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Related Experiment Videos

Thyroxine affects physiological and morphological development of the ear

S Freeman1, L Cherny, H Sohmer

  • 1Department of Physiology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.

Hearing Research
|August 1, 1996
PubMed
Summary

Neonatal hyperthyroidism accelerates auditory system development in rat pups, but impairs cochlear amplifier function, leading to reduced distortion product otoacoustic emissions (DPEs) later in life.

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Area of Science:

  • Otoacoustic Emissions
  • Auditory Evoked Potentials
  • Developmental Biology

Background:

  • Distortion product otoacoustic emissions (DPEs) reflect cochlear amplifier activity.
  • Auditory nerve-brainstem evoked responses (ABRs) assess overall cochlear function.
  • Neonatal hyperthyroidism's impact on auditory development is not fully understood.

Purpose of the Study:

  • To investigate the effects of neonatal hyperthyroidism on the onset and maturation of DPEs and ABRs in rat pups.
  • To compare auditory development with morphological ear development.
  • To determine if hyperthyroidism impacts cochlear amplifier function and overall auditory function.

Main Methods:

  • Studied DPEs and ABRs in neonatal hyperthyroid and control rat pups.

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  • Recorded DPEs at high (8 kHz) and low (3 kHz) frequencies.
  • Assessed ABRs to high-intensity clicks and compared with histological ear development.

    • Main Results:

    • Hyperthyroid rats showed earlier onset of both ABRs and DPEs, with earlier ear morphological development.
    • Despite earlier onset, ABR thresholds and DPE amplitudes matured slower in hyperthyroid rats.
    • Adult hyperthyroid rats had no difference in ABR/DPE thresholds but exhibited smaller DPE amplitudes, especially at low frequencies.

    Conclusions:

    • Neonatal hyperthyroidism accelerates auditory structure and function onset in rats.
    • Hyperthyroidism negatively affects later cochlear states, impairing cochlear amplifier function (DPEs), particularly for low frequencies.
    • This suggests a lasting impact of neonatal hyperthyroidism on cochlear physiology despite initial developmental acceleration.