The Laboratory of Comparative Psychoacoustics

Why do we study hair cell regeneration?

Loss or damage of sensory cells in the inner ear, called hair cells, results in hearing impairment. These cells can be damaged by overexposure to intense sounds (e.g., loud music at a rock concert) and by ototoxic drugs (e.g., the antibiotic kanamycin). In mammals, including humans, once these hair cells are lost, they are not replaced - which explains why hearing loss in humans is permanent. Birds, however, have the remarkable ability to regenerate and replace the hair cells of the inner ear following damage or loss.  Because the bird inner ear has the ability to repair itself, birds have become an important model for studying hair cell regeneration. Our laboratory is working with Brenda Ryals (James Madison University), Joelle Presson (University of Maryland), and Otto Gleich (University of Regensburg) to develop this bird model in order to better understand the process of hair cell regeneration and its functional consequences in the bird ear.

 How long does hair cell regeneration take?

Click on image to see larger view Dooling, Ryals & Manabe 1997

Scanning electron microscopic pictures of bird inner ears at three different time periods are shown to the left. After 8 days of injections (200 mg/kg/day)  kanamycin (0-day post injection) almost all hair cells are missing. After an additional two weeks (14-day post injection), some new hair cells are beginning to appear. After 28 days (28-day post injection), the number of hair cells in the regenerated bird ear has nearly returned to normal levels.

How is hearing affected by hair cell loss?

Redrawn from Dooling & Dent 2001

Birds had their hearing tested behaviorally before, during, and after they were injected with high doses of kanamycin. A few days after injections began, birds experienced a hearing loss of almost 70 dB (above). Hearing thresholds gradually recovered for about a month (corresponding to the time course of hair cell regeneration) but birds still suffered a permanent hearing loss of about 23 dB. In other words, hearing is affected when hair cells are lost and hearing recovers considerably when hair cells are regenerated.

If birds regenerate hair cells, can there be a deaf bird?

A number of years ago we discovered a strain of canary, the Belgian Waterslager canary, that has missing and damaged hair cells evident shortly after hatching. Not surprisingly, these birds also have a hearing loss. Scanning electron microscopic pictures of the ear of a normal canary and a Belgian Waterslager canary are shown below (left). Audiograms for normal and Belgian Waterslager canaries are also shown below (right). Notice that at high frequencies, Belgian Waterslager canaries have a profound hearing loss of almost 40-50 dB (hatched area below). Our research has shown that this is due to missing and damaged hair cells.

Redrawn from Dooling, Ryals, Gleich & Presson 1997

Redrawn from Dooling, Ryals, Gleich & Presson 1997