What do hunger and "withdrawal" have in common?
Drug addiction was associated with a feeling of hunger, scientists found
Craving for drugs and other elements of drug addiction affect the same neurons in the brain as hunger, scientists have found out, who published an article in the journal Nature (Homeostatic circuits selectively gate food cue responses in insular cortex).
"To put it very simply, at the moment when you are hungry, the picture of a cheeseburger can greatly influence your behavior. When you are full, the same picture can dramatically become less appetizing. Those "hunger feeling" neurons in the insular cortex that are responsible for this reaction may play an important role in the development of unexplained cravings for overeating and drugs," says Yoav Livneh from Harvard University (in a press release Scientists Reveal a Key Link between Brain Circuits Governing Hunger and Cravings – VM).
Scientists have long drawn attention to the fact that the behavior of former drug addicts and alcoholics and the likelihood of their return to a bad habit affects not only how their psyche is arranged, but also the environment in which they live after rehabilitation. Familiar faces of drinking buddies and other drug addicts, premises, characteristic "attributes" of addiction – syringes, spoons, bottles and glasses – can make a person break down and return to a bad habit.
Livni and his colleagues found out what such relapses are related to by observing the work of those regions of the brain of mice that are associated with digestion, food search and hunger. Violations in their work, as scientists explain, have long been associated with the development of obesity and extreme forms of overeating, which are in many ways similar to drug addiction.
To observe these areas of the cortex and deep layers of the brain, scientists inserted special genes into their cells that made neurons glow when they were activated. This allowed biologists to literally see how the nerve cells in the center of hunger "lit up" at the sight of food and track which other parts of the brain they affected.
After all these operations, Livni and his colleagues put the rodents in a special cage, on one of the walls of which there were three buttons with pictures of food, which the rodent could either poke his nose or lick. When one of them was pressed, a portion of sweet syrup fell into the feeder, and the other two filled it with either ordinary water or a bitter quinine solution.
Observing the work of the brain of mice when licking these buttons, scientists tried to understand which of them are responsible for "turning on" the feeling of hunger at the sight of food and "turning it off" when receiving a portion of food.
As it turned out, this role is played by a set of small nerves in the insular cortex of the brain, directly connected to the so-called AgRP neurons – cells of the hypothalamus, the deep part of the brain that plays the role of the "hunger center". When a hungry mouse sees food, the cells in its insular cortex forcibly turn on AgRP neurons, which increases the feeling of hunger and makes the rodent actively search for food.
Having discovered such a connection, the scientists tested how the work of these cells would change if the "hunger center" was forcibly turned on, bypassing the insular cortex. These experiments led to an unexpected discovery – it turned out that there is a hidden feedback between the cortex and AgRP neurons, which makes the mouse react very strongly to pictures of food even when it has already eaten.
This relationship, according to scientists, may explain why many people suffering from obesity cannot stop themselves and begin to eat uncontrollably at the sight of food, and may also be one of the main reasons for the development of drug addiction and a return to drugs after giving up them. Accordingly, suppressing the activity of AgRP neurons can help both obese people and former drug addicts cope with cravings for food or drugs.
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15.06.2017