Extruding auditory hair cells in rats exposed to subchronic 3,3′-iminodipropionitrile

Hair cell loss by extrusion of nearly intact cells towards the endolimphatic cavity has been reported in the vestibular epithelia of rats subchronically exposed to 3,3′-iminodipropionitrile (IDPN). To investigate whether hair cell extrusion also occurs in the auditory system, adult male Long-Evans rats were exposed to IDPN through drinking water (0.2-0.4% for 4-14 weeks), and their organ of Corti were examined by light and scanning electron microscopy. IDPN exposure caused loss and protrusion of the outer hair cells. The surface appearance of the protruding outer hair cells was similar to that of extruding vestibular hair cells. However, the former showed cell shrinkage and irregularly shaped nucleus, by contrast to the almost normal ultrastructure shown by the latter. The results indicate that outer hair cells can suffer extrusion, but the final outcome of this process (complete extrusion versus apoptosis) remains to be determined.