Throughout history we’ve blushed and called it la petite mort, the sting of pleasure, the balsamic injection, the flood of bliss—the list continues. But let’s cut to the chase: I’m talking about ejaculation. It’s almost seems as if some deep-seated Puritanical modesty compels us to semantically sidestep addressing this perfectly natural function. Perhaps we’re just a bit bashful that it feels really, really good. It’s not polite to discuss such scrumptious pleasures publicly. Humans are hardly the only species that enjoy a good climax. Pigs, bonobos, gorillas, chimpanzees and perhaps a few species of dolphins have all shown they pursue recreational flings for the fun of it. Sure, these are all highly intelligent, emotional, social creatures. But, as it turns out, even the tiny-brained fruit fly enjoys “taking a load off.” Shir Zer-Krispil and colleagues from Bar-Ilan University in Israel genetically engineered fruit flies in a way that made it possible for them to control neural activity with light. In this case, they engineered flies with neurons that would express the neuropeptide corazonin when exposed to red light. Studies have shown that corazonin neurons in the fly abdomen trigger the release of sperm when activated.
With their finger on the trigger, researcher could set up simple experiments to see if fruit flies enjoyed ejaculating, even in the absence of a female. "We wanted to know which part of the mating process entails the rewarding value for flies," Galit Shohat-Ophir said in a news release. "The actions that males perform during courtship? A female's pheromones? The last step of mating which is sperm and seminal fluid release?" In one experiment, researchers split an enclosure into two zones, one with normal light and another bathed in ejaculation activating red light. If flies spent more time in the red light zone, it could be inferred that it was a more pleasurable experience. The flies, of course, hung around in the red light zone far more than the control. Then, they performed an olfactory test that combined the red light stimulation with a specific odor. The flies showed a preference for the odor, even when the red light wasn’t turned on. In other words, the odor reminded them of the ejaculation experience, which is another sign they find it quite rewarding. Researchers published their findings Thursday in Current Biology. Intuitively their findings make a lot of sense. Behaviors that benefit our survival—eating, drinking, expelling waste—feel good. But things that feel good can be awfully addicting, and that’s the next step for this research team. Because scientists can control ejaculation activation, and that fruit flies like it, they can design basic experiments to study the underlying mechanisms of addiction. Fruit flies probably won't mind being subjects in future research along these lines.