Kölliker's organ and the development of spontaneous activity in the auditory system: implications for hearing dysfunction

Abstract

Prior to the "onset of hearing," developing cochlear inner hair cells (IHCs) and primary auditory neurons undergo experience-independent activity, which is thought to be important in retaining and refining neural connections in the absence of sound. One of the major hypotheses regarding the origin of such activity involves a group of columnar epithelial supporting cells forming Kölliker's organ, which is only present during this critical period of auditory development. There is strong evidence for a purinergic signalling mechanism underlying such activity. ATP released through connexin hemichannels may activate P2 purinergic receptors in both Kölliker's organ and the adjacent IHCs, leading to generation of electrical activity throughout the auditory system. However, recent work has suggested an alternative origin, by demonstrating the ability of IHCs to generate this spontaneous activity without activation by ATP. Regardless, developmental abnormalities of Kölliker's organ may lead to congenital hearing loss, considering that mutations in ion channels (hemichannels, gap junctions, and calcium channels) involved in Kölliker's organ activity share strong links with such types of deafness.

Figure 1

The immature organ of Corti and the adjacent Kölliker's organ. (a) A cross sectional diagram of a rat organ of Corti (approximately 10 days old) outlining the sensory hair cells and supporting epithelia. Kölliker's organ is found immediately adjacent to the inner hair cells (IHCs), shaded in darker colour (HC-Hensen's cells; DC-Deiters' cells; OHC-outer hair cells; PC-pillar cells; IHC-inner hair cells; and KO-Kölliker's organ). (b) A diagram outlining a horizontal section of the same developing organ of Corti, detailing the positions of various sensory and nonsensory cells. (c) Resin embedded toluidine-blue stained 1 μm cross section of a 10-day-old Wistar rat organ of Corti. (d) Resin embedded horizontal section of an 11-day-old Wistar rat organ of Corti, postfixed in 1% osmium tetroxide. Scale bar: 20 μm.