Erythropoietin and erythropoietin receptor expression in the guinea pig inner ear

The erythropoietin receptor (EPOR) is expressed in the brain and erythropoietin (EPO) has been shown to have neurotrophic and neuroprotective functions in the central nervous system and in the retina. These findings may be applied to the inner ear, pending EPO receptor presence. Accordingly, this study determines expression of EPO and EPOR in the inner ear of the guinea pig. Normal guinea pig inner ears were processed for immunohistochemistry, using poly-clonal antibodies against EPO and the EPO receptor. EPO expression was exclusively found in most, but not all spiral ganglion neurons. Expression of the EPO receptor was found in the cytoplasm of the inner and outer phalangeal cells (Deiters' cells), as well as the inner sulcus cells and the supporting cells of the organ of Corti (Hensen, Claudius and some Boettcher cells). Some spiral ganglion neurons or glial cells expressed the receptor, as did spiral ligament fibrocytes, some intermediate cells of stria vascularis and the endothelial cells of some modiolar vessels. No parts of the vestibular system stained positive for either antibody. We conclude, that EPO is expressed by spiral ganglion neurons and that the EPO receptor is widely expressed by several cell types within the guinea pig cochlea. We hypothesize on the existence of a local paracrine system and that EPO treatment may be feasible following inner ear damage.