Developmental Regulation of Nicotinic Synapses on Cochlear Inner Hair Cells
Open Access
- 8 September 2004
- journal article
- research article
- Published by Society for Neuroscience in Journal of Neuroscience
- Vol. 24 (36), 7814-7820
- https://doi.org/10.1523/jneurosci.2102-04.2004
Abstract
In the mature cochlea, inner hair cells (IHCs) transduce acoustic signals into receptor potentials, communicating to the brain by synaptic contacts with afferent fibers. Before the onset of hearing, a transient efferent innervation is found on IHCs, mediated by a nicotinic cholinergic receptor that may contain both α9 and α10 subunits. Calcium influx through that receptor activates calcium-dependent (SK2-containing) potassium channels. This inhibitory synapse is thought to disappear after the onset of hearing [after postnatal day 12 (P12)]. We documented this developmental transition using whole-cell recordings from IHCs in apical turns of the rat organ of Corti. Acetylcholine elicited ionic currents in 88-100% of IHCs between P3 and P14, but in only 1 of 11 IHCs at P16-P22. Potassium depolarization of efferent terminals caused IPSCs in 67% of IHCs at P3, in 100% at P7-P9, in 93% at P10-P12, but in only 40% at P13-P14 and in none of the IHCs tested between P16 and P22. Earlier work had shown byin situhybridization that α9 mRNA is expressed in adult IHCs but thatα10 mRNA disappears after the onset of hearing. In the present study, antibodies toα10 and to the associated calcium-dependent (SK2) potassium channel showed a similar developmental loss. The correlated expression of these gene products with functional innervation suggests thatAlpha10andSK2, but notAlpha9,are regulated by synaptic activity. Furthermore, this developmental knock-out of α10, but not α9, supports the hypothesis that functional nicotinic acetylcholine receptors in hair cells are heteromers containing both these subunits.Keywords
This publication has 45 references indexed in Scilit:
- Developmental mRNA expression of the α10 nicotinic acetylcholine receptor subunit in the rat cochleaDevelopmental Brain Research, 2002
- Development of the inner ear efferent system across vertebrate speciesJournal of Neurobiology, 2002
- Olivocochlear innervation of inner and outer hair cells during postnatal maturation: an immunocytochemical studyDevelopmental Brain Research, 1996
- Nicotinic Receptors in the Development and Modulation of CNS SynapsesNeuron, 1996
- Synaptophysin and Gap-43 proteins in efferent fibers of the inner ear during postnatal developmentDevelopmental Brain Research, 1995
- Innervation and target tissue interactions differentially regulate acetylcholine receptor subunit mRNA levels in developing neurons in situNeuron, 1995
- α9: An acetylcholine receptor with novel pharmacological properties expressed in rat cochlear hair cellsCell, 1994
- Synaptic structure and development: The neuromuscular junctionCell, 1993
- Afferent and efferent innervation of the cat cochlea: Quantitative analysis with light and electron microscopyJournal of Comparative Neurology, 1990
- Biochemical and morphological differentiation of acetylcholinesterase‐positive efferent fibers in the mouse cochleaJournal of Electron Microscopy Technique, 1990