A CHARACTERISTIC OF ASPIRIN-INDUCED HEARING-LOSS IN AUDITORY BRAIN-STEM RESPONSE OF CONSCIOUS RATS

The acute effects of aspirin on auditory functions were examined elect rophysiologically in conscious rats with chronically implanted electro des for auditory brainstem response (ABR) recording. A single intraven ous injection of aspirin at a dose of 225 mg/kg caused a reduction in the amplitude of the ABR P1 wave evoked by a 2 kHz tone pip 1 and 24 h r after dosing at almost all sound intensity levels, while the P1 ampl itude at 4 kHz was reduced mainly 1 hr after dosing, and the P1 amplit ude at 8 kHz was not significantly affected at middle and high intensi ties even 1 hr after dosing. The audiogram obtained from the P1 amplit ude showed a significant increase in the sound threshold 1 and 24 hr a fter dosing at 2 kHz, and 1 hr after dosing at 4 kHz, but not at 8 kHz . The peak latency of the PI wave was also prolonged. Furthermore, red uction of the P2 and P4 wave amplitude and prolongation of the P1-P2 a nd P2-P4 interpeak latency were also observed at 2 kHz but not at 4 or 8 kHz. These results suggest that the rat auditory function for low f requency is vulnerable to the effects of aspirin. This paradigm, i.e., frequency selectivity, in rats may be useful to further assess the di fferent outer hair cells along the cochlear duct and provide additiona l evidence for the mechanism(s) or site underlying aspirin ototoxicity .