Animals and humans have internal biological clocks that regulate their daily activities, such as sleeping, waking up, and eating. These patterns, known as circadian rhythms, play a crucial role in maintaining overall health and well-being. Disruptions to these rhythms can adversely affect both physical and mental health. Neuroscientists have long been studying the neural mechanisms behind circadian rhythms to understand better and treat disorders characterized by disrupted sleep or eating patterns.

In a recent study published in Nature Neuroscience, researchers from the University of Iowa and Yeditepe University have made significant progress in unraveling the role of a specific group of neurons in regulating feeding time in mice. The researchers focused on a class of neurons called agouti-related protein (AgRP) neurons, which are known to play a vital role in hunger responses in the brain.

Traditionally, it was believed that hunger gradually increases as energy resources diminish over time. The researchers expected the AgRP neurons to exhibit a slowly increasing firing rate as hunger intensifies. This would align with the classical “homeostatic” regulation concept, where the body strives to maintain specific values within a set range. However, the study’s findings challenged this assumption.

Using fiber photometry, the researchers monitored the activity of AgRP neurons in living mice over an extended period. Contrary to expectations, they discovered that the activity of these neurons did not follow a simple homeostatic pattern. Instead, the activity of AgRP neurons appeared to be synchronized with the mice’s past feeding patterns, suggesting a more complex form of “allostatic” regulation.

Allostatic regulation involves proactive defense of energy levels before the actual need to eat arises. The AgRP neurons predict future energy deficits based on cues learned from past experiences. The researchers found that a yet-to-be-clarified biological clock is synchronized to past mealtimes, turning the activity of AgRP neurons on and off accordingly. This finding suggests that the rhythmic nature of hunger observed in mice may also extend to humans.

The implications of this study are significant. Understanding how AgRP neurons regulate feeding patterns could lead to the development of new treatments for disorders characterized by dysregulated eating patterns. The researchers plan to investigate the molecular mechanisms behind this food-tuned “clock” and explore its potential therapeutic applications. They also aim to examine whether other neurons involved in satiety, the feeling of fullness, exhibit similar rhythmic patterns and how this may impact anti-obesity treatments.

In conclusion, this study sheds light on the intricate mechanisms that govern feeding patterns in mice. While further research is needed to validate these findings in humans, they provide valuable insights into the role of AgRP neurons and the influence of time of day on appetite physiology. By understanding these mechanisms, scientists may be able to develop more targeted interventions for individuals with eating disorders or other conditions related to disrupted feeding patterns.

References

• Fadelli, I. & Medical Xpress. (2023, December 7). Study shows that AgRP neurons encode circadian feeding time in mice. Medical Xpress; Medical Xpress. https://medicalxpress.com/news/2023-12-agrp-neurons-encode-circadian-mice.html

• Sayar-Atasoy, N., Aklan, I., Yavuz, Y., Laule, C., Kim, H., Rysted, J., Alp, M. I., Davis, D., Yilmaz, B., & Atasoy, D. (2023). AgRP neurons encode circadian feeding time. Nature Neuroscience, 1–14. https://doi.org/10.1038/s41593-023-01482-6