[Huffington Post] Mary Roach's irreverent orgasm trivia reminds us that researchers, like porn makers, tend to snap their notebooks shut right after the money shot. Yet some of the most intriguing findings about orgasm may lie beyond its brief fireworks. Post-O data could one day help solve all kinds of mysteries, such as why lovers' libidos often go out of sync -- especially after those initial "honeymoon poppers" wear off.
Sex clues from the humble lab rat
After a rat satiates himself sexually (which is how rats normally mate, and requires an average of 2.5 hours and up to 7 ejaculations), he exhibits a pronounced 4-day cycle. He's a bit fragile. His sexual motivation (libido) is nil-to-sluggish, and he's hyper-reactive to a range of drugs. Why does this happen? His neuroendocrine equilibrium is off in various brain structures.
After about four days, Mr. Rat can copulate more than once, but it will take him 15 days to return to full studliness. According to scientists, the long lasting character of these effects can only be explained by plastic brain changes that gradually reverse themselves. The changes apparently protect the brain against overstimulation from too many orgasms in a short period.
One of the most interesting post-O changes measured in male rats is a drop in sensitivity to testosterone. With each ejaculation, testosterone receptors decline in the sexual centers of the brain, gradually putting the brakes on libido. How? Less response to testosterone also quells response to dopamine. Dopamine is the "go-get-it!" signal at the heart of desire, so when it flags so do erections.
Female rats also reveal a cycle. For example, a bout of vigorous sexual stimulation will set off a twice daily surge of prolactin for 10 to 13 days. Prolactin (a multi-purpose hormone) is known to put the brakes on desire temporarily by inhibiting dopamine and prepare females for possible pregnancy.
Postcoital discoveries in women
Just last year German neuroscientists got the bright idea to check whether sex also initiates a lingering neuroendocrine "memory" in women (possibly dampening their libido). Lo and behold, sexual intercourse with orgasm indeed produced a prolactin "echo" a day later in the women they tested!
One of the most intriguing findings about orgasm may lie beyond its brief fireworks. Post-O data could one day help solve all kinds of mysteries, such as why lovers' libidos often go out of sync -- especially after those initial "honeymoon poppers" wear off. - Marnia Robinson
In other words, it's possible that women are subject to a perfectly normal neuroendocrine cycle after orgasm. If so, are additional hormonal events involved? How long do they linger? Might they affect some women more than others (think PMS)? How would these events interact with a menstrual cycle? It's too soon to say.
Intriguingly, however, UK and Australian researchers ended up baffled when they analyzed women who report recurring depression, irritability, or tears after sex (8 percent of women, in the UK study). Researchers expected to find that childhood abuse/marital distress correlated with symptoms. Not so. Some unknown factor produces those pronounced postcoital mood swings. Might it turn out to be a neuroendocrine cycle with the potential to alter both mood and sexual desire? Are the 8 percent simply at one end of a bell curve, and thus conscious of neurochemical fluctuations the rest of us disregard?
In any case, the ardent German scientists next plan to see if post-O prolactin blips are related to lack of desire (suppressed dopamine). Such research may help explain why she's not always in the mood.
What about post-O events in men?
First, that notorious "roll over and snore" effect is palpable evidence of orgasm's neuroendocrine aftermath. It's apparently prolactin-related as well, but may also entail the decline in testosterone sensitivity (and other changes) seen in male rat brains. Some receptor-counting research is, as yet, too invasive for human brains.
Second, research on human males has turned up a neuroendocrine cycle of at least seven days following ejaculation. Serum testosterone spikes around day seven -- assuming a guy doesn't ejaculate in the meantime. (So far, only the Chinese display the self-discipline required for this experiment!) What related neuroendocrine dominoes are falling, and for how long?
Third, according to neurologists even healthy young men show evidence of sexual satiety (limits to libido). Experts believe the limits arise from neurochemical inhibition of guys' dopamine response. Additional evidence implicating dopamine comes from psychiatrist Richard A. Friedman. He "cured" a guy's post-O achiness and depression by reducing the intensity of his climaxes with an SSRI (Prozac). SSRIs inhibit dopamine in the sexual centers of the brain, which is why they're associated with low libido.
In short, neurochemical events can mess with a guy's post-O satisfaction too. Perhaps the real anomalies are couples who don't fall out of sync.
UPDATE (2014): Researchers have shown that ejaculation, even twice a week, shrinks the dopamine-producing neurons in the VTA, which reduces a male's response to the pleasure of morphine. This also happens with repeated heroin use in both rats and humans. Scientists have also learned that amphetamine activates the exact same nerve cells as orgasm, urging the brain to "remember and repeat." In other words, drugs of abuse "work" because they're hijacking the mechanisms that evolved to make us want sex...and yet experience aftereffects from too frequent sex.
In addition, researchers found that sexual behavior in females altered dopamine signaling and induced,
persistent structural alterations to the [reward] circuit that can increase reproductive success and are analogous to the persistent structural changes following repeated exposure to many drugs of abuse. (2013)
For more science see What Do the Scientists Say?
For millennia, cultures around the globe have recorded ways of managing mutual desire for well-being and sustainable harmony. Kosher sex, for example, mandates a two-week sexual time-out during each menstrual cycle. Other traditions put the emphasis on frequent intercourse with a willingness to forego climax. Think of the Chinese Daoist dual cultivation, karezza, (which evolved in the States), cortezia in Europe, Polynesian lovemaking, or this version of Indian tantra.
Couples who practice these techniques commonly report more dependable, easier-to-mesh libidos. Maybe research on postcoital neuroendocrine events will someday reveal why.
[This article first appeared in the Huffington Post]
And for science buffs: Growing evidence of a lingering post-orgasm cycle (links to studies)