Effects of early auditory deprivation and stimulation on auditory brainstem responses in the rat.

The purpose of this study was to investigate the effect of auditory sound deprivation or stimulation on auditory brainstem responses (ABRs) during the maturation period of the rat auditory system. At postnatal day (PND) 21, 40 newborn Norway Brown male rats were categorized into 3 groups: (i) an auditory deprivation group in which a bilateral average conductive hearing loss of 27 dB was induced; (ii) an auditory activation group exposed to 65-90 dB sound pressure level; and (iii) a control group. ABR recordings were made on PND 84. In order to compare group differences in interpeak latency (IPL), sensation level (SL), defined as stimulus intensity above threshold, was used. IPL measurements and analysis were restricted to the 20-60 dB SL range. No differences were observed in the IPLs of peaks I-IV between the three groups. Small, but not statistically significant, differences in mean estimated IPLs of peaks I-IV were shown in the ranges > 50 dB SL and < 25 dB SL. Possible confounding factors explaining the apparent discrepancy between these results and those of other animal studies are reviewed.