Effects of salicylates and aminoglycosides on spontaneous otoacoustic emissions in the Tokay gecko
Proc Natl Acad Sci U S A 97[1]:454-9 2000 Jan 4
by
Stewart CE, Hudspeth AJ
The high sensitivity and sharp frequency discrimination of hearing
depend on mechanical amplification in the cochlea. To explore the basis of this
active process, we examined the pharmacological sensitivity of spontaneous otoacoustic
emissions (SOAEs) in a lizard, the Tokay gecko. In a quiet environment, each
ear produced a complex but stable pattern of emissions. These SOAEs were reversibly
modulated by drugs that affect mammalian otoacoustic emissions, the salicylates
and the aminoglycoside antibiotics. The effect of a single i.p. injection of
sodium salicylate depended on the initial power of the emissions: ears with
strong control SOAEs displayed suppression at all frequencies, whereas those
with weak control emissions showed enhancement. Repeated oral administration
of acetylsalicylic acid reduced all emissions. Single i.p. doses of gentamicin
or kanamycin suppressed SOAEs below 2.6 kHz, while modulating those above 2.6
kHz in either of two ways. For ears whose emission power at 2.6-5.2 kHz encompassed
more than half of the total, individual emissions displayed facilitation as
great as 35-fold. For the remaining ears, emissions dropped to as little as
one-sixth of their initial values. The similarity of the responses of reptilian
and mammalian cochleas to pharmacological intervention provides further evidence
for a common mechanism of cochlear amplification.
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