Dear Anne, Every time I try to have a meaningless one-night stand, I end up developing feelings for the guy. My roommate is a biology major and blames some chemical called "oxytocin." What exactly is this chemical and why won't it let me have casual sex?!
-- Overly-Attached
The answer to your commitment conundrum may indeed involve oxytocin. Measuring nine amino acids in length, this unassuming peptide is produced by neurons in the hypothalamus and is secreted into the bloodstream by the pituitary. We once thought its role was limited to fairly provincial tasks, such as releasing milk for lactation and stimulating uterine contractions with birth. More recently, however, oxytocin has been implicated in a much broader range of social behaviors ranging from bonding between mother and newborn to spooning after sex.
The idea of oxytocin as a potential love potion was first born not of a failed attempt at no-string-attached sex between undergrads, but of a 24-hour fornication session between prairie voles. So what do nearly blind, marathon-mating, tunnel-dwelling rodents have to do with you?
Monogamy, it turns out, is relatively rare among mammals. Only three percent of warm-blooded, furry types prefer mating for life over dating around. Prairie voles and -- despite our occasional indiscretions -- humans are in that generally monogamous minority. Prairie voles are particularly committed: At the tender age of 30 days, they reach sexual maturity and emerge from their burrows with noses primed for the opposite sex. After encountering another vole and completing a thorough olfactory evaluation of its genitals, an appropriately paired prairie vole will then commence a full day of copulation with its new partner. From then on the voles are inseparable: They nest together, parent their pups together and defend their territory together.
So how does oxytocin contribute to this coupling? Some of the most pivotal research in vole lovin' was published in 1992 in the Proceedings of the National Academy of Sciences. This study, authored by Thomas R. Insel and Lawrence E. Shapiro of the National Institute of Mental Health's Laboratory of Neurophysiology, investigated the role of oxytocin in the prairie vole's bonding process. Their research compared prairie voles to a related species known as montane voles which, unlike their committed cousins, seem quite content to live a life of promiscuity and relative social isolation. These two species share more than 99 percent of their genetic makeup, but Insel and Shapiro found they differ in one essential area: their expression of oxytocin receptors. In voles, as in people, orgasm releases a huge surge of oxytocin, but the effect of this hormone varies based on whether you have receptors for it. Not surprisingly, the prairie vole brain is fertile ground for oxytocin binding, while the montane voles have negligible numbers of receptors, making the wham, bam, thank-you-ma'am method of copulation perfectly acceptable for this species.
Hypothesizing that this high density of oxytocin receptors may be central to the prairie vole's social behavior, researchers later found that blocking the oxytocin receptors in female prairie voles could prevent them from pair-bonding after sex. Similarly, administering oxytocin, even in the absence of sex, was sufficient to facilitate pair-bonding for female voles. Later studies found a related hormone known as vasopressin seems to work with oxytocin to facilitate pair-bonding in male voles.
Given our tendency toward post-sex spooning and long-term relationships, it's not surprising that the human brain looks fairly similar to that of a prairie vole. Does this mean blocking your oxytocin receptors would allow you to have casual sex to your heart's content -- without risking a broken heart? Maybe. But sex and the emotions it engenders are inherently complicated, and the role of hormones such as oxytocin is likely much less straightforward in humans than it is in our rodent relatives.
It does, however, appear that this hormone plays an important role in solidifying human bonds, especially when sex is involved. It may be that some people are more susceptible to the chemical charms elicited by intercourse simply because they have higher levels of oxytocin or vasopressin receptors. Likewise, low receptor levels in others may contribute to a more Hugh Hefnerian approach to pair-bonding ... although I've learned from "The Girls Next Door" that only one of the girlfriends shares a bedroom with Hef, so perhaps even our favorite Playboy has a little prairie vole in him.
Anne Mills is a Cavalier Daily Health & Sexuality Columnist. She can be reached at mills@cavalierdaily.com or through the Sex & Balances submission page at cavalierdaily.com/sex.asp. This column should be used for educational purposes only and is not meant to substitute advice from your doctor.
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