Regeneration of cochlear hair cells of guinea pigs following gentamicin ototoxicity

Yueqiu NI; Hao TANG; Cheng CUI

ABSTRACT

BACKGROUND:

Formerly, it was thought that the damaged hair cells could not have the repair ability. Recent studies demonstrate that mammal vestibule hair cells also possess certain repair ability after being destroyed.Then, whether mammalia animal cochlea hair cells possess regenerative ability after being destroyed is disputed.

OBJECTIVE:

To observe cochlear hair cells condition and threshold value change of auditory brainstem response (ABR) at different time following gentamicin ototoxicity by using scanning electron microscope (SEM) technique combined with ABR test, so as to investigate whether cochlear hair cells of mammals can be regenerated after being injured.

DESIGN:

A randomized and controlled animal experiment.

SETTING:

Department of Physiology, Shenyang Medical College.MATERIALS This experiment was carried out at the Hearing Research Room of China Medical University from November 2001 to May 2002. Totally 60 healthy adult white Guinea pigs, with red eyes and sensitive auricle reflex, of clean degree, were used and randomly divided into gentamicin group and normal control group with 30 guinea pigs in each one.

METHODS:

100 mg/kg gentamicin was intraperitoneally daily injected into the guinea pigs, serving as gentamicin group. Same volume of normal saline (2.5 mL/kg) was intraperitoneally daily injected into the guinea pigs,serving as normal control group. All the guinea pigs were given medication for 10 successive days. Threshold value of ABR was detected respectively pre-operatively and at the 1st, 3rd, 30th days postoperatively; after withdrawal and execution, scanning electron microscope was used to observe cochlear hair cells of guinea pigs in each group.MAIN OUTCOME

MEASURES:

① Threshold value of ABR. ②Cochlear hair cell change of guinea pigs at different time following gentamicin ototoxicity.

RESULTS:

All the 60 experimental animals entered the stage of result analysis with no loss in the midway. ①At 1,3 and 30 days after withdrawal of gentamicin, threshold value of ABR was significantly higher as compared with normal control group, with significant difference [(38.00±3.75), (2.22 ±3.63) dB nHL,t=30.651, P ＜ 0.001];[(39.09±4.22), (2.50±3.54) dB nHL, t=29.708, P ＜ 0.001];[(14.50±3.69), (1.50±2.42) dB nHL,t =13.175, P ＜ 0.001]. Threshold value of ABR recovered obviously on day 30, but did not reach the normal level. ②On the first day after withdrawal of gentamicin , stereocilium of hair cells in second turn of cochlea of guinea pigs presented fusion, distortion, lodging, loss or incompetence and other pathological changes , especially severe in the third turn , also cystic form protrutions appeared outside the stereocilium of inner hair cell; On day 3 after withdrawal of gentamicin, stereocilium of outer hair cells in the second turn of cochlea of guinea pigs still presented fusion, loss, lodging and other pathological changes. Stereocilium of inner hair cell still showed lodging,but the outside cystic form protrutions decreased; On day 30 after withdrawal of gentamicin, stereocilium of outer hair cells in the second turn of cochlea presented fusion, loss , lodging and other pathological change ,which were obviously weaker than those on the 1st day and 3rd day after withdrawal of gentamicin , and at the same time , new born stereocilium appeared in the third turn of cochlea.

CONCLUSION:

Cochlear hair cell morphology recovery appears in those which survive for 30 days after cochlear hair cells of guinea pigs are damaged following gentamicin ototoxicity, and threshold value of ABR also recovers to some extent, suggesting that cochlear hair cells possess regenerative and repair ability following gentamicin ototoxicity. Hair cells after gentamicin-induced cochlear damage possess regenerative ability.