Growth factors, auditory neurones and cochlear implants: A review

The total number and the integrity of the auditory neurones available for s timulation govern the benefits that patients can derive from cochlear impla nts. Although electrical stimulation of the cochlea has been reported to pr omote auditory neuronal survival; this trophic effect is insufficient to re generate cie novo fibres. Hence, any agent that can maximize the number of or regenerate functional auditory neurones would be of great benefit. Sever al studies have identified various growth factors crucial to the normal dev elopment of auditory neurones. In addition, in vitro studies have demonstra ted that several growth factors are important for the maintenance; rescue a nd repair of adult auditory neurones. In vivo studies confirm the in vitro findings, reporting that specific growth factors are able to support audito ry neuronal survival following injury or trauma, and in lower species growt h factors have been associated with regenerating auditory neurones. In addi tion to their trophic actions, several growth factors have also been report ed to affect ion channels thus the electrical response of neuronal fibres. Indeed, growth factors have been reported to enhance neuronal excitation an d to improve the efficacy of synaptic transmission. Taken in concert, these effects suggest that exogenous growth factors delivered to the cochlea may improve the transmission of the electrical stimuli from the implanted elec trode to the auditory pathway. Further studies are warranted to investigate how the adjunct delivery of growth factors with the cochlear implant may c onstitute a better treatment for hearing-impaired individuals.