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Ensemble spontaneous activity in the guinea-pig cochlear nerve
G D Searchfield1, D J B Muñoz, P R Thorne
1Discipline of Audiology and Division of Physiology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, New Zealand. g.searchfield@auckland.ac.nz
Hearing Research
|May 26, 2004
Summary
Ensemble spontaneous activity (ESA) reflects auditory nerve function and is modulated by auditory neurotransmission. This study confirms ESA
Area of Science:
- Neuroscience
- Auditory Physiology
- Otolaryngology
Background:
- Ensemble spontaneous activity (ESA) is the spectral analysis of electrical noise from the cochlear round window (RW), representing summed auditory nerve fiber activity.
- Changes in ESA spectral characteristics are observed in humans with tinnitus.
- The relationship between ESA and auditory neurotransmission requires further investigation.
Purpose of the Study:
- To determine the relationship between ESA and auditory neurotransmission.
- To investigate the generation site and neural correlates of ESA.
- To explore the potential of ESA as a model for tinnitus research.
Main Methods:
- Spectral analysis of electrical noise recorded from the guinea-pig cochlear RW.
- Pharmacological manipulation using P2X receptor agonist (ATPgammaS), glutamate receptor antagonist (DNQX), and sodium channel antagonist (TTX).
- Assessment of ESA changes following furosemide injection and correlation with endocochlear potential (EP).
Main Results:
- ESA energy is centered around 900 Hz and its amplitude correlates with auditory sensitivity (12-30 kHz).
- Suppression of ESA by pure tones (12-22 kHz) indicates basal cochlear neuron generation.
- Round window perfusion of ATPgammaS, DNQX, and TTX significantly suppressed ESA; furosemide affected ESA and EP similarly. A 200 Hz peak, a potential tinnitus correlate, was observed after DNQX and ATPgammaS treatment.
Conclusions:
- ESA spectral characteristics are confirmed in guinea-pigs and depend on auditory nerve sensitivity and neurotransmission.
- ESA represents summed spontaneous neural activity in the cochlea.
- ESA provides a valuable platform for studying ototoxic compound effects and tinnitus mechanisms.