L O S   A N G E L E S,   Nov. 10 — 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.
     “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.”
     Meinecke discussed the role of sex hormones in development and aging today at the Society for Neuroscience annual meeting.
     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.
     Nancy Forger, a psychologist at the University of Massachusetts, said she’s found that sex hormones can prevent cell death.

Specific Neurons in Each Gender
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.
     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.
     Margaret McCarthy, a physiologist at the University of Maryland School of Medicine, suggested that early exposure to male hormones can create permanent brain changes.
     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.”
     Similarly, if testosterone-producing organs are removed from the male rat, he ends up with a “female brain,” she said.

Hormones Produced Different Times
Only male reproductive organs produce sex hormones during development, she said. Female sex organs, which produce estrogen, are inactive until later.
     “As far as we know, it is also true for humans,” Ms. McCarthy said.
     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.
     “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.
     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.
     He has that found the number of receptors on hippocampal cells fluctuates, depending on how much estrogen is present.
     “The hippocampus mediates memory and loss of memory is one of the key events to aging,” he said.

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