Introduction Nowadays, corticosteroids are widely used to treat Meniere's disease
or sudden deafness, and also during cochlear implantation. Corticosteroids have anti-inflammatory
and immunomodulatory effects. In this study, we used four different already clinically
tested corticosteroids (fludrocortisone, triamcinolone, dexamethasone, and prednisolone)
and examined their effects on the survival rate and neurite length of spiral ganglion
neurons (SGN).
Method The SGN were isolated from neonatal (P3-5) Sprague-Dawley rats and were precultured
with 10% fetal calf serum (FCS) for 24 h. A dose-response curve was then determined
for each of the corticosteroids. Two inhibitors (mifepristone and spironolactone)
were then used to reverse the inhibitory effect of the corticosteroids. After 48 h,
the SGN were fixed, stained and the survival rate and neurite length of the SGN were
determined.
Results For each of the corticosteroids, one concentration was determined for normal
(positive control, 10% FCS) and one for lower (negative control) survival of SGN.
For fludrocortisone, we identified 0.4 mg as the concentration for normal SGN survival
and 4.0 mg as the concentration for lower SGN survival. For triamcinolone 1.0 mg and
4.0 mg, for dexamethasone 0.005 µg and 0.010 µg and for prednisolone 0.25 mg and 1.5
mg respectively. In particular, for prednisolone, the neurite length was reduced in
a dose-dependent manner.
Conclusion The results indicated that there is only a small therapeutic window for
protective treatment of SGN. This is particularly important with regard to the maintenance
of functional residual hearing in the context of cochlear implantation.
Das Projekt wurde durch das Exzellenzcluster Hearing4all der Deutschen Forschungsgemeinschaft
(DFG, EXC 2177/1) unterstützt.
