| Studies
at the UI have identified a specific brain pathway in which neurons
activate in times of low oxygen (hypoxia) and trigger increased breathing.
The findings of the research—based on studies of
electrical currents in rat brains—have led the scientists to postulate
that many newborns don’t have enough neurons to respond sufficiently to
hypoxia. Such a deficit in response capability, they say, possibly is a
factor in sudden infant death syndrome, which each year claims the lives
of 3,000 babies under a year old in the United States.
"It is not fully understood why newborns,
whether they are humans, rats, cats, dogs or whatever, do not have a
maintained response to low oxygen," said Tony G. Waldrop, professor
of Molecular & Integrative Physiology. "My lab has shown that
neurons in some of the brain areas involved in the control of breathing
are inherently sensitive to low oxygen. This sensitivity increases over
developmental time. Newborn animals have far fewer neurons that respond to
hypoxia than do adults.
"It may be that babies prone to SIDS do not
have the same level of ability of typical newborns," he said.
"Maturation of these cells may be at lower levels in these
babies."
In a study published in the November Journal of
Neurophysiology, Waldrop and his colleagues describe the activity of
sodium currents—electrical streams of ions or group of atoms—involved
in neuron communication in the caudal hypothalamus and the ventrolateral
medulla of rat brains.
In times of hypoxia in adult brains, they found,
there is "a significant increase in the persistent sodium
current," which is most likely the primary mechanism for the
activation of neurons that help to regulate cardiorespiratory activity.
Such a reaction, however, was not seen in rats less than 12 days old,
suggesting that the brain pathway in neonatal rats may not be sufficiently
developed to respond.
The research was part of the doctoral dissertation
of Eric M. Horn, now a neurosurgery resident at the Barrow Neurological
Institute in Phoenix. Waldrop is the UI vice chancellor for research and a
professor in the College of Medicine. Their research was funded by grants
from the National Heart, Lung, and Blood Institute and the American Heart
Association.
In the October issue of Neuroscience, Waldrop
and Horn reported that in live, conscious rats, the neurons activate and
generate a protein called Fos when exposed to a period of hypoxia.
"This work has clearly shown that sodium ions mediate the neuronal
response to low oxygen."
Story by Jim Barlow, News Bureau Staff
Writer, University of Illinois. Appeared in Inside Illinois, November 16,
2000.
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