Cochlear hair cell densities in the rabbit

Fang Yuan,Dalian Ding,Weidong Qi,Yitan Cao

doi:10.1007/s12565-018-0461-y

Abstract

A typical cochleogram was plotted to investigate hair cell densities as a percentage along the whole length of the basilar membrane (BM) of the rabbit, the length of the BM and the width of the organ of Corti. We generated surface preparations of cochlea from adult, healthy New Zealand White (NZW) rabbits. The numbers of inner hair cells (IHCs) and outer hair cells (OHCs) were counted from images acquired from a digital camera attached to an Olympus light microscope with a scale of 100 μm as a primary unit drawn continuously, and the numbers of IHCs and OHCs were converted to densities at 10% intervals along the length of the cochlea. Meanwhile, the length of the BM and the width of the organ of Corti were calculated. The average length of the cochlea was 14.504 ± 0.403 mm, while the total number of IHCs and the numbers of OHCs in the first, second, and third rows were 1556 ± 13, 1840 ± 47, 1842 ± 46, and 1840 ± 45, respectively, accounting for 21.98%, 26.00%, 26.02%, and 26.00% of the total number of cells, respectively. The densities of each row of OHCs reported in 10% intervals were greater than the densities of the IHCs corresponding to their anatomical locations within the cochlea. The densities of OHCs in each row were distributed uniformly along the BM, while the IHCs densities were not and showed a bimodal distribution with a maximum density at the apex and at 70–80% of the cochlear length from the apex but a lower density in the remaining cochlea. The width of the organ of Corti decreased successively from the apex to the base.

Highlights

Cochlear hair cells are the primary receptors in the inner ear that perceive sound-induced vibrations
The numbers of inner hair cells (IHCs) and outer hair cells (OHCs) in the first, second, and third rows accounted for 21.98%, 26.00%, 26.02%, and 26.00% of the total number of cells, respectively, and the results revealed higher densities of OHCs in each row in 10% intervals along the length of the cochlea than IHCs corresponding their anatomical locations within the cochlea (P < 0.01, Fig. 2)
More than 50 years ago, the cochleogram was introduced as a tool to visualize properties of the cochlea in relation to the location within the cochlea using a surface preparation technique, and it represents a feasible method for assessing the damage to both the IHCs and OHCs by depicting the percentage of hair cell loss along the length of the cochlea (Saunders 1967)

Summary

Introduction

Cochlear hair cells are the primary receptors in the inner ear that perceive sound-induced vibrations. Cochlear hair cell loss is one of the common causes of permanent sensorineural deafness and is caused by ototoxic drugs, heavy metal poisoning, high-intensity noise, pesticide poisoning, and other factors (Ding et al 2012; Li et al 2015; Prakash Krishnan Muthaiah et al 2017; Yu et al 2015). Quantitative observations designed to evaluate the loss of cochlear hair cells have been used widely in various common experimental animal models, including guinea pigs, chinchillas, rats, and mice (Ding et al 2011, 2013; Muller et al 2005). The rabbit is a commonly used experimental animal model, rabbits are used far less frequently in auditory research than in other medical studies.

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