What happens when human brain cells that surround and support neurons are implanted into the brains of newborn mice? Researchers reporting in the March 7th issue of the Cell Press journal Cell Stem Cell recently found that such mice had enhanced learning and memory when compared with normal mice that hadn't received the transplanted human cells. The findings indicate that these supportive cells, called glia, play an important role in human cognition.
As the human brain evolved, glia became much larger and more varied than those in the brains of rodents. Glia do not conduct electrical impulses like neurons do, but they can modulate neural activity, leading researchers to wonder how these evolutionary changes have benefited humans.
"To assess the species-specific contribution of glia to neural processing and plasticity and the specific advantages, if any, of human glia in cognition, we grafted human glial progenitor cells into the brains of newborn mice and then waited for the mice to grow to adulthood," explains Dr. Steve Goldman, who together with his collaborator Dr. Maiken Nedergaard directs the Center for Translational Neuromedicine at the University of Rochester Medical Center. "We then assessed both neurophysiological and behavioral measures of learning and memory, finding that the engrafted mice exhibited more rapid learning of both conditioned associations and goal-directed tasks." The neuronal connections within their brains also demonstrated characteristics of enhanced learning.
These findings indicate that human glia differ functionally from those of rodents and that they contribute significantly to learning. "As such, our findings suggest that the evolution of human cognition may reflect the development of human-specific glial form and function," says Dr. Goldman.
In a parallel study published in the journal in early February, Dr. Goldman and his team reported that they could efficiently generate glial progenitor cells from human skin cells reprogrammed into induced pluripotent cells. As a result, the researchers can now establish glial progenitor cells on a patient-specific basis from individuals with brain diseases, including a number of neuropsychiatric and neurological disorders that are relatively specific to humans. By implanting these cells into mice as they did in this most recent study, the investigators can assess the role of glial cells in these disorders, as well as test different treatment strategies that target abnormal glial function. They are currently carrying out these experiments with cells from patients with schizophrenia and Huntington's disease.
Cell Stem Cell, Han et al.: "Forebrain engraftment by human glial progenitor cells enhances synaptic plasticity and learning in adult mice."