Abstracts of the XXVth Congress of the European Association of Veterinary Anatomists (EAVA). July 28-31, 2004. Oslo, Norway

The oral cavity in vertebrates plays a very important role in food intake mechanics and also contains chemical sensors for food and environmental water. Comparative studies revealed morphological and functional inter‐specific differences that can be correlated to evolutionary events and might represent the adaptation to environmental conditions present in different habitats (Iwasaki, 2002). Particularly these events are strictly dependent on the food intake mechanisms determining the success of the adaptation of vertebrates to their environment and therefore their survival (Roth and Wake, 1989). Since data about the morphology of the zebrafish oral cavity are scarce the aim of the present research was to study it by light, scanning and transmission electron microscopy and immunohistochemistry for some growth factor receptors, i.e. trkA and trkB. The zebrafish was chosen because as a vertebrate it has valuable features as a model for study of vertebrate development (Withfield, 2002). Adult zebrafishes were anesthesized with MS222 and the samples were taken and routinely processed for light and electron microscopy and for indirect peroxidase immunohistochemistry. The topographical and ultrastructural study demonstrated the presence of three different zones. The outer zone is characterized orally by the presence of a papilla and by an epithelium with numerous taste buds that are chemosensory endorgans consisting of modified epithelial cells. Their function is to sample potential food and selecting it according to its edibility (Hansen et al., 2002). Both in upper and lower intermediate zones, the presence of internal valves with a semi‐lunar shape was evident, probably able to regulate the mouth closure. The most internal lower zone corresponds to the tongue that in zebrafish is only a thickening of the pavement mucosa with a stratified epithelium. Immunohistochemistry demonstrated both in upper and lower zones the presence of numerous taste buds that were immunoreactive to TrkA and TrkB‐like neurotrophin receptors, confirming the role of these receptors in taste buds sensory cells (Germanà et al., 2004). The present results give a contribution to the morphological knowledge of the zebrafish oral cavity, an animal model commonly used for developmental studies of vertebrates.