Scientists have implanted human embryonic stem cells into mouse brains and restored both memory and learning function.
The use and research of embryonic stem cells is controversial, perhaps even more so now that scientists have been able to both harvest stem cells from umbilical cords and adults, and synthesise them in laboratories. The fact remains, though, that the pluripotency of embryonic stem cells gives them the most potential when it comes to medical applications.
Case in point, scientists at the University of Wisconsin-Madison, led by senior author and professor of neuroscience and neurology Su-Chun Zhang and postdoctoral author Yan Liu, have successfully implanted human stem cells into the brains of mice, restoring the mice's abilities to remember and learn.
The study began with inflicting deliberate damage to the part of the mouse's brain that controls learning and memory — the medial septum, which connects to the hippocampus by gamma-aminobutyric acid (GABA) and cholinergic neurons. The stem cells, which were cultured in a medium used to promote nerve cell development, were then implanted in the brains of the mice — nude mice, which, due to an inhibited immune system, do not reject grafts or implants from other species.
This is where it gets interesting: the stem cells then evolved to form GABA receptors — two common but vital types of neurons that communicate with GABA. "These two neuron types are involved in many kinds of human behaviour; emotions, learning, memory, addiction and many other psychiatric issues," said Zhang.
The mice were then given a series of standard tests that measure learning and memory — such as maze puzzles — and scored significantly better than they had before the implantation.
Although it is hoped that stem cell research will be able to provide cures for many ills, brain repair is like the Holy Grail, according to Zhang. "Cholinergic neurons are involved in Alzheimer's and Down syndrome, but GABA neurons are involved in many additional disorders, including schizophrenia, epilepsy, depression and addiction," he said.
Just last week, another group of scientists from the University of Texas Health Science Center made a breakthrough in memory recovery when they successfully managed to reverse memory loss in Californian sea slugs.
You can read the full study, "Medial ganglionic eminence-like cells derived from human embryonic stem cells correct learning and memory deficits", on Nature.com.