Effects of hypergravity on the prenatal development of peripheral vestibulocerebellar afferent fibers

The relationship between vestibular stimulation and the distribution of peripheral vestibulocerebellar sensory fibers was studied in embryonic rats that developed in normal gravity (1G), 1.75G, 2.0G, or rotational environments from 10 to 20 days of gestation. Subsequently a fluorescent neuronal tracer was applied to the cerebellum, and allowed to diffuse retrogradely to the vestibular periphery. The distribution of labeled fibers and terminals in the posterior vertical canal and the utricle was analyzed. Sensory fibers in the rotation- and hypergravity-exposed embryos of the posterior semicircular canal and utricle displayed fewer long extending fibers and more terminal fields, suggesting faster rates of maturation as compared to the synchronous controls. Hypergravity exposures in the posterior canal caused increased terminal formation in the central zone of the cristae, and in the utricle caused increased terminal formation, including calyces, in the medial extrastriolar zone. These results show the importance of the vestibular environment in the development of peripheral vestibular innervation.