Studying mice, scientists at Washington University School of Medicine in St. Louis have identified a neural circuit and a neuropeptide — a chemical messenger that carries signals between nerve cells — that transmit the sensation known as pleasant touch from the skin to the brain.
Such touch — delivered by hugs, holding hands or caressing, for example — triggers a psychological boost known to be important to emotional well-being and healthy development. Identifying the neuropeptide and circuit that direct the sensation of pleasant touch eventually may help scientists better understand and treat disorders characterized by touch avoidance and impaired social development, including autism spectrum disorder.
The study is published April 28 in the journal Science.
“Pleasant touch sensation is very important in all mammals,” said principal investigator Zhou-Feng Chen, PhD, director of the Center for the Study of Itch & Sensory Disorders at Washington University. “A major way babies are nurtured is through touch. Holding the hand of a dying person is a very powerful, comforting force. Animals groom each other. People hug and shake hands. Massage therapy reduces pain and stress and can provide benefits for patients with psychiatric disorders. In these experiments with mice, we have identified a key neuropeptide and a hard-wired neural pathway dedicated to this sensation.”
Chen’s team found that when they bred mice without the neuropeptide, called prokinecticin 2 (PROK2), such mice could not sense pleasant touch signals but continued to react normally to itchy and other stimuli.
“This is important because now that we know which neuropeptide and receptor transmit only pleasant touch sensations, it may be possible to enhance pleasant touch signals without interfering with other circuits, which is crucial because pleasant touch boosts several hormones in the brain that are essential for social interactions and mental health,” he explained.