Differences Between Stereocilia Numbers on Type I and Type II Vestibular Hair Cells

Department of Biological Sciences and Neuroscience Program, Ohio University, Athens, Ohio 45701 Submitted 27 April 2004; accepted in final form 13 June 2004 A major outstanding goal of vestibular neuroscience is to understand the distinctive functional roles of type I and type II hair cells. One important question is whether these two hair cell types differ in bundle structure. To address this, we have developed methods to characterize stereocilia numbers on identified type I and type II hair cells in the utricle of a turtle, Trachemys scripta . Our data indicate that type I hair cells, which occur only in the striola, average 95.9 ±16.73 (SD) stereocilia per bundle. In contrast, striolar type II hair cells have 59.9 ± 8.98 stereocilia, and type II hair cells in the adjacent extrastriola average 44.8 ± 10.82 stereocilia. Thus type I hair cells have the highest stereocilia counts in the utricle. These results provide the first direct evidence that type I hair cells have significantly more stereocilia than type II hair cells, and they suggest that the two hair cell types may differ in bundle mechanics and peak mechanoelectric transduction currents. Address for reprint requests and other correspondence: E. H. Peterson, Dept. Biological Sciences, Irvine Hall, Ohio Univ., Athens, OH 45701 (E-mail: peterson{at}ohiou.edu ).