[The cochlear implant. Molecular arguments favouring early implantation]

Abstract

Background: An important factor in the clinical outcome of cochlear implantation is the age of the patient. Compared to older patients, children with congenital deafness have a better outcome when the implantation is made before the age of 2 years. The cause may lie in the molecular biology of the brain, which changes during postnatal maturation.

Methods: Protein probes were obtained from tissue of the rat inferior colliculus at different ages. The probes were analyzed using 2-dimensional SDS electrophoresis.

Results: The expression of GAP-43, a protein expressed by neurons during axonal outgrowth and synaptogenesis, and the total number of the protein species showed a significant reduction during ontogenesis. This shows that while neurons gradually assume their specific function, they downregulate GAP-43 and the molecular complexity decreases.

Conclusions: Due to a lack of neuronal pluripotency at later developmental stages, the flexibility to adapt to the afferent activation provided by a cochlear implant is increasingly limited.