Dr. Tatsuo Matsunaga of the National Tokyo Medical Center used a rat model of drug-induced hearing loss that specifically destroys cochlear fibrocytes and leads to acute hearing loss.

Matsunaga injected stem cells into the inner ear of the injured rats, and about half survived. These stem cells divided in the new environment and expressed several proteins necessary for hearing, suggesting tissue-specific differentiation. The transplanted cells that migrated to the damaged area of the inner ear displayed a shape similar to that of cochlear fibrocytes.

Stem cell migration into the damaged area of the inner ear improved hearing of high-frequency sound -- 40 kHz -- by 23 percent compared with natural recovery in untreated animals, according to the study published in The American Journal of Pathology.