Oct. 24, 2000 Scientists have known for years that birds' ears do something human ears cannot: when hair cells in the avian ear are destroyed, the bird goes deaf only temporarily. Now, research at the University of Washington is showing why.
In a paper published in the Oct. 24 issue of the Proceedings of the National Academy of Sciences, Dr. Edwin W. Rubel, the Bloedel professor of hearing science, and Research Assistant Professor Jennifer Stone explain what is known about how the process works in birds. Once that mechanism is completely traced, the next step will be studies of how that knowledge might be transferred to mammals, including humans.
"What we detail in this paper is the sequence of events the cells go through in order to make new hair cells. In most cases, this involves a support cell that sits near the base of a hair cell," Rubel said in a recent interview at the UW Virginia Bloedel Hearing Research Center and Department of Otolaryngology. "When the nearby avian hair cell dies, this support cell is stimulated by some external process to develop into a new hair cell, just like human skin cells."
The new hair cell then somehow gets linked to the brain and the nervous system and develops all the same biochemical characteristics the original hair cell had. This doesn't happen in mammals. Stone said the discovery of this capability in birds at the UW 12 years ago contradicted everything then known about neurobiology and hearing. When hair cells in humans and other warm-blooded vertebrates are killed, the nearby cells do not start dividing as they did before birth.
Rubel said the key is understanding how the mechanism for the destruction of a hair cell could be stopped. If researchers can establish the cascade of steps involved in the cellular death, they would be able to interrupt the process, and prevent the development of some forms of deafness before they start.
Stone and Rubel agreed their research would not lead directly to a cure for human deafness in the near future.
"It's really important to recognize the increased complexity of the mammalian auditory organ, compared to the birds'," Stone said. "Simply making a hair cell, while it seems like an automatic process in a chicken, is a much larger task in a human, because of the complexity of the mammalian auditory system."
The research has opened new paths for significant progress in hearing protection and conservation directly as a result of the avian hair cell research. Rubel and Stone said they hope their work attracts more investigators to the field, in search of more solutions to hearing loss.
"When people ask me if we have cured deafness, I say what we've done is establish the question. We established the possibility that other approaches could be used besides hearing aids and cochlear implants," Rubel said. "These are areas that researchers weren't even considering before. That's how one establishes a new area of research and draws more researchers into it, multiplying the progress dramatically."
Rubel first reported the phenomenon of avian auditory hair cell regeneration in a Science article 12 years ago.
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