gms | German Medical Science

The benefit of the cochlea implant (CI) is depending on the number of surviving spiral ganglion neurons (SGN) and an efficient nerve-electrode interaction indicating that side effects as like connective tissue formation around the electrode or induction of inflammation have to be reduced. Neurotrophic factors (NTF) are known to enhance SGN survival, whereas glucocorticoids, i.e. dexamethasone (Dex), are potential anti-inflammatory agents. However, protective or toxic effects of glucocorticoids on SGN directly remains to be elucidated.

Method: The gene expression profile of relevant NTF (artemin (ART), GDNF, BDNF), as well of the glucocorticoid receptor GR1 and the inducible nitric oxide synthase iNOS were determined in the auditory nerve (AN) of normal hearing and deafened rats with and without Dex application, respectively, by semiquantitative RT-PCR.

Results: Our data revealed significant upregulation of iNOS in the AN of normal hearing rats treated with Dex. Also, higher mRNA levels were found in deafened rats injected with Dex and those without further treatment, as well in normal hearing rats following perilymphe injection (as control). GR1 showed significant downregulation in deafened rats, but increased gene expression in the other animal groups. ART, GDNF and BDNF revealed upregulated gene expression profiles for all animal groups, independently of the hearing status and the Dex treatment.

Conclusion: In the context of apoptosis it could not be demonstrated that application of Dex to the inner ear has beneficial effects on SGN. However, it has to be considered that the injection procedure alone may induce apoptosis or inflammation. The increase of NTF expression indicate that they play key roles in protection of SGN and counteract the apoptosis signaling.

Unterstützt durch: EU-project "Bioear"