Degeneration of axons in the brainstem of the chinchilla after auditory overstimulation

Hear Res. 1997 Jan;103(1-2):169-91. doi: 10.1016/s0378-5955(96)00173-6.


The patterns of axonal degeneration following acoustic overstimulation of the cochlea were traced in the brainstem of adult chinchillas. The Nauta-Rasmussen method for axonal degeneration was used following survivals of 1-32 days after a 105 min exposure to an octave-band noise with a center frequency of 4 kHz and a sound pressure level of 108 dB. Hair-cell and myelinated nerve-fiber loss were assessed in the cochlea. The cochleotopic pattern of terminal degeneration in the ventral cochlear nucleus correlated with the sites of myelinated fiber and inner-hair-cell loss: this correlation was less rigorous with outer-hair-cell loss, especially in the dorsal cochlear nucleus. These results are consistent with a dystrophic process with a slow time course depending on hair-cell loss and/or direct cochlear nerve-fiber damage. However, in a number of cases with no damage in the apical cochlea, fine fiber degeneration occurred with a faster course in low-frequency regions in the dorsal cochlear nucleus and, transynaptically, in a non-cochleotopic pattern in the superior olive and inferior colliculus. These findings suggest that neuronal hyperactivity plays a role in the central degeneration following acoustic overstimulation, possibly by an excitotoxic process.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acoustic Stimulation / adverse effects
  • Animals
  • Auditory Pathways / injuries
  • Auditory Pathways / pathology
  • Axons / pathology*
  • Brain Stem / injuries
  • Brain Stem / pathology*
  • Chinchilla / anatomy & histology*
  • Chinchilla / physiology
  • Cochlea / injuries*
  • Cochlea / pathology*
  • Cochlear Nucleus / pathology
  • Hair Cells, Auditory, Inner / pathology
  • Hair Cells, Auditory, Outer / pathology
  • Inferior Colliculi / pathology
  • Nerve Degeneration
  • Nerve Fibers, Myelinated / pathology
  • Noise / adverse effects*
  • Olivary Nucleus / pathology