Tension fibroblasts and the connective tissue matrix of the spiral ligament

Fibroblasts with stress fibers (tension fibroblasts) have previously been described in the marginal region of the spiral ligament of bats and mice (Henson et al., 1984, 1985). The location, structure and attachments of these cells and the fact that they contain contraction associated proteins, have suggested a role in the generation of tension within the basilar membrane-spiral ligament complex. In this study the structure of these fibroblasts and their relationships to different types of connective tissue matrices were examined in representative Marsupalia, Insectivora, Chiroptera, Rodentia, Lagomorpha, Carnivora and Primates. Tension fibroblasts occur in all species but they are remarkably different in their actin filament content, their structure and distribution, and in their association with the extracellular matrix and otic capsule. Six types of matrices are described (dense filamentous, bundled, laminated, honeycombed, trabeculated and loose filamentous). The configurations of the cells and fibers indicate that tension on the basilar membrane may be accomplished in different ways and to different degrees in different mammals. The arrangement of the matrix and cells in some animals is markedly different in the parts of the cochlea that respond to high, middle and low frequencies.