Auditory Brainstem Response (ABR) in Spontaneously Epileptic Rats (SER) and Their Parent Mutants

Abstract

Postnatal development of auditory brainstem response (ABR) in spontaneously epileptic rats (SER; zi/zi, tm/tm), a double mutant, their parent mutants, tremor rats (tm/tm) and zitter rats (zi/zi), and Kyo:Wistar rats (control), was studied by repeated ABR recordings from 2 to 13 weeks of age. In tremor rats and Kyo:Wistar rats at 2 weeks of age, ABR pattern was almost the same and 2 or 3 waves were identified. However, no further development in ABR was observed in tremor rats nd prolongation of latency and lowering of amplitude were marked. Only wave I with prolonged latency and lowered amplitude was recognized in zitter rats, SER and SER-N (zitter phenotype without epilepsy; zi/zi, tm/+ or zi/zi, +/+). ABR pattern was almost the same from 2 to 13 weeks of age in them. Electrocochleography revealed delay of N1 latency of compound action potential in SER. Vacuolation was observed in the cochlear nuclei and the brainstem of tremor rats and SER from 3 weeks of age in histopathological examination. The organ of Corti and cochlear nerve of tremor rats and SER exhibited no remarkable histopathological findings. The deafness in SER and its parent mutants was considered to occur as a result of impairment of inner ear, cochlear nerve and brainstem as well.