Researchers have learned that rats overwhelmingly prefer water sweetened with saccharin to cocaine, a finding that demonstrates the addictive potential of sweets.
Offering larger doses of cocaine did not alter the rats' preference for saccharin, according to the report.
In the experiment, 43 rats were placed in cages with two levers, one of which delivered an intravenous dose of cocaine and the other a sip of highly sweetened water. At the end of the 15-day trial, 40 of the rats consistently chose saccharin instead of cocaine.
When sugar water was substituted for the saccharin solution, the results were the same, researchers said.
Further testing the rat sweet tooth, scientists subjected 24 cocaine-addicted rats to a similar trial. At the end of 10 days, the majority of them preferred saccharin.
"Intense sweetness is more rewarding to the rats than cocaine," said coauthor Magalie Lenoir of the University of Bordeaux in France.
Lenoir said mammalian taste receptors evolved in an environment that lacked sugar and so were not adapted to the high concentrations of sweets found in the modern diet. Excess sugar could increase levels of the brain chemical dopamine, she said, leading to a craving for sweets.
Cocaine also increases dopamine, she said, but through a different brain mechanism.