Neuropeptide linked to excessive alcohol and food intake
may share chemical pathways in the brain. Scientists identified the
neuropeptide galanin, already known to increase food consumption,
as a key starter in stimulating rodents to voluntarily up their
alcohol intake.
Peptides are the family of molecules formed from the linking, in a defined order, of various amino acids. They occur, like proteins, in nature and are responsible for a wide array of functions, many of which are not yet understood.
"It is conceivable that galanin plays an important role in the excessive drinking of alcohol dependence. For example, the role of galanin may be altered in alcoholics such that instead of increasing food intake, it motivates drinking," said study authors Michael J. Lewis and Sarah Leibowitz, from Princeton University and Rockefeller University in the US respectively.
Alcohol is the only drug of abuse that can also qualify as a calorie-rich food, and it undoubtedly has important interactions with systems that control food intake and nutrition, they add.
Understanding the role the neuropeptide might play in modulating alcohol intake could eventually unlock tools to stem the tide of alcohol use disorders that impact some 76.3 million people across the world.
"A key finding is that a galanin receptor antagonist by itself reduces alcohol drinking," said Todd Thiele, associate professor in the department of psychology at the University of North Carolina at Chapel Hill.
"This suggests a possible role for galanin receptor antagonists in the treatment of uncontrolled alcohol drinking, otherwise known as alcohol dependence or alcoholism."
The authors of the study speculate that galanin may play a role in the development of alcohol dependence through what they call 'a positive feedback mechanism.'
These latest findings also add to the growing list of peptides that may have overlapping control of both alcohol and food ingestion.
"While many brain neurochemicals have been examined for their role in modulating neurobiological responses to alcohol, the role of neuropeptide pathways, particularly those that have been shown to be involved with feeding and body weight regulation, have largely been ignored," added Thiele.
Excessive food intake has led to epidemic proportions of obesity, in turn associated with a raft of health conditions, with more than 1 billion adults overweight of which at least 300 million are clinically obese.
Increased consumption of more energy-dense, nutrient-poor foods with high levels of sugar and saturated fats, combined with reduced physical activity, has contributed to the three-fold rise in obesity rates since 1980 in some areas of the world, including the UK and North America.
The US group Centers for Disease Control and Prevention cites obesity as the number one cause of death related to preventable disease.
For this latest research, male Sprague Dawley rats were surgically implanted with a cannula, and given access to increasing concentrations of alcohol for a 12-hour light/12-hour dark day cycle until all had acquired a preference for 7 per cent alcohol over water in a two-bottle choice.
The rats were then given three microinjections - galanin alone, galanin in combination with a galanin receptor antagonist, and the galanin receptor antagonist alone - to determine effects on alcohol and water intake.
Food was freely available; however, as a control for galanin-induced calorie intake, both the alcohol and food were measured in a subset of rats.
"The injection of galanin into the third ventricle increased alcohol intake, but not water," said Lewis.
The scientists state that more research is needed to determine if galanin plays a role in human, as opposed to rodent, alcohol drinking.
Full findings are published in the December issue of Alcoholism: Clinical & Experimental Research.
