When it comes to recovering from insult, the adult human brain has
very little ability to compensate for nerve-cell loss. Biomedical
researchers and clinicians are therefore exploring the possibility of
using transplanted nerve cells to replace neurons that have been
irreparably damaged as a result of trauma or disease.
have suggested there is potential to remedy at least some of the
clinical symptoms resulting from acquired brain disease through the
transplantation of fetal nerve cells into damaged neuronal networks.
However, it is not clear whether transplanted intact neurons can be
sufficiently integrated to result in restored function of the lesioned
‘Embryonic nerve cells can functionally integrate into local neural networks when transplanted into damaged areas of the visual cortex of adult mice, revealed a new study.’
A new study shows that embryonic nerve cells can functionally
integrate into local neural networks when transplanted into damaged
areas of the visual cortex of adult mice.
Researchers based at LMU Munich, the Max Planck Institute
for Neurobiology in Martinsried and the Helmholtz Zentrum München have
demonstrated that, in mice, transplanted embryonic nerve cells can
indeed be incorporated into an existing network in such a way that they
correctly carry out the tasks performed by the damaged cells originally
found in that position.
Such work is of importance in the potential
treatment of all acquired brain disease including neurodegenerative
illnesses such as Alzheimer's or Parkinson's disease, as well as strokes
and trauma, given each disease state leads to the large-scale,
irreversible loss of nerve cells and the acquisition of a what is
usually a lifelong neurological deficit for the affected person.
In the study published in Nature
, researchers of the Ludwig
Maximilians University Munich, the Max Planck Institute of
Neurobiology, and the Helmholtz Zentrum München have specifically asked
whether transplanted embryonic nerve cells can functionally integrate
into the visual cortex of adult mice.
"This region of the brain is ideal
for such experiments," says Magdalena Götz, joint leader of the study
together with Mark Hübener. Hübener is a specialist in the structure and
function of the mouse visual cortex in Professor Tobias Bonhoeffer's
Department (Synapses - Circuits - Plasticity) at the MPI for
As Hübener explains, "We know so much about the functions
of the nerve cells in this region and the connections between them that
we can readily assess whether the implanted nerve cells actually perform
the tasks normally carried out by the network."
In their experiments,
the team transplanted embryonic nerve cells from the cerebral cortex
into lesioned areas of the visual cortex of adult mice. Over the course
of the following weeks and months, they monitored the behavior of the
implanted, immature neurons by means of two-photon microscopy to
ascertain whether they differentiated into so-called pyramidal cells, a
cell type normally found in the area of interest.
"The very fact that
the cells survived and continued to develop was very encouraging,"
Hübener remarks. "But things got really exciting when we took a closer
look at the electrical activity of the transplanted cells." In their
joint study, PhD student Susanne Falkner and Postdoc Sofia Grade were
able to show that the new cells formed the synaptic connections that
neurons in their position in the network would normally make, and that
they responded to visual stimuli.
The team then went on to characterize, for the first time, the
broader pattern of connections made by the transplanted neurons.
Astonishingly, they found that pyramidal cells derived from the
transplanted immature neurons formed functional connections with the
appropriate nerve cells all over the brain. In other words, they
received precisely the same inputs as their predecessors in the network.
In addition, they were able to process that information and pass it on
to the downstream neurons which had also differentiated in the correct
"These findings demonstrate that the implanted nerve cells have
integrated with high precision into a neuronal network into which, under
normal conditions, new nerve cells would never have been incorporated,"
explains Götz, whose work at the Helmholtz Zentrum and at LMU focuses
on finding ways to replace lost neurons in the central nervous system.
The new study reveals that immature neurons are capable of correctly
responding to differentiation signals in the adult mammalian brain and
can close functional gaps in an existing neural network.