Oxytocin is a result of neurons sending electrical signals to the hypothalamus that then sends the action potential to the posterior petuity, which then releases oxytocin. This release of oxytocin is known to be present during stress, social bonding, and childbirth or breastfeeding. We have also come to know that oxytocin helps with nociception and pain (Valery, G. & Alexandre, C., 2017). However, we do not know how various amounts of oxytocin that are released or specific physiological changes such as Irish descent and red hair alter the pain threshold or pain tolerance in such individuals. While there is not a lot of literature or research dedicated towards these questions, we can look to a study conducted by Kathleen C. Robinson, et al. In this study, they looked at the question of red hair in relation to a higher pain tolerance.
We know that red hair is caused by a loss of function variant alleles at the melanocortin 1 receptor (MC1R) (Valverde, P., et al., 1955). The study conducted by Robinson, et al. specifically looked at mice with MC1R (red-haired mice) and compared them to C57BL/6J mice (black-haired). Using only male mice at least eight weeks of age (p56), they observed the mechanical nocieception and the thermal nocieception between these groups. Their data suggests that there is an elevated nociecptive threshold in the red-haired mice (MC1R). This elevated threshold suggests that there is a relationship between red hair and pain thresholds.
It would be interesting to take this study further and see if the same results are found in humans with red hair or, more broadly, of Irish descent. Additionally, to see if there is an altered MC1R or MC4R signaling across males and females, red hair/Irish descent and non, and other physiological differences between populations. We know that oxytocin levels impact our nociceptive and pain thresholds, but we still do not have very much information on how physiological changes alter these thresholds as well as the amount of oxytocin produced by each individual.
References:
Grinevich, V. & Charlet, A. (2017). Oxytocin: pain relief in skin. PAIN, 158 (11), 2061-2063. doi: 10.1097/j.pain.0000000000001006.
Kathleen C. Robinson et al.,Reduced MC4R signaling alters nociceptive thresholds associated with red hair.Sci. Adv.7,eabd1310(2021).DOI:10.1126/sciadv.abd1310
Valverde, P., Healy, E., Jackson, I., Rees, J. L., & Thody, A. J. (1995). Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans. Nature genetics, 11(3), 328–330. https://doi.org/10.1038/ng1195-328
This is a very interesting topic as I have always wondered why those with red hair have a different pain tolerance than others. I have also heard that those with red hair often require more anesthesia when undergoing surgeries. For example, an article by a dental clinic (lakesidedentallc.com) reviewed this topic as well, and they also came to the conclusion that hair becomes red when a receptor on the certain cells that lend pigment to hair doesn’t work properly. These same cells also release a hormone that stimulates a brain receptor to increase pain sensitivity. This would explain why red-headed people are more sensitive to pain and require more anesthesia as well.
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