POSTNATAL-DEVELOPMENT OF THE STRUCTURE OF THE PERIPHERAL VESTIBULAR SYSTEM OF THE GERBIL

Postnatal development of the peripheral vestibular system and surround ing components in the gerbil was studied to obtain topological informa tion for electrical vestibular stimulation. At postnatal day 1, the pe ripheral vestibular nerve had already reached the vestibular apparatus . The central vestibular nerve extended posteriorly to enter the brain stem at a sharp angle to anterior-posterior axis. During development, the vestibular ganglion was progressively displaced caudally, along wi th the vestibular nerve and the ventrally located facial nerve, increa sing the angle to the anterior-posterior axis to nearly 900 by postnat al day 30. Contact between the anterior part of the vestibular ganglio n and the facial nerve, and that between the posterior part of the gan glion and the cochlear nerve were observed at all ages. These regions were considered unsuitable for electrical stimulation because of the h igh risk of stimulating the facial or cochlear nerve, similar to those regions in the adult. These results as well as the observation that t he diameter of the lateral semicircular canal remained nearly constant showed that the technique we used for electrical vestibular stimulati on in adult animals was apparently a good choice in younger animals as well.