Sneezing and coughing are two different ways of accomplishing the same. One involves the nose and mucus, the other the mouth and mucus, but both are defensive respiratory reflexes designed to expel pathogens and irritants. Since they’re so similar, doctors have generally assumed they both involved a common set of sensory receptors and neural passageways. As new research suggests, this assumption was wrong.
Indeed, in a new study published in the journal Cell, doctors from Washington University School of Medicine in St. Louis, led by anesthesiologist Haowu Jiang, found that this is not the case, a discovery that could potentially offer relief to cold and allergy sufferers in the future.
For the study, the researchers opted to trigger tiny, presumably somewhat adorable, sneezes and coughs in mice. They stimulated groups of nasal passage neurons already known to react to various conditions connected to sneezing, such as those dedicated to sensing cold or itching. That allowed them to figure out exactly which sets of neurons were actually involved in triggering a sneeze. They found that, while the tissue lining the nasal passage can be activated by several different sets of neurons, tingling only a single one of those sets—a type of itch receptor called MrgprC11—actually resulted in a sneeze.
To verify the findings, the doctors infected the poor mice with the flu. In mice where MrgprC11 was deactivated, the mice got sick and coughed, but couldn’t sneeze. When they tried to stimulate tracheal MrgprC11 neurons to generate a cough, they found the trachea did get irritated, but no coughing arose. Instead, coughing was connected to a completely different set of neurons.
“At the circuit level, sneeze and cough signals are transmitted and modulated by divergent neuropathways,” the doctors wrote.
The research also resulted in a happy accident. Among some scientists, it’s apparently controversial as to whether mice can actually cough. Some studies have argued they can, a conclusion the Washington University scientists said they confirmed by identifying the audio and respiratory patterns of the tiny sounds. So now we know mice can cough, which is nice.
It may not seem like a big deal that sneezing and coughing are caused by different mechanisms. Both are essentially the body spewing out microbes and some icky fluids. Jiang and his colleagues acknowledged in the study the need to determine if the pathways discovered in mice have an equivalent in humans. But they expressed hope that their work could lead to the development of new drugs and symptom treatments for respiratory infections and allergies.
Aside from better relief during flu and cold season, that could reduce unpleasant side effects connected to antihistamines and corticosteroids, such as airway dryness, bleeding, and infections. As any allergy sufferer can attest, that’s nothing to sneeze at.
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