Effects of salicylates and aminoglycosides on spontaneous otoacoustic emissions in the Tokay gecko

The high sensitivity and sharp frequency discrimination of hearing depend o n mechanical amplification in the cochlea. To explore the basis of this act ive process, we examined the pharmacological sensitivity of spontaneous oto acoustic emissions (SOAEs) in a lizard, the Tokay gecko. In a quiet environ ment, each ear produced a complex but stable pattern of emissions. These SO AEs were reversibly modulated by drugs that affect mammalian otoacoustic em issions, 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 a ll frequencies, whereas those with weak central emissions showed enhancemen t. Repeated oral administration of acetylsalicylic acid reduced all emissio ns. 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 initia l values. The similarity of the responses of reptilian and mammalian cochle as to pharmacological intervention provides further evidence for a common m echanism of cochlear amplification.