The ultrastructure of the olfactory epithelium of the lamprey Lampetra fluviatilis

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Abstract
In common with those on other vertebrate olfactory receptors, the short cilia on the sensory cells are arranged in a ring on the tip of the dendrite. The cilia have two distinct regions—a proximal region, having a typical ciliary structure, and a distal region in which only single peripheral fibres are present. One or more basal feet are present, projecting from the basal body of the olfactory cilium. A 40–50 Å subunit structure in the peripheral fibres of the olfactory cilium is described. Numerous microtubules are present in the dendrite and in the basal cells, but are absent from the supporting cells. The supporting cells contain an extensive system of tonofilaments. Junctional complexes are situated between the plasma membranes at the apex of supporting cells and between supporting cells and neurons. Degenerating neurons and supporting cells are present as well as possible regenerating cells. On the basis of this evidence it is postulated that limited cell replacement may occur. It is also postulated that the arrangement of olfactory nerve fibres within the Schwann cell may allow some processing of information to take place at this level by means of electrotonic field effects.