23 November 2023

Brain cells 'forced' to eat even after a recent heavy lunch

An international group of scientists has come to the conclusion that brain cells are able to regulate the time of eating. It depends not on when it was the last time or even how densely we ate before, but on the arrival of the signal "it's time for lunch" in the brain.

It is known that the body has many mechanisms that regulate the feeling of hunger. The most important of them are neurons called AgRP, which "read" the physiological need for food and signal to the brain that it is time to eat again. It is these cells that are targeted by injections of popular weight loss drugs - they inhibit their activity. But the regulation of AgRP neurons is not sufficiently studied. Scientists from the Universities of Iowa (USA) and Istanbul Medipol (Turkey) have solved this problem, and presented their findings in the journal Nature Neuroscience.

It was previously thought that the activity of neurons is regulated by the level of nutrients in the body. For example, blood sugar levels, which drop a few hours after a meal, indicate that they are insufficient. But a study on mice showed that the activity of AgRP neurons can be controlled in a different way.

In the first part of the experiment, scientists let the mice eat whenever they wanted. As a result, the researchers were surprised to find that brain cell activity did not increase gradually throughout the day, as would be expected if it was caused by a drop in blood sugar levels, but increased sharply when the animals woke up. And at the same time it decreased sharply at the end of the night (mice are nocturnal animals, they are awake mostly during the dark hours), even if the rodents were not fed for several hours.

The process was similar to the work of a clock: neurons as if informing the brain "it's time to eat again", regardless of when and how much the animals last ate. Or vice versa: "it's time to stop eating", even if the rodents had been starving before that.

The second part of the experiment took place only in daylight: the mice were given food only during a short period of time - between 10 am and 2 pm. Thus the unfortunate animals were forced to stay awake in order to eat. And what happened? After 7-10 days, their neurons gradually switched to a new mode: they became active after 10 am. That is, the rodents felt hunger not when their body really needed food, but at a time when they are already used to eating.

The researchers believe that a similar mechanism of regulation of neurons AgRP is in humans. This explains, for example, why we do not wake up in the middle of the night to eat, although a lot of time passes between dinner and breakfast - much more than between the day's meals.

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