Brain Repair: Fish Can Grow Back Cells After Being Frozen

Crucian carp
Crucian carp were the kind of fish studied in a new paper that shows that fish can regenerate brain cells after they’ve been frozen for a week. The findings were published in the Journal of Experimental Biology on Tuesday. James Palinsad via Flickr

Being able to repair a damaged human brain would be nothing short of groundbreaking. While any and all clinical applications of regenerative medicine for stroke survivors or Parkinson's patients are decades away, scientists have been conducting studies in animals to find out how we might force the brain to grow new neurons. The latest addition to the menagerie of research animals that might offer guidance is frozen fish.

In the adult human brain, neurons don't just grow. They have to be coaxed. So far, a lot of the research has been done in mice and monkeys, including one study that transformed glia—often called the support cells of the brain—into neurons and another that involved transplanting immature brain cells.

But in a new paper published in the Journal of Experimental Biology on Tuesday, researchers from the University of Oslo and the University of the West of Scotland measured the number of cells that were dying and the number of cells being born after fish were frozen and rewarmed. Specifically, they focused on the animal's telencephalon, which is an area of a fish brain associated with learning and memory.

To test what actual impact the cells dying and being reborn might have, the scientists sent the fish through mazes. Though the fish made more wrong turns after they were frozen—after their cells died—they eventually got to the food. And they were just as good at relearning the maze as fish who had never done the maze before being frozen.

Any brain cells will die if they don't have oxygen. But while ours seem to die because we lack oxygen, fish brain cells seem to die because the oxygen eventually comes back.

Why exactly the cells die is still a mystery. There are a few possible options, including one pathway that is based on an enzyme called caspase 3. However, though they found that the levels of this enzyme were elevated, it didn't seem to be triggering the brain cells' death. In fact, researchers found that while brain cells were dying, new ones were also being born.

"This makes the crucian carp an interesting model from a biomedical perspective," the researchers concluded. Though it's not likely that human brains would be able to survive without oxygen for long without incurring some serious damage, they said, "it is feasible that studies on animals like the crucian carp can provide knowledge for how we can limit and repair the damage."