How do the gut and brain influence each other?

The connection between the gastrointestinal tract and the brain is a complex and extensive network that regulates much more than digestion. Our gut and its neural circuits play an essential role in the regulation of substances, but also in other processes in the brain, like stress regulation.

Communication between the digestive system and the brain

Communication between the digestive system and the brain is not only crucial for digestion, but also regulates metabolism [Rhee et al., 2009; Osadchiy et al., 2019]. The neurons of the vagus nerve are crucial for this communication. The afferent neurons of the vagus nerve carry information from the gastrointestinal tract to the brain. They can detect mechanical changes, such as the stretching of organs in the digestive tract, as well as chemical signals, like hormones released by certain cells in the intestine. The efferent neurons of the vagus nerve, which have their cell bodies in the brainstem, carry information from the brain to the organs.

Hormonal signals like GLP-1 (glucagon-like peptide 1) provide the brain with information about food intake and energy levels. Via complex circuits, these signals ultimately act on a large number of nerve cells, including the so-called AgRP and POMC nerve cells, which significantly regulate food intake and energy expenditure [Brüning & Fenselau, 2023; Betley et al., 2013; Burnett et al., 2019]

More information about the neuronal circuits involved in metabolism can be found here.

In addition to GLP-1, other signals can be released in the gut after ingestion, including CCK (cholecystokinin), PYY (peptide YY) and serotonin [Brüning & Fenselau, 2023].

Researchers at the Max Planck Institute for Metabolism Research were able to identify the functions of the groups of nerve cells involved in communication between the gut and the brain. They discovered that nerve cells with endings in the gut send information to the brain, influencing food intake and glucose metabolism. One group of these nerve cells detects the expansion of the stomach and, when activated, sends signals to the brain to reduce appetite and lower blood sugar levels. Another group of nerve cells detects chemical signals from food. These do not affect food intake but, when activated, raise blood glucose levels [Borgmann et al, 2021].

More information about this study can be found here.

References:

• Betley, J. N., Cao, Z. F. H., Ritola, K. D., & Sternson, S. M. (2013). Parallel, redundant circuit organization for homeostatic control of feeding behavior. Cell, 155(6), 1337-1350.
• Borgmann, D., Ciglieri, E., Biglari, N., Brandt, C., Cremer, A. L., Backes, H., ... & Fenselau, H. (2021). Gut-brain communication by distinct sensory neurons differently controls feeding and glucose metabolism. Cell metabolism, 33(7), 1466-1482.
• Brüning, J. C., & Fenselau, H. (2023). Integrative neurocircuits that control metabolism and food intake. Science, 381(6665), eabl7398.
• Burnett, C. J., Funderburk, S. C., Navarrete, J., Sabol, A., Liang-Guallpa, J., Desrochers, T. M., & Krashes, M. J. (2019). Need-based prioritization of behavior. Elife, 8, e44527.
• Osadchiy, V., Martin, C. R., & Mayer, E. A. (2019). The gut–brain axis and the microbiome: mechanisms and clinical implications. Clinical Gastroenterology and Hepatology, 17(2), 322-332.
• Rhee, S. H., Pothoulakis, C., & Mayer, E. A. (2009). Principles and clinical implications of the brain–gut–enteric microbiota axis. Nature reviews Gastroenterology & hepatology, 6(5), 306-314.

This text was written by Lisa Weiher.