Comparative anatomy of melanin pigment in the stria vascularis. Evidence for a distinction between melanocytes and intermediate cells in the cat.

Although Corti in 1851 first described the presence of cochlear pigmentation in the stria vascularis (SV) of "very old" cats, modern studies have failed to find pigment consistently in the feline stria. While the variable presence of pigment in the feline SV would appear to contrast with this structure's uniform pigmentation in other mammalian species, variability in both the distribution and abundance of inner ear pigment has rarely been studied in any species. In the present study, the SV was examined light microscopically in sectioned material or whole-mounts from pigmented and albino animals of 5 species, including the cat, guinea pig, rabbit, ferret and mouse. In these species, the SV of each pigmented animal contained varying amounts of melanin pigment and none was found in the albino inner ear. Pigmented guinea pigs contained the most uniformly dense and least variable distribution of strial melanin, followed by the rabbit, mouse, ferret and cat. Several species also displayed more strial pigment apically and less basally. In cats, pigmented cells were principally located adjacent to the strial capillaries. Ultrastructural studies of the stria in pigmented cats revealed that these perivascular cells frequently contained an abundance of pigmented organelles and other structural features which allowed them to be distinguished from intermediate cells.