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Age-independent plasticity of the auditory brainstem following CI stimulation in a model of adult deafness
18 April 2018 (online)
As a result of aging, the prevalence of age-related hearing loss rises in our society. An increasing number of profoundly deaf or completely deaf patients are supplied with cochlear implants (CIs). Up to now, it is unknown whether there are age-dependent differences in the plasticity of the central auditory system. For this purpose, we investigated the expression of the plasticity marker Gap43 after CI stimulation of adult rats deafened at different ages.
Bilateral deafness was induced at 3 (n = 11) or 12 (n = 12) months after birth by injecting a loop diuretic in combination with an aminoglycoside. In both groups, a rapid and permanent increase of hearing thresholds by around 90 dB was measured. One month after onset of deafness, a CI was inserted into the left cochlea and after recovering from surgery rats received an electrical intracochlear stimulation for 14 days. In controls (n = 6), the same CI implantation was performed without stimulating the ear for 14 days. For immunoreacitivity, brainstem sections containing the lateral superior olive (LSO) were stained for Gap43 mRNA and protein.
Unilateral CI stimulation induces increased expression of Gap43 mRNA and protein in adult deafened rats. This Gap43 rise occurs in young and old deafened rats only in the LSO of the stimulated side.
The adult deafened auditory system responds to re-activation by CI stimulation with plasticity on its molecular level. This remodeling of the central auditory system occurs independent of the age and shows that adaptation to a novel sensory stimulus can take place in the adult mammalian brain even after a long period of deafness.