RELEASE ON RECEIPT




MUSK SHREW LOVE:  Research Suggests Stress-Induced Hormone May
Facilitate Sex

        CHARLOTTESVILLE, Va., Nov. 13 Ñ Biologists at the
University of Virginia have found that a hormone normally associated
with periods of high stress may play a key role in the sexual behavior
of certain mammals.
        Elevations in 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 U.Va.'s Department of Biology.
Schiml is the lead author in studies of musk shrews and cortisol that
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 and associate professor Emilie Rissman of U.Va.'s
Department of Biology were intrigued by anecdotal evidence in the scientific
literature that suggested a positive, not negative, relationship
between elevated cortisol levels and sex may exist at certain times in
humans and primates.  In many primate species, 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
daily surges in cortisol secretion.
        In humans, treatment with cortisol can result in increased
sexual excitement and arousal and a reduction in tiredness. In the
case of 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, the
researchers found.
        To test the idea that cortisol was involved with musk shrew
reproduction, Schiml examined hormones and behavior of females in a
variety of social situations. When female musk shrews are initially
introduced to males, they are very aggressive, but will still approach
and investigate males. Following a brief period of this intense
aggression, 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. The drug
metyrapone 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 an injection of a high dose of
metyrapone, those receiving an injection of a low dose of metyrapone,
and those receiving a placebo injection. Females that received both
high and low doses of metyrapone exhibited impaired sexual behavior
when compared to females receiving blank injections. 
        Finally, Schiml performed a study that replicated the drug
treatment experiment but added an additional twist: some females who
received metyrapone were given an injection of cortisol to replace
their naturally secreted cortisol. Again, metyrapone treatment, which
eliminated a female's own cortisol, reduced sexual behavior, but the cortisol
injections restored some aspects of female sexual behavior.
         Future research at the University of Virginia will include
studies looking at the interaction of cortisol with neurons in the brain and
studies that examine the role of other hormones closely related to
cortisol, Schiml said.
       The results of these three studies offer a new perspective on
the role of cortisol, researchers 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. Also, a
closer examination of adrenocortical function and reproduction in
humans could be a potentially exciting research direction."

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                                                    November 12, 1997
For more information, call Patricia Schiml at (804) 982-4742 or
contact her via e-mail at pas4n@faraday.clas.virginia.edu; or contact
Dan Heuchert at the University News Office at (804) 924-7676 or via
e-mail at dnh6n@virginia.edu. Television reporters are asked to call
the TV News Office at (804) 924-7550.