| Objective: Lots of medicines and chemistries have been proved ototoxic whether in clinical observations or experiment researches, they can damage cochlea and vestibular, resulte in deafness and disorder of vestibular function. Now we don't know how aminoglycoside antibiotics (AmAn) damages hair cells, but there are some theories about it, such as: (1)AmAn affects the transformation among phosphoinositoln, inositol- 3-phophate and glycerine-2-acyl, also, it can cause the change of Ca2+ concentration in endocellular. (2)AmAn can inhibite the activity of G-protein and ornithine decarboxylase. (3)AmAn can cause languish of inner ear hair cell. In the last semicentury, lots of researches about the mechanism of AmAn ototoxicity and its prevention and treatment have been done, while obtaining some achievements, it dissatisfied any one. Neurotrophic factors ( NTFs) is a kind of chemistry which can increase the survival rate of neurone and the growth of nerval spines, it is important in neurone development, neurite growth, transmitter synthesis and cell languish. The existence, migration, growth and differentiation of cells, the establishment of function connection with other cells, even the survival and regeneration of damaged neurone are all affected by these materias. The abnormality or shortage of NTFs may induce some neuropathy or disorder of nerve regeneration. NTFs can accelerate the development of auditory nerve and maintain its normal function, it runs through whole process from auditory plate forming to the establishment of synapse connection between corti's organ hair cells and introduction and efferent nerve twig. But nerve growth factor (NGF) is one of the most characterized factor in NTFs. In this study, we investigated the influence of exogenous nerve growth factor(NGF) on ABR thresholds shift following the ototoxicity of gentamicin, aimed at finding its mechanism and providing basis of the clinical prevention and treatment on hearing loss induced by GM. Methods: ABR and SEM was used to analysis the influence of exogenous nerve growth factor(NGF) on ABR thresholds shift following the ototoxicity of gentamicin. (1) Experimental animals and its treatment. Selected 30 guinea pigs with normal auricle reflect which was health, white, male and weight about 250~300g, according weight we randomized these guinea pigs into NS group, GM+NS group and GM+NGF group, each group contained 10 guinea pigs. 10 guinea pigs of NS group which was injected NS(1ml/kg·d) acted normal sample for SEM; we injected NS(1ml/kg·d) and added GM (120 mg /kg·d) after 15min~30min into GM+NS group guinea pig abdomen; with the same way we injected NGF(1000U/kg·d) and GM (120mg/kg·d) into GM+NGF group guinea pigs abdomen, 3 groups all continued 4 weeks. (2) ABR test. Adopted ABR test instrument to measure ABR threshold of all guinea pigs before experiment, after used GM, we test ABR of sober guinea pigs each one week. Recording electrode was placed on the top of head, reference electrode and grounding electrode were placed respectively on ipsolateral and contralateral mastoid. Observed all wave shape, looked the stimulate intensity of short-sound when Ⅲ wave appeared as ABR threshold. (3) SEM sample preparation and observation. We took 3 guinea pigs from 3 groups respectively and chose left cochlea of these guinea pigs acting SEM objects. After last administration and ABR testing, we decapitated guinea pigs quickly, drew both temporal bone, opened auditory vesicle in anatomy microscope, sticked round window, pulled stapes out, bored in helicotrema, pefusioned with 2.5% glutaraldehyde, exuviated calcium with 10%EDTA for fifteen days, shelt cochlea in anatomy microscope, fixed 4h with 2.5% glutaraldehyde, then washed 3 times(10min each times) with 0.1mol/L phosphate buffer, again fixed 2h with 1% osmic acid, dehydrated and dried gradiently with alcohol, plated metal membrane, finally we observed cochlear hair cell structure changes with SEM.Results: (1) Changes of ABR threshold. After injected GM into the tested guinea p... |
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