Appetite regulator – melanocortin-4 receptor
Biologists have found a hunger switch in the human brain
An international team of biologists has discovered a special region in the hypothalamus of the human brain that encodes signals of hunger and satiety. During the experiments, scientists learned how to control the work of this region using the example of mice, which they deprived of hunger and all the unpleasant sensations associated with it, according to an article published in the journal Nature Neuroscience (Garfield et al., A neural basis for melanocortin-4 receptor–regulated appetite – VM).
"One of the reasons that the diet is so difficult to follow is that we experience extremely unpleasant sensations associated with constant hunger. Our results show that the inclusion of this zone causes pleasant sensations and reduces the feeling of hunger to almost zero in mice. This makes such therapy equivalent in strength to conventional diets, but without the unpleasant sensations associated with them," said Bradford Lowell from Harvard University (in a press release from Beth Israel Deaconess Medical Center How to Short Circuit Hunger – VM).
Over the past two decades, Lowell and his colleagues have been studying the work of those parts of the brain that are presumably associated with appetite, feelings of satiety and hunger, and other gastronomic sensations and human traits. A few years ago, they found out that in the hypothalamus – the endocrine center of the brain – there is a special group of cells, the so-called AgRP neurons, which are responsible for almost all food sensations.
Over the following years, Lowell's group and hundreds of other biologists experimented with various hormones, trying to find the key to these nerve cells. Scientists quickly managed to learn how to "turn on" AgRP neurons, turning animals into gluttons, but they had big problems with "switching off", since for this you need to know which nerve cells control their behavior.
The authors of the article drew attention to the fact that these cells secrete a large amount of the hormone AgRP, which turns on or off only those nerve cells on whose surface there are MC4R type receptors. As previous studies have shown, a large number of such protein outgrowths in the human brain are associated with a high mass index and a tendency to obesity, which forced Lowell and his colleagues to find out where they are and how they are related to AgRP neurons.
After long experiments, the authors of the article managed to identify a group of MC4R neurons that were located in another part of the hypothalamus and are directly connected to the appetite nerve cells. When scientists started turning them on and off, they managed to uncover several extremely curious effects.
Disabling these nerve cells in the brain of rodents led to the same effect as turning on AgRP neurons - the mice began to eat continuously and did not experience a feeling of satiety. The activation of these nerves led to the opposite results – the mice refused to eat and behaved as if they had recently eaten, even if three or four days had passed after the last meal.
Apparently, the activation of these neurons causes pleasant sensations – when scientists allowed rodents to turn on MC4R neurons on their own, looking into a special "room" in their cells, mice preferred to spend most of their time in it if they did not eat for a long time. If the rodents had recently had lunch, then they behaved normally.
Now Lowell and his colleagues are working on creating drugs that could penetrate the brain and include this group of nerve cells. If they manage to do this, then, in their opinion, they will create a more pleasant alternative for diets that will help people fight obesity and extra pounds.
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29.04.2015