Abstract： Objective To investigate the mechanism of intense noise-induced apoptosis of vestibular hair cells in guinea pigs and the effect of phosphorylated c-Jun N-terminal kinase (JNK) signal transduction pathway in intense noise-induced apoptosis of vestibular hair cells.Methods Thirty-two guinea pigs were randomly and equally divided into 1,5,and 15 d experimental groups and control group.The guinea pigs in the experimental groups were exposed to 4 kHz narrow-band noise at 120 dB SPL for 4 h and then subjected to measurement of auditory brainstem response at 1,5,or 15 d after noise exposure.In each group,four guinea pigs were used to prepare paraffin sections of vestibular hair cells,and the rest for extraction of total protein from vestibular hair cells.The apoptosis of vestibular hair cells was detected by terminal deoxynucleotidyl transferase (TdT)-mediated d-UTP nick-end labeling (TUNEL).The expression levels of p-JNK and pc-Jun were measured by immunohistochemistry and Western blot.Results TUNEL-positive cells were found in the vestibular hair cells in the experimental groups,most in the 1 d experimental group and least in the 15 d experimental group,but no positive cells were found in the control group.The immunohistochemical results showed that p-JNK and pc-Jun were detected in the cell nuclei in the experimental groups,but no p-JNK-and pc-Jun-positive cells were found in the control group.The Western blot showed that p-JNK and pc-Jun were increased and activated quickly at 1 d after noise exposure,reached the peak levels at 5 d after noise exposure,and were then decreased gradually,but they were still at relatively high levels at 15 d after noise exposure.Conclusion Intense noise can cause injury to vestibular hair cells by inducing cell apoptosis,and p-JNK marks the activation of JNK signal transduction pathway,suggesting that JNK signal transduction pathway plays an important role in intense noise-induced apoptosis of vestibular hair cells in guinea pigs.