A vagal-brainstem interoceptive circuit for cough-like defensive behaviors in mice

Respiratory defensive behaviors, like coughing, play a crucial role in protecting the respiratory system, ensuring its integrity and optimal function. How these critical behaviors are regulated by sensory stimuli within the body remains largely unknown. Here, we show that the nucleus of the solitary tract (NTS) in mice, a key hub in the brain for processing internal sensory signals and mediating interoceptive processes, contains heterogenous neuronal populations that differentially control breathing. Within these subtypes, activation of tachykinin 1 (Tac1) neurons triggers a specific respiratory behavior. Our detailed characterization of respiratory defensive behaviors reveals that these responses are cough-like behaviors. Chemogenetic silencing or genetic ablation of Tac1 neurons significantly reduces cough-like behaviors induced by tussive challenges. These Tac1 neurons receive synaptic inputs from the bronchopulmonary chemosensory and mechanosensory neurons in the vagal ganglion, and directly integrate the medullary regions to control sequential phases of cough-like defensive behaviors. We propose that these Tac1 neurons are a key component of the airway-vagal-brain neural circuit that controls cough-like defensive behaviors in mice, and they coordinate the downstream modular circuits to elicit the sequential motor pattern of forceful expiratory responses. Overall design: Five mice at postnatal day 5 were euthanized by isoflurane inhalation followed by decapitation. The brain was isolated and embedded in 4% agarose II in artificial cerebrospinal fluid (ACSF) and sectioned at 200um thickness on a VT 1000S vibratome (Leica). The caudal NTS tissue and adjacent regions in the dorsal vagal complex were manually dissected based on the morphology (the relative position to area postrema, 4th ventricle, and central canal), and referred as the NTS. Tissue was pulled together in hibernate A solution (Gibco), followed by digestion with 20 u/ml papain (Worthington Biochemical Corporation) and serial trituration by Pasteur pipets to generate single cell suspension. The cells were stained with 0.2% DyeCycle Ruby (Invitrogen) at 37 degree for 15 minutes before passing through a 70um cell strainer (Falcon). The live cell suspensions were sorted and collected by a BD FACSAria III Cell Sorter (BD Biosciences) with a nozzle diameter of 100 um. The FACS sample was loaded to the 10X Chromium platform for capturing. The following cDNA synthesis with PCR and library preparation were done according to the manufacturer's protocol. Sequencing was performed on a NovaSeq sequencer (Illumina)