When she says no, the bottle beckons more brightly for men and for fruit flies, according to a new study that found that male flies that had been repeatedly spurned by females were more likely to turn to alcohol to self-medicate their frustration.

As a topic of study, drunk fruit flies may seem trifling, but what the findings reveal about the neurochemistry that drives behaviors like sex and eating may point the way to new drugs to fight both addiction and obesity.

Researchers performed several clever experiments to determine the relationship between sexual frustration and drinking in male flies. Some lucky males were allowed four days of mating for six-hour sessions at a time (each bout of fruit fly copulation takes 20 minutes) with an abundance of sexually receptive females the female-to-male ratio was a satisfying 5-to-1. The male flies were housed either together or alone.

The unlucky experimental group was introduced to females that had already mated and had no desire to mate again. The females ran away, kicked and stuck out their egg-laying organ to fend males off. The male flies underwent this exercise in sexual frustration and rejection three times a day, for an hour at a time, over four days. Again, some of the males were kept in containers with other male flies, while others were isolated.

A third group of males was exposed to the sad sight of decapitated virgin females a situation that resulted in sexual frustration, but no active rejection.

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After these experiences, the flies were given a choice of ordinary food (yeast and sugar) or food that had been spiked with the kick of 30-proof spirits (yeast, sugar and 15% alcohol). Not surprisingly, the sexually rejected flies boozed much more than the mated group with those males that had been spurned and alone hitting the sauce the hardest. The flies that had been sexually frustrated but not rejected also drank more than those that had been allowed to mate. However, when flies that had first been rejected were later given a chance to mate, their extra preference for alcohol disappeared.

So what was going on in the flies brains? Researchers found that a neurotransmitter called neuropeptide F, or NPF, which seems to be linked with fruit flies reward system, was strongly predictive of whether the flies drank. NPF was low in sexually frustrated flies lower in flies that had been isolated than in those that had company in their misery which appeared to drive them to drink.

Both mating and drinking alcohol increased NPF levels. Moreover, when NPF levels were artificially reduced in mated flies, they continued to show an extra preference for alcohol just as if they hadnt mated. These data suggest that activity of the NPF system is regulated by at least two rewarding experiences, mating and [alcohol] intoxication, the authors write.

The researchers also found that activating the NPF system was itself pleasurable to the flies, suggesting that it may create the feeling of satisfaction associated with drinking and sex.

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Bizarre Science: Sexually Frustrated Flies Are Driven to Drink