ABSTRACT
At the cochlear level, transplanting tissue or cells into the inner ear can have different purposes. The most obvious reason for transplantation is to “replace” missing or injured cells with exogenous cells. This goal imposes, however, considerable requirements for the transplantation to be successful. The new cells must not only survive at the proper site in the host inner ear but also completely integrate both structurally and functionally, and, if transplanting immature cells, differentiate to the specific cell type they are to replace. Inner ear pathologies primarily affect the sensory inner and outer hair cells within the hearing organ and, as a secondary effect of hair cell loss, the spiral ganglion neurons. The mammalian hearing organ has an exquisite threedimensional organisation where each cellular element needs to be precisely positioned and connected in order to maintain normal auditory function. For the hair cells, this is especially true. Realistically, it is hard to imagine exogenous cells to functionally replace inner or outer hair cells. A more probable cell target would be the spiral ganglion neurons, which are less-strictly organised. In addition to replacing the neurons per se, implanted exogenous cells could function as an intermediate cellular “building block,” bridging the distance between a cochlear prosthesis electrode and the spiral ganglion neurons (Fig. 22.1).
