A brainstem circuit controls cough-like airway defensive behaviors in mice

The respiratory tract is subject to complex neural control for eupneic breathing and distinct airway defensive reflexes. Growing evidence has highlighted significant heterogeneity of airway-innervating vagal sensory neurons in mediating various respiratory functions, however, the central neuronal pathways and neural circuits involved in the airway regulation remain less understood. Combining whole-body plethysmography (WBP), audio, and video tracking to access breathing and airway defensive behaviors in conscious animals, we developed a quantitative paradigm implementing the mouse as a model to study cough-like defensive behaviors. Using TRAP2 transgenic mice and in vivo fiber photometry, we found that the neural activity in the caudal spinal trigeminal nucleus (SP5C) is strongly correlated with tussigen-evoked cough-like responses. Impairing synaptic outputs or chemogenetic inhibition of the SP5C effectively abolished these cough-like reflexes. Optogenetic stimulation of SP5C excitatory neurons or their projections to the ventral respiratory group (VRG) triggered robust cough-like behaviors without tussive stimuli. Notably, tonic elevation of SP5C excitability caused spontaneous cough-like activities chronically in mice. Together, our data provide strong evidence for a previously unrecognized brainstem circuit that controls cough-like defensive behaviors in mice.