Cross-links between stereocilia in the guinea pig cochlea

Cross-links between stereocilia on guinea pig cochlear hair cells have been examined using high resolution scanning (SEM) and transmission electron microscopy (TEM), confirming recent descriptions of these structures. Links from the tips of shorter stereocilia to the sides of the adjacent taller stereocilia (upward-pointing links), between stereocilia of the same row (side-to-side links) and between adjacent rows (row-to-row links), have been observed on inner and outer hair cells. These links have been seen in material fixed using (1) glutaraldehyde only, (2) glutaraldehyde/osmium and (3) glutaraldehyde/osmium/thiocarbohydrazide (a technique which makes gold coating unnecessary). Upward-pointing links were seen less frequently, and the surfaces of stereocilia and microvilli were smoother after fixation (3) compared with fixations (1) and (2) in which they were usually roughened in appearance. In TEM, side-to-side and row-to-row links form a regular lattice between stereocilia, and consist of a number of strands. Upward-pointing links consist of a single strand, the ends of which are associated with electron-dense material. This lies between the stereociliary membrane and the actin filament bundle, at the tip of the shorter stereocilium and the side of the taller stereocilium.