NEW YORK – Guys, when your sweetheart says she is not in the mood, do you knock back a few stiff drinks to feel better? Turns out fruit flies do pretty much the same thing. That’s the word from a new study that may explain why both species react that way.

In Friday’s issue of Science, researchers propose a biological explanation for why “Not tonight, dear” may lead to “Gimme another beer.” If it proves true, it may help scientists find new medications to fight alcoholism.

One by one, these eager fruit fly Lotharios were put into a container with a female that had just mated. So she was really, really not interested in doing it again anytime soon. She would run away.

The male flies went through three hour-long sessions of this every day for four days, enough rejection to discourage them from trying any more. After that experience, rejected flies were put in vials and given a choice of regular food or alcohol-laced food. They consistently went for the alcohol more than did the male flies that had just mated. In fact, they evidently got plastered.

Some rejected males were moved to a different environment, where groups mingled with receptive females. After the guys had sex, their yen for alcohol declined.

Researchers theorize that pleasurable activities like sex boost the activity of brain circuits that use a substance called NPF. If a fly is denied sex, the system goes into deficit, driving the fly to seek other rewards such as drinking alcohol.