Changes Of Ribbon Synapse Of Cochlear Inner Hair Cell In Two Modes Of Ionizing Radiation And Gentamicin

ObjectiveRibbon synapse of cochlear inner hair cell is the first synapse in theauditory passway.Ribbon synapse plays a very important role in thetransduction of hearing message.The changes of morphology、number、structure and function of ribbon synapse may cause sensorineuraldeafness.This study will study the changes of ribbon synapse of cochlear innerhair cell in two modes of sensorineural deafness.MethodsIn this experiment,1105weeks old C57BL/6J mice were selected,withexception with auricle and middle ear disease. ABR were used to assesshearing threshold. The hearing threshold is normal before the model wasmade. The mice were randomly divided into2parts.The first part has70mice,divided into seven groups(each group10mice).The seven groups are asfollows:①n ormal control group;②7days after10Gy radiation;③14days after10Gy radiation;④21days after10Gy radiation;⑤7days after20Gy radiation;⑥14days after20Gy radiation;⑦21days after20Gy radiation.The secondpart(40mice) were divided into4groups:①normal control group;②intraperitoneally injected with gentamiein(100mg/kg) for7days(the7dgroup);③intraperitoneally injected with gentamicin(100mg/kg) for14days(the14d group);④14daysafter intraperitoneally injected withgentamiein(100mg/kg) for14days (the28d group).At each time point ABRhearing threshold were assessed and then cochlear were collected for following experiment:①cochlear sections were stained with haematoxylin andeosin for observation of Corti’s organ,neurofilamnet and spiral ganglioncells;②The cochlear basilar membranes were separated，immunofluorescenceof CaV1.3/CtBP2、 VGLUT3、 MyosinⅦ a、 prestin；③cochlear sectionsimmunofluorescence of NF(neurofilament)、MyosinⅦ a；④SEM observationof sterocillia of hair cells.Results1.ABR threshold alteration10Gy radiation group:The ABR threshold was gradually elevated.Therewas significant statistical differences(P＜0.01).20Gy radiation group: TheABR threshold was gradually elevated.There was significant statisticaldifferences(P＜0.01).There was significant differences between7days or14days and21days(P＜0.01),while there was no differences between7daysand14days(.P＞0.05).At the same time point,there was statistical differencesbetween10Gy goup and20Gy group.Gentamicin group: The ABR thresholdwas gradually elevated until14days,the ABR threshold was descented at thetime point of28days. there was significant differences between7days、14daysor28days and control group(P＜0.01).There was also significant differencesbetween7days or28days and14days(P＜0.01).2.Changes of CaV1.3/CtBP2immnostaing points.Radiation group:The number of CaV1.3/CtBP2immnostaing pointgradually decreasd.There was significant differences(P＜0.01).At the sametime point,there was significant differences between10Gy groups and20Gygroups(P＜0.01). The number of CaV1.3/CtBP2immnostaing point of20Gygroups was more lesser than that of10Gy groups.Gentamicin group: Thenumber of CaV1.3/CtBP2was elevated in7day group,decreased in14daygroup and mild elevated in28day group.There was significant differences(P＜0.01).3. Immnostaing of VGLUT3. Radiation group: The immnuostaing of VGLUT3was graduallydecreased.20Gy group was more sever than10Gy group.Gentamicin group:There was no siginificant difference between control groups.4. Immnostaing of Neurofilament.Radiation group:The immostaing of neurofilament was graduallydecreased.20Gy group was more sever than10Gy group.5.Number of spiral ganglion cells.Radiation group:The number of spiral ganglion cell was graduallydecreased.20Gy group was more sever than10Gy group. There wassignificant differences between each groups(P＜0.01). Gentamicin group:There was no siginificant difference between control groups(P＞0.05).6.Immunostaing of prestin.Gentamicin group: There was no siginificant difference between controlgroups.7.SEM observation of sterocillia of hair cells.The sterocillia of hair cells showed no obervious differences betweencontrol groups.Conclusions1.ABR threshod gradually elevated after radiation. With the increase ofdose of radiation,the ABR threshod elevated more severely.2.After radiation,the number of CaV1.3/CtBP2decreases.3. After radiation,the number of spiral ganglion cell decreases.4.The ribbon synapse is more sensitive to gentamicin than outer hair cell.