Brains of male mice boast extra nerve insulation

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.

Robert Skoff of the Wayne State University School of Medicine in Detroit, US, and colleagues found an unexpected difference when they compared the composition of white matter in the brains of male and female mice. White matter consists of nerve cells coated with insulating myelin, which helps the cells to relay signals efficiently.Skoff’s team determined the density of oligodendrocytes – cells which produce myelin – in the male and female mouse central nervous system by testing for their molecular signature. They found that these specialised cells are roughly one-third more dense within the brains and spinal cords of male rodents. They add that the differences are present in young and old mice, and independent of strain and species.On top of that, oligodendrocytes appear to live longer in male mice. According to Skoff, the turnover of oligodendrocytes is twice as great in female mice.The reasons male brains contain more oligodendrocytes – which in turn means more myelin – are unclear. Skoff speculates that selective pressures may have caused males to evolve more myelin, which may mean better nerve-signal transmission in parts of the brain and faster reaction times.Testosterone influenceThe new study also reveals how hormones can regulate the composition of the brain’s white matter. Castrated male mice showed a greater turnover of myelin-forming cells than their normal male counterparts. This suggests that testosterone can influence the amount of white matter produced in the brain.Skoff says the findings from their study could shed light on why some human neurological disorders commonly affect one sex over the other. One such illness is multiple sclerosis, which affects about twice as many women as men. With MS, an apparent autoimmune reaction against myelin leads to disrupted nerve pathways and loss of coordination. 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.(Source: The Journal of Neuroscience (DOI: 10.1523/jneurosci.2219-05.2006): New Scientist: Roxanne Khamsi: February 2006.)