A neural circuit mechanism for mechanosensory feedback control of ingestion.

Mechanosensory feedback from the digestive tract to the brain is critical for limiting excessive food and water intake, but the underlying gut-brain communication pathways and mechanisms remain poorly understood1-12. Here we show that, in mice, neurons in the parabrachial nucleus that express the prodynorphin gene (hereafter, PBPdyn neurons) monitor the intake of both fluids and solids, using mechanosensory signals that arise from the upper digestive tract. Most individual PBPdyn neurons are activated by ingestion as well as the stimulation of the mouth and stomach, which indicates the representation of integrated sensory signals across distinct parts of the digestive tract. PBPdyn neurons are anatomically connected to the digestive periphery via cranial and spinal pathways; we show that, among these pathways, the vagus nerve conveys stomach-distension signals to PBPdyn neurons. Upon receipt of these signals, these neurons produce aversive and sustained appetite-suppressing signals, which discourages the initiation of feeding and drinking (fully recapitulating the symptoms of gastric distension) in part via signalling to the paraventricular hypothalamus. By contrast, inhibiting the same population of PBPdyn neurons induces overconsumption only if a drive for ingestion exists, which confirms that these neurons mediate negative feedback signalling. Our findings reveal a neural mechanism that underlies the mechanosensory monitoring of ingestion and negative feedback control of intake behaviours upon distension of the digestive tract.

Large-Scale 3D Optical Mapping and Quantitative Analysis of Nanoparticle Distribution in Tumor Vascular Microenvironment.

Nanoparticles (NPs) are a promising carrier for cancer therapeutics. Systemically administered NPs are transported to tumor tissues via the bloodstream, extravasated from microvessels, and delivered to cancer cells. The distribution of NPs in the tumor vascular microenvironment critically determines the therapeutic efficacy of NP-delivered drugs, but its precise assessment in 3D across a large volume remains challenging. Here, an analytical platform-termed OMNIA (for Optical Mapping of Nanoparticles and Image Analysis)-integrating tissue clearing, high-resolution optical imaging, and semiautomated image analysis is presented, which enables accurate, unbiased, and quantitative analysis of the distribution of NPs in relation to the vasculature across a large 3D volume. Application of OMNIA to tumor tissues revealed higher accumulation and more efficient extravasation of NPs in the tumor periphery than the core. Time-course analysis demonstrated that the accumulation of NPs in tumor peaked at 24 h after injection, but the relative distribution of NPs from the vasculature remained remarkably stable over time. Comparisons between 45- and 200-nm-sized NPs showed a lower accumulation of smaller NPs in tumors relative to the liver, yet better vessel permeation. Together, our results demonstrate that OMNIA facilitates precise and reliable evaluation of NP biodistribution, and mechanistic investigations on NP delivery to tumor tissues.

Expansion Microscopy with a Thermally Adjustable Expansion Factor Using Thermoresponsive Biospecimen-Hydrogel Hybrids.

Expansion microscopy (ExM) is a technique in which swellable hydrogel-embedded biological samples are physically expanded to effectively increase imaging resolution. Here, we develop thermoresponsive reversible ExM (T-RevExM), in which the expansion factor can be thermally adjusted in a reversible manner. In this method, samples are embedded in thermoresponsive hydrogels and partially digested to allow for reversible swelling of the sample-gel hybrid in a temperature-dependent manner. We first synthesized hydrogels exhibiting lower critical solution temperature (LCST)- and upper critical solution temperature (UCST)-phase transition properties with N-alkyl acrylamide or sulfobetaine monomers, respectively. We then formed covalent hybrids between the LCST or UCST hydrogel and biomolecules across the cultured cells and tissues. The resulting hybrid could be reversibly swelled or deswelled in a temperature-dependent manner, with LCST- and UCST-based hybrids negatively and positively responding to the increase in temperature (termed thermonegative RevExM and thermopositive RevExM, respectively). We further showed reliable imaging of both unexpanded and expanded cells and tissues and demonstrated minimal distortions from the original sample using conventional confocal microscopy. Thus, T-RevExM enables easy adjustment of the size of biological samples and therefore the effective magnification and resolution of the sample, simply by changing the sample temperature.