Objective: This paper describes a convenient histochemical technique that allows one to simultaneously assess the cochlear efferent neurons and inner (IHCs) and outer hair cells (OHCs).
Method: Selective labeling of the sensory cells and efferent fibers was carried out by first labeling the hair cells for dehydrogenase activity and then staining the efferent fibers for acetylcholinesterase activity. Double-labeled specimens were prepared as a surface preparation and counts were made of the number of hair cells and the number of discreate fiber bundles crossing the tunnel of Corti along the entire length of the cochlea.
Result: The utility of this technique for assessing ototoxic damage was demonstrated by constructing cochleograms showing the percentage of missing hair cells and tunnel-crossing efferent fibers in chinchillas treated with carboplatin. In the region of the cochlea associated with most IHC loss and a part of OHC missing showed by succinate dehydrogenase in the region of hair cells; however, the loss of tunnel-crossing efferent fibers showed by acetylcholinesterase staining was closely correlated with the percentage of OHC loss. But, if only damage the IHC, the efferent fibers showed normal.
Conclusion: These results suggest that carboplatin damaged efferent systems may be due to the damage of OHC.