The flies also enjoy when you ejaculate and take to drink if you don’t mate

Humans and flies have in common amazing traits. We already knew that the Drosophila or fruit fly drowns his sorrows in alcohol when deprived of sex. Now, an international study has shown that we also share with these insects the pleasure of the ejaculation.

The importance of the discovery, published in Current Biology, is that it was not yet known what part of the mating is rewarding to flies. Some options were the stage of courtship, pheromones from the female, or the release of sperm.

“We have shown that male flies enjoy the last step of the copula –the release of sperm and seminal fluid– that follows the increase in the level of the neuropeptide F (NPF). This increase occurs even in the absence of a female, and can prevent the male to locate the pleasure in substitutes like alcohol,” explains to Sinc the researcher Shir Zer-Krispil, of the university of Bar-Illan (Israel).

To explore the reward system in the brain associated with ejaculation, the scientists used tools optogenéticas that allow you to control the activity of neurons using light with an appropriate wavelength.

With red light, the researchers were able to activate neurons that express the neuropeptide called corazonin (CRZ). According to previous studies, this small peptide controls the ganglion abdominal in males, that is responsible for the release of sperm.

Although the study also used female flies, the neurons CRZ only involved in the ejaculation of the male. Further studies are required to know the system of rewards and female neurons that are involved in it.

The experiment

One of the tests of the research consisted of placing male flies in a scenario with one end illuminated by red light and the other end in darkness to observe their preferences. The insects preferred the red light, which activated the neurons CRZ related to the expulsion of sperm. This shows that ejaculation by itself is a pleasurable experience.

In another of the tests we trained the flies to associate the red light with the aroma of concrete. When presenting flies to two different aromas, they picked the one that reminded them of the red light, and his past experience of ejaculation.

After several days of repeated activation of the neurons CRZ, the male virgin had high levels of NPF, similar to the level of the males that they mate. When these males are given a choice between the liquids with and without alcohol, they preferred the non-alcoholic. By contrast, the flies were not exposed to the red light preferred the liquid with alcohol.

“The principles by which the mind processes the rewards are retained until the end in all animals. Are the basic machinery that helps animals to survive”, says Galit Shohat-Ophir, a researcher leading the study at the university of Bar-Illan.

The addiction to drugs

“The mind processes natural rewards in the same way that the induced by drugs of abuse”, says Shohat-Ophir. “This allows you to use simple organisms to study the relationship between natural rewards and those provided by the drugs, as well as the mechanisms behind addiction,” he adds.

Scientists are investigating now how it gets to the brain the information about the ejaculation to know more about the risks of developing an addiction.

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