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Source: The Independent
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Sex Hormones May Shape Brain
By JANE E. ALLEN AP Science Writer
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LOS ANGELES (AP) — Sex hormones can influence brain development in the young, memory
in the old and may explain why young men tend to develop neurological problems like autism and
dyslexia while older women suffer from depression and anxiety, scientists say.
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``We are recognizing with some surprise the extent to which the brain responds'' to sex steroids,
said Douglas Meinecke of the National Institute of Mental Health in Washington. ``These
hormones — testosterone, progesterone and estrogen — have profound effects on the brain and
the brain is profoundly responsive.''
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Meinecke discussed the role of sex hormones in development and aging Monday at the Society for
Neuroscience annual meeting.
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Researchers hope the hormones can be used to fend off the ravages of aging and disease. Already,
estrogen replacement therapy has been observed to protect older women against Alzheimer's
disease.
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Nancy Forger, a psychologist at the University of Massachusetts, said she's found that sex
hormones can prevent cell death.
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Men have more motor neurons in their spinal cords that govern muscles attached to the penis, she
found. The neurons are found both in men and women before birth; however, in the absence of
male hormones, the neurons degenerate in females.
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Ms. Forger is trying to learn how male hormones save these cells and understand the role of
proteins that regulate growth and survival of neurons.
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Margaret McCarthy, a physiologist at the University of Maryland School of Medicine, suggested
that early exposure to male hormones can create permanent brain changes.
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Testosterone levels in rats are as high in development as they're going to be in adulthood, she said.
Giving a female rat testosterone creates ``a male brain never to be switched back.''
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Similarly, if testosterone-producing organs are removed from the male rat, he ends up with a
``female brain,'' she said.
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Only male reproductive organs produce sex hormones during development, she said. Female sex
organs, which produce estrogen, are inactive until later.
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``As far as we know, it is also true for humans,'' Ms. McCarthy said.
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Asked about male and female brain differences, she noted that boys suffer from more neurological
disorders than girls. They're more likely to have schizophrenia, autism and dyslexia, while girls are
more likely to suffer neurological illnesses later in life such as major depression, anxiety disorders,
panic disorders or eating disorders.
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``This hormonal difference early in life may set up a situation that more easily goes awry and
explains why boys are more susceptible at an early age,'' she said.
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John Morrison, a neurobiology professor at Mount Sinai Medical School in New York, said his
studies of estrogen's effects on a brain region called the hippocampus may shed light on aging.
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He has that found the number of receptors on hippocampal cells fluctuates, depending on how
much estrogen is present.
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``The hippocampus mediates memory and loss of memory is one of the key events to aging,'' he
said.
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``We are seeing significant changes,'' said Richmond neuropsychologist Craig Kinsley, who
conducted the study with Randolph Macon psychologist Kelly Lambert. ``Pregnancy, a perfectly
natural biological experience for the female, appears to mark the brain for a lifetime.''
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Special brain cell structures called dendrites — necessary for communication between neurons —
doubled in pregnant and nursing lab mice, the research indicates. At the same time, the number of
the brain's glial cells, which act as scaffolding and communication conduits, also doubled.
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The pregnant mice were bolder, more curious and energetic. They learned mazes more quickly,
made fewer mistakes and retained their new knowledge longer. And the effects appeared to be
long-lasting, researchers found.
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``In a way, the brain of a late-pregnant female resembles a toy factory at Christmas time, receiving
orders and gearing up for the increased demands about to be placed on it,'' Kinsley said in today's
Los Angeles Times.
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The findings are inconsistent with research at the University of Southern California indicating that
pregnant women perform poorly on cognitive tests designed to test memory, perceptual speed and
learning ability. (656)