For the first time, human embryonic stem cells have been transformed into nerve cells that helped mice regain the ability to learn and remember.
A study at UW-Madison is the first to show that human stem cells can successfully implant themselves in the brain and then heal neurological deficits, says senior author Su-Chun Zhang, a professor of neuroscience and neurology.
Once inside the mouse brain, the implanted stem cells formed two common, vital types of neurons, which communicate with the chemicals GABA or acetylcholine. “These two neuron types are involved in many kinds of human behavior, emotions, learning, memory, addiction and many other psychiatric issues,” says Zhang.
The human embryonic stem cells were cultured in the lab, using chemicals that are known to promote development into nerve cells — a field that Zhang has helped pioneer for 15 years. The mice were a special strain that do not reject transplants from other species.
After the transplant, the mice scored significantly better on common tests of learning and memory in mice. For example, they were more adept in the water maze test, which challenged them to remember the location of a hidden platform in a pool.
The study began with deliberate damage to a part of the brain that is involved in learning and memory.
Three measures were critical to success, says Zhang: location, timing and purity. “Developing brain cells get their signals from the tissue that they reside in, and the location in the brain we chose directed these cells to form both GABA and cholinergic neurons.”
The initial destruction was in an area called the medial septum, which connects to the hippocampus by GABA and cholinergic neurons. “This circuitry is fundamental to our ability to learn and remember,” says Zhang.
The transplanted cells, however, were placed in the hippocampus — a vital memory center — at the other end of those memory circuits. After the transferred cells were implanted, in response to chemical directions from the brain, they started to specialize and connect to the appropriate cells in the hippocampus.
The process is akin to removing a section of telephone cable, Zhang says. If you can find the correct route, you could wire the replacement from either end.
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