| Abstract #61, Date 2/14/99, Session E1, Poster (J29) |
| Development of the Xenopus laevis amphibian papilla: Scanning electron microscopy of the sensory epithelia |
| *V.L. Lopez-Anaya, E.E. Serrano (New Mexico State University, Las Cruces, NM) |
Characterizing the ultrastructural anatomy of auditory and vestibular sensory hair cells is one key to understanding the ontogeny of inner ear sensory endorgans. Earlier studies in our laboratory have examined saccular hair cell bundle types during development in X. laevis (Diaz et al., 1995, Hear. Res. 91:33-42). In this study we examine the development of the sensory epithelia of an X. laevis auditory endorgan, the amphibian papilla (AP). Results from ultrastructural analysis of stereociliary bundles from the AP in five different ages of X. laevis life (stage 52, stage 56, 1-5 day postmetamorphic juveniles, 6-9 month old adolescents, and two year old adults) are presented here. A portion of the data from adult animals are reported elsewhere (Neurosci. Abstr. 23:180.13). The AP sensory macula is of the "U" or "horseshoe" type, and is divided into two distinct patches, rostral and caudal, with stereociliary bundles oriented in several different directions. AP stereociliary bundles may contain over 100 stereocilia, and contain a single kinocilium that can reach twice the height of the stereociliary bundle. The AP, like the sacculus, contains sensory patches comprising central and peripheral regions, each with characteristic bundle types. At all ages, hair cells with larger stereociliary bundles tended to be localized at the innermost margin of the caudal patch with smaller, longer bundles and kinocilia along the outermost margins of the caudal patch. A gradient of intermediate forms of these bundle morphologies is also evident across the sensory epithelia between inner and outer margins at all ages. SEM of the sensory epithelia shows developmental differences between ages in the morphology and orientation of the stereociliary bundles within the sensory epithelia. As in the X. laevis sacculus, a trend towards an increase in the number of AP stereociliary bundles was positively correlated with age of the animals. Stage 52 animals averaged 120 bundles with 24% lying in the rostral patch, juveniles averaged 350 bundles with 27% in the rostral patch and adults averaged 440 bundles with 27% in the rostral patches. These data suggest that in X. laevis, auditory hair cells are produced throughout the life of the animal. |