The paintfill method as a tool for analyzing the three-dimensional structure of the inner ear

The mammalian inner ear is a complex epithelial tube designed to detect sound, angular and linear acceleration, as well as gravity. The major parts of the ear include three orthogonal semicircular canals, a central vestibule, a coiled cochlea, and an endolymphatic duct and sac allowing fluid balance with the cerebrospinal system. Located throughout this tubular system are six separate sensory areas composed of hair cells and support cells that are essential for the transduction of hearing and balance information. Deafness and vestibular dysfunction are extremely common sensory disorders in the human population, with one in every 1000 children born profoundly hearing impaired and many progressive forms diagnosed later in life. Approximately 20–30% of patients with congenital sensorineural hearing loss demonstrate radiographic abnormalities of the inner ear, indicating that malformations of the inner ear make a significant contribution to the high frequency of deafness and balance disorders. Unfortunately, the very complexity that makes the inner ear such an exquisite structure has also made it an extremely difficult organ to tackle for researchers. Here, I describe a histological method involving paintfilling of the inner ear that provides easy analysis of the three-dimensional structure of this complex organ. The paintfill method can be used to quickly assess inner ear morphology and can help identify defects that may cause or contribute to deafness and/or vestibular dysfunction.