Intracochlear salicylate reduces low-intensity acoustic and cochlear microphonic distortion products

Abstract

Salicylate is well-known to produce reversible hearing loss and tinnitus. The site and mechanism of salicylate's ototoxic actions, however, remain unresolved. Recent experiments demonstrating primarily low-intensity effects on cochlear afferent outflow and effects on otoacoustic emissions (OAEs) suggest that salicylate acts to compromise active, energy-enhancing processes within the cochlea (i.e., the active process). We tested this hypothesis by examining the effect of salicylate on distortion product emissions. Distortion product responses to two-tone stimulation were monitored in the guinea pig before, during, and after intracochlear administration of increasing concentrations of salicylate (0.6-5 mM). These responses were recorded as acoustic signals in the ear canal spectrum (ADP), and as present in the cochlear microphonic (CM) recorded from a wire in basal turn scala vestibuli (CMDP). We also recorded the CM response to a single tone. Cochlear perfusion of salicylate resulted in a dose-responsive reduction in ADPs that was greater for low intensities of stimulation. CMDPs also demonstrated a concentration-dependent reduction at low intensities, but were increased slightly, though not significantly, by salicylate when elicited by high intensity primaries. CM was essentially unchanged by intracochlear salicylate. These results are consistent with an action of salicylate that involves the outer hair cells (OHCs) and are in harmony with the hypothesis that salicylate may selectively compromise the active process.