Expression Of P75NTR And TrkB In Deafness Rats Induced By Gentamicin

BackgroundHearing impairment was still one of the most common disabilities in modernsociety, which seriously affected the life of patients. The information provided by theauthorities showed that there were about20,570,000suffered from deafness, of which7years old children were up to800,000, and presbycusis were9,490,000. Thenewborn deaf increased by30,000because of the drugs, heredity, infection, disease,environmental noise pollution, accidents and other causes. Of these patients, a smallpart was congenital, while mostly was acquired. The deafness acquired was caused bydrugs majority. Aminoglycoside antibiotics was the majority, especially Gentamicin,which often caused irreversible permanent hearing loss.Although cochlear implants could improve hearing to a certain degree, therewere still many restrictions. In addition, the target cells of cochlear implant werespiral ganglion cells (SGN), which were induced secondary degeneration afterdeafness. Animal experiments showed that the degeneration of spiral ganglion cellwas due to lacking of neurotrophic factors partly. Many researchers were alsoconfirmed that giving a certain amount of neurotrophic factors were capable ofprotecting spiral ganglion cells from damage, either in vitro or in vivo. Neurotrophicfactors were useful only by binding to cell surface receptors. Presumably,neurotrophic factor receptors played an important role in the development of the inner ear and damage process. Domestic research on neurotrophic factor receptors in deafcochlea was poor, so in this experiment, a animal model of deafness was established,and immunohistochemical method was applied to observe the expression ofneurotrophin receptors in the cochlea after deafness.Objective1. To research the expression of p75NTR and TrkB in deafness rat cochlea.2. To explore the relationship between Gentamicin-induced deafness and theexpression of neurotrophic factor receptors.Materials and methods1. To establish deafness animal model. A total of30healthy adult male SDrats(provided by the Experimental Animal Center of Henan Province) were analyzed.They were randomly divided into2groups: the experimental group and the controlgroup,15rats in each group. Experimental groups: intraperitoneal injection ofgentamicin sulfate160mg/kg, one times a day for14days. Control group:intraperitoneal injection of normal saline of the same volume, one times a day for14days too. All the animals were sacrificed at the fifteenth days too. Before sacrifice allthe animals underwent auditory brainstem response (ABR) test, and at the same timerecorded ABR test results.2. Harvest cochlea and immunohistochemical staining. Firstly, intraperitonealinjection of10%chloral hydrate with a dose of0.4ml/100g, secondly, cardiacperfusion with saline and4%paraformaldehyde respectively, and then rapidlysnipped head, removed the cochlea, opened oval window and the round window,fixed48hours with4%paraformaldehyde. After fixation they were decalcified in10%EDTA for10days. Then graded alcohol dehydration, embedded in paraffin,serially sectioned parallel to modiolus, and each specimen for4. The4slices wereused respectively for HE staining, p75NTR immunohistochemical staining, TrkBimmunohistochemical staining and a negative control. SPSS17.0statistical softwarewas used for statistical analysis. Results1. The animal model of deafness induced by gentamicin was successfullyestablished.2. The mean ABR thresholds of experimental group increased significantlycompared with the control group.3. HE staining showed: the Cochlear Corti’s of experimental group wasdamaged accompanying with stained spiral ganglion cells and thinned stria vascularis,while the control group was normal.4. Immunohistochemical results showed: TrkB expression of the experimentalgroup was significantly decreased compared with the control group, and thedifference was statistically significant (P<0.05); while p75NTR expression of theexperimental group increased significantly compared with the control group, and thedifference was statistically significant (P<0.05).Conclusions1. Gentamicin sulfate by intraperitoneal injection could establish a deafnessmodel of ototoxic drugs injury.2. The expression of TrkB reduced while p75NTR increased, which could reflectthat the two neurotrophin receptor played different roles in the process of cochleardamage and p75NTR may be pro-apoptosis.