Our studies have revealed that the spiral ganglion is more than just a collection of axon-like elements that act merely as a simple relay into the central nervous system. Instead, we and others have found that this relatively homogeneous group of neurons possesses a rich complexity that is only now beginning to be understood. In fact, the powerful regulation of spiral ganglion neurons by neurotrophins, in combination with their precise and frequency-specific organization, makes this an exemplary model system to study the molecular and cellular foundations that regulate the initial stages of parallel processing and sensory encoding. Not only do these neurons have a prominent functional role, they are also the targets of therapeutic remediation with cochlear implant technology. Understanding their endogenous firing properties and membrane characteristics will undoubtedly be helpful in tailoring electrical input for optimal stimulation. Furthermore, our studies suggest that should neurotrophins be used clinically to enhance neuronal survival, care must be taken with their administration in order to maintain firing patterns and thresholds that are appropriate for the particular frequency region of innervation. However, before such conclusions can be drawn, critical issues must first be resolved. It is important to understand the basic foundation upon which this organization is actually constructed, determine precisely how exogenously-applied neurotrophin regulation occurs, and examine whether the effects of neurotrophins can be reproduced by manipulation of hair cell-neuronal contact. With the push to move cochlear-infused neurotrophins into clinical trials, it is imperative now more than ever to examine the biophysical impact of neurotrophins on the spiral ganglion in model systems. The use of electrophysiological, molecular, and immunocytochemical methods combined with innovative tissue culture systems will provide new insights into the precise organization of spiral ganglion neurons, cells that may hold the key to remediation of hearing loss following disease or injury. Loss of hearing is a devastating sensory disorder that affects millions of Americans, but effective therapies to treat this communication impairment are still being developed. Although the hearing sciences have been on the forefront of delivering an `artificial ear'or cochlear implant, there is much that needs to be learned to bring this device to its potential. Our studies provide the basic scientific foundation necessary to move the existing therapeutic innovations forward. By studying the neurons that are the targets of the cochlear implant, the precise signals that must be conveyed into the brain are being identified and the mechanisms critical for neuronal survival and specification are being revealed.
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