Auditory function and inner ear pathology in guinea pigs with peripheral nerve demyelination

The audiological or physiological data showed that auditory neuropathy was due to the demylination disease in peripheral nerve, especially in auditory nerve. The aim of this study was to explore the changes of auditory function and auditory nerve pathology through establishing a guinea pig model with demyelinated peripheral nerve. The guinea pig model was established by immunizing guinea pigs with heterologous peripheral nerve myelin. Auditory brainstem response (ABR) and compound action potential (CAP) were tested weekly before and after immunization for a period of 7 weeks. Serum anti MBP-IgG levels, sciatic nerve conduction velocity (NCV), the immunization associated lesions in the inner ear, and pathological changes in the auditory nerve, sciatic nerve and cochlea were tested. In comparison with the control group, the experimental group showed the existence of demyelination in sciatic nerve and auditory nerve, had a significant increase in serum anti MBP-IgG levels (P<0.01), ABR, CAP thresholds and the latencies of wave I, III, V and N1 (P<0.01) with no noticeable changes in the inter-peak latencies of I-III, III-V (P>0.05), while had a marked decrease in sciatic NCV (P<0.01). Immunohistochemistry revealed that the antibodies to inner ear from the MBP-sensitized animals distributed in cochlear nerve, nerve fiber of inner ear, and spiral ganglion cells. Cochlear scanning electron microscopy indicated the pathological changes of stereociliary disorder and cytoplasmic protrusions in the inner hair cell. In the present experiment, the EAN animal model which has been proved a reliable model with peripheral nerve demyelination demonstrated auditory nerve demyelination and auditory malfunction. The results suggest that this model can be an effective one for the study of the auditory dysfunction due to demyelination disorders.