An in vitro model for the study of the role of innervation in circumvallate papillae morphogenesis

The following study was done to demonstrate the reliability of an in vitro model for use in the study of early events and the role of innervation in m ouse circumvallate papillae development. Gestational day (gd)-11 fetuses we re partially dissected to produce explants that included the mandibular, hy oid, third and fourth branchial arches and their ganglia. In ganglionectomi zed explants, the nodose ganglia and either the geniculate, petrosal or bot h ganglia were removed. Explants were cultivated in roller tube culture for 24, 48, 72, and 96 h of culture and examined for the presence of papillary structures. Innervation was verified by immunostaining for neural cell adh esion molecule (NCAM). In all control explants, circumvallate papillae had formed by 72 h in culture. These papillae were innervated by fibers origina ting in petrosal or nodose ganglia, although, in a small number, fibers fro m the geniculate also contributed. Circumvallate papillae also formed in so me explants in which either the geniculate or petrosal ganglia had been rem oved. However, placodal structures failed to mature into papillary structur es even by 96 h in explants in which both ganglia had been removed. Our res ults demonstrate that an in vitro model using branchial arch explants suppo rts the morphogenesis of an epithelial placode through the formation of a d efinite papillary structure, the circumvallate papilla, with an integrated nerve. Our results also indicate that, whereas the initial stages in gustat ory papillae formation, the formation of a placode, are nerve-independent, the maturation of the placodal structure to form a papilla requires the pre sence of an intact nerve. (C) 1999 Elsevier Science B.V. All rights reserve d.