72 DISCOVERMAGAZINE.COM
FROM TOP: NATIONAL INSTITUTE ON AGING/NATIONAL INSTITUTES OF HEALTH; PIXOLOGICSTUDIO/SCIENCE SOURCE; NATIONAL INSTITUTES OF HEALT HNEUROSCIENCE
Can We Grow New
Brain Cells or Not?
For the last two decades, neuroscientists
generally agreed that neurogenesis — the growth
of new neurons — happens in mature brains.
Now, two papers, one published in March in Nature
and the other in April in Cell Stem Cell, have reached
contradictory conclusions, forcing experts to rethink that
belief.
The team behind the March paper, led by Arturo Alvarez-Buylla,
a developmental neuroscientist at the University of California,
San Francisco, studied samples from 59 people. They focused
on sections of the hippocampus — one of the brain’s memory
centers and where previous studies have found evidence of
neurogenesis. Looking at samples from life stages ranging
from fetal to adulthood, they found that around the age of 1,
neuron growth drops sharply and peters out by the early teens.
The April paper, though, found the opposite. Lead
author Maura Boldrini, a neurobiologist at Columbia
University, and her team examined brain samples from
28 people age 14 to 79. Like Alvarez-Buylla’s team,
Boldrini’s group studied hippocampal samples, but they
looked at the entire area and found neurogenesis continues
through adulthood.
The discrepancy could jeopardize newer theories
about memory that might hinge on adult hippocampal
neurogenesis, an issue that would force experts to reevaluate
how we learn and retain information as we age. Still, both groups
agree more work is needed to ind out what’s really going on.Neurons Go Viral
It’s one of the first things you
learn in neuroscience: Neurons are
the brain’s messengers, ferrying
information via electrical impulses
and chemical signals. Now, we
know they have another way of
communicating.
Researchers announced in two
papers published in January in Cell
that neurons carrying a gene called
Arc — involved in learning and
memory — exchange information
like viruses do.
Cells with the Arc gene crank
out proteins that clump intocapsids. Inside is messenger RNA
(mRNA), which relays DNA’s
genetic blueprints to cells. The
capsids travel to neurons, where
Arc’s mRNA is then transferred;
the cells then also start releasing
Arc capsids. Viruses use the
same system to spread their
genes throughout an organism,
a similarity that surprised
researchers.
Next, they aim to figure out why
neurons use this method and if it
has any role in memory-related
diseases such as Alzheimer’s.HippocampusClumps of proteins form protective
shells called capsids (above) in both
viruses and, researchers learned in
January, neurons.Researchers thought
that even mature
brains continue to
grow new neurons
(left). A study of
neuronal activity in
the hippocampus
(below) raises
questions about that
assumption.