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Can nerve cells regenerate?

Deep inside the inner ear are tiny structures known as hair cells. The exposed part of these sensory cells are hair-like offshoots called cilia, which are surrounded by liquid within the balance organs of the inner ear and send a signal to the brain when they are swished about by the head changing positions. Without the cilia, a person's sense of balance is compromised.

Doctors long have known that streptomycin can destroy the hair cells and, for this reason, avoid prescribing the antibiotic when something less potent will work. Since streptomycin often is the most effective treatment of certain bacterial infections such as tuberculosis, seriously ill patients may have to accept permanent inner-ear damage as the lesser of two undesirable outcomes.

The destruction of hair cells always has been regarded as permanent because these sensory cells share many similarities with brain neurons, which are known not to regenerate. However, experiments suggest that the sensory cells in the ear's balance organs--known as the vestibular apparatus--may be able to regenerate themselves if conditions are right. Pedro Weisleder, University of Texas at Austin Department of Zoology, points out that promising new research could lead to drugs or treatment processes that would stimulate the vestibular apparatus to regenerate its sensory cells. This essentially could be a cure for certain balance difficulties or types of hearing loss and could lead to a better general understanding of cell regeneration in the human body.

"Up until four years ago, it was accepted that when these cells were destroyed, they could not be replaced. The rule is that the more specialized the organism is, by tendency, the more capacity for regeneration is lost. But [in 1988], a Danish researcher injected some parrots with a cell proliferation marker, and waited for a couple of weeks and discovered that the parrots had incorporated some of these markers in the cell nuclei."

The results of the study indicated that the parrots were regenerating the cells in their vestibular apparatus. Weisleder is trying to find out the conditions whereby such regeneration takes place after the cells have been destroyed by streptomycin, because the balance organs of all vertebrates are so similar that those conditions might be reproducible in humans. In observing regeneration of the sensory cells in chickens and fish, he has found "that indeed there is a low level of ongoing regeneration, as described by the Danish research, and also that the vestibular system has the ability to recover from a severe toxic insult."

Moreover, Weisleder has discovered that the cells deeper within the vestibular epithelium--the surface of the balance organ--tend to migrate to the top after the original sensory cells have been destroyed. "There is good evidence that the supporting cells are progenitors of newly generated cells. These are not sensory cells, yet they have this characteristic--this ability to lead to new sensory cells somehow." If the chemical or electrochemical means by which these cells are stimulated to migrate can be found, then similar cells in the human vestibular apparatus also might be stimulated to regenerate. "Given that the vestibular systems of birds and humans have virtually no differences, we strongly believe that we should be able to find clues to trigger the replication of sensory cells in humans."
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Publication:USA Today (Magazine)
Date:Feb 1, 1993
Words:539
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