Humans can make new neurons, but only from specialised stem cells. Crayfish, meanwhile, can convert blood to neurons that resupply their eyestalks and smell circuits. Although it’s a long way from crayfish to humans, the discovery may one day help us to regenerate our own brain cells.
Olfactory nerves are continuously exposed to damage and so naturally regenerate in many animals, from flies to humans, and crustaceans too. It makes sense that crayfish have a way to replenish these nerves. To do so, they utilise what amounts to a “nursery” for baby neurons, a little clump at the base of the brain called the niche.
In crayfish, blood cells are attracted to the niche. On any given day, there are a hundred or so cells in this area. Each cell will split into two daughter cells, precursors to full neurons, both of which migrate out of the niche. Those that are destined to be part of the olfactory system head to two clumps of nerves in the brain called clusters 9 and 10. It’s there that the final stage of producing new smell neurons is completed.
Without resupply, the niche’s stash of precursor neurons should gradually dry up, but does not happen, suggesting the existence of a secret source of them. Barbara Beltz of Wellesley College in Massachusetts knew from Petri dish experiments that crayfish blood cells – haemocytes – are attracted to the niche.