Vestibular Apparatus Damage In Guinea Pigs Exposed To60Co γ-Ray Irridiation

Objective:Nasopharyngeal carcinoma(NPC) is a head and neck malignancy with high incidence in south China. Radiotherapy(RT) is the treatment of choice for NPC. Middle ear and inner ear are included in the regulation area of NPC Radiotherapy. Sensorineural hearing loss(SNHL), secretory otitis media(SOM) and vertigo are common complications after radiotherapy of NPC, these complications decrease the quality of the NPC patients’life. So far, most of the domestic and foreign scholars’researches were about radiation-induced cochlear damage, the researches about radiation-induced vestibular damage were fewer. And most of the contents of research about radiation-induced vestibular damage were restricted to the functional and morphological level. In this study, we established radiation-induced vestibular damage model and observed the change of vestibular function, the expression of caspase-3, bax, bcl-2in vestibular apparatus by pathological examine, immunohistochemistry, and transmission electron microscopy (TEM). To explore the relationship between radiation-induced vestibular damage and the apoptosis protein caspase-3、 bax、bcl-2.Methods:48guinea pigs were randomly divided into5groups, including control group(8guinea pigs) and radiation groups(40guinea pigs). The control group didn’t receive60Co γ-ray irradiation. The right ears of the guinea pigs in radiation groups were radiated. The guinea pigs were sacrificed on ld、4d、14d and30d after irradiation of40Gy. Before sacrificed the guinea pigs were given ice water irrigation. After sacrificed all specimens were dehydrated, cryoembedded in paraffin, serially cutted into4μm slices.2of the otocyst vestibular apparatus were for transmission electron microscopy (TEM) in control group and irradiation groups, and8of the otocyst vestibular apparatus were for pathological examine and immunohistochemistry.Results:(1) Gross specimens observation, the otocyst had no purulent discharge in1,4,7,14days after irradiation of40Gy. There was a guinea pig died in30days after irradiation, and the otocyst of this guinea pig had some purulent discharge.(2) Vestibular function examine, when given ice water irrigation, the horizontal nystagmus time of irradiation groups decreased compared with the control group (P<0.05). The horizontal nystagmus time at30days (48.50±5.44s) after irradiation increased compared with other irradiation groups (P<0.05).(3) Pathological examine, the structure of macula utriculi of control group was normal. In irradiation group, the cilia of hair cells in macula utriculi became shorter, the number of cilia and hair cells decreased and the otolith disappeared. The structure of crista ampullaris of control group was normal. In irradiation group, the cilia in of hair cells in crista ampullaris became shorter and the number of cilia decreased, and the number of hair cells decreased.(4) Transmission electron microscopy (TEM) examine, there were no morphological change occured in macula utriculi and crista ampullaris in the control group. In the irradiation group, the mitochondria in macula utriculi and crista ampullaris became oncotic, the mitochondria crista became shorter and broken. The chromatin assemble around the nucleolus. And the chromatin of hair cells in macula utriculi and crista ampullaris disappeared on the30th day after irradiation.(5) Compared with the control group, the expression of caspase-3、 bax、bcl-2of macula utriculi and crista ampullaris was higher in the irradiational groups (P<0.05). Compared with other irradiational groups, the expression of caspase-3of macula utriculi and crista ampullaris of30d group was lower (P<0.05). The expression of bax of macula utriculi and crista ampullaris was much higher than that of bcl-2of group4d, bax/bcl-2increased. The expression of bcl-2of macula utriculi and crista ampullaris was much higher than that of bax on group30d, bax/bcl-2decreased.Conclusion:(1)40Gy60Co γ-ray could lead to the damage of vestibular function and vestibular apparatus. (2) Caspase-3played an important role in the injury of vestibular function which caused by the irradiation of60Co; The unbalance expression between bax and bcl-2may played an important role in the damage which caused by irradiation of60Co on vestibular apparatus.(3) The apoptosis process depend on apoptosis protein caspase-3, bax, bcl-2may play an important role in the damage which caused by irradiation of60Co on vestibular apparatus.