Freeman S, Cherny L, Sohmer H
Department of Physiology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Hear Res. 1996 Aug;97(1-2):19-29.
The onset and development of distortion product otoacoustic emissions (DPE) representing cochlear amplifier activity were studied in neonatal hyperthyroid (n = 10) and control (n = 10) rat pups. These were compared to the onset and development of auditory nerve-brainstem evoked responses (ABR) representing overall cochlear function, and to morphological development of the ear. DPEs were recorded at an earlier postnatal age to high (8 kHz) frequencies and progressed to lower (3 kHz) frequencies with age. ABRs to high-intensity clicks were recorded at least 2 days before DPEs, although DPE onset at 8 kHz preceded adult-like ABR thresholds. Both ABR and DPEs appeared earlier in the hyperthyroid rats. Histological evidence showed earlier morphological development of the ear in these animals. ABR thresholds and DPE amplitudes matured at a slower rate in the experimental group despite their earlier onset. There was no difference in ABR and DPE thresholds between adult hyperthyroid and control rats. However, in the experimental group, DPEs had smaller amplitudes to high (70 dB SPL) and to low (50 dB SPL) stimulus intensities at low frequencies. Hence, despite thyroxine-injected rat pups having earlier onset of auditory structure and function (lower ABR thresholds and earlier functioning active cochlear amplifier), it appeared that neonatal hyperthyroidism affected the later state of the cochlea, such that DPEs, especially to low-frequency stimuli, were depressed during and after maturation.
在新生甲状腺功能亢进大鼠（n = 10）和对照大鼠（n = 10）幼崽中，研究了代表耳蜗放大器活动的畸变产物耳声发射（DPE）的起始和发展。将这些结果与代表耳蜗整体功能的听神经 - 脑干诱发反应（ABR）的起始和发展以及耳朵的形态发育进行比较。DPE在出生后较早的年龄即可记录到高频（8 kHz），并随着年龄增长向低频（3 kHz）发展。高强度短声诱发的ABR至少在DPE记录前2天即可记录到，尽管8 kHz处的DPE起始先于类似成人的ABR阈值。ABR和DPE在甲状腺功能亢进大鼠中均出现得更早。组织学证据表明这些动物的耳朵形态发育更早。尽管实验组的ABR阈值和DPE振幅起始较早，但其成熟速度较慢。成年甲状腺功能亢进大鼠和对照大鼠的ABR和DPE阈值没有差异。然而，在实验组中，低频下高强度（70 dB SPL）和低强度（50 dB SPL）刺激的DPE振幅较小。因此，尽管注射甲状腺素的大鼠幼崽听觉结构和功能起始较早（较低的ABR阈值和较早发挥作用的活跃耳蜗放大器），但新生儿甲状腺功能亢进似乎影响了耳蜗的后期状态，使得DPE，尤其是对低频刺激的DPE，在成熟期间和成熟后受到抑制。
