Lack of effect of cochlear round window (RW)-administered (+)-MK-801 (8 mmol) on the CAP - N1 amplitudes, recorded at the six indicated stimulus intensities in experiment 3. Shown are the amplitude changes obtained in the [(+)-MK-801 + APS / DMSO (n = 5)]-treated control animals of experiment 3 (open characters), and the amplitude changes obtained in the APS / DMSO + APS / DMSO-treated control animals (n = 7) of experiment 2 (solid characters). At each of the three baseline (time 30, 60 and 90 min) and three post-baseline recording periods (time 120, 150 and 180 min) each point represents a mean percent change in neural amplitude relative to the grand baseline mean (±S.E.M.). Open arrow at time 60 min indicates the 1μl administration of APS(50%) / DMSO(50%), delivered to the cochlear round window membrane in the presence (n = 5; experiment 3) or absence of (+)-MK-801 (n = 7; experiment 2) prior to the final 30 min baseline recording period. Filled arrow at time 90 min indicates the 2μl post-baseline administration of the APS(50%) / DMSO(50%) solution delivered to all animals.