The ultrastructure of the vomero-nasal organ in reptilia

Summary There are three types of cells in the vomero-nasal organ of Lacerta sicula and Natrix natrix: receptor cells, supporting cells and basal cells. The receptor cells bear microvilli and no cilia. In Lacerta centrioles are lacking, indicating that the ciliary apparatus can have no essential significance in the transducer process. In Natrix centrioles occur in the deeper dendritic region. The structural constituents of the dendrites are mitochondria, microtubules and characteristic vesicles the properties of which are described. The perikarya which have uniform structure send off axons of about 0.2 diameter. The supporting cells show signs of a very moderate secretory activity, which is different among the species investigated. The microvilli of the supporting cells are not distinguishable from those of the receptor cells. The dendrites of the latter are completely isolated by the apical parts of the supporting cells. The sheet-like processes of the supporting cells contain strands of tonofilaments and do not cover the perikarya of the receptor cells completely. Thus adjacent sensory cells or dendrites and sensory cells are separated among themselves only by the normal intercellular space. The ratio of sensory cells to supporting cells is about 71. The basal cells resemble the supporting cells and replace these in the lower portion of the epithelium. The typical cellular junctions between sensory cells and supporting cells are described. There are no true tight junctions in the vomero-nasal sensory epithelium, and they are most probably absent from the nasal mucosa too. This absence would seem to indicate special conditions for cellular communication and the accessibility of the intercellular space for certain molecules. There is no sign of regeneration of sensory cells. Both immature blastema cells and degenerating receptor cells are not discernible.