The satisfaction of a massage, the delight of a touch, the softness of a caress… The ability of touch to cause almost immediate pleasure may seem obvious. For neuroscientists, however, it remains largely mysterious. The path that leads from our epidermis to the center of the reward, deep in our brain, remains strewn with questions.
In an article published on January 23 in the journal Cell, an American team announces that it has traced the complete itinerary of what it calls “touch of pleasure and sexual receptivity”. As always, this pioneering work was carried out on mice. But they show the promise of an understanding of the phenomenon in humans and even new treatments and manual therapies.
It all started in 2018, in the laboratory of Ishmail Abdus-Saboor, at the University of Pennsylvania, in the United States. Specializing in the study of pain, the researcher had proposed to a young doctoral student, Leah Elias, to look into the role of specific sensory cells in the skin called Mrgprb4. Highlighted in 2007, these neurons had no known use. The student undertook to study them by optogenetics. This delicate but now common technique consists of modifying the neurons in order to then activate them with a simple colored light ray, and therefore to monitor the effects. “To our great surprise, by activating these sensory neurons on the backs of female mice, they assumed a posture of lordosis”, says the young researcher, now a postdoctoral fellow at Johns-Hopkins University in Baltimore.
GPR83 neurons, middle link
Common in the eyes of yoga enthusiasts and cat owners, lordosis, in mice, is the position taken by the female to promote penetration by a male. Should we see a feeling of pleasure there? The team continued the experiment in a study chamber by turning on the light on the animal and then dragging it out of the room. When she let him in again, the rodent headed straight for the place where he had been lit. A serious indication of the gratifying nature of the activation of these neurons.
Interrupted by the Covid-19 pandemic, the research resumed in 2021. This time, the team set out to genetically modify the mice in order to suppress the activity of Mrgprb4 neurons. Not only did the lordosis disappear but the females became hostile to the sexual approaches of the males.
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