title: Position-dependent patterning of spontaneous action potentials in immature cochlear inner hair cells.
abstract: Spontaneous action potential activity is crucial for mammalian sensory system development. In the auditory system, patterned firing activity has been observed in immature spiral ganglion and brain-stem neurons and is likely to depend on cochlear inner hair cell (IHC) action potentials. It remains uncertain whether spiking activity is intrinsic to developing IHCs and whether it shows patterning. We found that action potentials were intrinsically generated by immature IHCs of altricial rodents and that apical IHCs showed bursting activity as opposed to more sustained firing in basal cells. We show that the efferent neurotransmitter acetylcholine fine-tunes the IHC's resting membrane potential (V(m)), and as such is crucial for the bursting pattern in apical cells. Endogenous extracellular ATP also contributes to the V(m) of apical and basal IHCs by triggering small-conductance Ca(2+)-activated K(+) (SK2) channels. We propose that the difference in firing pattern along the cochlea instructs the tonotopic differentiation of IHCs and auditory pathway.
authors.affiliation: Department of Biomedical Science, University of Sheffield, Sheffield, UK.
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Johnson
authors.forename: Tobias
authors.initials: T
authors.lastname: Eckrich
authors.forename: Stephanie
authors.initials: S
authors.lastname: Kuhn
authors.forename: Valeria
authors.initials: V
authors.lastname: Zampini
authors.forename: Christoph
authors.initials: C
authors.lastname: Franz
authors.forename: Kishani M
authors.initials: KM
authors.lastname: Ranatunga
authors.forename: Terri P
authors.initials: TP
authors.lastname: Roberts
authors.forename: Sergio
authors.initials: S
authors.lastname: Masetto
authors.forename: Marlies
authors.initials: M
authors.lastname: Knipper
authors.forename: Corné J
authors.initials: CJ
authors.lastname: Kros
authors.forename: Walter
authors.initials: W
authors.lastname: Marcotti
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004594:Electrophysiology; D005849:Gerbillinae; D006199:Hair Cells, Auditory, Inner / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D051381:Rats