A model for implanting neuronal tissue into the cochlea

Immature dorsal root ganglion (DRG) neurons have previously been shown to survive implantation to the cavity of extirpated adult native DRG, send axons via the dorsal root into the host spinal cord and make functional sypnatic connections. Regeneration or replacement of the auditory nerve would provide a major intervention in the clinical treatment of severe hearing impairment. In this study we have exploited the potential of fetal DRG neurons to survive allografting into the cochlea of adult guinea pigs. In some animals implantation of fetal DRGs was combined with infusion of neurotropic substances into the cochlea. Survival of the implanted DRG neurons was found in the majority of grafted animals. Treatment with neurotrophic factors significantly increased the number of surviving implanted DRG neurons. However, even in the absence of neurotrophic substances survival of DRG neurons was found in a majority of the animals, indicating the presence of endogenous growth promoting factors within the cochlea and/or an intrinsic capacity of fetal DRG neurons themselves to survive in this heterotropic location.