Male fruit flies become barflies when rejected by females, choosing alcohol-spiked food more often than their successful brothers in a study that suggests it may be due to a brain chemical also found in humans.
The spurned flies had lower levels of a molecule in their brains called neuropeptide F than the males who were allowed to mate, according to findings published today in the journal Science. Neuropeptide Y, the version found in humans, has been tied to addiction and mental illness, said Ulrike Heberlein, one of the researchers.
The molecule may begin to explain how experience and environment shape human addictions, said Heberlein. About half of a person’s risk of addiction is genetic, and environment is known to play a role. The experiment may help explain the biological triggers that affect certain behavior or cravings and could help research into treatments for addiction.
“We wanted to really find a molecular mechanism that links experiences to drug-related behavior,” said Heberlein, who is a neuroscientist at the University of California, San Francisco, in a telephone interview. “We are really hoping that this will encourage those working with mice and rats and humans to look at what happens to this neuropeptide in psychiatric conditions.”
Male flies that mated were less likely to drink the alcohol solution than either virgin or rebuffed ones, and had higher levels of neuropeptide F in their brains, the research showed.
In the experiment, some flies were spurned by already-mated females for one hour a day, three times a day, for four days. The successful flies had six-hour mating sessions with multiple virgin females for four days. They were then allowed to choose food that was either plain or spiked with a 15 percent alcohol solution.
Another experiment was done to see whether sexual deprivation or social isolation was the main difference between the groups. A set of flies, consisting of both virgin and mated males, were housed in a group. The virgin males showed a higher preference for alcohol.
Next, the researchers checked to see whether it was lack of sex or the actual rejection that made the flies likelier to drink. For that test, researchers put virgin males in with decapitated females, so they would experience neither rejection nor copulation. They also preferred alcohol more than mated flies, suggesting that a lack of sex rather than rejection was the major factor in their alcohol preference.
The researchers then lowered the amount of neuropeptide F in the brains of mated flies and found that they acted as though they had been rejected, drinking more. Conversely, flies that had been spurned whose neuropeptide F was increased boozed less.
“What we did, in order to establish a causal relationship, was manipulated the system,” Heberlein said. “We were able to prove it in both directions, so that’s strong evidence of causality.”
Levels of neuropeptide Y are lower in people who are depressed and have post-traumatic stress disorder. It’s found all over the brain and may have roles in eating and sleeping, as well as addiction and anxiety.