[Influences of two different endolymphatic infusion ways to cochlear morphology and function in guinea pigs]

To explore the influence of two different endolymphatic infusion ways on cochlear morphology and function.

Forty healthy pigment guinea pigs (250 - 350 g) with normal Prey's reflex were divided into A and B group with 20 animals respectively. The right ears served as treated ears and the left ones as control ones. In group A, 5 microl of adenovirus 5-enhanced green fluorescence protein (Ad5-EGFP) suspension was infused into the scala media through an opened cochleostomy on the lateral wall of the scala media (LWS). In group B, the same volume of Ad5-EGFP suspension was infused into the scala media through punctured round window membrane and the basilar membrane (RBM). Cochlear morphology was examined under scan electric microscope and phalloidin staining was used to observe the hair cells in the infused ears after the animals were sacrificed. Auditory brainstem thresholds of the ears of all the animals were measured before and after treatment.

All the animals recovered well after operation. The holes on the lateral wall of the scala media and punctures on the round window membrane were healed completely. EGFP labeling appeared in the organ of Corti and lining wall of the stria vascularis indicated that adenovirus suspension was injected into the scala media using LWS (succeed in 14 animals accounted for 70%) and RBM (in 8 animals accounted for 40%) ways. Viruses were inoculated into the scala media with only locally inflammation reaction. In group A the hearing threshold decreased significantly in the treated ears compared with the control ears after the operation [(33.1+/-10.3) dB, (9.4+/-3.9) dB, F=46.34, P=0.0005]. However, in group B there was no significantly different between the treated ears and the control ears after the operation [(2.5+/-3.8) dB, (2.5+/-3.8) dB, F=0.00, P=1.000]. Phalloidin staining indicated that in group A the extension of hair cells loss was bigger than in group B. In some animals of two groups, EGFP labeling appeared in the extra-lymphatic system indicating that some of the injected suspension leaked out of the scala media.

Ad5-EGFP could be infused into the scala media through LWS or RBM and adenovirus could infect the lining cells of scala media and supporting cells in the basal membrane successfully without causing immunoreaction in the whole cochlea. LWS caused more hair cell loss and hearing loss than RBM. However, the cochlear morphology could be recovered completely after surgery. The positive inoculation rate was relatively higher that through LWS than that through RBM.