The purpose of the study titled "Sexual Deprivation Increases Ethanol Intake in Drosophila"
was to find out whether rejection during courtship had any effect on consumption of alcohol in male fruit flies. The study abstract, published in the journal Science
"The brain’s reward systems reinforce behaviors required for species survival, including sex, food consumption, and social interaction. Drugs of abuse co-opt these neural pathways, which can lead to addiction...we used Drosophila melanogaster to investigate the relationship between natural and drug rewards."
According to BBC
, the researchers working at the University of California, San Fransisco, did an experiment in which male flies were placed in a box with virgin females receptive to male sexual advances. In another, the males were placed in a box with females that had already mated and thus rejected the males.
The researchers found that while flies who had successful courtship and mating showed no preference for food charged with 15% ethanol, rejected males showed a clear preference for alcohol-containing preparations. Lead author Galit Shohat-Ophir, said: "To our surprise the rejected males had much higher consumption of the food with alcohol." Shohat-Ophir said they had not expected that rejected males would show a preference for alcohol-containing food.
reports that study of the neurochemical basis of the behaviour revealed that a neuropeptide tagged "F" (NPF) involved in sexual behavior of the fruit flies was also involved in alcohol consumption. This led to the conclusion that the flies were substituting alcohol for sex, that is, in anthropomorphic terms, seeking to "drown their woes in alcohol."
The study report
, said: "In males, mating increased, whereas sexual deprivation reduced, neuropeptide F (NPF) levels. Activation or inhibition of the NPF system in turn reduced or enhanced ethanol preference. These results thus link sexual experience, NPF system activity, and ethanol consumption."
reports Shohat-Ophir said: "What we think is that these NPF levels are some kind of 'molecular signature' to the experience."
To show that low NPF level was responsible for the preference the rejected males showed for alcohol, the researchers artificially manipulated the levels of NPF in the flies' brains and found that those with artificially induced lower levels of NPF behaved as though they had been sexually rejected while those with artificially induced higher levels behaved as though sexually satiated.
The study report
, said: "Artificial activation of NPF neurons was in itself rewarding and precluded the ability of ethanol to act as a reward. We propose that activity of the NPF–NPF receptor axis represents the state of the fly reward system and modifies behavior accordingly."
Shohat-Ophir, according to BBC
, said: "What this leads us to think is that the fly brain - and presumably also other animals' and human brains - have some kind of a system to control their level of internal reward, that once the internal reward level is down-regulated it will be followed by behaviour that will restore it back."
Flies have brains much smaller than humans', about 100,000 neurons compared to 100 billion in humans, but scientists believe their simple neuronal circuitry may illustrate the neurochemical process that leads to humans seeking solace in the bottle in times of stress. The scientists also believe that studying fruit flies may lead to new insights about how addiction develops. According to Gregg Roman, biologist at the University of Houston: "Understanding the molecular pathways that guide behavior in flies is a step toward fully understanding the more complex behaviors in mammals."
reports the study and similar ones reveal the remarkable unity of life. Molecules that regulate behaviour in lower animals are also active in higher animals. For instance, studies have shown that mice and human beings have similar neuropeptides in their brains and blocking production of the neuropeptide in mice brain increases alcohol consumption resulting in "alcoholic mice." BBC
reports the corresponding neuropeptide in mammals is called neuropeptide Y (NPY).
reports that study author Ulrike Heberlein, said: “I think it’s a pretty good bet that it will translate to humans. One can say we could now understand why a negative experience, such as a sexual rejection, could drive somebody to drink.”
Dr. Herman Dierick, a neuroscientist at Baylor College of Medicine, said: "For some it may be remarkable that we see these similarities. But it's only natural as we're all evolutionarily linked."
Troy Zars of the University of Missouri, however, cautioned on anthropomorphizing the results. He said: "Anthropomorphising the results from flies is difficult to suppress, but the relevance to human behaviour is obviously not yet established".