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The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU 69 ) has been largely undisturbed since its formation. We studied its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through irradiation of simple molecules. Water ice was not detected. This composition indicates hydrogenation of carbon monoxide-rich ice and/or energetic processing of methane condensed on water ice grains in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, which suggests that Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29 ± 5 kelvin., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU 69 , a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU 69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU 69 's origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Cometary nuclei consist mostly of dust and water ice. Previous observations have found nuclei to be low-density and highly porous bodies, but have only moderately constrained the range of allowed densities because of the measurement uncertainties. Here we report the precise mass, bulk density, porosity and internal structure of the nucleus of comet 67P/Churyumov-Gerasimenko on the basis of its gravity field. The mass and gravity field are derived from measured spacecraft velocity perturbations at fly-by distances between 10 and 100 kilometres. The gravitational point mass is GM = 666.2 ± 0.2 cubic metres per second squared, giving a mass M = (9,982 ± 3) × 10(9) kilograms. Together with the current estimate of the volume of the nucleus, the average bulk density of the nucleus is 533 ± 6 kilograms per cubic metre. The nucleus appears to be a low-density, highly porous (72-74 per cent) dusty body, similar to that of comet 9P/Tempel 1. The most likely composition mix has approximately four times more dust than ice by mass and two times more dust than ice by volume. We conclude that the interior of the nucleus is homogeneous and constant in density on a global scale without large voids. The high porosity seems to be an inherent property of the nucleus material.

Background: There is extensive evidence implicating the metabotropic glutamate 5 (mGlu5) receptor in aspects of addiction-related behaviours., Methods: Here, we used a well-characterized line of mGlu5-deficient mice to further examine the role of this receptor in cocaine-driven behaviours. We confirmed the previously reported deficit in hippocampal long-term potentiation and associated spatial learning impairment., Results: Despite a spatial learning deficit, mGlu5-deficient mice developed and maintained a conditioned place preference to cocaine, suggesting cocaine reward and Pavlovian conditioning are intact in these animals. Notably, however, mGlu5-deficient mice exhibited a marked deficit in the extinction of a cocaine-conditioned place preference compared to wild type littermates. Moreover, in a fixed ratio operant intravenous self-administration paradigm, both genotypes showed similar responding for cocaine over two different doses, while mGlu5-deficient mice displayed enhanced responding on a progressive ratio schedule. In addition, cue-induced drug-seeking after abstinence was exaggerated in mGlu5-deficient mice., Conclusion: Collectively, these findings suggest that while the mGlu5 receptor may be involved in mediating the rewarding effects of cocaine, it appears necessary for the extinction of cocaine-driven behaviours., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Asteroid 21 Lutetia was approached by the Rosetta spacecraft on 10 July 2010. The additional Doppler shift of the spacecraft radio signals imposed by 21 Lutetia's gravitational perturbation on the flyby trajectory were used to determine the mass of the asteroid. Calibrating and correcting for all Doppler contributions not associated with Lutetia, a least-squares fit to the residual frequency observations from 4 hours before to 6 hours after closest approach yields a mass of (1.700 ± 0.017) × 10(18) kilograms. Using the volume model of Lutetia determined by the Rosetta Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) camera, the bulk density, an important parameter for clues to its composition and interior, is (3.4 ± 0.3) × 10(3) kilograms per cubic meter.

Drugs of abuse have the ability to instantiate plastic adaptations within the central nervous system, and this property may relate to the development and persistence of addiction. In this context, a single exposure to cocaine in rodents may induce synaptic plasticity by increasing the AMPA/NMDA receptor excitatory post-synaptic current (EPSC) amplitude ratio in dopaminergic cells of the ventral tegmental area (VTA). Here, we examine the role of the metabotropic glutamate 5 (mGlu5) receptor in this regard using a genetic mouse model. The control AMPA/NMDA EPSC ratio is reduced in mGlu5-deficient mice compared to wild-types. Moreover, cocaine-induced enhancement of this EPSC ratio is also absent in mutant mice, which suggests that mGlu5 receptors are required for single-dose cocaine-induced plasticity onto VTA cells. While the temporal profile of hyperactivity to acute cocaine is altered in mGlu5-deficient mice; these mice still develop and express sensitized psychomotor responses to cocaine. These data suggest that the mGlu5 receptor is required for cocaine-induced plasticity in VTA dopaminergic cells. In contrast, the mGlu5 receptor may not be essential for psychostimulant behavioural sensitization; although it probably impacts other aspects drug addiction, such as motivation to self-administer.

The issue of non-specific effects for potential therapeutics is particularly salient in neurological/psychiatric disorders, where adverse drug reactions could impair critical brain functions. The issue of specificity is not limited to candidate molecules, as receptor targets themselves often influence physiological as well as pathological outcomes. Metabotropic glutamate receptor 5 (mGlu5) is an example of a "promiscuous" receptor target that has been implicated in addiction, but also many other processes. However, if receptor modulation could be restricted to specific pathways/brain regions, mGlu5 may still prove to be a viable therapeutic target for various indications. Using this premise, a number of possible methods to refine drug development strategy are discussed, including exploiting specific interactions of mGlu5 with other receptors to narrow the influence of pharmacological agents, and also the use of RNA interference targeted to specific cells/regions of the brain.

L-glutamate is the principal excitatory neurotransmitter at fast synapses in the mammalian central nervous system, and signals though a number of ionotropic and metabotropic receptors. Among the latter are the group I metabotropic glutamate (mGlu1 and mGlu5) receptors that upon activation elevate intracellular calcium levels through activation of the phospholipase C pathway. The role of glutamatergic transmission in both the development of addiction and the phenomenon of relapse that may occur after prolonged abstinence, has come under intense scrutiny in recent times. While both mGlu1 and mGlu5 receptors have been implicated in certain aspects of the addictive state, the exact roles these receptors play in this process is, as yet, unclear. This review will introduce contemporary theories on drug addiction, including neural circuitry, before critically assessing the current body of knowledge on group I metabotropic glutamate receptors in this regard. This will involve an in-depth discussion of the distribution of these receptors in the brain, their presence in neural pathways known or postulated to be involved in addiction and their involvement in drug-related behavioral paradigms. The effect of acute and chronic drug administration on the activity and expression of group I metabotropic glutamate receptors will be investigated, as will the effect these receptors have on behavioral and biochemical responses to drugs of abuse. Finally, there will be a brief discussion on current and future therapeutic applications using our knowledge of these receptors, and the direction that future studies will need to take to close the gaps in our understanding.

The metabotropic glutamate receptor 5 (mGlu5) has been implicated in ethanol- and drug-seeking behaviours in rodent studies. Here we examine a number of ethanol-related behavioural assays in mice lacking mGlu5 and wild-type littermates. In a two-bottle free-choice paradigm, mGlu5-deficient mice consumed less ethanol with a reduced preference compared to wild-type mice. Indeed, mGlu5-deficienct mice were ethanol-avoiding at both concentrations of ethanol proffered (5% and 10% v/v). However, there was no difference in the rate of hepatic ethanol and acetaldehyde metabolism between genotypes and consumption of saccharin was similar. In a conditioned place preference study, mGlu5-deficient mice displayed a place preference for ethanol when conditioned with a low dose (1g/kg) of ethanol. Thus, while mGlu5-deficient mice consume less ethanol (with a reduced preference) than wild-type mice, this is not apparently related to impaired hepatic metabolism or a lack of reward from ethanol. Rather, we provide evidence that deletion of the mGlu5 receptor increases sensitivity to centrally mediated effects of ethanol.

The atmosphere and ionosphere of Venus have been studied in the past by spacecraft with remote sensing or in situ techniques. These early missions, however, have left us with questions about, for example, the atmospheric structure in the transition region from the upper troposphere to the lower mesosphere (50-90 km) and the remarkably variable structure of the ionosphere. Observations become increasingly difficult within and below the global cloud deck (<50 km altitude), where strong absorption greatly limits the available investigative spectrum to a few infrared windows and the radio range. Here we report radio-sounding results from the first Venus Express Radio Science (VeRa) occultation season. We determine the fine structure in temperatures at upper cloud-deck altitudes, detect a distinct day-night temperature difference in the southern middle atmosphere, and track day-to-day changes in Venus' ionosphere.

One of Titan's most intriguing attributes is its copious but featureless atmosphere. The Voyager 1 fly-by and occultation in 1980 provided the first radial survey of Titan's atmospheric pressure and temperature and evidence for the presence of strong zonal winds. It was realized that the motion of an atmospheric probe could be used to study the winds, which led to the inclusion of the Doppler Wind Experiment on the Huygens probe. Here we report a high resolution vertical profile of Titan's winds, with an estimated accuracy of better than 1 m s(-1). The zonal winds were prograde during most of the atmospheric descent, providing in situ confirmation of superrotation on Titan. A layer with surprisingly slow wind, where the velocity decreased to near zero, was detected at altitudes between 60 and 100 km. Generally weak winds (approximately 1 m s(-1)) were seen in the lowest 5 km of descent.

Jupiter's nonthermal microwave emission, as measured by a global network of 11 radio telescopes, increased dramatically during the Shoemaker-Levy 9 impacts. The increase was wavelength-dependent, varying from approximately 10 percent at 70 to 90 centimeters to approximately 45 percent at 6 and 36 centimeters. The radio spectrum hardened (flattened toward shorter wavelengths) considerably during the week of impacts and continued to harden afterward. After the week of cometary impacts, the flux density began to subside at all wavelengths and was still declining 3 months later. Very Large Array and Australia Telescope images of the brightness distribution showed the enhancement to be localized in longitude and concentrated near the magnetic equator. The evidence therefore suggests that the increase in flux density was caused by a change in the resident particle population, for example, through an energization or spatial redistribution of the emitting particles.

Radio signals from Ulysses were used to probe the lo plasma torus (IPT) shortly after the spacecraft's closest approach to Jupiter. The frequencies of the two downlinks at S-band (2.3 gigahertz) and X-band (8.4 gigahertz) were recorded, differenced, and integrated in order to derive the columnar electron density of the IPT. The measurements agree qualitatively with contemporary models of the IPT based on Voyager data, but significant differences are apparent as well. The overall level of the IPT electron density is approximately the same as the prediction, implying that the amount of gas (or plasma) injected from lo is similar to that observed during the Voyager era. On the other hand, the IPT seems to be less extended out of the centrifugal equator, implying a smaller plasma temperature than predicted.