The adult mouse utricle as an in vitro preparation for studies of ototoxic-drug-induced sensory hair cell death

Abstract

Sensory hair cells of the inner ear are susceptible to death from a variety of stresses including aging, noise trauma, genetic disorders, and exposure to certain therapeutic drugs. Ototoxic drugs include the aminoglycoside antibiotics and the antineoplastic agent cisplatin. This is a short technical report describing the dissection and culture of the adult mouse utricle. This in vitro preparation allows for detailed studies of ototoxic-drug-induced hair cell death in an adult mammalian system. In addition, this preparation allows for examination of the effects of specific gene products through the use of transgenic and knockout mouse models.

Figure 1. Opening the auditory bulla

The first step in the fine dissection is to break open the auditory bulla using two pairs of forceps. One fork of each forceps is placed all the way down the bulla from the external auditory canal to the bony apex. The bulla is broken open by pulling the two pairs of forceps away from one another. The bony cochlea is much harder than the bulla, so this manipulation will break the bulla without damaging the bony cochlea beneath.

Figure 2. Views of the bony cochlea

After the bulla is removed, the bony cochlea is visible. A: The lateral surface (bulla side) of the cochlea, with both the oval and round windows visible. B: the medial (brain side) of the cochlea, with the VIIIth nerve root visible. RW, round window; PSC, posterior semicircular canal; CN VIII, root of the VIIIth cranial nerve.

Figure 3. Opening the apex

The apical portion of the bony cochlea is removed using a scalpel. The scalpel blade should be lowered onto the cochlea just apical of the VIIIth nerve root. Cut the apex by pushing straight down onto the bone without sawing. PSC, posterior semicircular canal; CN VIII, root of the VIIIth cranial nerve.

Figure 4. Base of the cochlea

After most of the soft tissue of the cochlea is removed, only the basal “hook” region remains. The Osseous Spiral Lamina will be lifted up from beneath using a fine probe. OSL, Osseous Spiral Lamina.

Figure 5. Utricle and stapes footplate

With the Osseous Spiral Lamina removed, the utricle is visible immediately adjacent to the stapes footplate. The utricle is removed gently using fine forceps.