“…Retinoic acid is essential for normal inner ear development (Kelley et al, 1993;Raz & Kelley, 1999;Romand, 2003;Romand et al, 2006) and imbalances can cause sensorineural hearing loss and vestibular deficits in man (Lohle, 1982;Biesalski, 1984;Raz & Kelley, 1997). It has been tested as a potential agent for protection (Ahn et al, 2005) and regeneration of mammalian hair cells (Lefebvre et al, 1993;Kopke et al, 2001) although the results regarding regeneration have been controversial (Chardin & Romand, 1995;Romand & Chardin, 1999).…”