Unbiased Stereologic Type I and Type II Hair Cell Counts in Human Utricular Macula

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Abstract
Objective The objective of the study was to obtain unbiased estimates of the total number of type I and type II hair cells in human utricular macula from individuals with documented normal vestibular function. Study Design Application of unbiased stereology using microdissected human temporal bone specimens was conducted in an observational study. Methods Postmortem temporal bones were obtained from 10 normal patients (age range, 42–96 y; mean age, 82 y). The utricular maculae were microdissected, embedded in plastic, and cut into serial 2-μm sections. Unbiased estimates of the total number of type I and type II hair cells were obtained using the physical fractionator technique of stereology. Results The average total number of hair cells was 27,508 (CV = 11%) consisting of 17,326 (coefficient of variation [CV] = 11%) type I hair cells and 10,182 (CV = 13%) type II hair cells. The ratio of type I to type II hair cells was 1.70:1. In the age range of the study, there was no statistically significant correlation between hair cell counts and age. Conclusions Morphometric studies of the human utricular sensory epithelium can be accomplished using unbiased stereology on microdissected specimens. There was no effect of age on total hair cell counts or on the ratio of type I to type II hair cells in the age range of the study. Further studies on younger subjects are needed to establish the effect of age. The results from the present study are closely aligned with prior studies that estimated total hair cell counts using surface mount preparations. The current data represent the first total type I and type II hair cell counts in human utricular neuroepithelium.