Faculty Bibliography

Injury to either the peripheral or central nervous system results in the accumulation of growth factors at the wound site. Some of these growth factors have been shown to participate in the neural repair process. Adult auditory neurons grown in dissociated spiral ganglion cell cultures are injured (i.e. bilateral axotomy) as a result of the initial preparation of these cultures. Therefore, cell cultures of dissociated spiral ganglia provide a model for the study of repair processes of adult auditory neurons (e.g. effects of exogenous growth factors on the process of neuritogenesis by injured neurons). Auditory neurons do not survive in these dissociated ganglion cell cultures when only exogenous NGF is added to the defined culture medium. Previous work has identified substrate bound basic fibroblast growth factor (bFGF) as a survival factor for adult auditory neurons in vitro. Auditory neurons cultured on substrate bound bFGF also do not show increased survival in response to the addition of increasing concentrations of nerve growth factor (NGF) to the defined medium. This is in sharp contrast to the pronounced neurite outgrowth-promoting effects (concentration dependent) observed when exogenous NGF is added to adult auditory neurons cultured on substrate bound bFGF. We propose that several neuronotrophic factors (e.g. TGFB1, bFGF, NGF and other neurotrophins) are active in the spiral ganglions' response to injury. Several of these growth factors (i.e. bFGF, NGF) act in cooperation to promote the regeneration or repair of severed or traumatized neuritic processes.

Eighteen patients using the Nucleus multichannel cochlear prosthesis underwent annual evaluations for electrical thresholds, dynamic range, and speech recognition abilities for a period of 1 to 5 years. Results revealed no correlation between length of usage of a cochlear implant and electrical thresholds. The dynamic range was initially wider in the patients with open-set speech recognition, but narrowed in subsequent years. There was a correlation between length of deafness and postoperative performance

Reinnervation of paralyzed intralaryngeal muscles by axonal sprouting from adjacent intact muscles (the phenomenon of muscular neurotization) has been observed, but the source is uncertain. The potential for laryngeal reinnervation of the posterior cricoarytenoid muscle (PCA) from contralateral PCA motor nerve sprouting in a rabbit model was investigated. Unilateral PCA denervation was produced by vagotomy. The rabbits were examined for signs of PCA recovery for up to 6 months, using fiberoptic endoscopy, electromyography (EMG), and histology. No return of vocal cord abduction, EMG activity, or any nerve sprouting across the midline from the intact PCA was found. We conclude that there is no significant spontaneous intralaryngeal muscular neurotization to the paralyzed PCA. The clinical ramifications of our data will be discussed.