August 10, 2008

Bruce Trapp and his colleagues have published an interesting pathology study of MS brain tissue. (I get very excited every time an MS brain tissue study comes out -- I wish there were more!) In this study, the research team investigated autopsy samples of subcortical lesions (white matter MS lesions located just within the cerebral cortex). Subcortical white matter contains a type of neurons called interneurons -- so-called because they connect to other neurons -- and while they are numerous, they are not as densely packed as neurons in the gray matter are, which makes them easier to study. The scientists analyzed active and chronic subcortical lesions from nine MS subjects, looking for the presence of interneurons.

In the seven active lesions studied, there were no or very few neurons left. The same was true in 44 of the 59 chronic lesions studied. However, the other 15 chronic lesions had an increased number of neurons compared to the neighboring non-lesion areas. Synapses could be seen extending from these neurons, which is appropriate for subcortical white matter neurons. There was also a population of immature neural precursor cells in these lesions. An increased number of precursor cells was found in the subventricular zone bordering demyelinated areas, implying that this region may have been the source of the newly generated interneurons. Finally, these 15 chronic lesions also contained a certain type of activated microglia that was not found in the other lesions.

The findings from this study indicate that unmyelinated neurons like interneurons are destroyed in MS, but in some cases they can be replaced, most likely by migrating precursor cells. Why this happens in some lesions but not others is not known, but perhaps other cells like microglia present in the lesions play a role in this neurogenesis. At any rate, signs of regeneration are encouraging, and hopefully these results can eventually lead to strategies to encourage rebuilding of damaged tissue.