BOSTON — Redheads have a reputation for being hot-tempered. They also are said to have a higher pain threshold than others. Although there may not be scientific proof of their short fuse, according to a recent study, there may be some science behind their pain tolerance. Researchers at Massachusetts General Hospital (MGH) have shed light as to why those with red hair respond differently to some types of pain than those with different colored hair.
Specialized skin cells, called melanocytes, are responsible for producing different skin pigmentations and hair colors. Those with red hair – animals and humans alike – have slightly different protein receptors on the surface of their melanocytes. Previous research from MGH shows that when these receptors do not function properly, as in redheads, it causes decreased pigmentation.
The research team tested a breed of red-haired mice that, like humans, have melanocytes that lack the properly functioning receptor. Additionally, these mice also showed a greater capacity for pain tolerance, making them the best candidates for this particular study.
The results indicate an association between the melanocyte receptor (melanocortin 1 receptor) and the hormone proopiomelanocortin (POMC). The absence of melanocortin 1 receptor activity in the red-haired mice prompted their melanocytes to generate less POMC. This results in the splitting of POMC into several hormones, one of which increases sensitivity to pain and another that reduces sensitivity to pain.
When these hormones are produced, they help to keep the equilibrium between opioid receptors, which decrease pain, and melanocortin 4 receptors, which heighten sensitivity to pain. Reduced concentrations of both hormones in red-haired mice (and, thus, presumably in humans) should counterbalance each other. However, the body creates other substances unrelated to melanocytes that trigger pain receptors. As a result, downregulation of melanocyte-related chemicals causes an increased number of opioid impulses, which raises the tolerance level for pain.
“These findings describe the mechanistic basis behind earlier evidence suggesting varied pain thresholds in different pigmentation backgrounds,” says lead researcher Dr. David E. Fisher of Massachusetts General Hospital, in a statement. “Understanding this mechanism provides validation of this earlier evidence and a valuable recognition for medical personnel when caring for patients whose pain sensitivities may vary.”
Scientists have found new methods to influence the body’s normal mechanisms that govern pain, such as by developing drugs that block the melanocortin 4 receptors engaged in pain perception. “Our ongoing work is focused on elucidating how additional skin-derived signals regulate pain and opioid signaling,” adds co-lead author Dr. Lajos V. Kemény, a research fellow in dermatology at MGH. “Understanding these pathways in depth may lead to the identification of novel pain-modulating strategies.”
This study is published in Science Advances.