Spatial transcriptomics reveals the distinct organization of mouse prefrontal cortex and neuronal subtypes regulating chronic pain.

The prefrontal cortex (PFC) is a complex brain region that regulates diverse functions ranging from cognition, emotion and executive action to even pain processing. To decode the cellular and circuit organization of such diverse functions, we employed spatially resolved single-cell transcriptome profiling of the adult mouse PFC. Results revealed that PFC has distinct cell-type composition and gene-expression patterns relative to neighboring cortical areas-with neuronal excitability-regulating genes differently expressed. These cellular and molecular features are further segregated within PFC subregions, alluding to the subregion-specificity of several PFC functions. PFC projects to major subcortical targets through combinations of neuronal subtypes, which emerge in a target-intrinsic fashion. Finally, based on these features, we identified distinct cell types and circuits in PFC underlying chronic pain, an escalating healthcare challenge with limited molecular understanding. Collectively, this comprehensive map will facilitate decoding of discrete molecular, cellular and circuit mechanisms underlying specific PFC functions in health and disease.

MAFG-driven astrocytes promote CNS inflammation.

Multiple sclerosis is a chronic inflammatory disease of the CNS1. Astrocytes contribute to the pathogenesis of multiple sclerosis2, but little is known about the heterogeneity of astrocytes and its regulation. Here we report the analysis of astrocytes in multiple sclerosis and its preclinical model experimental autoimmune encephalomyelitis (EAE) by single-cell RNA sequencing in combination with cell-specific Ribotag RNA profiling, assay for transposase-accessible chromatin with sequencing (ATAC-seq), chromatin immunoprecipitation with sequencing (ChIP-seq), genome-wide analysis of DNA methylation and in vivo CRISPR-Cas9-based genetic perturbations. We identified astrocytes in EAE and multiple sclerosis that were characterized by decreased expression of NRF2 and increased expression of MAFG, which cooperates with MAT2α to promote DNA methylation and represses antioxidant and anti-inflammatory transcriptional programs. Granulocyte-macrophage colony-stimulating factor (GM-CSF) signalling in astrocytes drives the expression of MAFG and MAT2α and pro-inflammatory transcriptional modules, contributing to CNS pathology in EAE and, potentially, multiple sclerosis. Our results identify candidate therapeutic targets in multiple sclerosis.

Publisher Correction: Reply to: On the ferroelectricity of CH3NH3PbI3 perovskites.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Energetics at the Surface: Direct Optical Mapping of Core and Surface Electronic Structure in CdSe Quantum Dots Using Broadband Electronic Sum Frequency Generation Microspectroscopy.

Understanding and controlling the electronic structure of nanomaterials is the key to tailoring their use in a wide range of practical applications. Despite this need, many important electronic states are invisible to conventional optical measurements and are typically identified indirectly based on their inferred impact on luminescence properties. This is especially common and important in the study of nanomaterial surfaces and their associated defects. Surface trap states play a crucial role in photophysical processes yet remain remarkably poorly understood. Here we demonstrate for the first time that broadband electronic sum frequency generation (eSFG) microspectroscopy can directly map the optically bright and dark states of nanoparticles, including the elusive below gap states. This new approach is applied to model cadmium selenide (CdSe) quantum dots (QDs), where the energies of surface trap states have eluded direct optical characterization for decades. Our eSFG measurements show clear signatures of electronic transitions both above the band gap, which we assign to previously reported one- and two-photon transitions associated with the CdSe core, as well as broad spectral signatures below the band gap that are attributed to surface states. In addition to the core states, this analysis reveals two distinct distributions of below gap states, providing the first direct optical measurement of both shallow and deep surface states on this system. Finally, chemical modification of the surfaces via oxidation results in the relative increase in the signals originating from the surface states. Overall, our eSFG experiments provide an avenue to directly map the entirety of the QD core and surface electronic structure, which is expected to open up opportunities to study how these materials are grown in situ and how surface states can be controlled to tune functionality.

A new approach to vibrational sum frequency generation spectroscopy using near infrared pulse shaping.

We have developed a multipurpose vibrational sum frequency generation (vSFG) spectrometer that is uniquely capable of probing a broad range of chemical species, each requiring different experimental conditions, without optical realignment. Here, we take advantage of arbitrary near infrared (NIR) waveform generation using a 4f-pulse shaper equipped with a 2D spatial light modulator (SLM) to tailor upconversion pulses to meet sample dependent experimental requirements. This report details the experimental layout, details of the SLM calibration and implementation, and the intrinsic benefits/limitations of this new approach to vSFG spectroscopy. We have demonstrated the competency of this spectrometer by achieving an ∼3-fold increase in spectral resolution compared to conventional spectrometers by probing the model dimethyl sulfoxide/air interface. We also show the ability to suppress nonresonant background contributions from electrode interfaces using time delayed asymmetric waveforms that are generated by the NIR pulse shaper. It is expected that this advancement in instrumentation will broaden the types of samples researchers can readily study using nonlinear surface specific spectroscopies.

Probing ligand removal and ordering at quantum dot surfaces using vibrational sum frequency generation spectroscopy.

HYPOTHESIS: Controlling nanomaterial interfaces for emerging technologies has driven the need to understand the molecular species located there; however, challenges arise using traditional analytical techniques to directly characterize the molecular structure and local environments of these interfacial species due to their low relative populations. We hypothesized that vibrational sum frequency generation (vSFG) spectroscopy would be uniquely sensitive to the chemical modification of nanoparticle surfaces that is obscured using traditional bulk sensitive methods. EXPERIMENTS: Octadecylamine ligands were removed from model CdSe quantum dot surfaces using a common precipitation-resuspension procedure with polar protic and aprotic nonsolvents. Vibrational spectra of the ligands at the surface were collected with vSFG to directly probe the ligand ordering and coverage. Photoluminescence (PL), optical absorption, NMR, and mass spectrometry measurements were conducted for comparison. FINDINGS: vSFG was found to be sensitive to subtle changes in ligand disorder over multiple precipitation-resuspension washes, and a limit to the number of ligand molecules removed from the surface and subsequent amount of disorder introduced to their packing was clearly observed. We also find that nonsolvents do not remain associated with the surface after washing.

Chemical nature of ferroelastic twin domains in CH3NH3PbI3 perovskite.

The extraordinary optoelectronic performance of hybrid organic-inorganic perovskites has resulted in extensive efforts to unravel their properties. Recently, observations of ferroic twin domains in methylammonium lead triiodide drew significant attention as a possible explanation for the current-voltage hysteretic behaviour in these materials. However, the properties of the twin domains, their local chemistry and the chemical impact on optoelectronic performance remain unclear. Here, using multimodal chemical and functional imaging methods, we unveil the mechanical origin of the twin domain contrast observed with piezoresponse force microscopy in methylammonium lead triiodide. By combining experimental results with first principles simulations we reveal an inherent coupling between ferroelastic twin domains and chemical segregation. These results reveal an interplay of ferroic properties and chemical segregation on the optoelectronic performance of hybrid organic-inorganic perovskites, and offer an exploratory path to improving functional devices.

Flexible approach to vibrational sum-frequency generation using shaped near-infrared light.

We describe a new approach that expands the utility of vibrational sum-frequency generation (vSFG) spectroscopy using shaped near-infrared (NIR) laser pulses. We demonstrate that arbitrary pulse shapes can be specified to match experimental requirements without the need for changes to the optical alignment. In this way, narrowband NIR pulses as long as 5.75 ps are readily generated, with a spectral resolution of about 2.5 cm-1, an improvement of approximately a factor of 3 compared to a typical vSFG system. Moreover, the utility of having complete control over the NIR pulse characteristics is demonstrated through nonresonant background suppression from a metallic substrate by generating an etalon waveform in the pulse shaper. The flexibility afforded by switching between arbitrary NIR waveforms at the sample position with the same instrument geometry expands the type of samples that can be studied without extensive modifications to existing apparatuses or large investments in specialty optics.