In the epithelium of the lower airways, a cell type of unknown function has been termed "brush cell" because of a distinctive ultrastructural feature, an apical tuft of microvilli. Morphologically similar cells in the nose have been identified as solitary chemosensory cells responding to taste stimuli and triggering trigeminal reflexes. Here we show that brush cells of the mouse trachea express the receptors (Tas2R105, Tas2R108), the downstream signaling molecules (α-gustducin, phospholipase C β2 ) of bitter taste transduction, the synthesis and packaging machinery for acetylcholine, and are addressed by vagal sensory nerve fibers carrying nicotinic acetylcholine receptors. Tracheal application of an nAChR agonist caused a reduction in breathing frequency. Similarly, cycloheximide, a Tas2R108 agonist, evoked a drop in respiratory rate, being sensitive to nicotinic receptor blockade and epithelium removal. This identifies brush cells as cholinergic sensors of the chemical composition of the lower airway luminal microenvironment that are directly linked to the regulation of respiration.airway sensory innervation | respiratory epithelium | jugular-nodose ganglion | bitter-tasting substances

Adult hippocampal neurogenesis occurs in an exceptional permissive microenvironment. Neuroimmunological mechanisms might be prominently involved in the endogenous homeostatic principles that control baseline levels of adult neurogenesis. We show in this study that this homeostasis is partially dependent on CD4-positive T lymphocytes. Systemic depletion of CD4-positive T lymphocytes led to significantly reduced hippocampal neurogenesis, impaired reversal learning in the Morris water maze, and decreased brain-derived neurotrophic factor expression in the brain. No such effect of CD8 or B cells was observed. Repopulation of RAG2−/− mice with CD4, but not with CD8 cells again increased precursor cell proliferation. The T cells in our experiments were non-CNS specific and rarely detectable in the healthy brain. Thus, we can exclude cell-cell contacts between immune and brain cells or lymphocyte infiltration into the CNS as a prerequisite for an effect of CD4-T cells on neurogenesis. We propose that systemic CD4-T cell activity is required for maintaining cellular plasticity in the adult hippocampus and represents an evolutionary relevant communication route for the brain to respond to environmental changes.

Transient receptor potential (TRP) A1 and TRPM8 are ion channels that have been localized to afferent nociceptive nerves. These TRP channels may be of particular relevance to respiratory nociceptors in that they can be activated by various inhaled irritants and/or cold air. We addressed the hypothesis that mouse vagal sensory nerves projecting to the airways express TRPA1 and TRPM8 and that they can be activated via these receptors. Single cell RT-PCR analysis revealed that TRPA1 mRNA, but not TRPM8, is uniformly expressed in lung-labelled TRPV1-expressing vagal sensory neurons. Neither TRPA1 nor TRPM8 mRNA was expressed in TRPV1-negative neurons. Capsaicin-sensitive, but not capsaicin-insensitive, lung-specific neurons responded to cinnamaldehyde, a TRPA1 agonist, with increases in intracellular calcium. Menthol, a TRPM8 agonist, was ineffective at increasing cellular calcium in lung-specific vagal sensory neurons. Cinnamaldehyde also induced TRPA1-like inward currents (as measured by means of whole cell patch clamp recordings) in capsaicin-sensitive neurons. In an ex vivo vagal innervated mouse lung preparation, cinnamaldehyde evoked action potential discharge in mouse vagal C-fibres with a peak frequency similar to that observed with capsaicin. Cinnamaldehyde inhalation in vivo mimicked capsaicin in eliciting strong central-reflex changes in breathing pattern. Taken together, our results support the hypothesis that TRPA1, but not TRPM8, is expressed in vagal sensory nerves innervating the airways. TRPA1 activation provides a mechanism by which certain environmental stimuli may elicit action potential discharge in airway afferent C-fibres and the consequent nocifensor reflexes.

Background Antivirals are needed to combat the COVID-19 pandemic, which is caused by SARS-CoV-2. The clinically-proven protease inhibitor Camostat mesylate inhibits SARS-CoV-2 infection by blocking the virus-activating host cell protease TMPRSS2. However, antiviral activity of Camostat mesylate metabolites and potential viral resistance have not been analyzed. Moreover, antiviral activity of Camostat mesylate in human lung tissue remains to be demonstrated. Methods We used recombinant TMPRSS2, reporter particles bearing the spike protein of SARS-CoV-2 or authentic SARS-CoV-2 to assess inhibition of TMPRSS2 and viral entry, respectively, by Camostat mesylate and its metabolite GBPA. Findings We show that several TMPRSS2-related proteases activate SARS-CoV-2 and that two, TMPRSS11D and TMPRSS13, are robustly expressed in the upper respiratory tract. However, entry mediated by these proteases was blocked by Camostat mesylate. The Camostat metabolite GBPA inhibited recombinant TMPRSS2 with reduced efficiency as compared to Camostat mesylate. In contrast, both inhibitors exhibited similar antiviral activity and this correlated with the rapid conversion of Camostat mesylate into GBPA in the presence of serum. Finally, Camostat mesylate and GBPA blocked SARS-CoV-2 spread in human lung tissue ex vivo and the related protease inhibitor Nafamostat mesylate exerted augmented antiviral activity. Interpretation Our results suggest that SARS-CoV-2 can use TMPRSS2 and closely related proteases for spread in the upper respiratory tract and that spread in the human lung can be blocked by Camostat mesylate and its metabolite GBPA. Funding NIH, Damon Runyon Foundation, ACS, NYCT, DFG, EU, Berlin Mathematics center MATH+, BMBF, Lower Saxony, Lundbeck Foundation, Novo Nordisk Foundation.