What do male fruit flies do when their sexual advances are rejected by females?
They do what many people would do – get drunk.
According to researchers at the University of California, San Francisco (UCSF) jilted male fruit flies have a tiny molecule in their brain – called neuropeptide F – that drives them to drink much more than their sexually-satisfied counterparts.
Levels of neuropeptide F were higher in sexually-satisfied males than in those who got no sex.
Scientists said their study could have a number of important social implications and help shed light on what governs addiction in humans.
A similar human molecule called neuropeptide Y may link social triggers to behaviours like heavy drinking and drug abuse, the team claimed.
"If neuropeptide Y turns out to be the transducer between the state of the psyche and the drive to abuse alcohol and drugs, one could develop therapies to inhibit neuropeptide Y receptors," said lead researcher Ulrike Heberlein, a professor of anatomy and neurology at UCSF.
She said clinical trials are underway to look at whether delivery of neuropeptide Y could alleviate anxiety and other mood disorders, as well as obesity.
The research is published in the journal Science.
Under the study, UCSF scientists placed male fruit flies in a container with female flies, including both virgins and some that had already mated.
Virgin females were receptive to courting males and readily mated but female flies who had mated lost interest in sex for a short time because of sex peptide, a substance that males inject with sperm during the encounter.
Rejected males then gave up altogether trying to mate, even when placed in the same container as virgin flies.
However, when they were placed by themselves in another container with two straws – one containing plain food and the other containing food supplemented with 15 per cent alcohol – the rejected males "binged" on the alcohol.
The scientists said the behaviour was "completely predicted" by the levels of neuropeptide F in their brains.
"It's a switch that represents the level of reward in the brain and translates it into reward-seeking behaviour," said lead author Galit Shohat-Ophir of the Howard Hughes Medical Institute Janelia Farm Research Center in Virginia.