A degenerative disorder of the central auditory system of the gerbil

A previously unidentified disorder which affects primarily the cochlear nucleus was observed in two species of gerbils, Meriones unguiculatus and M. libycus. Unusual lesions were observed in the cochlear nucleus bilaterally in all animals examined. In light and electron microscopic specimens these lesions were characterized by the presence of microcysts and vacuolar neuronal degeneration. The microcysts resembled large holes, containing trabeculae, organelles and cellular remnants. Also observed were light and dark degeneration of neuronal perikarya and degenerated axons, dendrites, and synapses, accompanied by phagocytosis. Astrocytosis was not conspicuous. In the one cochlea examined, no microcysts were observed. In young animals the microcysts were prevalent in the cochlear nerve root region and the posteroventral cochlear nucleus. In older animals the microcysts increased in number and area. In the oldest animals, the microcysts had spread to other central auditory structures, including the superior olivary complex, the nuclei of the lateral lemniscus, and the inferior colliculus. Other regions of the brain were largely free of microcysts. The etiology and behavioral manifestations of this disorder are unknown, although it is clearly neurodegenerative and perhaps genetically determined.