Ah-choo! It is the sound that represents sneeze, a sudden burst of air expelled from the lungs through the nose and mouth. Sneezing throws irritants and disease-causing pathogens out of the nose.
Sometimes, a sneeze is a symptom of problems such as seasonal allergies and viral infections. A better understanding of the neural mechanism behind sneezing could help scientists understand how neurons behave in response to allergies and viral infections, including how they contribute to itchy eyes, sneezing, and other symptoms.
A team led by researchers at Washington University School of Medicine in St. Louis has identified, in mice, specific cells and proteins that control the sneeze reflex. As mentioned, scientists conducted a study on a mouse model to determine which nerve cells send signals that make mice sneeze.
Scientists exposed the mouse to aerosolized droplets containing either histamine or capsaicin. Both compounds were found to trigger sneezes in mouse, as they do in people.
Later on, scientists examined nerve cells that react to capsaicin: they found a class of small neurons linked to sneezing caused by that compound. The observation of neuropeptides molecules revealed that a molecule called neuromedin B (NMB) was required for sneezing. Neuropeptides could transmit sneeze signals to those nerve cells.
Eliminating the NMD-sensitive neurons in the part of the nervous system blocked the sneeze reflex. These NMD-sensitive neurons make a protein called the neuromedin B receptor. The absence of that receptor significantly reduces sneezing.
Qin Liu, associate professor of anesthesiology and the study’s senior investigator, said, “Interestingly, none of these sneeze-evoking neurons were housed in any of the known regions of the brainstem linked to breathing and respiration. Although we found that sneeze-evoking cells are in a different region of the brain than the region that controls breathing, we also found that the cells in those two regions were directly connected via their axons, the wiring of nerve cells.”
Scientists also found that exposing part of the mouse brain to the NMB peptide could stimulate the sneeze reflex.
Liu said, “Because many viruses and other pathogens — including the majority of human rhinoviruses and coronaviruses such as Middle East respiratory syndrome coronavirus (MERS-CoV) and SARS-CoV-2, the coronavirus that causes COVID-19 — are spread in part by aerosolized droplets. It may be possible to limit the spread of those pathogens by targeting NMB or its receptor to limit sneezing in those known to be infected.”
“A sneeze can create 20,000 virus-containing droplets that can stay in the air for up to 10 minutes. By contrast, a cough produces closer to 3,000 droplets, or about the same number produced by talking for a few minutes. To prevent future viral outbreaks and help treat pathological sneezing caused by allergens, it will be important to understand the pathways that cause sneezing to block them. By identifying neurons that mediate the sneeze reflex, as well as neuropeptides that activate these neurons, we have discovered targets that could lead to treatments for pathological sneezing or strategies for limiting the spread of infections.”
- Fengxian Li, Haowu Jiang, Xiaolei Shen, Weishan Yang, Changxiong Guo, Zhiyao Wang, Maolei Xiao, Lian Cui, Wenqin Luo, Brian S. Kim, Zhoufeng Chen, Andrew J.W. Huang, Qin Liu. The sneezing reflex is mediated by a peptidergic pathway from nose to brainstem. Cell, 2021; DOI: 10.1016/j.cell.2021.05.017