Study of protective effect on rat cochlear spiral ganglion after blast exposure by adenovirus-mediated human β-nerve growth factor gene.

Objective: To study whether adenovirus-mediated human β-nerve growth factor (Ad-hNGFβ) gene has any protective effect on rat cochlear spiral ganglion after blast exposure.

Methods: Deafness was induced by blast exposure (172.0 dB) in 20 healthy rats. Seven days after blast exposure, Ad-hNGFβ was infused into the perilymphatic space of 10 animals as the hNGFβ/blast group, and artificial perilymph fluid (APF) was infused into the perilymphatic space of 10 animals as the APF/blast control group. An additional control group consisted of 10 healthy rats which received Ad-hNGFβ target gene with no blast exposure (hNGFβ/control group). Auditory functions were monitored by thresholds of auditory brain stem responses (ABR). At weeks 1, 4, and 8 postoperatively, the animals were killed, and the cochleae were removed for immunohistochemical, hematoxylin and eosin staining study.

Results: The ABR threshold shifts in the hNGFβ/blast group were significantly smaller than that of APF/blast control group. There were no significant differences of the ABR values between before and after operation in the hNGFβ/control group. Expression of Ad-hNGFβ protein was detected in each turn of the cochlea in the first week, with almost equal intensity in all turns. In the fourth week, the reactive intensity decreased. In the eighth week, no reaction was detectable. The results of hematoxylin and eosin stain showed that the number of spiral ganglions in the hNGFβ/blast group was significantly greater than that of the APF/blast control group in the 4th week (P < .01).

Conclusion: Adenovirus-mediated human β-nerve growth factor can be expressed at a high level and for a relatively long period in the blast impaired cochlea, suggesting that Ad-hNGFβ has a protective effect on rat cochlear spiral ganglion cells after blast exposure.