[Amelioration of nerve growth factor against noise-induced threshold shift: a transmission electron microscope...

To study the protective effects of nerve growth factor(NGF) on noise-induced hearing damage in guinea pigs.

NGF injected Guinea pigs were consecutively exposed to white noise of 115 dB(A) for 6 days continually (45 min.d-1). Auditory thresholds were measured using auditory cortex evoked response to tone bursts in different post-exposure intervals (1 h, 1 d, 2 d, 3 d and 6 d). The ultrastructural changes within hair cells were also observed by a transmission electron microscope(TEM).

The auditory threshold shifts in test group A(NGF:1,000 U.kg-1.d-1, i.m.), B(NGF:2,000 U.kg-1.d-1, i.m.) and C(NGF:3,000 U.kg-1.d-1, i.m.) were significantly fewer than that in the control group(Saline: 1 ml.kg-1.d-1, i.m.). Threshold shifts almost recovered in test group B and C 3 days after the exposure; while a threshold shift of (16.43 +/- 6.91) dB was present 6 days after the exposure in the control group. TEM showed that all three rows of the outer hair cells(OHCs) of the basal turn in the control group displayed significant pathological changes. Depolymerization of actin filiaments within stereocilia, swelling of submembraneous cistern and the efferent nerve-ending and slight edema of hair cells were evident. In test group A, the hair cells display slight pathological changes, which are confined in the third row of OHCs in a local position of the basal turn. In group B and C hair cells have nearly normal appearance.

NGF is able to reduce threshold shift, and promote the recovery of auditory threshold in acoustic trauma. This factor can, to some extent, protect against noise-induced hearing damage.