New Media Department            Yu Jie, Duan Yuqing            May 29, 2023

Eating tasty food can be a beautiful thing, but some people suffer from swallowing problems and may experience malnutrition, weight loss and dehydration. Swallowing disorders are common in older adults, along with neurological disorders such as multiple sclerosis and Parkinson's disease, as well as certain medications that can prevent the normal movement of food from the mouth to the stomach.

In a recent study published in Neuron, a research team led by Prof. Carmen Birchmeier at the Max Delbrück Center for Molecular Medicine in Germany describes how the sensory cells of the vagus nerve respond to mechanical stimuli in the esophagus and trigger different voluntary muscle movement. They found that signals from these sensory cells help transport food to the stomach, and that a malfunction in the signaling can lead to swallowing disorders. The findings may eventually lead to better treatments for swallowing disorders.

"Single-cell sequencing made our work possible," explains Birchmeier. "Using the sequencing results, we constructed genetic models that allowed us to study the function of sensory neurons in the vagus ganglion in more detail." 

The scientists first stained the neurons to identify which organs these innervates and to determine how they responded to mechanical stimuli in the esophagus. Next, the research team inactivated the cells to analyze how this affected swallowing. They used a tool developed by Teresa Lever, Ph.D., at the University of Missouri School of Medicine in Columbia, that enables real-time observation of swallowing in normally behaving, non-anesthetized mice.

"When mice lost the neurons that provide the information for mechanical stimulation of the esophagus, they lost the ability to reflexively carry out the muscular movement that transports food to the stomach, and soon they lost weight," said Dr. Elijah Lowenstein, first author on the paper , the weight loss suggests that these neurons play a key role in body homeostasis, "thus, the esophagus is more than just a passage connecting the mouth and stomach, it also uses mechanosensory feedback for its function."

Without these neurons in the vagus, food would get stuck in the esophagus. In some mice, this did cause food to back up the throat.

"Our work could help develop new treatments for swallowing disorders. One option is to activate the mechanoreceptors we discovered pharmacologically," says Prof. Birchmeier, who also wants to use genetic models to determine the function of other vagal sensory neurons, For example, neurons that control the lungs or the aorta, "these neurons may play a crucial but hitherto unknown role in the development of certain respiratory diseases, or cardiovascular diseases."