Femtosecond electronic response of atoms to ultra-intense X-rays.

An era of exploring the interactions of high-intensity, hard X-rays with matter has begun with the start-up of a hard-X-ray free-electron laser, the Linac Coherent Light Source (LCLS). Understanding how electrons in matter respond to ultra-intense X-ray radiation is essential for all applications. Here we reveal the nature of the electronic response in a free atom to unprecedented high-intensity, short-wavelength, high-fluence radiation (respectively 10(18) W cm(-2), 1.5-0.6 nm, approximately 10(5) X-ray photons per A(2)). At this fluence, the neon target inevitably changes during the course of a single femtosecond-duration X-ray pulse-by sequentially ejecting electrons-to produce fully-stripped neon through absorption of six photons. Rapid photoejection of inner-shell electrons produces 'hollow' atoms and an intensity-induced X-ray transparency. Such transparency, due to the presence of inner-shell vacancies, can be induced in all atomic, molecular and condensed matter systems at high intensity. Quantitative comparison with theory allows us to extract LCLS fluence and pulse duration. Our successful modelling of X-ray/atom interactions using a straightforward rate equation approach augurs favourably for extension to complex systems.

A new perspective for schizophrenia: TAAR1 agonists reveal antipsychotic- and antidepressant-like activity, improve cognition and control body weight.

Schizophrenia is a chronic, severe and highly complex mental illness. Current treatments manage the positive symptoms, yet have minimal effects on the negative and cognitive symptoms, two prominent features of the disease with critical impact on the long-term morbidity. In addition, antipsychotic treatments trigger serious side effects that precipitate treatment discontinuation. Here, we show that activation of the trace amine-associated receptor 1 (TAAR1), a modulator of monoaminergic neurotransmission, represents a novel therapeutic option. In rodents, activation of TAAR1 by two novel and pharmacologically distinct compounds, the full agonist RO5256390 and the partial agonist RO5263397, blocks psychostimulant-induced hyperactivity and produces a brain activation pattern reminiscent of the antipsychotic drug olanzapine, suggesting antipsychotic-like properties. TAAR1 agonists do not induce catalepsy or weight gain; RO5263397 even reduced haloperidol-induced catalepsy and prevented olanzapine from increasing body weight and fat accumulation. Finally, TAAR1 activation promotes vigilance in rats and shows pro-cognitive and antidepressant-like properties in rodent and primate models. These data suggest that TAAR1 agonists may provide a novel and differentiated treatment of schizophrenia as compared with current medication standards: TAAR1 agonists may improve not only the positive symptoms but also the negative symptoms and cognitive deficits, without causing adverse effects such as motor impairments or weight gain.

Single-photon multiple detachment in fullerene negative ions: absolute ionization cross sections and the role of the extra electron.

We have obtained experimental photo-double- and photo-triple-detachment cross sections for the fullerene negative ion using Advanced Light Source photons of 17-90 eV. The cross sections are 2 and 2.5 times larger than those for C60 and appear to be compressed and shifted in photon energy as compared to C60. Our analysis reveals that the additional electron in C60- primarily produces screening which is responsible for the modification of the spectrum. Both screening effects, the shift and the compression, can be quantitatively accounted for by a linear transformation of the energy axis. Applying the transformation allows us to map the neutral and negative ion cross sections onto each other, pointing out the close relationship of correlated few-electron dynamics in neutral and negatively charged extended systems. In contrast, dynamics of neutral and negatively charged atoms or small molecules are typically not closely related.

Ultrafast x-ray scattering of xenon nanoparticles: imaging transient states of matter.

Femtosecond x-ray laser flashes with power densities of up to 10(14) W/cm(2) at 13.7 nm wavelength were scattered by single xenon clusters in the gas phase. Similar to light scattering from atmospheric microparticles, the x-ray diffraction patterns carry information about the optical constants of the objects. However, the high flux of the x-ray laser induces severe transient changes of the electronic configuration, resulting in a tenfold increase of absorption in the developing nanoplasma. The modification in opaqueness can be correlated to strong atomic charging of the particle leading to excitation of Xe(4+). It is shown that single-shot single-particle scattering on femtosecond time scales yields insight into ultrafast processes in highly excited systems where conventional spectroscopy techniques are inherently blind.

Explosions of xenon clusters in ultraintense femtosecond x-ray pulses from the LCLS free electron laser.

Explosions of large Xe clusters ( ~ 11,000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 10(17) W/cm(2) from the Linac Coherent Light Source were investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating.

Unveiling and driving hidden resonances with high-fluence, high-intensity x-ray pulses.

We show that high fluence, high-intensity x-ray pulses from the world's first hard x-ray free-electron laser produce nonlinear phenomena that differ dramatically from the linear x-ray-matter interaction processes that are encountered at synchrotron x-ray sources. We use intense x-ray pulses of sub-10-fs duration to first reveal and subsequently drive the 1s↔2p resonance in singly ionized neon. This photon-driven cycling of an inner-shell electron modifies the Auger decay process, as evidenced by line shape modification. Our work demonstrates the propensity of high-fluence, femtosecond x-ray pulses to alter the target within a single pulse, i.e., to unveil hidden resonances, by cracking open inner shells energetically inaccessible via single-photon absorption, and to consequently trigger damaging electron cascades at unexpectedly low photon energies.

Nonlinear atomic response to intense ultrashort x rays.

The nonlinear absorption mechanisms of neon atoms to intense, femtosecond kilovolt x rays are investigated. The production of Ne(9+) is observed at x-ray frequencies below the Ne(8+), 1s(2) absorption edge and demonstrates a clear quadratic dependence on fluence. Theoretical analysis shows that the production is a combination of the two-photon ionization of Ne(8+) ground state and a high-order sequential process involving single-photon production and ionization of transient excited states on a time scale faster than the Auger decay. We find that the nonlinear direct two-photon ionization cross section is orders of magnitude higher than expected from previous calculations.

Time-resolved pump-probe experiments at the LCLS.

The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs.

Double core-hole production in N2: beating the Auger clock.

We investigate the creation of double K-shell holes in N2 molecules via sequential absorption of two photons on a time scale shorter than the core-hole lifetime by using intense x-ray pulses from the Linac Coherent Light Source free electron laser. The production and decay of these states is characterized by photoelectron spectroscopy and Auger electron spectroscopy. In molecules, two types of double core holes are expected, the first with two core holes on the same N atom, and the second with one core hole on each N atom. We report the first direct observations of the former type of core hole in a molecule, in good agreement with theory, and provide an experimental upper bound for the relative contribution of the latter type.

Ultraintense x-ray induced ionization, dissociation, and frustrated absorption in molecular nitrogen.

Sequential multiple photoionization of the prototypical molecule N2 is studied with femtosecond time resolution using the Linac Coherent Light Source (LCLS). A detailed picture of intense x-ray induced ionization and dissociation dynamics is revealed, including a molecular mechanism of frustrated absorption that suppresses the formation of high charge states at short pulse durations. The inverse scaling of the average target charge state with x-ray peak brightness has possible implications for single-pulse imaging applications.

Auger electron angular distribution of double core-hole states in the molecular reference frame.

The Linac Coherent Light Source free electron laser is a source of high brightness x rays, 2×10(11) photons in a ∼5 fs pulse, that can be focused to produce double core vacancies through rapid sequential ionization. This enables double core vacancy Auger electron spectroscopy, an entirely new way to study femtosecond chemical dynamics with Auger electrons that probe the local valence structure of molecules near a specific atomic core. Using 1.1 keV photons for sequential x-ray ionization of impulsively aligned molecular nitrogen, we observed a rich single-site double core vacancy Auger electron spectrum near 413 eV, in good agreement with ab initio calculations, and we measured the corresponding Auger electron angle dependence in the molecular frame.

A pressurized flow reactor combustion experiment interfaced with synchrotron double imaging photoelectron photoion coincidence spectroscopy.

A new pressurized low-temperature combustion experiment has been commissioned at the Swiss Light Source, Paul Scherrer Institute. The experiment uses photoionization with tunable synchrotron radiation and double imaging photoelectron photoion coincidence (i2PEPICO) detection at the vacuum ultraviolet beamline. The experimental setup is described, including the high-pressure reactor experiment, sampling interface, and reactant delivery system. The CRF-PEPICO (Combustion Reactions Followed by Photoelectron Photoion Coincidence) endstation and VUV beamline are briefly elaborated. The novel aspects of the apparatus and the new components are elucidated in detail, such as the fluid supply system to the reactor and the reactor integration into the endstation. We also present a system overview of the experimental setup. The technical details are followed by a description of the experimental procedure used to operate the pressurized flow reactor setup. Finally, first experimental results demonstrating the capability of the setup are provided and analyzed. A major advantage of this new experiment is that the excellent isomer resolution capabilities of the i2PEPICO technique can be transferred to the investigation of reactions at elevated pressures of several bars. This enables the investigation of pressure effects on the reactivity of fuel mixtures and covers more realistic conditions found in technical combustors. The capability to obtain quantitative oxidation data is confirmed, and the main and certain intermediate species are quantified for a selected condition. The results show excellent agreement with a chemical kinetics model and previously published reference measurements performed with a gas chromatography setup.

Glycosyl-phosphatidylinositol-specific phospholipase D. Interaction with and stimulation by apolipoprotein A-I.

Glycosyl-phosphatidylinositol-specific phospholipase D (GPI-PLD) is an amphiphilic protein which, in serum, is associated with high-density lipoproteins (HDL). It is shown that the major component of the HDL fraction, apolipoprotein A-I (apo A-I), is responsible for this association. In the absence of apo A-I, purified GPI-PLD occurred as virtually inactive aggregates which became disaggregated by apo A-I. The enzyme/apo A-I complex efficiently hydrolyzed the solubilized GPI-anchored substrate, acetylcholinesterase. Triton X-100 was also able to dissociate aggregated GPI-PLD, however, it strongly inhibited enzyme activity at detergent concentrations above the critical micellar concentration.

Partial cortical devascularization results in elevations of cortical nerve growth factor and increases nerve growth factor protein within basal forebrain cholinergic neurons.

Previous studies have demonstrated that partial cortical devascularization results in increased levels of nerve growth factor protein within the tissue immediately surrounding the infarcted region. In the present study, we have used this lesion model to further characterize the nerve growth factor increase by investigating: (i) the time course for this phenomenon; (ii) the impact of the devascularizing lesion on cortical regions not directly impinged upon by the lesion; and (iii) the response of nerve growth factor-sensitive nucleus basalis neurons providing afferent cortical innervation to the increased availability of nerve growth factor within their target territory. Our results indicate that, within the infarcted cortex, nerve growth factor levels increase rapidly following the lesion (up 51% by one day post lesion), reach a maximum of 136% above controls by three days and undergo a slow decline back to baseline levels by 23 days. Within the frontal and cingulate cortices, which are not devascularized by the lesion and show no signs of pathological damage, nerve growth factor levels increase over a similar time course, and with a similar magnitude, to those in the lesioned cortex. Nerve growth factor-sensitive nucleus basalis neurons on the side ipsilateral to the lesion respond to increased cortical nerve growth factor levels with an increased accumulation of nerve growth factor within their cell bodies (revealed by nerve growth factor immunohistochemistry and quantitative enzyme-linked immunosorbent assay) which was apparent at three days following the lesion, but no longer discernible at seven or 14 days or later. The present study investigated a model of cortical devascularization for its ability to alter nerve growth factor levels within the cortex. Nerve growth factor levels were rapidly increased within the infarcted cortical tissue beneath the lesion but were also elevated to a similar extent, and with a similar time course, in cortical regions not directly impinged upon by the lesion. The retrograde impact of elevated cortical nerve growth factor levels was demonstrated by an increased accumulation of nerve growth factor within the cell bodies of nucleus basalis neurons providing innervation to the cortex. This lesion model should provide a potential avenue for investigating the functional role(s) of nerve growth factor in the intact and lesioned adult central nervous system, as well as the internal mechanisms for regulating its synthesis, release, uptake, and degradation.

Are there differences between the secretion characteristics of NGF and BDNF? Implications for the modulatory role of neurotrophins in activity-dependent neuronal plasticity.

In previous experiments the activity-dependent secretion of nerve growth factor (NGF) from native hippocampal slices and from NGF-cDNA transfected hippocampal neurons showed unusual characteristics [Blochl and Thoenen (1995) Eur J Neurosci 7:1220-1228; (1996) Mol Cell Neurosci 7:173-190]. In both hippocampal slices and cultured hippocampal neurons the activity-dependent secretion proved to be independent of extracellular calcium, but dependent on the release of calcium from intracellular stores. Under different experimental conditions, Goodman et al. [(1996) Mol Cell Neurosci 7:222-238] reported that the high potassium-mediated secretion of brain-derived neurotrophic factor (BDNF) from hippocampal cultures was dependent on extracellular calcium. Mowla et al. [(1997) Proc 27th Annu Meet Soc Neurosci New Orleans 875.10] reported on even further-reaching differences between NGF and BDNF secretion, namely, that in hippocampal neurons and in pituitary cell lines NGF was secreted exclusively according to the constitutive pathway, whereas BDNF was exclusively sorted according to the activity-dependent regulated pathway. In view of the crucial importance of such potential differences between the processing, sorting, and secretory mechanisms of different neurotrophins for their modulatory roles in activity-dependent neuronal plasticity, a thorough analysis under comparable experimental conditions was mandatory. We demonstrate that in native hippocampal slices and adenoviral-transduced hippocampal neurons there are no differences between NGF and BDNF with respect to the subcellular distribution and mechanism of secretion; that the activity-dependent secretion of both NGF and BDNF is dependent on intact intracellular calcium stores; and that the differences between our own observations and those of Goodman et al. (ibid.) regarding the dependence on extracellular calcium do not reflect differences between NGF and BDNF sorting and secretion, but reflect the differing experimental conditions used.

Reversible sedimentation and masking of nerve growth factor (NGF) antigen by high molecular weight fractions from rat brain.

Nerve growth factor (NGF) was recently found to be largely associated with sedimentable fractions of adult rat brain and treatments of the fractions by alkaline pH increased the measurable amount of their NGF antigen as well as its solubilization [M.C. Hoener, E. Hewitt, J.M. Conner, J.W. Costello and S. Varon, Nerve growth factor (NGF) content in adult rat brain tissues is several-fold higher than generally reported and is largely associated with sedimentable fractions, Brain Res., 728 (1996) 47-56; M.C. Hoener and S. Varon, Effects of sodium chloride, Triton X-100, and alkaline pH on the measurable contents and sedimentability of the nerve growth factor (NGF) antigen in adult rat hippocampal tissue extracts, J. Neurosci. Res., in press (1997); C. Zettler, D.C.McL. Bridges, X.-F. Zhou and R.A. Rush, Detection of increased tissue concentrations of nerve growth factor with improved extraction procedure, J. Neurosci. Res., 46 (1996) 581-594]. We have further investigated the reversibility of these pH effects. Reversal of the pH of an adult rat hippocampal tissue extract from 10.5 to 7.4 led to an almost complete transfer of NGF back from nonsedimentable to sedimentable fractions and to a remasking of the previously unmasked portion of NGF antigen. Thus, molecules causing masking and sedimentation of NGF at pH 7.4 were likely to be present in the alkaline extract. A gel filtration column in PBS, pH 10.5 was used to separate such putative binding molecules from the NGF. All of the NGF antigen from rat hippocampal alkaline extract was found to elute with 19 kDa fractions. The same apparent molecular weight was found for mouse submaxillary beta-NGF and recombinant human beta-NGF. Masking and sedimentation no longer occurred when newly generated 19 kDa rat brain NGF was returned to pH 7.4. When high molecular weight fractions derived from the same gel filtration (in PBS, pH 10.5) were added back to the 19 kDa NGF pool at pH 7.4 and the mixture incubated and centrifuged, the measurability of 19 kDa rat brain NGF antigen was markedly reduced and half of the antigen was recovered in sedimentable fractions. Similar but less dramatic results were obtained when mixing the same high molecular weight fractions with 19 kDa mouse or human beta-NGF. These findings provide new opportunities to identify molecules to which NGF may be bound within intact brain tissues.

Nerve growth factor (NGF) content in adult rat brain tissues is several-fold higher than generally reported and is largely associated with sedimentable fractions.

Initial studies had revealed that the bioactivity of nerve growth factor (NGF) in sonicates of adult rat hippocampal formation (HF) is several-fold greater in their pellet than their supernatant fractions. Such observations have prompted an analysis of NGF antigen (NGF-Ag) contents in pellets and supernatants from a variety of adult rat CNS tissues, both in the absence and the presence of exogenous beta-NGF. With HF tissues, NGF-Ag in the supernatants was comparable to most literature values, but pellet NGF-Ag was 3 to 5 times that amount. All other CNS tissue sonicates also revealed 3-6 fold higher NGF-Ag in their pellets than their supernatants, hence overall NGF-Ag contents were greatly in excess of reported ones. Presentation of mouse beta-NGF to a tissue, its sonicate, or its standard pellet resulted in a transfer to the final pellet of 30-50% of the added soluble NGF-Ag (and 30% of the added bioactivity). This percentage is much lower than that present in native pellets (80%), suggesting that the association of endogenous NGF with particulate matter may involve at least two compartments. Treatments of pellets with salt, alkaline pH, and/or the detergent Triton X-100 have revealed a third subset, namely additional pellet NGF-Ag that was not initially recognized by the antibody in our ELISA assay. The treatments also caused substantial release of NGF from pellet to supernatant. Further studies should clarify the nature of the association between NGF and the three subsets of pellet NGF and allow the investigation of the pellet molecules responsible for it.

Monoamine transporter and receptor interaction profiles of a new series of designer cathinones.

Psychoactive ß-keto amphetamines (cathinones) are sold as "bath salts" or "legal highs" and recreationally abused. We characterized the pharmacology of a new series of cathinones, including methedrone, 4-methylethcathinone (4-MEC), 3-fluoromethcathinone (3-FMC), pentylone, ethcathinone, buphedrone, pentedrone, and N,N-dimethylcathinone. We investigated norepinephrine (NE), dopamine (DA), and serotonin (5-HT) uptake inhibition using human embryonic kidney 293 (HEK 293) cells that express the respective human monoamine transporter, the drug-induced efflux of NE, DA, and 5-HT from monoamine-preloaded cells, and binding affinity to monoamine transporters and receptors. All of the cathinones were potent NE uptake inhibitors but differed in their DA vs. 5-HT transporter inhibition profiles and monoamine release effects. Methedrone was a more potent 5-HT than DA transporter inhibitor and released NE and 5-HT similar to para-methoxymethamphetamine (PMMA), para-methoxyamphetamine (PMA), 4-methylthioamphetamine (4-MTA), and 3,4-methylenedioxymethamphetamine (MDMA). 4-MEC and pentylone equipotently inhibited all of the monoamine transporters and released 5-HT. Ethcathinone and 3-FMC inhibited NE and DA uptake and released NE, and 3-FMC also released DA similar to N-ethylamphetamine and methamphetamine. Pentedrone and N,N-dimethylcathinone were non-releasing NE and DA uptake inhibitors as previously shown for pyrovalerone cathinones. Buphedrone preferentially inhibited NE and DA uptake and also released NE. None of the cathinones bound to rodent trace amine-associated receptor 1, in contrast to the non-ß-keto-amphetamines. None of the cathinones exhibited relevant binding to other monoamine receptors. In summary, we found considerable differences in the monoamine transporter interaction profiles among different cathinones and compared with related amphetamines.

Taar1-mediated modulation of presynaptic dopaminergic neurotransmission: role of D2 dopamine autoreceptors.

Trace Amine-Associated Receptor 1 (TAAR1) is a G protein-coupled receptor (GPCR) expressed in several mammalian brain areas and activated by "trace amines" (TAs). TAs role is unknown; however, discovery of their receptors provided an opportunity to investigate their functions. In vivo evidence has indicated an inhibitory influence of TAAR1 on dopamine (DA) neurotransmission, presumably via modulation of dopamine transporter (DAT) or interaction with the D2 DA receptor and/or activation of inwardly rectifying K(+) channels. To elucidate the mechanisms of TAAR1-dependent modulation, we used TAAR1 knockout mice (TAAR1-KO), a TAAR1 agonist (RO5166017) and a TAAR1 antagonist (EPPTB) in a set of neurochemical experiments. Analysis of the tissue content of TAAR1-KO revealed increased level of the DA metabolite homovanillic acid (HVA), and in vivo microdialysis showed increased extracellular DA in the nucleus accumbens (NAcc) of TAAR1-KO. In fast scan cyclic voltammetry (FSCV) experiments, the evoked DA release was higher in the TAAR1-KO NAcc. Furthermore, the agonist RO5166017 induced a decrease in the DA release in wild-type that could be prevented by the application of the TAAR1 antagonist EPPTB. No alterations in DA clearance, which are mediated by the DAT, were observed. To evaluate the interaction between TAAR1 and D2 autoreceptors, we tested the autoreceptor-mediated dynamics. Only in wild type mice, the TAAR1 agonist was able to potentiate quinpirole-induced inhibitory effect on DA release. Furthermore, the short-term plasticity of DA release following paired pulses was decreased in TAAR1-KO, indicating less autoinhibition of D2 autoreceptors. These observations suggest a close interaction between TAAR1 and the D2 autoreceptor regulation.

Pharmacological characterization of designer cathinones in vitro.

BACKGROUND AND PURPOSE: Designer ß-keto amphetamines (e.g. cathinones, 'bath salts' and 'research chemicals') have become popular recreational drugs, but their pharmacology is poorly characterized. EXPERIMENTAL APPROACH: We determined the potencies of cathinones to inhibit DA, NA and 5-HT transport into transporter-transfected HEK 293 cells, DA and 5-HT efflux from monoamine-preloaded cells, and monoamine receptor binding affinity. KEY RESULTS: Mephedrone, methylone, ethylone, butylone and naphyrone acted as non-selective monoamine uptake inhibitors, similar to cocaine. Mephedrone, methylone, ethylone and butylone also induced the release of 5-HT, similar to 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) and other entactogens. Cathinone, methcathinone and flephedrone, similar to amphetamine and methamphetamine, acted as preferential DA and NA uptake inhibitors and induced the release of DA. Pyrovalerone and 3,4-methylenedioxypyrovalerone (MDPV) were highly potent and selective DA and NA transporter inhibitors but unlike amphetamines did not evoke the release of monoamines. The non-ß-keto amphetamines are trace amine-associated receptor 1 ligands, whereas the cathinones are not. All the cathinones showed high blood-brain barrier permeability in an in vitro model; mephedrone and MDPV exhibited particularly high permeability. CONCLUSIONS AND IMPLICATIONS: Cathinones have considerable pharmacological differences that form the basis of their suggested classification into three groups. The predominant action of all cathinones on the DA transporter is probably associated with a considerable risk of addiction.