, the contribution to Kα production from photo-pumping is only 2%. We present, for the first time, 2D spatially resolved images of zirconium plasmas generated by a high intensity short pulse laser interacting with Zr solid targets.

Ray tracing flux calculation for the small and wide angle x-ray scattering diffraction station at the SESAME synchrotron radiation facility

The calculation for the optics of the synchrotron radiation small and wide angle x-ray scattering beamline, currently under construction at SESAME is described. This beamline is based on a cylindrically bent germanium (111) single crystal with an asymmetric cut of 10.5 degrees , followed by a 1.2 m long rhodium coated plane mirror bent into a cylindrical form. The focusing properties of bent asymmetrically cut crystals have not yet been studied in depth. The present paper is devoted to study of a particular application of a bent asymmetrically cut crystal using ray tracing simulations with the SHADOW code. These simulations show that photon fluxes of order of 1.09x10(11) photons/s will be available at the experimental focus at 8.79 keV. The focused beam dimensions will be 2.2 mm horizontal full width at half maximum (FWHM) by 0.12 mm vertical (FWHM).

Dose distribution from x‐ray microbeam arrays applied to radiation therapy: An EGS4 Monte Carlo study

We present EGS4 Monte Carlo calculations of the spatial distribution of the dose deposited by a single x-ray pencil beam, a planar microbeam, and an array of parallel planar microbeams as used in radiation therapy research. The profiles of the absorbed dose distribution in a phantom, including the peak-to-valley ratio of the dose distribution from microbeam arrays, were calculated at micrometer resolution. We determined the dependence of the findings on the main parameters of photon and electron transport. The results illustrate the dependence of the electron range and the deposited in-beam dose on the cut-off energy, of the electron transport, as well as the effects on the dose profiles of the beam energy, the array size, and the beam spacing. The effect of beam polarization also was studied for a single pencil beam and for an array of parallel planar microbeams. The results show that although the polarization effect on the dose distribution from a 3 cm x 3 cm microbeam array inside a water phantom is large enough to be measured at the outer side of the array (16% difference of the deposited dose for x-ray beams of 200 keV), it is not detectable at the array's center, thus being irrelevant for the radiation therapy purposes. Finally we show that to properly compare the dose profiles determined with a metal oxide semiconductor field emission transistor detector with the computational method predictions, it is important to simulate adequately the size and the material of the device's Si active element.

Placebo adverse events in headache trials: headache as an adverse event of placebo

We analysed the adverse events of placebo in acute and preventive randomized, double-blind, placebo-controlled studies for migraine treatment. Fifty-seven trials (oral triptans, non-steroidal anti-inflammatory drugs, nasal ergot alkaloids and preventive agents) were included. From 10 to 30% of subjects reported adverse events after placebo. Most common were features associated with a migraine attack, such as nausea, phono- and photophobia. Other frequent complaints resembled those of the active drug (e.g. chest pressure in triptan trials). A third group of adverse events appeared to be coincidental (e.g. sleep disturbance). Adverse events following placebo are probably related to the drug under study and the symptomatology of migraine; some have no obvious explanation.

5-Hydroxytryptamine(1B/1D) and 5-hydroxytryptamine1F receptors inhibit capsaicin-induced c-fos immunoreactivity within mouse trigeminal nucleus caudalis

In order to investigate the c-fos response within the trigeminal nucleus caudalis (Sp5C) after noxious meningeal stimulation, capsaicin (0.25, 0.5, 1 and 5 nmol) was administered intracisternally in urethane (1 g/kg) and alpha-chloralose (20 mg/kg) anaesthetized male mice. Capsaicin induced a robust and dose-dependent c-fos-like immunoreactivity (c-fos LI) within Sp5C. C-fos LI was observed within laminae I and II of the entire brain stem from the area postrema to C2 level, being maximum at the decussatio pyramidum level. The area postrema, solitary tract, medullary and lateral reticular nuclei were also labelled. The 5-hydroxytryptamine(1B/1D/1F) receptor agonist sumatriptan (0.01, 0.1, 1 and 10 mg/kg), administered intraperitoneally 15 min before capsaicin stimulation (1 nmol), decreased the c-fos response within Sp5C, but not within solitary tract. The novel specific 5-hydroxytryptamine1F agonist LY 344864 (0.1 and 1 mg/kg, i.p.) significantly decreased the c-fos LI within the Sp5C as well. These findings suggest that intracisternally administered capsaicin activates the trigeminovascular system and that the pain neurotransmission can be modulated by 5-hydroxytryptamine(1B/1D/1F) receptors in mice. Thus, the availability of this model in mice, taken together with the possibility of altering the expression of specific genes in this species, may help to investigate further the importance of distinct proteins in the neurotransmission of cephalic pain.

Delayed inflammation in rat meninges: implications for migraine pathophysiology

Nitric oxide (NO) has been implicated in migraine pathogenesis based on the delayed development of typical migraine headache 4-6 h after infusing the NO donor nitroglycerin [glyceryl trinitrate (GTN)] to migraineurs. Furthermore, inhibiting the synthesis of NO by treatment with a NO synthase (NOS) inhibitor attenuates spontaneous migraine headaches in 67% of subjects. Because NO has been linked to inflammation and cytokine expression, we investigated the delayed consequences of brief GTN infusion (30 min) on the development of meningeal inflammation in a rat model using doses relevant to the human model. We found dose-dependent Type II NOS [inducible NOS (iNOS)] mRNA upregulation in dura mater beginning at 2 h and an increase in the corresponding protein expression at 4, 6 and 10 h after infusion. Type II NOS immunoreactivity was expressed chiefly within resident meningeal macrophages. Consistent with development of a delayed inflammatory response, we detected induction of interleukin 1beta in dura mater at 2 and 6 h and increased interleukin 6 in dural macrophages and in rat cerebrospinal fluid at 6 h after GTN infusion. Myeloperoxidase-positive cells were rarely found. Leakage of plasma proteins from dural blood vessels was first detected 4 h after GTN infusion, and this was suppressed by administering a specific Type II NOS inhibitor [L-N(6)-(1-iminoethyl)-lysine (L-NIL)]. In addition to cytokine induction, macrophage iNOS upregulation and oedema formation after GTN infusion, dural mast cells exhibited granular changes consistent with secretion at 4 and 6 h. Because iNOS was expressed in dural macrophages following topical GTN, and in the spleen after intravenous injection, the data suggest that the inflammatory response is mediated by direct actions on the dura and does not develop secondary to events within the brain. Our findings point to the importance of new gene expression and cytokine expression as fundamental to the delayed response following GTN infusion, and support the hypothesis that a similar response develops in human meninges after GTN challenge.

Hypothalamic involvement in chronic migraine

OBJECTIVES

Chronic migraine (CM), previously called transformed migraine, is a frequent headache disorder that affects 2%-3% of the general population. Analgesic overuse, insomnia, depression, and anxiety are disorders that are often comorbid with CM. Hypothalamic dysfunction has been implicated in its pathogenesis, but it has never been studied in patients with CM. The aim was to analyze hypothalamic involvement in CM by measurement of melatonin, prolactin, growth hormone, and cortisol nocturnal secretion.

METHODS

A total of 338 blood samples (13/patient) from 17 patients with CM and nine age and sex matched healthy volunteers were taken. Melatonin, prolactin, growth hormone, and cortisol concentrations were determined every hour for 12 hours. The presence of comorbid disorders was also evaluated.

RESULTS

An abnormal pattern of hypothalamic hormonal secretion was found in CM. This included: (1) a decreased nocturnal prolactin peak, (2) increased cortisol concentrations, (3) a delayed nocturnal melatonin peak in patients with CM, and (4) lower melatonin concentrations in patients with CM with insomnia. Growth hormone secretion did not differ from controls.

CONCLUSION

These results support hypothalamic involvement in CM, shown by a chronobiologic dysregulation, and a possible hyperdopaminergic state in patients with CM. Insomnia might be an important variable in the study findings.

How to pick optimal acute treatment for migraine headache

Drug selection for the acute treatment of migraine is based on comorbid disorders, coexistent diseases, and the patient's pain profile and specific needs and expectations. Patients should be instructed to tailor their treatment strategy to meet their specific needs by varying their medications according to pain intensity. This will aid in successful headache management, by increasing compliance and decreasing disability and cost.

Central and peripheral mechanisms of migraine

Central (cortex and upper brainstem) and peripheral (trigeminovascular) mechanisms are involved in the pathophysiology of migraine. We propose that unknown migraine triggers initiate depolarization of cortical neurons followed concomitantly by a transient increase in blood flow. This transient hyperemia spreads at a rate of 3-6 mm/min followed by hypoperfusion which is more long-lasting. Through unknown mechanisms (probably chemical), we hypothesize that this wave activates or sensitizes trigeminovascular axons which is a consequence of neuropeptide release and neurogenic inflammation. Orthodromic conduction along trigeminovascular fibers transmits information centrally via the trigeminal caudalis and other brainstem nuclei to higher cortical structures for registration and modulation of nociceptive information.

Experimental models of migraine

Experimental models have been developed to study various aspects of migraine. Here we describe the most commonly used models--mostly animal models--which led to the development of a pathophysiological concept of migraine. We focus on activation studies of the trigeminovascular system, the sphenopalatine ganglion, the superior sagittal sinus, the dura mater as well as blood vessels. The most common consequences of activation are noted and include protein extravasation, neuropeptide release, rCBF and diameter changes, c-fos expression and electrical neuronal activity. In addition, we briefly summarize the results of cortical spreading depression studies, as they relate to the human migraine aura. These models will continue to be useful to elucidate migraine pathophysiology and explore drug mechanisms.

Receptor systems mediating c-fos expression within trigeminal nucleus caudalis in animal models of migraine

In intracranial structures unmyelinated C- and Adelta-fibers of the trigeminal nerve transmit pain stimuli from meninges to the trigeminal nucleus caudalis (Sp5C). Peripheral nerve endings surround meningeal vessels (the so-called trigeminovascular system) and contain vasoactive neuropeptides (calcitonin gene-related peptide, substance P and neurokinin A). Activation of the trigeminovascular system promotes a meningeal sterile inflammatory response through the release of neuropeptides by peripheral endings. Orthodromic conduction along trigeminovascular fibers transmits information centrally with induction of immediate early c-fos gene within post-synaptic Sp5C neurons, as a marker of neuronal activity within central nociceptive pathways. In laboratory animals the system is activated by either electrical stimulation of the TG, chemical stimulation of the meninges, electrical or mechanical stimulation of the superior sagittal sinus or by induction of cortical spreading depression. All these techniques induce c-fos within Sp5C and are used as a rodent/feline model of vascular headache in humans. Up-to-date there is evidence that at least ten receptors (5-HT(1B), 5-HT(1D), 5-HT(lF), 5-HT(2B), NK-1, GABA(A), NMDA, AMPA, class III metabotropic glutamate receptors, and opioids mu receptors) modulate c-fos expression within Sp5C. These receptors represent potential targets for anti-migraine drugs as shown by triptans (5-HT(1B/1D/1F)) and ergot alkaloids (5-HT(1A1B/1D/1F)). This review discusses the importance of c-fos expression within Sp5C as a marker of cephalic nociception, the different cephalic pain models that induce c-fos within Sp5C, the receptors involved and their potential role as targets for anti-migraine drugs.

Functional neuroimaging: enhanced understanding of migraine pathophysiology

Research into migraine pathophysiology has been hampered by the episodic nature and unpredictable onset of migraine attacks. Recently, newer imaging techniques have been providing noninvasive methods of studying metabolism and hemodynamics in the brains of migraineurs during and between acute attacks. 133Xe blood flow techniques, transcranial Doppler, and SPECT have all been employed to investigate hemodynamic changes during migraine aura. PET has been useful in the study of migraine without aura, with findings of increased blood flow related to pain in cortical areas and in the medial brainstem. Currently, three functional MRI imaging techniques are being used in migraine research. Diffusion-weighted imaging has shown normal findings in measures of the ability of neurons to maintain osmotic gradients. Studies using perfusion-weighted imaging have shown alterations in relative cerebral blood flow (CBF), relative cerebral blood volume, and mean transit time during migraine visual aura. The blood oxygen level-dependent technique can supply information related to neuronal activation during acute migraine aura. MRS has been used with mixed success to look for evidence of abnormal energy metabolism in the brains of migraineurs. Magnetoencephalography studies support the presence of a spreading depression-like phenomenon in migraine with aura. Two groups have used transcranial magnetic stimulation to assess whether neurons in the occipital cortex are hyperexcitable, predisposing patients to develop aura symptoms. Despite conflicting findings, migraine with visual aura appears to be generally associated with transient decreases in regional CBF.

X-ray topographic determination of the granular structure in a graphite mosaic crystal: a three-dimensional reconstruction

Section topographs recorded at different spatial locations and at different rocking angles of a highly oriented pyrolytic graphite (HOPG) crystal allow three-dimensional maps of the local angular-dependent scattering power to be obtained. This is performed with a direct reconstruction from the intensity distribution on such topographs. The maps allow the extraction of information on local structural parameters such as size, form and internal mosaic spread of crystalline domains. This data analysis leads to a new method for the characterization of mosaic crystals. Perspectives and limits of applicability of this method are discussed.

High altitude headache. Lessons from headaches at sea level

There is little known about high altitude headache, except that it is an important and serious problem that often heralds the onset of acute mountain sickness. We do know that the brain itself is an insensate organ except for its meninges which contain sensory axons projecting from the trigeminal nerve. These nerve fibers travel in proximity to meningeal blood vessels and constitute an important component of the trigeminovascular system. Signals generated at high altitude which may activate the trigeminovascular system can arise from brain, blood or the blood vessel wall, include protons, neurotransmitters and other potential noxious agents which can discharge or sensitize small unmyelinated fibers. Brain edema and raised intracranial pressure may cause headache by compressing brain structures leading to displacement and stretching of the pain-sensitive intracranial structures. Small hemorrhage may irritate and discharge these fibers chemically. Furthermore, high altitude seems capable of decreasing the threshold of response to sensory stimulation. Therefore, headache can be attributed to activation of a common pathway, the trigeminovascular system by both chemical or mechanical stimulation.

Attenuation by butalbital of capsaicin-induced c-fos-like immunoreactivity in trigeminal nucleus caudalis

We examined the effects of butalbital (30, 100, and 1000 micrograms/kg) on the number of cells expressing c-fos-like immunoreactivity (c-fos-LI), a marker of neuronal activation, within lamina I, IIo of the trigeminal nucleus caudalis and the nucleus of the solitary tract 2 hours after the intracisternal injection of capsaicin (0.1 mL; 15.25 mg/mL) or vehicle in urethane-anesthetized guinea pigs (N = 45). Robust c-fos-LI was observed within nuclei of cells in the trigeminal nucleus caudalis after capsaicin (329 +/- 35). Butalbital dose-dependently reduced the number of labeled cells to a maximum of 66% (1000 micrograms/kg intraperitoneally [i.p.], P < .01) in lamina I, IIo but not within area postrema, medial reticular nucleus, or the nucleus of the solitary tract. Pretreatment with bicuculline (30 micrograms/kg i.p.) blocked the effect of butalbital, thereby suggesting the importance of the GABAA receptor to activation involved in the transmission of nociceptive information. Our studies suggest the possibility that GABAA receptors might provide an important therapeutic target in migraine and related headache disorders.

Perfusion weighted imaging during migraine: spontaneous visual aura and headache

Using perfusion weighted imaging, we studied 28 spontaneous migraine episodes; 7 during visual aura (n = 6), 7 during the headache phase following visual aura (n = 3), and 14 cases of migraine without aura (n = 13). The data were analyzed using a region-of-interest-based approach. During aura, relative cerebral blood flow (rCBF) was significantly decreased (27% +/- 0.07) in occipital cortex contralateral to the affected hemifield. rCBV was decreased (15% +/- 0.12) and mean transit time increased (32% +/- 0.3), persisting up to 2.5 h into the headache phase. Other brain regions did not show significant perfusion changes. During migraine without aura, no significant hemodynamic changes were observed. In one patient who experienced both migraine with and without aura, perfusion deficits were observed only during migraine with aura. These findings suggest that decremental blood flow changes in occipital lobe are most characteristic of migraine with aura.

Both 5-HT1B and 5-HT1F receptors modulate c-fos expression within rat trigeminal nucleus caudalis

A possible mechanism of action of antimigraine drugs such as sumatriptan is inhibition of the trigeminovascular pathway. Sumatriptan's effects might be mediated by 5-HT1B, 5-HT1D or 5-HT1F receptors. To establish the relative importance of these subtypes, we compared the effects of sumatriptan with those of a selective 5-HT1F receptor agonist (LY 344864) on c-fos protein expression in the trigeminal nucleus caudalis. c-fos expression was induced in urethane-anaesthetized rats by intracisternal capsaicin administration. Sumatriptan and LY 344864 decreased the number of capsaicin-induced c-fos-like immunoreactive cells within trigeminal nucleus caudalis (ID50 = 0.04 and 0.6 mg kg(-1)). The effect of sumatriptan, but not of LY 344864, was prevented by pretreatment with the antagonist SDZ 21-009, which displays high affinity for rat 5-HT1B receptors. LY 344864 appears to attenuate c-fos-like immunoreactivity via 5-HT1F receptors, while sumatriptan acts via 5-HT1B receptors. The fact that activation of 5-HT1F receptors is sufficient to modulate the activity of the trigeminal system suggests that this receptor may be a target for antimigraine drugs with improved safety profile.

The NMDA receptor antagonist MK-801 reduces capsaicin-induced c-fos expression within rat trigeminal nucleus caudalis

The effect of the N-methyl-D-aspartate (NMDA) receptor antagonist (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-i mine hydrogen maleate (MK-801) was examined on c-fos-like immunoreactivity (c-fos-LI) in urethane-anesthetized Sprague-Dawley rats using a polyclonal antibody. C-fos, an indicator of neuronal activation, was assessed within the trigeminal nucleus caudalis (TNC), area postrema. lateral reticular and solitary tract nuclei 2 h after intracisternal injection of capsaicin. C-fos-positive cells were counted at three representative levels corresponding to obex, -2.05 mm and -6.45 mm in 18 tissue sections (50 microm). A weighted average was obtained reflecting total brainstem expression within lamina I, II of TNC using a recently validated method. Capsaicin (0.1, 1, 5, 10 and 15 nmol) caused a dose-dependent labeling of cells in lamina I, II at obex similar to that previously reported after intracisternal blood or carrageenin administration in rats and guinea pigs. MK-801 (0.3, 1 and 3 mg/kg) administered i.p. 30 min before capsaicin (5 nmol in 100 microl artificial CSF) reduced significantly and dose-dependently (12%, 36% and 47%, respectively) the c-fos-LI cells in TNC at each level from rostral to caudal but not in solitary tract, area postrema and lateral reticular nuclei, and for unexplained reasons, increased c-fos-LI within the inferior olive. These results suggest that NMDA receptors provide a potential therapeutic target for cephalic pain (e.g. migraine) due to trigeminovascular activation from meningeal afferents.

Perfusion-weighted imaging defects during spontaneous migrainous aura

Perfusion- and diffusion-weighted magnetic resonance imaging was performed during spontaneous visual auras in four migraineurs. Alterations in relative cerebral blood flow (16-53% decrease), cerebral blood volume (6-33% decrease), and tissue mean transit time (10-54% increase) were observed in the gray matter of occipital cortex contralateral to the affected visual hemifield. No changes in the apparent diffusion coefficient were observed either while the patients were symptomatic or after resolution of the visual symptoms but before the onset of headache. Functional magnetic resonance imaging can be a useful noninvasive tool to study hemodynamic changes during spontaneous attacks of migraine with aura.