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04/24/2003
Romantic Rodent
Last week I sallied forth to begin my annual quest to break a
hundred. Thankfully, my usual golfing buddies were not present
to witness the horrific trashing of that seemingly impossible
dream. The next day I joined my wife’s Wednesday matinee
theater group to see “Man of La Mancha” on Broadway. In
contrast to my golfing experience, “The Impossible Dream (The
Quest)” rendered by Brian Stokes Mitchell’s Don Quixote was
glorious, eliciting a wildly enthusiastic audience response.
The demented Don Quixote’s chaste love for his pure and lovely
Dulcinea, actually Aldonza the prostitute, stands as one of the
more touching and sad cases of unrequited love in literature and
theater. What is love? I looked up the term in one dictionary
and the definitions ranged from “an intense affectionate concern
for another person” or “an intense sexual desire for another
person” to “a zero score in tennis”. I’m not a tennis person so
let’s skip that one. B. R. Komisaruk and B. Whipple of Rutgers,
where I’m a visiting scientist, define love as “one’s having
stimulation that one desires”. Their idea of “stimulation”
embraces emotional bonding as well as sensory stimulation of
the types purveyed ad infinitum in our media.
Love is often discussed in terms of the right “chemistry” between
two persons. But is there really a chemistry of love? The May
2003 issue of Discover magazine contains an article by Steven
Johnson that gives at least a partial answer to this question. The
article, titled “Love [Are we finally getting good enough at
biochemistry to understand the mystery-and magic-of
romance?]”, deals primarily with the work of psychology
professor Shelley Taylor, neuroendocrinologist Sue Carter and
others.
Of course, any mention of the subject of love brings to mind that
romantic character the prairie vole, perhaps known to you better
by its biological name of microtus ochrogaster. Prairie voles are
small rodents about six inches in size that weigh only a couple
ounces and frequent the central grasslands of North America.
They lead a precarious life, considered as pests by those who
tend lawns or gardens and serving as tasty meals for predators
such as owls, snakes, foxes and even some domestic animals.
What do prairie voles have to do with love? Unlike about half of
those who marry in the U.S., the prairie voles are among the
relatively few (5 percent) species of mammals that, once they
mate, stick together with the same mates for life. Certainly,
voles provide a romantic role model that is difficult for many of
us humans to emulate. Whoops! I misspoke when I said
“voles”. The prairie vole’s cousin, the mountain vole, eschews
this romantic monogamous behavior and messes around in the
rodent version of one-night stands.
Why the difference between the two species of vole? Enter the
peptide oxytocin, sometimes called the “cuddle hormone”.
Oxytocin is a chemical produced in the brain’s limbic system.
The limbic system is a portion of the brain involved in emotional
responses such as fear and aggression, mood changes and also in
the cementing of memories. It has been known for many years
that oxytocin is released during intense emotional experiences –
notably during childbirth, breast-feeding and orgasm (both in
men and women in the latter case). It appears that in women
estrogen adds to oxytocin’s effects while in men testosterone
diminishes them. Oxytocin in some way plays an important role
in stimulating what Shelley Taylor calls the “tend and befriend”
response.
You’ve probably heard of the “fight or flight” response to stress.
When faced with a threatening situation, say another guy with a
spear, our early ancestors would either fight or run away. In
today’s society, stressful situations arise daily where neither fight
or flight are viable options. At a talk on this subject, Taylor
learned of experiments with caged rats subjected to repeated
electrical shocks. The stressed-out rats ended up biting and
clawing each other to death. Taylor was surprised by the finding
and found that the subjects were all male rats. At the time,
human studies on reactions to stress were also performed
predominantly on male subjects. Taylor and her group decided
that women and men, under certain circumstances, react to stress
in a different way, namely, by reaching out to loved ones.
Specifically, if a parent or partner finds his or her child or partner
threatened, he or she will risk greater danger to protect the loved
one. Taylor posed the alternative to “fight or flight” as being
“tend and befriend”. Women especially are well known to
search out social interactions (befriend) with others. These
social interactions in turn provide a network of support for the
woman in her tending roles.
Back to the voles, Sue Carter was aware of research that
indicated that oxytocin facilitated parent-child bonding in sheep.
When she injected oxytocin into the brains of prairie voles they
paired off even faster than usual. When she and her coworkers
tried the opposite approach by injecting substances that blocked
the receptors for oxytocin, the prairie voles’ sexual behavior
became more like that of certain NBA basketball players. This
was pretty good evidence that oxytocin plays a key role in the
prairie vole’s normal romantic monogamy.
What about the mountain vole? One of Carter’s colleagues, Tom
Insel decided to take a look at the brains of the two breeds of
vole. Sure enough, they turned out to be wired quite differently.
In the prairie vole, the oxytocin receptors are located in an area
of the brain known as one of the brain’s pleasure centers that also
contains overlapping dopamine receptors. In the mountain vole,
the oxytocin receptors were located in a different area of the
brain, with no overlapping dopamine receptors. Without the
overlap with dopamine receptors, it seems that the mountain
voles just don’t get the feel good response enjoyed by the prairie
voles.
In humans, the oxytocin receptors also overlap the dopamine-rich
areas of the brain. Unfortunately, it’s hard to do experiments on
humans to pin down the oxytocin role so we have to rely on more
indirect observations such as those on the voles. The bottom line
seems to be that you can choose between the adrenaline-loaded
fight or flight response or the oxytocin-loaded tend and befriend
response. Lest you think that oxytocin is the coming love potion,
however, be advised that it is not that simple.
Oxytocin isn’t the whole story. Jaak Pansksepp, a neuroscientist
at Bowling Green State University, calls oxytocin a “big-ticket
item” and credits it with triggering the tend and befriend
response. However, he believes that other opioids in the body
deliver the “warm fuzzy feeling” when you’re around your loved
ones. There’s a downside to this picture. Heroin and other drugs
can hijack the love connection by causing that same warm fuzzy
feeling that the body’s natural opioids engender. This is believed
to explain how drug addicts can turn away from loved ones,
preferring the heroin that gives them a more powerful version of
the feeling that caused the emotional attachment to the loved one
in the first place.
What about the birds, you might ask? Some 90 percent of them
are monogamous and many species mate for life. Yet there’s no
oxytocin. However, there is vasotocin in birds at significant
levels and vasotocin is in the same evolutionary line of
hormones as oxytocin. The cherry and magnolia trees are in
bloom, the robins are mating in our yard and the sun is shining.
Should I spoil the picture by setting out again to pursue my
impossible dream?
Allen F. Bortrum
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