Some axons fair better than others - discuss

Sometimes you come across a poster that is really visually impacting and PR Williams [Presentation #550.26] produced one of these this morning. When the cord is injured by an impact some axons that cross the injury site are seen to degenerate over time. Williams wanted to understand why one axon might befall this fate whilst a near neighbour doesn’t even after apparently experiencing a similar trauma - what causes this?

Using an elegant 2-photon microscopy technique he was able to look at what happens early during the first few hours after injury at the resolution of individual axons. He saw spontaneous and previously unappreciated dynamics of damage. Some axons could be seen to swell or “bleb” up before degenerating entirely. Others would bleb but return to normal. When he used a dye to measure calcium concentration he saw that blebbing was most often accompanied by high calcium concentrations in the axon; he was able to demonstrate the cause of this high calcium concentration was most likely due to the axon having holes in the membrane as a result of the trauma allowing calcium to flood in. This was not always the case. Sometimes axons would bleb and return to normal but this was most frequently found in those axons that had maintained their calcium levels near normal.

Overall it was a stunning piece of fundamental research and gave some insight as to importance of maintaining tight control over calcium concentrations in cells (calcium homeostasis) and perhaps even some potential for this technique to screening compounds that shift the balance in these dynamics in the favour of axonal survival after injury.