The Spiral Ganglion in an Out-of-Body Experience: A Brief History of in Vitro Studies of the Spiral Ganglion

Abstract

Honor Fell first succeeded in culture of the cochlea in 1928. Throughout most of the time since then, the principal use of cochlear or spiral ganglion cultures has been to facilitate the study of cochlear development: cell differentiation, structural and physiological maturation, and innervation of the sensory cells. More recently, use of spiral ganglion cultures has been extended to additional issues. One of these is neuronal survival in response to neurotrophic factors and electrical activity. The goal of such studies is to prevent degeneration or death of spiral ganglion neurons (SGNs) in the hearing impaired and so improve efficacy of cochlear implants. A second topic is degeneration or death of SGNs following direct trauma, particularly noise-induced excitotoxic trauma. The goal of these studies is to identify means of protecting the SGNs and their synapses on hair cells following trauma and to promote regeneration. The success of these studies has been due to clever exploitation of several technical innovations. Culture conditions have been improved by the use of serum and specialized culture media and the use of more physiological substrate materials. Electrophysiological methods have been applied. Microscopy has advanced from conventional optical methods to the use of electron, conventional fluorescence, and confocal microscopy, greatly improving observations of fixed or live cochlear cultures. Highly specialized substrates have allowed study of SGN axon guidance by chemical or physical cues. There is a greatly expanded repertoire of small molecule pharmacological agents, peptide growth and trophic factors targeting surface molecules and receptors, and cell membrane-permeable reagents for modulating intracellular signaling and regulation. Further expanding the range of experimental manipulations has been the introduction of molecular and genetic techniques, including gene transfer by transfection or viral transduction and culture of cells or organs from transgenic mice. Here we provide a historical overview of the study of the spiral ganglion in vitro noting key experiments exemplifying the application of increasingly sophisticated experimental and observational techniques to the research goals. We hope that readers will obtain, from this overview, ideas for experimental approaches applicable to their own research questions.