The brains and spinal cords of male mice contain more of the protective, fatty substance called myelin, which insulates nerve cells, than their female counterparts, new research reveals. The finding could help to explain why some neurological diseases, including multiple sclerosis, strike one sex more than another. Dr. Robert Skoff, Wayne State University School of Medicine, and colleagues found an unexpected difference when they compared the composition of white matter in the brains of male and female mice. Skoff says the findings help to explain why hormone therapy has yielded promising results against multiple sclerosis in experimental trials. He explains that further studies in mice will shed light on how these treatments work. "We can sort out exactly which hormones are regulating these changes," he says.