Human Stem Cells Restore Memory and Learning in Mice Brains

There's a new breakthrough when it comes to restoring memory--at least in mice. Researchers have used human embryonic stem cells in the small mammals which allowed them to regain the ability to learn and remember.

The mice themselves were specially bred so that they wouldn't reject transplants from other species. In order to simulate memory issues in the mice, the researchers intentionally damaged the part of the brain that is involved in both learning and memory--an area called the medial septum, which connects to the hippocampus by GABA and cholinergic neurons. They then cultured the embryonic stem cells in the lab, using chemicals that are known to promote development in nerve cells.

The next step was actually transplanting the cells. They didn't place these cells in the medial septum, though. Instead, the researchers placed the cells in the hippocampus, a vital memory center, located at the other end of the memory circuits. After this transplant, the cells slowly began to specialize and connect to the appropriate cells in the hippocampus in response to chemical directions from the brain.

This specialization didn't come easily. The researchers had to ensure that the transplanted cells became neural cells--a critical part of the experiment.

"That means you are able to predict what the progeny will be, and for any future use in therapy, you reduce the chance of injecting stem cells that could form tumors," said Su-Chun Zhang, the senior author, in a press release. "In many other transplant experiments, injecting early progenitor cells resulted in masses of cells--tumors. This didn't happen in our case because the transplanted cells are pure and committed to a particular fate so that they do not generate anything else."

In order to actually accomplish this cell direction, the researchers chemically directed the embryonic stem cells to begin differentiation into neural cells. They then injected these intermediate cells to prevent unwanted cell formation.

The most important step was yet to come, though. The researchers had to test to make sure that the implantation was actually effective. The mice were assessed with several common tests used to judge memory and and memory in the rodents. In the end, the researchers found that the mice scored significantly better than they had before the transplant.

The findings are a huge step forward when it comes to brain repair. Cell replacement with stem cells could potentially help people with memory-based conditions such as Alzheimer's disease.

"Cholinergic neurons are involved in Alzheimer's and Down syndrome, but GABA neurons are involved in many disorders, including schizophrenia, epilepsy, depression and addiction," said Zhang in a press release.

Don't get too excited, though. Stem-cell therapy is unlikely to be a cure-all. Psychiatric disorders are often complicated, and researchers aren't always sure which part of the brain has gone "wrong." That said, the research could be a vital step when it comes to better understanding what can be done to help those with memory disorders.

The findings are published in the journal Nature Biotechnology.