Glial cells as an important proliferation matrix in neural communication

Neil M. Fournier neil.fournier at sympatico.ca
Sun Aug 31 16:45:47 EST 2003


Most studies focus extensively upon neuronal-based activity as the necessary
correlate for the emergence of behavior.  As a result from this, the
specific involvement of glial cells in regards to a potential role in
neuronal transmission as been relatively ignored.  Although glial cells have
been arbitrarily labeled as the major supporting matrix within the brain,
many studies have shown a dynamic relationship with respect to glial cells
modulating various important processes that affect global brain
transmission.  Glial behavior during epileptic seizures is a primary example
of this.  For those not familiar, seizures are accompanied by long-lasting
depolarization in glial cells (specifically astrocytes).  Furthermore around
many epileptic "foci", the normal levels of extracellular potassium is
considerably elevated (9 to 12 mEq/l from 3 mEq/l... a factor of about 3 to
4) leading to a potential impairment in the normal homeostatic
"potassium-detection" and gating processes that these astroglial cells
normally posses.  As a result, the elevation in extracellular potassium can
lead to driving the surround neuronal membrane toward firing threshold.

Although most studies have focused the involvement of glial cells in
neuropathological conditions such as epilepsy, there is extensive evidence
of glial involvement in the generation of field potentials and an
amplification role in extracellular field potentials within neuronal
aggregates.  Moreover, oligodendroglia (whose processes wrap around neurons
to provide the insulation, i.e. myelin, that speeds up neuronal
transmission) have been shown to exhibit pulsatile movements with which they
may play a steady state controller of neuronal action.  These rhythmatic
oscillations have been suggested to be important in producing an endogenous
rhythm (infra slow potentials) by which many cognitive processes can be
affected.  For example, these infraslow potentials (around 1000-20000msec in
length) have been found to occur 2 or more hours following a learning
episode. The infraslow rhythm fluctuates with dynamic changes in glial
membrane processes suggesting that although neuronal aspects are important,
an origin of this rhythm is due to glial-like processes.  It should also be
noted that whether a coincidence the shape and temporal characteristics of
this glial-driven cycle also resembles a key endogenous rhythm exhibited by
the Sun, which is responsible for radiation and micropulsation propagation.
Considering the literature on the effects of micropulsation and geomagnetic
activity upon behavior a potential involvement of glial cells may be
possible.

Glial cell processes are interconnected  in a vast syncitium composed
primarily of gap junctions.  Thus dynamic changes among only a few glial
cells can propagate extremely fast to affect the entire glial matrix.  It is
important to consider that although most recent studies have implemented
neuronal-based communication as the major constituent for the emergence of
such complex processes as consciousness, the necessary degrees of freedom
and propagation capacity needed to proliferate such a feature within brain
space is considerably short-coming with respect to neuronal-based
transmission.  Synchronization, in the 40-80 Hz range, has been considered a
potential solution to such problems, however, the precise mechanism involved
with this generation is currently not completely understood.  The vast
interconnections between neuronal and glial cells has suggested that each
can modulate each other in terms of signaling.

Here I suggest that such complex processes as consciousness may better be
understood if further investigation was placed upon glial cell processes.
Perturbations can quickly propagate throughout the entire syncitium of glial
cells that would have the capacity to quickly influence neuronal-based
transmission.  Consciousness and thought require a system whose degrees of
freedom are so vast that any dynamic change in the physical network
mediating such processes must take place on a very small time-scale.  For
this, I suggest glial cell processes as an important constituent.

I'm looking forward to your response and suggestions.










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