9 research outputs found
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Activity-dependent silencing reveals functionally distinct itch-generating sensory neurons
The peripheral terminals of primary sensory neurons detect histamine and non-histamine itch-provoking ligands through molecularly distinct transduction mechanisms. It remains unclear, however, whether these distinct pruritogens activate the same or different afferent fibers. We utilized a strategy of reversibly silencing specific subsets of murine pruritogen-sensitive sensory axons by targeted delivery of a charged sodium-channel blocker and found that functional blockade of histamine itch did not affect the itch evoked by chloroquine or SLIGRL-NH2, and vice versa. Notably, blocking itch-generating fibers did not reduce pain-associated behavior. However, silencing TRPV1+ or TRPA1+ neurons allowed AITC or capsaicin respectively to evoke itch, implying that certain peripheral afferents may normally indirectly inhibit algogens from eliciting itch. These findings support the presence of functionally distinct sets of itch-generating neurons and suggest that targeted silencing of activated sensory fibers may represent a clinically useful anti-pruritic therapeutic approach for histaminergic and non-histaminergic pruritus
Multi-scale evolution of KelvinâHelmholtz waves at the Earth's magnetopause during southward IMF periods
At the Earth's low-latitude magnetopause, the Kelvin-Helmholtz instability (KHI), driven by the velocity shear between the magnetosheath and magnetosphere, has been frequently observed during northward interplanetary magnetic field (IMF) periods. However, the signatures of the KHI have been much less frequently observed during southward IMF periods, and how the KHI develops under southward IMF has been less explored. Here, we performed a series of realistic 2D and 3D fully kinetic simulations of a KH wave event observed by the Magnetospheric Multiscale (MMS) mission at the dusk-flank magnetopause during southward IMF on September 23, 2017. The simulations demonstrate that the primary KHI bends the magnetopause current layer and excites the Rayleigh-Taylor instability (RTI), leading to penetration of high-density arms into the magnetospheric side. This arm penetration disturbs the structures of the vortex layer and produces intermittent and irregular variations of the surface waves which significantly reduces the observational probability of the periodic KH waves. The simulations further demonstrate that in the non-linear growth phase of the primary KHI, the lower-hybrid drift instability (LHDI) is induced near the edge of the primary vortices and contributes to an efficient plasma mixing across the magnetopause. The signatures of the large-scale surface waves by the KHI/RTI and the small-scale fluctuations by the LHDI are reasonably consistent with the MMS observations. These results indicate that the multi-scale evolution of the magnetopause KH waves and the resulting plasma transport and mixing as seen in the simulations may occur during southward IMF
Multi-scale observations of the magnetopause KelvinâHelmholtz waves during southward IMF
In this study, we present the first observations from the Magnetospheric Multiscale (MMS) mission of the Kelvin-Helmholtz instability (KHI) at the dusk-flank magnetopause during southward interplanetary magnetic field conditions on September 23, 2017. The instability criterion for the KHI was fulfilled for the plasma parameters observed throughout the event. An analysis of the boundary normal vectors based on the application of the timing method onto the magnetic field and the electron density data and the minimum directional derivative method onto the magnetic field data shows signatures of surface waves in the plane parallel to the velocity shear. A comparison to 2D fully kinetic simulations demonstrates reasonable consistencies with the formation of surface waves generated by the KH instability, as well as the structures of rolled-up KH waves. The observations further indicated low density faster than sheath plasma as an indicator of rolled-up vortices, which is also consistent with the simulations. All of these results show that the observed waves and vortices are most likely generated by the KH instability. High-time resolution MMS measurements further demonstrate kinetic-scale electric field fluctuations on the low-density side of the edges of surface waves. Detailed comparisons with the simulations suggest that the observed fluctuations are generated by the lower-hybrid drift instability excited by the density gradient at the edges of these surface waves. These secondary effects can lead to a flattening of the edge layers, indicating the connection between kinetic and larger scales within the KH waves and vortices
ElectronâScale Reconnecting Current Sheet Formed Within the LowerâHybrid WaveâActive Region of KelvinâHelmholtz Waves
Abstract We present Magnetospheric Multiscale observations of an electronâscale reconnecting current sheet in the mixing region along the trailing edge of a KelvinâHelmholtz vortex during southward interplanetary magnetic field conditions. Within this region, we observe intense electrostatic wave activity, consistent with lowerâhybrid waves. These waves lead to the transport of highâdensity magnetosheath plasma across the boundary layer into the magnetosphere and generate a mixing region with highly compressed magnetic field lines, leading to the formation of a thin current sheet associated with electronâscale reconnection signatures. Consistencies between these reconnection signatures and a realistic, local, fullyâkinetic simulation modeling this current sheet indicate a temporal evolution of the observed electronâscale reconnection current sheet. The multiâscale and interâprocess character of this event can help us understand plasma mixing connected to the KelvinâHelmholtz instability and the temporal evolution of electronâscale reconnection
Reconnection Inside a Dipolarization Front of a Diverging Earthward Fast Flow
International audienceAbstract We examine a Dipolarization Front (DF) event with an embedded electron diffusion region (EDR), observed by the Magnetospheric Multiscale (MMS) spacecraft on 08 September 2018 at 14:51:30 UT in the Earth's magnetotail by applying multiâscale multipoint analysis methods. In order to study the largeâscale context of this DF, we use conjunction observations of the Cluster spacecraft together with MMS. A polynomial magnetic field reconstruction technique is applied to MMS data to characterize the embedded electron current sheet including its velocity and the Xâline exhaust opening angle. Our results show that the MMS and Cluster spacecraft were located in two counterârotating vortex flows, and such flows may distort a flux tube in a way that the local magnetic shear angle is increased and localized magnetic reconnection may be triggered. Using multiâpoint data from MMS we further show that the local normalized reconnection rate is in the range of R âŒÂ 0.16 to 0.18. We find a highly asymmetric electron inâ and outflow structure, consistent with previous simulations on strong guideâfield reconnection events. This study shows that magnetic reconnection may not only take place at largeâscale stable magnetopause or magnetotail current sheets but also in transient localized current sheets, produced as a consequence of the interaction between the fast Earthward flows and the Earth's dipole field