| Abstract #759, Date 2/17/99, Session Y1, Poster (J24) |
| Developmental innervation patterns and morphology of the utricle in Xenopus laevis |
| *S.A. Cicero, V.L. Lopez-Anaya, Q.A. Quick, W.M. Doyon, E.E. Serrano (New Mexico State University, Las Cruces, NM) |
In previous investigations we examined the development of the saccular and the papillar branches of the X. laevis VIIIth cranial nerve (Lopez-Anaya et al., J. Morph, 1997, 234: 263-76) as well as the development of the saccular hair cell bundles (Diaz et al., 1995, Hear Res. 91:33-42). Here, we provide data about the development of axons of the utricular branch, as well as hair cell and utricle morphology. Our work is a comparative study utilizing three types of microscopy: light microscopy, TEM, and SEM. Our goal is to combine the results from anatomical studies of the endorgans and their nerves to develop an integrated model of inner ear development in X. laevis. For light microscopy studies of axon development, standardized sections from four ages of X. laevis life, ranging from Stage 52 larvae to 2 year adults, were analyzed for axon number, diameter, and area with a digital image analysis system. Preliminary data indicate that the average number of myelinated axons increases throughout the life of the animal, but the average size of myelinated axons does not increase. A portion of these data are reported elsewhere (Neurosci. Abstr. 24:322.9). When adjacent sections from the same animals were observed under TEM, we noted that increase in myelination is correlated with increase in axon size, with greatest myelination occurring after metamorphosis. The TEM images also show the developing ultrastructure of the axons and the Schwann cells. When SEM was used to observe hair cell bundles in the adult utricle, over 2500 hair cells were visible in the epithelia. Thus, in sharp contrast to our previous work with saccular and papillar axons, the myelinated axons of the developing utricle increase throughout the life of the animal. Comparison of the utricle with the sacculus shows that the number of hair cells, and the axon: hair cell ratio, is similar in these endorgans. Taken together, our findings punctuate the similarities and differences in auditory and vestibular development. Studies are underway to determine the age at which the utricle first produces hair cells. These investigations focus on hair cell development and the gross morphology of the developing utricle. |