Corticosterone Acts in the Nucleus Accumbens to Enhance Dopamine Signaling and Potentiate Reinstatement of Cocaine Seeking

Stressful life events are important contributors to relapse in recovering cocaine addicts, but the mechanisms by which they influence motivational systems are poorly understood. Studies suggest that stress may “set the stage” for relapse by increasing the sensitivity of brain reward circuits to drug-associated stimuli. We examined the effects of stress and corticosterone on behavioral and neurochemical responses of rats to a cocaine prime after cocaine self-administration and extinction. Exposure of rats to acute electric footshock stress did not by itself reinstate drug-seeking behavior but potentiated reinstatement in response to a subthreshold dose of cocaine. This effect of stress was not observed in adrenalectomized animals, and was reproduced in nonstressed animals by administration of corticosterone at a dose that reproduced stress-induced plasma levels. Pretreatment with the glucocorticoid receptor antagonist RU38486 did not block the corticosterone effect. Corticosterone potentiated cocaine-induced increases in extracellular dopamine in the nucleus accumbens (NAc), and pharmacological blockade of NAc dopamine receptors blocked corticosterone-induced potentiation of reinstatement. Intra-accumbens administration of corticosterone reproduced the behavioral effects of stress and systemic corticosterone. Corticosterone treatment acutely decreased NAc dopamine clearance measured by fast-scan cyclic voltammetry, suggesting that inhibition of uptake2-mediated dopamine clearance may underlie corticosterone effects. Consistent with this hypothesis, intra-accumbens administration of the uptake2 inhibitor normetanephrine potentiated cocaine-induced reinstatement. Expression of organic cation transporter 3, a corticosterone-sensitive uptake2 transporter, was detected on NAc neurons. These findings reveal a novel mechanism by which stress hormones can rapidly regulate dopamine signaling and contribute to the impact of stress on drug intake

Modelling chemical abundance distributions for dwarf galaxies in the Local Group: the impact of turbulent metal diffusion

We investigate stellar metallicity distribution functions (MDFs), including Fe and ${\alpha}$-element abundances, in dwarf galaxies from the Feedback in Realistic Environments (FIRE) project. We examine both isolated dwarf galaxies and those that are satellites of a Milky Way-mass galaxy. In particular, we study the effects of including a sub-grid turbulent model for the diffusion of metals in gas. Simulations that include diffusion have narrower MDFs and abundance ratio distributions, because diffusion drives individual gas and star particles toward the average metallicity. This effect provides significantly better agreement with observed abundance distributions of dwarf galaxies in the Local Group, including the small intrinsic scatter in [${\alpha}$/Fe] vs. [Fe/H] (less than 0.1 dex). This small intrinsic scatter arises in our simulations because the interstellar medium (ISM) in dwarf galaxies is well-mixed at nearly all cosmic times, such that stars that form at a given time have similar abundances to within 0.1 dex. Thus, most of the scatter in abundances at z = 0 arises from redshift evolution and not from instantaneous scatter in the ISM. We find similar MDF widths and intrinsic scatter for satellite and isolated dwarf galaxies, which suggests that environmental effects play a minor role compared with internal chemical evolution in our simulations. Overall, with the inclusion of metal diffusion, our simulations reproduce abundance distribution widths of observed low-mass galaxies, enabling detailed studies of chemical evolution in galaxy formation.Comment: 19 pages, 13 figures, published in MNRA

F21RS SGR No. 5 (Memorial Day)

A Resolution To Urge and Request LSU Faculty to not hold University classes on Memorial Da

Mechanisms of Chinese tallow (Triadica sebifera) invasion and their management implications – A review

Ecosystems are under increasing stress from environmental change, including invasion by non-native species that can disrupt ecological processes and functions. Chinese tallow [Triadica sebifera (L.) Small] is a highly invasive tree species in southeastern US forests, prairies, and wetlands, and effectively managing this invasive species is a significant challenge for scientists and land managers. In this review, we synthesize the literature on invasion ecology and management of Chinese tallow. Our review suggests that the invaded range of Chinese tallow is currently limited by dispersal in many areas and by low temperatures and low soil moisture, and by high soil salinity and frequent flooding in others, but these barriers may be overcome by increased dispersal, phenotypic plasticity, and/or rapid evolution. Invasions by Chinese tallow are facilitated by both the invasiveness of the species and the invasibility of the recipient communities. Invasiveness of Chinese tallow has been attributed to fast growth, high fecundity, a persistent seed bank, aggressive resprouting, abiotic stress tolerance, and the ability to transform fire maintained ecosystems. Some of these traits may be enhanced in invasive populations. Anthropogenic and natural disturbances, lack of herbivore pressure, and facilitation by soil microbes enhance the intensity of Chinese tallow invasions. Biological control of Chinese tallow is being developed. Treatments such as herbicides, prescribed fire, and mechanical control can effectively control Chinese tallow at the local scale. A combination of these treatments improves results. However, a proactive management approach would simultaneously achieve invasion control and promote subsequent ecological restoration, especially in the context of legacy effects, secondary invasions, and/or variable ecosystem responses to different control treatments. Future research should clarify the roles of species invasiveness and community invasibility, increase our understanding of the effects of Chinese tallow in invaded communities, and develop viable management regimes that are effective in both controlling or reducing the probability of Chinese tallow invasion and restoring desired native communities

The Stellar Kinematics of Void Dwarf Galaxies Using KCWI

Dwarf galaxies located in extremely under-dense cosmic voids are excellent test-beds for disentangling the effects of large-scale environment on galaxy formation and evolution. We present integral field spectroscopy for low-mass galaxies ($M_{\star}=10^{7}-10^{9}~M_{\odot}$) located inside (N=21) and outside (N=9) cosmic voids using the Keck Cosmic Web Imager (KCWI). Using measurements of stellar line-of-sight rotational velocity $v_{\mathrm{rot}}$ and velocity dispersion $\sigma_{\star}$, we test the tidal stirring hypothesis, which posits that dwarf spheroidal galaxies are formed through tidal interactions with more massive host galaxies. We measure low values of $v_{\mathrm{rot}}/\sigma_{\star}\lesssim2$ for our sample of isolated dwarf galaxies, and we find no trend between $v_{\mathrm{rot}}/\sigma_{\star}$ and distance from a massive galaxy $d_{L^{\star}}$ out to $d_{L^{\star}}\sim10$ Mpc. These suggest that dwarf galaxies can become dispersion-supported "puffy" systems even in the absence of environmental effects like tidal interactions. We also find indications of an upward trend between $v_{\mathrm{rot}}/\sigma_{\star}$ and galaxy stellar mass, perhaps implying that stellar disk formation depends on mass rather than environment. Although some of our conclusions may be slightly modified by systematic effects, our main result still holds: that isolated low-mass galaxies may form and remain as puffy systems rather than the dynamically cold disks predicted by classical galaxy formation theory.Comment: 19 pages including references; submitted to ApJ. Code used for analysis and figures can be found here: https://github.com/mdlreyes/void-dwarf-analysi

On Type Ia Supernovae From The Collisions of Two White Dwarfs

We explore collisions between two white dwarfs as a pathway for making Type Ia Supernovae (SNIa). White dwarf number densities in globular clusters allow 10-100 redshift <1 collisions per year, and observations by (Chomiuk et al. 2008) of globular clusters in the nearby S0 galaxy NGC 7457 have detected what is likely to be a SNIa remnant. We carry out simulations of the collision between two 0.6 solar mass white dwarfs at various impact parameters and mass resolutions. For impact parameters less than half the radius of the white dwarf, we find such collisions produce approximately 0.4 solar masses of Ni56, making such events potential candidates for underluminous SNIa or a new class of transients between Novae and SNIa.Comment: 4 pages, 4 figures, 1 tabl

The Arduous Journey to Black-Hole Formation in Potential Gamma-Ray Burst Progenitors

We present a quantitative study on the properties at death of fast-rotating massive stars evolved at low-metallicity, objects that are proposed as likely progenitors of long-duration gamma-ray bursts (LGRBs). We perform 1D+rotation stellar-collapse simulations on the progenitor models of Woosley & Heger (2006) and critically assess their potential for the formation of a black hole and a Keplerian disk (namely a collapsar) or a proto-magnetar. We note that theoretical uncertainties in the treatment of magnetic fields and the approximate handling of rotation compromises the accuracy of stellar-evolution models. We find that only the fastest rotating progenitors achieve sufficient compactness for black-hole formation while the bulk of models possess a core density structure typical of garden-variety core-collapse supernova (SN) progenitors evolved without rotation and at solar metallicity. Of the models that do have sufficient compactness for black-hole formation, most of them also retain a large amount of angular momentum in the core, making them prone to a magneto-rotational explosion, therefore preferentially leaving behind a proto-magnetar. A large progenitor angular-momentum budget is often the sole criterion invoked in the community today to assess the suitability for producing a collapsar. This simplification ignores equally important considerations such as the core compactness, which conditions black-hole formation, the core angular momentum, which may foster a magneto-rotational explosion preventing black-hole formation, or the metallicity and the residual envelope mass which must be compatible with inferences from observed LGRB/SNe. Our study suggests that black-hole formation is non trivial, that there is room for accommodating both collapsars and proto-magnetars as LGRB progenitors, although proto-magnetars seem much more easily produced by current stellar-evolutionary models.Comment: 10 emulateapj pages, 3 figures, 1 table, matches published versio

MJO-related intraseasonal variation in the stratosphere: gravity waves and zonal winds

Previous work has shown eastward migrating regions of enhanced temperature variance due to long-vertical wavelength stratospheric gravity waves that are in sync with intraseasonal precipitation and tropopause wind anomalies associated with the Madden-Julian Oscillation (MJO). Here the origin of these intraseasonal gravity wave variations is investigated with a set of idealized gravity wave-resolving model experiments. The experiments specifically test whether tropopause winds act to control gravity wave propagation into the stratosphere by a critical level filtering mechanism or play a role in gravity wave generation through an obstacle source effect. All experiments use identical convective latent heating variability but the large-scale horizontal wind profile is varied to investigate relationships between stratospheric gravity waves and zonal winds at different levels. Results show that the observed long vertical wavelength gravity waves are primarily sensitive to stratospheric zonal wind variations, while tropopause wind variations have only a very small effect. Thus neither the critical level filter mechanism nor the obstacle source play much of a role in the observed intraseasonal gravity wave variations. Instead the results suggest that the stratospheric waves follow the MJO precipitation sources, and tropopause wind anomalies follow the same sources. We further find evidence of intraseasonal wave drag effects on the stratospheric circulation in reanalyzed winds. The results suggest that waves drive intraseasonal stratospheric zonal wind anomalies that descend in altitude with increasing MJO phases 3 through 7. Eastward anomalies descend further than westward, suggesting that MJO-related stratospheric waves cause larger eastward drag forces

Fire in the field: simulating the threshold of galaxy formation

We present a suite of 15 cosmological zoom-in simulations of isolated dark matter haloes, all with masses of M_(halo) ≈ 10^(10) M_⊙ at z = 0, in order to understand the relationship among halo assembly, galaxy formation and feedback's effects on the central density structure in dwarf galaxies. These simulations are part of the Feedback in Realistic Environments (FIRE) project and are performed at extremely high resolution (m_(baryon) = 500 M_⊙, m_(dm) = 2500 M_⊙). The resultant galaxies have stellar masses that are consistent with rough abundance matching estimates, coinciding with the faintest galaxies that can be seen beyond the virial radius of the Milky Way (M_*/M_⊙ ≈ 10^5 − 10^7). This non-negligible spread in stellar mass at z = 0 in haloes within a narrow range of virial masses is strongly correlated with central halo density or maximum circular velocity V_(max), both of which are tightly linked to halo formation time. Much of this dependence of M_* on a second parameter (beyond M_(halo)) is a direct consequence of the M_(halo) ∼ 10^(10) M_⊙ mass scale coinciding with the threshold for strong reionization suppression: the densest, earliest-forming haloes remain above the UV-suppression scale throughout their histories while late-forming systems fall below the UV-suppression scale over longer periods and form fewer stars as a result. In fact, the latest-forming, lowest-concentration halo in our suite fails to form any stars. Haloes that form galaxies with M_⋆ ≳ 2 × 10^6 M_⊙ have reduced central densities relative to dark-matter-only simulations, and the radial extent of the density modifications is well-approximated by the galaxy half-mass radius r_(1/2). Lower-mass galaxies do not modify their host dark matter haloes at the mass scale studied here. This apparent stellar mass threshold of M_⋆ ≈ 2 × 10^6 − 2 × 10^(−4) M_(halo) is broadly consistent with previous work and provides a testable prediction of FIRE feedback models in Λcold dark matter