Bj. Spit et al., ULTRASTRUCTURE OF FREE NERVE-ENDINGS IN RESPIRATORY AND SQUAMOUS EPITHELIUM ON THE RAT NASAL-SEPTUM, Cell and tissue research, 274(2), 1993, pp. 329-335
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.