Ultrastructure of free nerve endings in respiratory and squamous epithelium on the rat nasal septum

Abstract

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 membrane of respiratory and squamous epithelium, a rather dense network of unmyelinated nerve fibres occurs. Some fibres in the respiratory epithelium ascend between the epithelial cells to reach up to the tight junctions. These fibres appeared in transverse sections to end as hooks or boutons, sometimes with branches. These shapes resemble the free nerve endings that are considered to act as nociceptors. The small intraepithelial fibres, with diameters of about 0.5-1 microns, contain both dense granules and clear vesicles comparable to synaptic vesicles. Substance P was found in dense granules in basal fibres; vasoactive intestinal peptide was absent throughout the epithelium. Acetylcholinesterase activity was observed closely associated with the basal fibres; the apical fibres showed little if any activity. Membrane specializations pointing to an efferent function as well as structures usually associated with mechanoreceptive functions were lacking in both respiratory and squamous epithelium.

Changes in nasal mucosal innervation in horses with grass sickness

“…The difference in the density of innervation demonstrated by the antibodies against SPand CGRPis in contrast to our previous report on normal equine nasal innervation (Corcoran et al 2000), but that study used an indirect immunofluorescence technique, making direct comparisons difficult. In the present study, large numbers of SP nerve fibres were located beneath the epithelium and coursing between epithelial cells in a pattern similar to that found with PGP and these fibres are likely to be sensory C-fibre afferents (Spit et al 1993;Zhao and Tao 1994). While there was a marginal increase in innervation score between the normal and acute groups, this was not statistically significant.…”

“…In man, rat, guinea pig and rabbit, an extensive network of CGRP fibres coursing beneath the respiratory epithelium in the nasal mucosa, with fibres extending through the epithelium towards the nasal lumen has been described (Kitajiri et al 1993;Lee et al 1995;Norlander et al 1996;Fang and Shen 1997). CGRP is usually found colocalised with SP, which has also been demonstrated in the rat nasal mucosa (Spit et al 1993;Grunditz et al 1994). CGRPand SP nerve fibres have their nerve cell bodies in the trigeminal ganglion indicating their role in sensory function (Grunditz et al 1994).…”

Intraepithelial Nerve Fibers in the Nasal Mucosa of the Rat with Special Reference to the Localization of CGRP, VIP and Nitric Oxide (NO).

“…A report is available showing the presence of acetylcholinesterase-positive reaction in the intraepithelial nerves, which may suggest the presence of parasympathetic mediator in the nasal epithelium (SPIT et al, 1993). However, there is no confirmatory evidence concerning sympathetic and parasympathetic mediators occurring in the intraepithelial nerve fibers of the nasal mucosa.…”

Direct reticular projections of trigeminal sensory fibers immunoreactive to CGRP: potential monosynaptic somatoautonomic projections

“…This suggests these latter areas in the reticular formation are innervated directly by primary afferent fibers of trigeminal origin. Numerous fibers immunoreactive to CGRP innervate the nasal mucosa (Petersson et al, 1989; Silverman and Kruger, 1989; Stjärne et al, 1989; Finger et al, 1990; Silver et al, 1991; Spit et al, 1993; Matsuda et al, 1994, 1998) which is supplied in part by the AEN. The character of CGRP in these reticular areas mimics the central projections of the AEN, and we suggest that this nerve is the origin of many CGRP immunoreactive fibers in these reticular areas.…”

“…Innervation of the nasal mucosa is via free nerve endings from small diameter fibers (Cauna et al, 1969), many of which contain peptides, notably calcitonin gene-related peptide (CGRP) and substance P (SubP) (Petersson et al, 1989; Silverman and Kruger, 1989; Stjärne et al, 1989; Finger et al, 1990; Silver et al, 1991; Spit et al, 1993; Matsuda et al, 1994, 1998) from trigeminal ganglion neurons (Silverman and Kruger, 1989; Ichikawa et al, 1993; Matsuda et al, 1994; Schaefer et al, 2002). Most of these fibers are sensory in function (Lucier and Egizii, 1989; Wallois et al, 1991, 1992; Sekizawa and Tsubone, 1994, 1996), and many respond as chemoreceptors (Lucier and Egizii, 1989), creating the “common chemical sense” or chemethesis (Cain and Murphy, 1980; Green and Lawless, 1991; Viana, 2011).…”