It turns out that a type of cell
found in the human central nervous system that had previously been thought
little more than a sort of "housekeeper" cell is actually really
important for cognitive function. How did we learn this? A team of researchers
used them to create mouse-human hybrids.
The cells are a type of glial cell
-- neuronal support cells -- called astrocytes. These are star-shaped cells
found in the spinal cord and brain -- and the most abundant cells found in the
brain. They provide biochemical support for the cells that make up the
blood-brain barrier, nutrients to the nervous tissue, regulation for the
transmission of electrical impulses in the brain, even structural support.
They're busy little guys; and, in humans,
they're larger, more abundant, more diverse and more complex than in other
species.
And, apparently, their role goes
far beyond support.
"This study indicates that glias
are not only essential to neural transmission, but it also suggests that the
development of human cognition may reflect the evolution of human-specific
glial form and function," University of Rochester Medical Center
neurologist Steven Goldman said of a study published last year.
"We believe that this is the
first demonstration that human glia have unique functional advantages,"
Goldman said. "This finding also provides us with a fundamentally new
model to investigate a range of diseases in which these cells may play a
role."
For the study, the team implanted
baby mice with mature astrocytes. These cells took over, to the point where
almost all the glial cells in the mouse's brain were human in origin -- and they
had a measurable effect. Firstly, brain signals spread farther and more quickly
than what's normally seen in mice -- closer to human brain activity. Secondly,
long-term potentiation (LTP) -- how long neurons are affected by electrical
stimulation, important for learning and memory -- occurred more rapidly and was
sustained longer, suggesting improved learning capability.
Mature cells, however, have
limitations. So for a new study, the team implanted
into baby mice astrocyte progenitor cells extracted from donated human
foetuses. These cells, unlike the mature astrocytes, divide and multiply --
completely taking over the host brain, limited only by its physical dimensions.
Each mouse received 300,000 human cells; within a year, that number had grown
to 12 million.
The result was a group of Jonathan Frisbys that
were much smarter than their buddies. In one test, mice were trained to
recognise a sound that was a precursor to a mild electric shock. The hybridised
mice froze in place for four times as long as the control group -- suggesting
that their memory was four times as long.
"These were whopping
effects," Goldman told New Scientist.
"We can say they were statistically and significantly smarter than control
mice."
In another experiment, performed in
parallel, the team injected immature human glial cells into baby mice poor at
producing nerve-insulating myelin. The cells developed into oligodendrocytes --
brain cells that make myelin -- which suggested that the glial cells identified
and compensated for the defect. This, Goldman said, could be useful in treating
diseases such as multiple sclerosis, and he has already applied for a trial of
the treatment on human patients.
The next step is attempting the
experiment on rats, which are smarter than mice. This is already under way --
but NIMH is
an unlikely scenario.
"This does not provide the
animals with additional capabilities that could in any way be ascribed or
perceived as specifically human," he says. "Rather, the human cells
are simply improving the efficiency of the mouse's own neural networks. It's
still a mouse."
Source: Cnet
previous article
Newer Post
No comments
Post a Comment