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Research could help develop better treatments for swallowing disorders

"Neuron" publication reveals how sensory cells in the vagus nerve aid food transportation and contribute to swallowing disorders.

Swallowing disorders, prevalent in older individuals but also linked to neurological diseases and certain medications, can disrupt the normal passage of food from the mouth to the stomach. This can result in potential complications such as malnutrition, weight loss, and dehydration.

In a recent study published in the journal "Neuron," Professor Carmen Birchmeier and her team from the Developmental Biology/Signal Transduction Lab at the Max Delbrück Center in Berlin delved into the intricacies of the swallowing process. Their research focused on the response of sensory cells in the vagus nerve to mechanical stimuli in the esophagus, which trigger involuntary muscle movements known as esophageal peristalsis. The vagus nerve, one of the cranial nerves, relays vital information about the inner organs to the brain. The team's findings offer promising insights for potential advancements in the treatment of swallowing disorders.

''Modern methods of single-cell sequencing made our work possible. Using the sequencing data, we constructed genetic models that allowed us to study the functions of the sensory neurons in the vagal ganglia in more detail."

Swallowing on camera

Ganglia, known as clusters of neuronal bodies in the peripheral nervous system, were the focus of the scientists' investigation.

To gain insights into their innervation patterns, the researchers employed staining techniques to identify the specific organs targeted by these neurons. Subsequently, they examined the ganglia's response to mechanical stimuli within the esophagus. In order to analyze the impact on swallowing, the scientists also conducted experiments where they deactivated these cells.

Dr. Teresa Lever, affiliated with the University of Missouri School of Medicine in Columbia, USA, devised a groundbreaking approach enabling the team to observe real-time swallowing in freely behaving, non-anesthetized mice using video fluoroscopy.

More than just a tube

According to Dr. Elijah Lowenstein, the lead author of the study and a former member of Birchmeier's team who is now a researcher at Harvard Medical School in Boston, the loss of neurons responsible for conveying information about mechanical stimuli in the esophagus resulted in an inability for mice to reflexively execute the necessary muscle movements for food transportation to the stomach. Consequently, the mice experienced rapid weight loss.

Lowenstein emphasizes that the weight loss demonstrates the significant role these neurons play in maintaining bodily homeostasis. He highlights that the esophagus serves a purpose beyond being a mere conduit between the mouth and the stomach, as it relies on mechanosensory feedback to fulfill its function.

Birchmeier further explains that the absence of these cells in the vagus nerve leads to food becoming trapped in the esophagus, with some instances even resulting in regurgitation into the throat.

A molecular atlas for all

Birchmeier asserts that their findings have the potential to advance the development of enhanced treatments for swallowing disorders. One potential approach involves the pharmacological activation of the identified mechanoreceptors. Additionally, Birchmeier expresses a desire to utilize the genetic models to unravel the functions of other vagal sensory neurons, specifically those governing the lungs or aorta.

She speculates that these neurons likely have significant, yet undiscovered roles in the progression of respiratory diseases or cardiovascular conditions like hypertension. Birchmeier encourages other researchers to join these endeavors, as her team has created a molecular atlas encompassing all vagal neurons in mice, which is freely accessible online.


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