[Indications of continuous hair cell regeneration in a song bird with genetically-induced cochlear hearing loss].

In recent years evidence has accumulated that birds in contrast to mammals have a great capacity to replace lost hair cells after cochlear trauma. Despite this capacity for cochlear repair, a hereditary hearing deficit for frequencies above 2 kHz has been described in a peculiar strain of canaries (Belgian Water-slagers). Because previous thresholds were determined by psychophysical methods, the origin of the hearing loss could not be identified. In order to determine if this loss originated in the cochlea and if these birds lack the potential for hair cell regeneration, we carried out physiological and morphological analyses of the hearing organ. Our results showed that most of the hair cells displayed severe pathologies. Also, found were small, microvilli-covered cells that resembled forms described during normal hair cell development. Small microvilli-covered cells with small sterovillar bundles have been described as regenerating hair cells in other birds after severe cochlear insults. These observations indicate that adult Belgian Waterslager canaries continuously produce new cochlear hair cells. They do not, however, succeed in reforming a normal basilar papilla. We believe that these birds are a promising model for future studies of cochlear hair cell repair mechanisms.