Sneezing and coughing are two different ways of accomplishing the same goal. One involves the nose and mucus, and the other involves the mouth and mucus, but both reflexes are defensive breathing reflexes designed to expel pathogens and irritants. Because they are so similar, doctors generally believe they both involve a common set of sensory receptors and nerve pathways. New research shows that this assumption is wrong.
In fact, in a new study published in the journal cellDoctors led by anesthesiologist Haowu Jiang of Washington University School of Medicine in St. Louis found that’s not the case, a finding that may one day ease symptoms in cold and allergy patients.
In this study, the researchers chose to trigger mild, possibly cute sneezing and coughing in mice. They stimulated groups of nasal passage neurons known to respond to various conditions associated with sneezing, such as those specialized in sensing cold or tickling. This allowed them to figure out exactly which groups of neurons were actually involved in triggering the sneeze. They found that while the tissue lining the nasal cavity can be activated by several different groups of neurons, only one group of neurons—a tickle receptor called MrgprC11—produces the tingling sensation that actually causes sneezing.
To test their findings, the doctors infected the poor mice with influenza. In mice in which MrgprC11 is inactivated, the mice become sick and cough, but are unable to sneeze. When they tried to stimulate MrgprC11 neurons in the trachea to produce a cough, they found that the trachea was indeed stimulated, but no cough occurred. Instead, coughing is linked to an entirely different set of neurons.
“At the circuit level, sneeze and cough signals are transmitted and regulated through different neural pathways,” the doctors wrote.
The research also produced a happy accident. There is apparently controversy among some scientists over whether mice can actually cough. Some studies suggest it can, and scientists at the University of Washington say they confirmed this conclusion by identifying the sounds of tiny sounds and breathing patterns. Now we know rats can cough, which is good.
It might not seem like a big deal that sneezing and coughing are caused by different mechanisms. Both essentially involve the body spewing out microorganisms and some nasty fluids. Jiang and his colleagues acknowledged in this study that it would be necessary to determine whether the pathways discovered in mice are the same in humans. But they say they hope their work will spur the development of new drugs and symptomatic treatments for respiratory infections and allergies.
In addition to better pain relief during flu and cold season, this can also reduce unpleasant side effects associated with antihistamines and corticosteroids, such as airway dryness, bleeding, and infection. As any allergy sufferer can attest, this is nothing to take lightly.