Myelin-deficiency in the cochlear nerve of the 'bt' mutant hamster

In a previous report, we showed abnormal auditory evoked potentials in the mutant hamster, 'black tremor (bt)', with significantly prolonged wave latencies of auditory brainstem responses and prolonged N1 latencies of compound action potentials, but normal cochlear microphonics. In this report, we present the results of morphological studies supporting the results of our electrophysiological studies of the auditory pathway in bt. Observation by transmission electron microscopy revealed an abnormal myelin sheath surrounding the spiral ganglion cells, and a thinner compact myelin sheath surrounding the axons in bt than in normal hamsters. The bt hamster has a myelin deficiency not only in the brainstem, but also in the cochlear nerve.