Vestibular primary afferent activity in an in vitro preparation of the mouse inner ear

Most information on the properties of mammalian vestibular primary afferents has been obtained in deeply anesthetized animals, in vivo. Generally, non-human primates and larger rodents have been the species of choice. Investigations using smaller rodents, such as the laboratory mouse, have been limited despite the increasing availability of naturally occurring or engineered mutants that result in balance disorders. Furthermore, in vitro preparations of the intact peripheral vestibular apparatus are only available for non-mammalian vertebrates. To take advantage of the genetic/molecular advances available in mice and the utility of in vitro preparations that permit manipulations of the extracellular milieu, we developed an isolated mouse inner ear preparation with the attached eighth cranial nerve for electrophysiological recording. Intra-axonal recordings of background activity in vestibular primary afferents were obtained in a modified Ringer's solution (0.25 mM Ca2+; 3.25 mM Mg2+) at 22 degrees C. We also recorded afferent activity in the presence of neuroactive drugs known to affect various stages of the transduction cascade. These results, together with responses to sinusoidal mechanical deformation of the membranous ducts, showed that transduction mechanisms remain viable. Where possible, we also obtained results in vivo for comparison. In future, the in vitro mouse preparation will allow investigation of the effects of genetic manipulations and pharmacological agents on the intact peripheral vestibular apparatus.