Transient focal cooling at the round window and cochlear nucleus shows round window CAP originates from cochlear neurones alone

C. M. McMahon, D. J. Brown, R. B. Patuzzi*

*Corresponding author for this work

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

We have measured the compound action potential (CAP) evoked by very brief high-frequency tone-bursts (20 kHz, 1/4 ms) at the round window (RW) and at the surface of the cochlear nucleus (CN) in guinea pigs before, during and after a localised chilling of either the cochlea or CN, with a non-toxic 'freeze spray'. CN chilling almost abolished the negative-going component of the CAP measured in the CN (generated by the CN and here called the cochlear nucleus response or CNR), leaving a positive-going localised response from the cochlear neurones as they leave the internal auditory meatus. Within 3 min, the CNR recovered to control values. During that time, the N1 component of the RW CAP was slightly increased and the P1 was larger, even though the CNR was abolished, indicating that the P1 was not due to electrotonic spread of current from the CN. The N2 and successive peaks at the RW were also abolished, but returned after 30 s. When the cochlea was chilled, the RW CAP was initially reduced in amplitude, presumably due to a drop in the number of cochlear neurones spiking in response to sound, but recovered within 3 min to be larger than the control waveform, with a more prominent N1 peak which was delayed slightly, making the CAP more monophasic. At the same time, the CNR was smaller, presumably due to fewer cochlear neurones responding, but overall the CN CAP was altered little in waveshape. These experiments indicate that that RW CAP is generated almost solely by cochlear neurones. We also suggest that some of the changes in the RW CAP during the chills were due to changes in the firing of the lateral olivo-cochlear system of efferent neurons.

Original languageEnglish
Pages (from-to)75-86
Number of pages12
JournalHearing Research
Volume190
Issue number1-2
DOIs
Publication statusPublished - Apr 2004
Externally publishedYes

Keywords

  • CAP, compound action potential
  • CN, cochlear nucleus
  • CNR, cochlear nucleus response
  • Cochlea
  • Cochlear nucleus
  • Compound action potential
  • Guinea pig
  • Lateral olivo-cochlear efferent neuron
  • PA, primary afferent
  • Spectrum of the averaged waveform

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