Tramadol-induced apoptosis in auditory hair cells of adult male rats.

Reports have emerged on the sudden opioid-induced auditory hearing loss, and the underlying pathology is not fully understood. The present study aimed to determine the mechanism of action of these drugs in the inner ear. For this purpose, 20 rats were treated with 50 mg/kg tramadol daily for three weeks. Next, the stereological and immunohistochemical alteration of the inner hair cells under chronic exposure to tramadol was evaluated. The results revealed that tramadol induced hair cell degeneration and decreased bipolar neurons of the spiral ganglion and the thickness of stria vascularis. Moreover, immunohistochemistry showed that tramadol caused apoptosis in inner hair cells and bipolar neurons. These findings indicate that tramadol induces apoptosis in auditory hair cells, suggesting that tramadol may cause hearing loss and ototoxicity.