Deaf chickens hear again.

Deaf chickens hear again

Scientists once presumed that when hearing was lost due to disease, loud noise, certain antibiotics or aging processes, the damage was permanent. This was because they believed the inner ear's hair cells, which convert sound into electrical activity, were produced in mammals and birds only during the first two-thirds of embryonic development.

In 1981, however, Jeffrey T. Corwin of the University of Hawaii found that certain fish and amphibians could produce hair cells throughout life. Now Corwin and Douglas A. Cotanche of Boston University report the regeneration of these cells in young chickens.

After exposing chicks to a loud noise for 48 hours, they administered radioactive thymidine as a tracer that is incorporated into replicating DNA, permitting detection of dividing cells. Shortly after exposing the chicks to the noise, Corwin and Cotanche examined tissue from the chicks' ears and found that hair cells were missing. Over the next 10 days, the damaged area gradually returned to normal, and the thymidine tracer turned up in the damaged area in the nuclei of both hair cells and supporting cells but not in undamaged regions of the chicks' cochleas -- the affected inner-ear structure -- or in chicks that received the tracer but were not subjected to loud noise.

At least in birds, some cochlear cells must retain the capacity to proliferate, Corwin and Cotanche conclude in the June 24 SCIENCE. They suspect the new hair cells originated from divisions of another cell type, then differentiated as hair cells.

Together with a report of hair-cell regeneration in adult quail that appears in the same issue, the discovery of replacement cells originating in progenitor cells carries implications for other species. "The possibility of self-repair," Corwin and Cotanche says, "should not be ruled out in mammalian ears."