Comparison of noise-induced changes of auditory brainstem and middle latency response amplitudes in rats.

摘要

Auditory brainstem responses (ABRs) and middle latency responses (MLRs) were compared after noise exposure to elucidate the specific effects of a loud sound on the central auditory system in rats. Rats were exposed twice for 1h to broad-band noise (BBN) of 118dB SPL (first exposure) and 122dB SPL (second exposure) with an interval between the exposures of three weeks. The first noise exposure produced threshold shifts (TSs) amounting to 5-45dB, and the second exposure resulted in 40-70dB TSs. The slope of MLR amplitude-intensity functions (AIFs) increased significantly in correlation with the TS, resembling loudness recruitment. However, maximal MLR amplitudes measured at 8kHz increased after the first and second noise exposures to almost equal values in individual animals regardless of the TS. In addition, maximum MLR amplitude enhancement was dependent on pre-exposure MLR voltage, probably reflecting the level of metabolic activity or neurotransmitter processes in individual animals. In contrast to MLR amplitudes, ABR amplitudes were suppressed after noise exposure without changing the slope of ABR AIFs. The MLR changes reflect the specific effects of noise exposure on the central auditory system.