Neural pathway identifies key to pleasurable touch

Working with mice, scientists at Washington University School of Medicine in St.

Such touch—such as hugging, holding hands, or caressing—invigorates a psychological stimulus that is important for emotional health and healthy development

"The pleasant sensation of touch is very important for all mammals," said lead researcher Zhoufeng Chen, PhD, director of the Center for Itching and Sensory Disorders at the University of Washington

Chen's team found that when they raised mice without this neuropeptide, called PROK2, the mice couldn't sense pleasant touch signals, but still responded normally to itching and other stimuli

"This is important because now that we know which neuropeptides and receptors transmit only pleasant touch sensations, it is possible to enhance pleasant touch signals without interfering with other circuits, which is critical because pleasant touch The touch of a person boosts several hormones in the brain, which are essential for social interaction and mental health

Among other findings, Chen's team found that engineered mice lacking PROK2, or the spinal neural circuit that expresses its receptor (PROKR2), also avoided activities such as grooming and showed signs of stress that normal mice did not

"Mothers like to lick their pups, and adults often groom each other for a reason, like helping with emotional connection, sleep and stress relief,

Scientists generally divide touch into two parts: discriminative touch and affective touch

Studying people's pleasant touch is easy because a person can tell researchers what a certain touch feels like

"If an animal doesn't recognize you, it usually stays away from any touch because it sees it as a threat," Chen said

To get the mice to cooperate, and to see if they felt pleasant to touch, the researchers separated the mice from the mice in their cages for a period of time, after which the mice preferred to be stroked with a soft brush, like pets are stroked and groomed

Next, Chen's team set out to work to identify the neuropeptides that are activated by pleasant brushing

In further experiments, they found that the neuropeptides they targeted were not involved in transmitting other sensory signals, such as itch

"Just as we have cells and peptides for itch, we now have neurons and peptides for pleasant touch to transmit these signals