Experimental Temporal Bone Histopathology in Rats Deprived of Dietary Retinol and Maintained with Supplemental Retinoic Acid

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Abstract
Hearing loss has been observed in humans and experimental animals in severe vitamin A deficiency. In experimental animals, vitamin A deficiency leads to periosteal bone overgrowth of the internal auditory canal, but atrophy or degeneration of vestibular and cochlear sensory cells does not occur. An analogous situation exists in the sensory cells of the retina; vitamin A deprivation leads to a functional impairment without a histological correlate. Experimental animals maintained with retinoic acid grow and mature normally, but the rods and cones of the retina slowly atrophy. If the sensory cells of the auditory and vestibular apparatus are also vitamin A dependent, degeneration may occur in animals deprived of dietary vitamin A, but supplemented with retinoic acid. To test this hypothesis, weanling rats were fed a diet totally lacking vitamin A but supplemented with retinoic acid. They were killed at intervals and their retinas and inner ears were examined histologically. After 8 months of the above regime, the visual cell nuclei had atrophied. By 12 months, the scala media of the cochlea was filled with an eosinophilic, amorphous substance particularly at the helicotrema. The sensory cells of the cochlea and the vestibular apparatus remained normal in appearance. These findings imply that the tissues of the inner ear depend upon retinol and that retinoic acid does not supply some of the metabolic requirements of the inner ear.