Dynorphin release by the lateral olivocochlear efferents may inhibit auditory nerve activity: a cochlear drug delivery study.

•The kappa opioid receptor agonist (−)pentazocine was applied to the cochlea.•Sound evoked neural potentials were reduced in amplitude after drug treatment.•Endogenous dynorphin at biologically plausible levels has an inhibitory effect.•Higher (nonbiological) concentrations of drugs excite the auditory nerve.•Transmitter effects should be assessed at biologically plausible concentrations.