Homing in on Hormones
By Karen Young
At first glance, sex and aging don’t seem to go together. In the
laboratory of Psychology Professor Kathleen Chambers, however, they
have a lot in common. She studies sex hormones to understand the
process of aging.
“I’m interested not only in the basic function of hormones, but the
changes that take place with aging and how hormones modulate learning
and regulate sexual activity,” says Chambers. “We’ve learned that
hormones play different roles in males and females. We’ve also learned
that although there is a great deal of similarity in the effects of
hormones across animal species, what works for rodents doesn’t always
work for monkeys and humans.”
Chambers began her career studying how animals learn to avoid certain
foods that have made them ill. Research on the relationship between
hormones from reproductive glands and aging developed later.As a
scientist at the Oregon Regional Primate Research Center, she learned
that imprisoned male
sexual offenders were being given testosterone progesterone, based on
research that had shown that rats dosed with progesterone exhibited a
decrease in sexual activity.
“The prisoner program was a disaster,” Chambers says. “Progesterone
doesn’t work that way in primates, although it does inhibit behavior in
rodents. One of the participants left the prison and repeated his
crimes. And the program shut down.” But it stimulated her interest in
the relationships between sex and behavior.
“I’d always been intrigued by the problem of sexual offenders and
wondered what could be done about sexual violence,” she says. She
thought if she could understand how and why male sexual activity
diminishes with age, she might be able to find a successful way to
treat sexual offenders.
When Chambers explored the relationship between a decrease in
testosterone and the decline of sexual activity in aging males she
found that adding more testosterone had little effect. Some of her
research with rats suggests a reduction in the brain’s receptors that
control behavior.
This may be why men who lose interest in sex as they get older cannot
retrieve their earlier desire by taking testosterone supplements,
Chambers says. She adds that drugs such as Viagra do not affect the
brain, so if a man loses interest in sex because of brain dysfunction,
there are no known treatments to bring it back. But for females, the
situation is different. They appear to retain interest in sex as they
get older, Chambers says. “With female rats and rhesus monkeys, we have
found that even past the equivalent of menopause, if you give them
hormones, their behavior will come back. This is not true with males.”
Chambers says one biological explanation might be so-called “affiliate
behavior.” In a monkey, for example, sexual behavior can be a way of
“affiliating” with a male who might offer her protection or something
else that would be beneficial in an evolutionary sense.
Her work on learned food aversions also has important implications for
aging. “There has been a great deal of press on the memory enhancing
abilities of estrogen,” Chambers says. “In fact, our research shows
that estrogen can have both facilitating and detrimental effects on
memory. Which effect it has depends on when it is present during the
learning and memory retrieval processes. Clearly, the idea that one
hormone or drug can enhance all memory processes is looking to be quite
simplistic.”
“These two systems, learned food aversion and sex, can shed light on
brain function,” she says. “The hope always is that if we can
understand how one system fails, it can teach us about other systems
more critical to our survival.”
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