Sex as stress? It sounds like an oxymoron. But then, many of us have been misdefining the word stress all along.
All stress is not equal. Indeed, as Bruce S. McEwen, Ph.D., director of the neurendocrinology lab at Rockefeller University, puts it, if we got rid of stress, "we'd be dead." Stress comes in flavors: "good" and "bad." Good, or "challenge," stress comprises moderate, transient stressors that we have the resources to cope with--in other words, stimulation. Exercise is a form of challenge stress, as is learning new things. Bad, or "threat," stress, on the other hand, refers to situations that are overwhelming, in which we feel helpless in the face of the onslaught. That's the stuff that doesn't let up, such as caring for a chronically ill child.
Stanford University neurobiologist Robert Sapolsky, Ph.D., author of the acclaimed "Why Zebras Don't Get Ulcers," conjures up a roller coaster to frame good stress this way: "Circumstances where you voluntarily relinquish a degree of control and predictability in a setting that overall is benevolent."
That sounds a lot like a roll in the hay to me, too. And a new study by Princeton neuroscientist Elizabeth Gould, Ph.D., and colleagues provides the science to give the theory legs (among other body parts).
Gould is a pioneer in the study of "neurogenesis"--that is, the birth of new brain cells, or neurons, in the adult brain. Neuroscientists shunned the idea of neurogenesis until the end of the 20th century. But then, in the late nineties, Gould showed in adult rats and primates that new neurons are born in a part of the brain called the hippocampus, the seat of memory consolidation and retrieval.
At the same time, Fred H. Gage, Ph.D., at the Salk Institute, revealed neurogenesis in humans, using brain cells of people who had died of cancer. The specific area of the hippocampus showing the growth is the "dentate gyrus," a worm of a structure sitting atop the seahorse-shaped hippocampus, and "good" stress activities, like exercise, spark it. Later research showed that the brain's olfactory bulb, which processes smell, generates new neurons, too. Ever wonder why pregnant women start heaving when they smell, say, broccoli or brussels sprouts? It's an evolutionary hangover: Pregnancy spurs neurogenesis in the olfactory bulb to ensure survival of the species--albeit generally for the nonhuman among us, for whom sniffing equals routing out danger.
Gould's new study, just out in the journal PloS ONE in July, shows that sex, too, increases neurogenesis, particularly in the brain area that regulates anxiety--and the more sex (not overdoing it, of course), the better.
Here's what she and Princeton colleagues Benedetta Leuner, Ph.D., and Erica R. Glasper, Ph.D., did:
The scientists exposed adult male rats to "sexually receptive" females either one time or--for the real Don Juans--for 14 consecutive days. Rigorously designed, the study also included "control" groups: male rats exposed to "non-receptive" females (the "I've got a headache" type), and male rats who got no action at all. Later, the researchers tested the male rats' eating behaviors in an unfamiliar environment to assess how anxious they were. Finally, they measured the level of stress hormones in their blood--specifically, the hormones known as "glucocorticoids"--and then "decapitated" (to use scientific parlance) the critters to see if new cells had sprouted in the dentate gyrus of their brains.
What did they find? In the one-timers, even though glucocorticoid levels had increased, new brain cells proliferated. As for the marathoners, they experienced a triple bonus (on top of the sex itself, that is): Their levels of glucocorticoids did not increase, new brain cells continued to sprout, and they chowed down anxiety-free in the food drill.
That the glucocorticoid levels rose but still new brain cells grew had the scientists scratching their own heads. Numerous earlier animal studies had shown that increases in glucocorticoid levels from stressors--predator odor, cold water, restraint--not only inhibited neurogenesis but impaired learning and memory functions.
The scientists wondered: Might the nature of the stressor, its so-called "emotional valence," make the difference?
It appeared so. The bad effects of excess glucocorticoids in the brain--no new neurons, problems with memory and learning--were apparently "overridden" in the rats getting it on by the "hedonic value," that is, the pleasure quotient, of the stressor (here, sex), they wrote. The scientists speculated that the benefits of brain chemicals let loose by sexual experience, such as endogenous opioids, the neurotransmitter dopamine and the neuropeptide oxytocin, might be outweighing the negative effects of the boosted stress hormones. In other words, the "hedonic value" of a stressor may be what determines whether it's Jeckyll or Hyde.
"It's uniquely important work showing that glucocorticoids are context dependent," says McEwen about Gould's promiscuous rats. "They don't have a unitary effect--they depend on other factors."
Thea Singer is a science/health journalist whose new book, "Stress Less: The New Science that Shows Women How to Rejuvenate the Body and the Mind," comes out on September 23 from Hudson Street Press. Learn more at www.theasinger.com.
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