Onset of apoptosis after NF-κB inhibition in the organ of Corti. Caspase-3 activation assay; untreated (NT), treated with 25 μg/ml of the inhibitor of NF-κB (INH), 25 μg/ml control for INH (INH-Mut), 50 mM parthenolide (PNT), or dimethyl sulfoxide (DMSO). Baseline buffer and Ac-DEVD-pNA activity (as measured in samples not containing protein lysates) were subtracted from each sample. Data bars represent mean values obtained in three independent experiments, and error bars represent standard deviation of the mean; optical density (OD).