97-11-21:  MUSK SHREW LOVE: RESEARCH SUGGESTS STRESS-INDUCED HORMONE MAY
FACILITATE SEX



By Dan Heuchert



U.Va. biologists have found that a hormone normally associated with
periods of high stress may play a key role in the sexual behavior of
female musk shrews.

Elevated levels of the hormone cortisol are likely to be associated
with stressful periods in an animal's life, and stress had been thought
to inhibit reproduction in a variety of species, including humans, said
postdoctoral fellow Patricia Schiml of the biology department, the lead
author in the studies, which were presented Oct. 29 in a meeting of the
Society for Neuroscience in New Orleans. (Musk shrews are
scientifically classified in the order Insectivora, which is closely
related to humans, Schiml said.)

Schiml and associate biology professor Emilie Rissman set out to
investigate anecdotal evidence in scientific literature that a
positive, not negative, relationship between elevated cortisol and sex
may exist at times in both humans and primates. In many primates,
annual cycles of sexual behavior are closely associated with annual
cycles of cortisol secretion. An early morning peak in sexual behavior
in humans also coincides with a daily surge in cortisol secretion.

In humans, treatment with cortisol can result in increased excitement
and arousal and a reduction in tiredness. In musk shrews, elevations in
cortisol are likely to be associated with the arousal and novelty of
being with an opposite-sex animal for the first time and may activate
sexual behavior.

When female musk shrews are initially introduced to males, they are
very aggressive for a brief period, but will still approach and
investigate males. Soon the behavior of the female changes
dramatically: aggression declines and the female indicates she is ready
to engage in sexual interactions by wagging her tail as she quickly
walks in front of the male.

Schiml first found that, though cortisol levels typically increase when
animals are exposed to new things and strange situations, elevated
cortisol was more likely to be associated with sexual receptivity than
social aggression. In that study, virgin female musk shrews with no
sexual experience were allowed to interact with males for up to 15
minutes. Females who became ready to engage in sex, as indicated by
tail-wagging, had very high levels of cortisol. Females who remained
aggressive and did not display tail-wagging behavior had very low
levels of cortisol -- so low, in fact, that they were indistinguishable
from the cortisol levels of undisturbed females.

A second study indicated that the cortisol secreted in a female is
necessary for the expression of sexual behavior. A drug was used to
block the adrenal gland's secretion of cortisol. Three different groups
of 10 virgin female musk shrews were allowed to interact with males:
those receiving a large dose of the blocking drug, those receiving a
low dose of the blocking drug, and those receiving a placebo. Females
that received both high and low doses exhibited impaired sexual
behavior when compared to females receiving placebos. Females who
received the blocking drug were less likely to exhibit tail-wagging
behavior and were less likely to mate with males.

Finally, Schiml performed a study that replicated the drug treatment
experiment but added an additional twist: some females who received the
blocking drug were given an injection of cortisol. Again, the blocking
treatment, which eliminated a female's own cortisol, reduced sexual
behavior, but the cortisol injections restored some aspects of female
sexual behavior.

The studies offer a new perspective on the role of cortisol, Schiml
said.

"Not only is this hormone involved in the body's response to stress,
but in this case also appears to be important for reproductive
behavior," said Schiml. "More research needs to be done examining in
detail the possibility of a reproductive role for cortisol in other
species, particularly in other insectivores, and in primates."