Melanocytes of the Vestibular Labyrinth and Their Relationship to the Microvasculature

The melanocytes of the vestibular labyrinth as seen in colored guinea pigs show a characteristic pattern of distribution in the wall of the utricle and in the ampullae, but they are not present in the wall of the saccule. They are found mainly in well-vascularized regions of apparent secretory or metabolic importance, including the “dark cell” areas. Their dendrite-like processes are often in intimate contact with the capillaries, although no pinocytotic vesicles or other indications of transfer of substances between the melanocytes and the capillary endothelium are seen under the electron microscope. In the human ear, the apparent density of the melanocytes varies with skin color. They are numerous in the cochlea, especially in the bony wall of the modiolus and on the osseous spiral lamina, and they occur also in Reissner's membrane and in the stria vascularis. In the vestibular system they are found in the wall of the saccule as well as in the utricle, the crus commune, and the ampullae, but not in the semicircular canals. They tend to be diffusely scattered, rather than to form the well-defined, intensely pigmented areas that are characteristic of the guinea pig. Close contacts with capillaries are seen mainly in the tympanic portion of the spiral ligament. The significance of melanin and the melanocytes in the labyrinth is unknown, but both the anatomical relation of certain melanocytes to capillaries, and the biochemical relation of melanin to the catecholamines support the hypothesis that they may have a vasomotor function. Other evidence, including the not infrequent association of sensorineural deafness with hereditary disorders of pigmentation also suggests that the melanocytes may play a role of some biological consequence in the inner ear.