Apoptosis and the injury of the inner ear

Objective To investigate whether or not apoptosis participates in the final injury of inner ear caused by laser,and explore the mechanism of the injury.Methods Twenty-four male guinea pigs with normal hearing were divided into the control group,in which only the otocyst was opened to expose the round window niche and experimental groups A,B and C.Each group had six guinea pigs.The last three groups underwent the fenestration on the basal turn of the left cochlea with superpulse CO2 laser at a power of 1 W,3 W and 5 W respectively.Auditory brainstem response(ABR)was recorded one day before the operation and antemortem.Scanning electron microscopy was used to evaluate cochlear morphology.The TUNEL method was used to detect apoptotic cells in the inner ear.Results The thresholds of postoperative ABR were higher than those preoprative in experimental groups B and C(P0.05).The cilla of hair cells mostly disappeared with spaces between the hair cells in experimental group C,were partially scattered in experimental B compared with the control group and group A which were normal.Obvious TUNEL-positive cells could be detected in spiral ganglion cells,cochlear nerve cells,outer hair cells in group C,while few were found in group B compared with the control group and group A which appeared normal.Conclusions The high peak power superpulse CO2 laser could damage the cochlear morphology and function of the guinea pig,and apoptosis plays a critical roll in it.