Hair cell counts in a rat model of sound damage: Effects of tissue preparation & identification of regions of hair cell loss

Abstract

Exposure to intense sound can damage or kill cochlear hair cells. This loss of input typically manifests as noise induced hearing loss, but it can also be involved in the initiation of other auditory disorders such as tinnitus or hyperacusis. In this study we quantify changes in HC number following exposure to one of four sound damage paradigms. We exposed adult, anesthetized Long-Evans rats to a unilateral 16 kHz pure tone that varied in intensity (114 dB or 118 dB) and duration (1, 2, or 4 hours) and sacrificed animals 2–4 weeks later. We compared two different methods of tissue preparation, plastic embedding/sectioning and whole mount dissection, for quantifying hair cell loss as a function of frequency We found that the two methods of tissue preparation produced largely comparable cochleograms, with whole mount dissections allowing a more rapid evaluation of hair cell number. Both inner and outer hair cell loss was observed throughout the length of the cochlea irrespective of sound damage paradigm. IHC loss was either equal to or greater than OHC loss. Increasing the duration of sound exposures resulted in more severe HC loss which included all HC lesions observed in an analogous shorter duration exposure.

Towards a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny – part II: how can key events of relevant adverse outcome pathways be addressed in toxicological assessments?

“…This non-invasive test could be added to the study design to supplement the assessment of the auditory startle response in rats. The cochlea could also be examined histopathologically for the loss of hair cells (Neal et al 2015); however, this procedure requires highly-specialized dissection skills and the results do not necessarily inform on cochlear function.…”

In Situ 3D-Imaging of the Inner Ear Synapses with a Cochlear Implant

“…Due to the compact lamellar bone, the densest in mammals [ 14 ], forming the otic capsule it is impossible to image the organ of Corti, which is the sensorineural organ of special interest, through the bony capsule. Therefore the common way is to separate the neuroepithelium [ 15 , 16 ], or to embed the tissue in various materials, e.g., paraffin [ 17 , 18 ], plastic [ 19 , 20 ] including resin [ 21 , 22 ], or gelatin [ 23 ] and produce serial sections or grind it for histological evaluation. The resulting 3D reconstructions are time-consuming procedures and are prone to artefacts [ 19 , 24 ].…”

“…Therefore the common way is to separate the neuroepithelium [15,16], or to embed the tissue in various materials, e.g., paraffin [17,18], plastic [19,20] including resin [21,22], or gelatin [23] and produce serial sections or grind it for histological evaluation. The resulting 3D reconstructions are time-consuming procedures and are prone to artefacts [19,24]. In addition, embedding materials can result in less tissue antigenicity, making it difficult to perform immunostaining.…”

Evaluation of the Efficacy of Dexamethasone-Eluting Electrode Array on the Post-Implant Cochlear Fibrotic Reaction by Three-Dimensional Immunofluorescence Analysis in Mongolian Gerbil Cochlea

“…Furthermore, the analysis of the scala tympani and therefore of the endo canal fibrosis is not allowed. Indeed, this study requires serial cochlear sections and 3D reconstruction which are time consuming and responsible for a loss of membrane information and architectural deformations of the organ of Corti [ 41 , 42 , 43 , 44 , 45 ]. Most importantly, serial sections of embedded implanted cochlea require the electrode array to be removed, which disrupts the tissue response.…”