Modulation Of Strial Macrophages In Mice After Noise Exposure

?Objective? To explore the modulation of strial macrophages after noise and try to figure out the relationships between strial macrophages and morphological strial properties following intense acoustic trauma.?Methods and Materials? C57BL/6J mice of 6-8 weeks were exposed to octave-band noise(8–16 k Hz)at 100,106,and 112 d B SPL for 2 hours.At various time points after noise exposure,from 1 hour to 2 weeks,immunofluorescence labeling was performed using anti-Iba1 rabbit Ig G to identify strial macrophages.In addition,fluorescently(Texas Red)tagged gentamicin(GTTR)was systemically administered to mice prior to cardiac perfusion and tissue collection.After perfusion and fixation,cochlear tissues were isolated and dissected without decalcification,then processed for immunohistochemical labeling.?Results? 1.Noise exposure of different level 1).Noise-induced ABR threshold shifts One day after noise exposure,overt ABR threshold shifts were observed with either noise intensity.Seven days after noise exposure,substantial recovery of ABR thresholds was observed in both conditions(106d B and 112 d B);Fourteen days after noise exposure,additional recovery was only seen with 106-d B exposure to noise.2).Effect of sound level Moderate reduction of Iba1-positive cells was only seen with 112-d B noise exposure 7 days after noise exposure,but not with 100-and 106 d B level.2.Intense noise exposure 1).Noise exposure modulated Iba1-positive strial macrophage A significant modulation of Iba1-positive strial macrophages in number and morphology occurred 1 and 9 days after the noise exposure.Iba1-positive macrophages located laterally to the strial counterparts were also examined.The number of these macrophages was also modulated,especially in 7 days.2).Effect of cochlear location on the Iba1-positive strial macrophage One day after noise exposure,the disappearance of strial macrophages occurred completely from the apical to middle coil of the cochlea,while few cells were observed towards the base.And post one day,the density of macrophages in the spiral ligament(SL)was lower than that in the spiral vascularis(SV).3.Other morphological strial properties and The change of relevant chemokine The thickness of the stria vascularis and the average diameter of strial capillaries both trend to increase.There are significant increasing of CCL2 which cause a trafficking of immune cells in post 1 day after noise treatment.?Summary? In the cochlea of adult mice,inside the stria vascularis(SV),Iba1-positive cells are distributed along the capillaries,identified as strial macrophages.Here,most Iba1-positive cells exhibit branched morphology,bipolar or multipolar ameba shape with pseudopodia attaching to strial capillaries or tentacles surveying the interstitial space.Acoustic trauma encouraged numerical and morphological change in the population of strial macrophages after a sufficient dosage of noise exposure.In the groups of mice with moderate noise exposure(100 and 106 d B SPL),primarily studied on day 3 and day 7 after exposure,negligible change was observed in cell number or morphology of the strial macrophages,regardless of their relevant cochlear location.With the highest exposed sound level,112 d B SPL,a brief apical depletion occurred 1 day after exposure.These cells were repopulated in the SV and sometimes exhibited expanded cell bodies with shorter processes,compared to the control group.Another wave of disappearance of Iba1-labeled strial macrophages appear evident around day 9 post noise exposure.The apical depletion of strial macrophages was correlated to the increase of SV thickness and capillary dilation that were observed during the same time window after noise exposure.In the cochlear lateral wall,the noise-induced modulation of Iba1-positive macrophages was also observed in the spiral ligament(SL)that is lateral to the SV.These SL macrophages exhibited higher fluorescent signals but lower degrees of noise-induced modulation.