Sex-Based Differences Found in Brains of Mice; May Help Explain Incidence of Some Disorders
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SEX-BASED DIFFERENCES FOUND IN BRAINS OF MICE; MAY HELP EXPLAIN INCIDENCE OF SOME DISORDERS
WASHINGTON, DC January 27, 2006 – The brains of male and female mice are strikingly different, according to a new report. Researchers found that male mice had a greater number of the cells that form myelin in the brain and spinal cord—by more than a third—than females. This suggests that the sheath of myelin on nerve cells in male brains is thicker, according the report published in the February 1 issue ofThe Journal of Neuroscience.
“We found unexpected differences in the white matter of male and female brains, which may have implications for the study of diseases that affect one gender more than the other, like multiple sclerosis,” says co-author and team leader Robert Skoff, PhD, of Wayne State University School of Medicine.
Myelin, a major component of the brain’s white matter, coats nerve cells and helps conduct messages through the central nervous system. The dramatic difference was “much greater than we anticipated,” the team noted.
Clarifying how sex differences in the brain are generated may provide critical insight into why disorders such as multiple sclerosis, autism, and depression have a much greater incidence in one gender over the other, says Christine Wagner, PhD, at the University at Albany, who has also reported on sex-based brain differences in rats.
Skoff’s team also discovered that the lifespan of myelin-forming cells is much shorter in female mice. Female mice produced up to twice the number of cells as males, and twice as many of these cells died in female brains. The greater turnover of cells in female brains may mean that myelin itself generates—and degenerates—at a greater rate in females, says Skoff. This finding could have implications for research on multiple sclerosis, a debilitating autoimmune disease characterized by myelin degeneration. About 400,000 Americans have multiple sclerosis, with two of three cases occurring in women.
Skoff’s team also showed that the composition of the brain’s white matter is regulated by hormones. Just like the female mice, castrated male mice showed greater turnover of myelin-forming cells. “These results show that hormones made outside the central nervous system, presumably testosterone, help regulate the number of myelin-forming cells and the amount of central nervous system myelin,” says Skoff. Recent studies show testosterone may have a protective effect in multiple sclerosis.
“The fact that sex hormones affect these cells and influence turnover rates extends our notions of how and where sex hormones act in the brain well beyond where most people are aware,” says Bruce McEwen, PhD, an expert on sex hormones at Rockefeller University.
The Journal of Neuroscience is published by the Society for Neuroscience, an organization of more than 37,500 basic scientists and clinicians who study the brain and nervous system. Skoff can be reached at rskoff@med.wayne.edu.
