Dense innervation of Deiters' and Hensen's cells persists after chronic deefferentation of guinea pig cochleas.

Innervation of Deiters' and Hensen's cells has been described in the organ of Corti of several mammalian species and has been suggested to arise from the olivocochlear (OC) efferent system (Wright and Preston [1976] Acta Otolaryngol. 82:41-47). In the present study, antineurofilament immunostaining was used to reveal these outer supporting cell fibers (OSCFs) in the normal guinea pig. In control ears, OSCFs were absent in the basal half of the cochlea but increased in number steadily toward the apex, peaking at values of over 1,200 fibers/mm. These values indicate a far more profuse innervation of supporting cells than has been described previously, suggesting that most OSCFs were not stained in previous immunohistochemical studies. Chronic cochlear deefferentation was used to test whether OSCFs are part of the OC system. The OC bundle was transected unilaterally, and the animals were allowed to survive for 4-8 weeks. Completeness of deefferentation was assessed by using acetylcholinesterase staining of the brainstem and measurement of the density of OC fascicles in the cochlea. By using these metrics, unilateral deefferentation was nearly complete in three animals. In successfully deefferented cases, the OSCF innervation density was not statistically different from control values. We conclude that the vast majority of OSCFs are not of OC origin. We speculate that they may be branches of type II afferent fibers to outer hair cells and that a smaller population of OSCFs with different morphology and immunoreactivity may arise from the OC system.