ULTRASTRUCTURE OF FREE NERVE-ENDINGS IN RESPIRATORY AND SQUAMOUS EPITHELIUM ON THE RAT NASAL-SEPTUM

The distribution of nerve fibres in the mucosa of the nasal septum of the rat was investigated by means of transmission electron microscopy on transverse and tangential ultrathin sections. Near the basement mem brane of respiratory and squamous epithelium, a rather dense network o f unmyelinated nerve fibres occurs. Some fibres in the respiratory epi thelium ascend between the epithelial cells to reach up to the tight j unctions. These fibres appeared in transverse sections to end as hooks or boutons, sometimes with branches. These shapes resemble the free n erve endings that are considered to act as nociceptors. The small intr aepithelial fibres, with diameters of about 0.5-1 mum, contain both de nse granules and clear vesicles comparable to synaptic vesicles. Subst ance P was found in dense granules in basal fibres; vasoactive intesti nal peptide was absent throughout the epithelium. Acetylcholinesterase activity was observed closely associated with the basal fibres; the a pical fibres showed little if any activity. Membrane specializations p ointing to an efferent function as well as structures usually associat ed with mechanoreceptive functions were lacking in both respiratory an d squamous epithelium.