A brain chemical that stokes hunger for food and fat also triggers thirst for alcohol and may play a role in chronic drinking, according to a study led by Princeton University scientists.
The study showed that rats injected with galanin, a natural signaling agent in the brain, chose to drink increasing quantities of alcohol even while consuming normal amounts of food and water. The finding helps explain one of the mechanisms involved in alcohol dependence and strengthens scientists' understanding of the neurological link between the desires for alcohol and food.
"There seems to be a cycle of positive feedback," said Bartley Hoebel, co-author of a paper appearing in the December issue of Alcoholism: Clinical and Experimental Research. "Consumption of alcohol produces galanin, and galanin promotes the consumption of alcohol. That would perpetuate the behavior."
The research was conducted by Michael Lewis, a visiting research fellow in Hoebel's lab, in collaboration with Hoebel, a professor of psychology; Deanne Johnson, a research staff member; Daniel Waldman, a senior undergraduate; and Sarah Leibowitz, a neurobiologist at Rockefeller University.
Galanin, a kind of small protein fragment called a neuropeptide, had previously been shown to play a role in appetite, particularly for fatty foods. Consumption of fat causes a part of the brain called the hypothalamus to produce more galanin, which, in turn, increases the appetite for fat. In a healthy person, however, there are counteracting signals that break this loop, said Hoebel.
In animals given galanin and access to alcohol, the role of the chemical appeared to be subverted: it boosted alcohol intake instead of eating. The effect was especially noticeable during daylight hours, when the nocturnal animals normally do not eat and drink much. Those given galanin drank alcohol during the day, but did not consume any more food or water than normal.
"Alcohol is the only drug of abuse that is also a calorie-rich food, and it undoubtedly has important interactions with systems that control food intake and nutrition," said Lewis, who is also a senior fellow of the National Institute on Alcohol Abuse and Alcoholism (NIAAA).
When the animals were given a drug that blocked the effects of galanin, they maintained normal eating and drinking habits. This observation helps confirm the conclusion that galanin affects alcohol consumption and also suggests the possibility of someday creating a drug that blocks galanin in order to fight alcoholism. However, Hoebel noted that such an achievement would be a long way off, because it is hard to make drugs that cross from the blood into the brain and interact with neuropeptide receptors. In addition, galanin plays many roles in other parts of the brain, which could be adversely affected by trying to block its effects related to food or alcohol.
The researchers plan to explore further the role of galanin and other neuropeptides in alcohol use, as well as the role of fat intake and metabolism on alcohol intake.
The research was funded by the NIAAA and by the Minnie & Bernard Lane Foundation and Edward Lane Foundation.
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