Sex-deprived male fruit flies are more likely to drink alcohol to excess than those whove had sex, new research finds.
And it seems that a tiny molecule in the flys brain known as neuropeptide F is responsible for the behaviour, according to the study by researchers at the University of California, San Francisco.
According to a study published Thursday in
http://www.sciencemag.org/Science MagazineEND, as the levels of this neuropeptide change in the brain so does the flys behaviour with lower levels of it causing increased drinking.
This neuropeptide in the fruit flys brain is similar to a human molecule called neuropeptide Y. Researchers hypothesize that this neuropeptide Y may play a similar role in people connecting social triggers like sex or the lack of sex to behaviours such as excessive drinking and drug abuse.
Some studies have already shown that reduced levels of neuropeptide Y play a role in people with post-traumatic stress disorder and depression both risk factors for alcoholism. And there is some evidence from human genetics although its still preliminary that neuropeptide Y may be involved in alcoholism as well.
If thats the case it could mean that therapies could be developed to inhibit neuropeptide Y receptors, the researchers believe, as a way to deal with alcohol and drug abuse.
Ulrike Heberlien and her lab at the University of California decided to look at how social experiences affect addiction after studying how genes affect alcoholism since the mid-1990s.
But since in humans only 50 per cent of the risk factor for alcoholism is genetic, Heberlein, a professor of anatomy and neurology, decided it was time to expand the investigation and look at what role social factors play on drinking.
So she along with post-doctoral fellow and lead author Galit Shohat-Ophir and others began conducting experiments on fruit flies to see whether not having sex would increase their consumption of alcohol.
Designing the experiments was fun, said Heberlein and watching the fruit flies get drunk eye-opening. The first time I saw a drunk fly, I thought: Oh my god, this is just like humans, she recounted.
According to Heberlein the flies become uncoordinated, hyperactive and uninhibited.
They bump into each other and the walls. If you give them more alcohol they become lethargic and uncoordinated. They fall over, pick themselves up and fall over again. Eventually they pass out.
In the experiments conducted for the study, one group of male fruit flies was put in with female fruit flies that had already sex, Heberlein explained in an interview with the Star.
These male flies were rejected because of a sex peptide that is transmitted in male fruit fly seminal fluid. This sex peptide does something to a female fruit flys brain and causes it to reject all other sexual advances.
Meanwhile, another group of male flies was put in a container with virgin females with their choice of sexual partners.
Shohat-Ophir took the rejected and non-rejected flies and put them in a vial where there was plain liquid food and liquid food mixed with ethanol, monitoring how much the groups of flies drank during the day.
The study found the males that had been rejected showed a much higher preference for the alcohol laced food compared to the regular food, Heberlein said.
The team then made an educated guess as to why this was happening and decided to see if neuropeptide F might be involved.
Shohat-Ophir and the team of researchers then measured the levels of this neuropeptide in the brain of the flies.
The results: the levels of this neuropeptide were low in the rejected male fruit flies and high in mated males.
This means the lack of this neuropeptide may be related to their increase in drinking alcohol, said Heberlein.
Then the team to set out to figure out if the relationship was causal. The beauty of working with flies is that we have so many tools to manipulate the flys brain genetically, Heberlein said.
Shohat-Ophir, now a research specialist at the Howard Hughes Medical Institute Janelia Farm Research Centre, reasoned that if neuropeptide F is in fact responsible for the change in drinking behaviour she should be able to transform mated males who have high levels of neuropeptide F into rejected males simply by inhibiting the receptor for this molecule.
So she did that and found that even though the flies had mated they began to drink a lot. That proves the neuropeptide F is responsible, said Heberlein.
And when she did the exact opposite in the rejected males activating the neuropeptide F system she found they reduced their dinking, Heberlein said.
We think its the act of sex itself that affects their reward system or neuropeptide F and this in turn affects drinking, Heberlein said.
The authors conclude in the study: Our findings are thus not only consistent with known functions of mammalian NPY (neuropeptide Y) and its mode of regulation, but also provide evidence for NPF (neuropeptide F) functioning as a key molecular transducer between social experience and drug reward.
Next Heberlein, who is to become the scientific program director at the Howard Hughes Medical Institute Janelia Farm Research Centre, plans to look at whether other social experiences have an affect on drinking.
She wants to test whether increased drinking is a phenomenon restricted to sexual rejection or whether other social experiences trigger a similar reaction.
And she hopes others will take up the mantle and do similar studies with mammals.
