The secretory activity of rat nasal glands and the effect of cholinergic drugs

Consensus on Methodology for Experimental Studies of Nasal Mucosal Injury

OBJECTIVES

The way wounds heal involves significant complexity, resulting in restoration of functional and anatomical integrity to tissues damaged as a result of trauma (whether mechanical, chemical, or radiation-induced). The authors reviewed the consensus on methodology for experimental studies of nasal mucosal injury.

METHODS

The review aims to find where consensus exists amongst different experimental studies in nasal wound healing about the use of animal models. To achieve this, the authors queried the Pubmed, Proquest Central and Google databases for the last 20 years (i.e. 1996-2016). The search terms were: "mucosa injury," "nasal mucosa injury," "injury," "wound healing," "nasal," "nasal wound healing," "experimental," "animal," "model," "rat," "rabbit," "guinea pig," and "mice." These terms were searched for whether they occurred singly or in combination. The search uncovered 18 papers, on the basis of which this review has been prepared.

RESULTS

The choice of an appropriate animal model is key in investigating nasal mucosal injury. Suitable animals include rodents such as rats or guinea pigs. There are reports in the literature concerning mechanical injury in rat nasal mucosae without attempts to treat it. Mechanical injury was induced unilaterally by means of an interdental brush. Other techniques involved the use of distilled water or irradiating the tissue to induce trauma.

CONCLUSION

In this review, the use of a rat, guinea pig or rabbit model for human nasal mucosal injury is reviewed. Such models are suitable for use in well-designed experimental studies.

Comparative histochemical analysis of glycoconjugates in the nasal vestibule of camel and sheep

While Corriedale sheep survive in a wide range of climates, which prevents them to specialize for one climatic condition only, dromedary camels strictly adapted to desert areas. This demands more adaptive mechanisms to hot, dry conditions in camels than in sheep. Being the entrance of the nasal cavity, nasal vestibule is subjected to various environmental stressors. A protective way is the lining epithelium which is cornified in camel, but not in sheep. Mucus nasal secretions also play a key role in the protection of underlyings. Additionally, arterio-venous anastomosis is present in the lamina propria of the nasal vestibule of camel. In the present paper, sugar residues in the nasal vestibule of camel were analyzed and compared with those of sheep using 14 types of lectins to explore the distribution of glycoconjugates that may help the function of camel nasal vestibule in desert environment. In camel, none of the lectins could label the basal cells of the vestibular epithelium, although the basal cells reacted with six lectins in sheep. In camel, LEL and RCA-120 markedly labeled the luminal surface. WGA, DBA, SBA, and VVA produced marked intensities on the luminal surface in sheep. The mucous glands reacted with six lectins: WGA, s-WGA, VVA, PNA, PHA-E, and PHA-L in camel, while all lectins used except s-WGA and PHA-E reacted in the sheep. In summary, great differences are observed in the glycoconjugate expression between camel and sheep. This suggests that these glycoconjugate are related to camel's tolerance for environmental stressors.

Effects of caffeic acid phenethyl ester on wound healing of nasal mucosa in the rat: an experimental study

PURPOSE

Wound healing of the nasal mucosa is a highly complex process that restores the anatomical and functional integrity of tissue that has been exposed to trauma. In this experimental study, our aim was to use histopathological examination to investigate the effects of caffeic acid phenethyl ester on the wound healing of rat nasal mucosa after mechanical trauma.

MATERIALS AND METHODS

The rats were randomly divided into 3 experimental groups: a non-treated group (n=7), a control saline group (n=7) and a caffeic acid phenethyl ester group (n=7). The non-treated group received no treatment for 15 days. The second group was administered saline (2.5 mL/kg, intraperitoneal) once a day for 15 days. The third group received caffeic acid phenethyl ester intraperitoneally at a dose of 10 μmol/kg once a day for 15 days. At the beginning of the study, unilateral mechanical nasal trauma was induced on the right nasal mucosa of all rats in the three groups using a brushing technique. Samples were stained using hematoxylin and eosin solution and were examined by a pathologist using a light microscope.

RESULTS

The severity of inflammation was milder in the caffeic acid phenethyl ester group compared with that in the non-treated and saline groups (P<0.05). The subepithelial thickness index was lower in the experimental group (P<0.05). Goblet cell and ciliated cell loss was substantially reduced in the experimental group compared with the non-treated and saline groups (P<0.05).

CONCLUSIONS

Caffeic acid phenethyl ester decreases inflammation and the loss of goblet cells and ciliated cells. Therefore, caffeic acid phenethyl ester has potential beneficial effects on the wound healing of nasal mucosa in the rat.

Decreased olfactory mucus secretion and nasal abnormality in mice lacking type 2 and type 3 IP3 receptors

Although nasal mucus is thought to play important roles in the mammalian olfactory system, the mechanisms of secretion of it and its physiological roles are poorly understood. Here we show that type 2 and type 3 IP3 receptors (IP3R2 and IP3R3) play critical roles in olfactory mucus secretion. Histological studies showed that IP3R2 and IP3R3 are predominantly expressed in two types of nasal glands, the anterior glands of the nasal septum and the lateral nasal glands (LNG), which contain mucosal proteins secreted to the main olfactory epithelium. We therefore examined LNG acinar cells, and found that acetylcholine-mediated calcium responses and fluid- and protein- secretion in the acinar cells were markedly decreased in IP3R2-R3 double-knockout (KO) mice. We also found nasal inflammation and a decrease in olfactory capacity in IP3R2-R3 KO mice. Despite intact signal transduction in the olfactory epithelium, IP3R2-R3 KO mice exhibited elevated threshold sensitivity to odorants on in vivo imaging of olfactory glomerular responses and behavioral tests. Our findings suggest that IP3R2 and IP3R3 mediate nasal mucus secretion, which is important for the maintenance of nasal tissue as well as the perception of odors.

Effects of repeated welding fumes exposure on the histological structure and mucins of nasal respiratory mucosa in rats

To investigate the effects of welding fumes on the histological structure and properties of mucins of the nasal respiratory mucosa, Sprague-Dawley rats were exposed to manual metal arc-stainless steel (MMA-SS) welding fumes at a concentration of 56-76 mg/m3 total suspended particulates for 2 h per day in an inhalation chamber for 90 days. Experimental animals were sacrificed at 2 h, 15, 30, 60 and 90 days after exposure. Loss of cilia, desquamation of epithelial cells, mucigenous epithelial cells and destruction of nasal septal glands were observed frequently in the welding fumes-exposed groups. These changes became more severe as the exposure continued. The amount of neutral mucins in goblet cells in the welding fumes-exposed group had a tendency to increase, the amount of sulfomucins decreased, while the sialomucins increased as the exposure continued. Mucinogenic epithelial cells, not visible in the control group, contained minimal to small amounts of neutral mucins. In the dorsal septal glands, neutral mucins not visible in the control group appeared, and neutral mucins in the ventral septal glands increased slightly. These results indicate that the observed changes in the properties of mucins due to inhalation of welding fumes may play roles in protection against toxicants.

Two-photon microscopic analysis of acetylcholine-induced mucus secretion in guinea pig nasal glands

The spatiotemporal changes in intracellular free Ca(2+) concentration ([Ca(2+)](i)) as well as fluid secretion and exocytosis induced by acetylcholine (ACh) in intact acini of guinea pig nasal glands were investigated by two-photon excitation imaging. Cross-sectional images of acini loaded with the fluorescent Ca(2+) indicator fura-2 revealed that the ACh-evoked increase in [Ca(2+)](i) was immediate and spread from the apical region (the secretory pole) of acinar cells to the basal region. Immersion of acini in a solution containing a fluorescent polar tracer, sulforhodamine B (SRB), revealed that fluid secretion, detected as a rapid disappearance of SRB fluorescence from the extracellular space, occurred exclusively in the luminal region and was accompanied by a reduction in acinar cell volume. Individual exocytic events were also visualized with SRB as the formation of Omega-shaped profiles at the apical membrane. In contrast to the rapidity of fluid secretion, exocytosis of secretory granules occurred with a delay of approximately 70s relative to the increase in [Ca(2+)](i). Exocytic events also occurred deep within the cytoplasm in a sequential manner with the latency of secondary exocytosis being greatly reduced compared with that of primary exocytosis. The delay in sequential compound exocytosis relative to fluid secretion may be important for release of the viscous contents of secretory granules into the nasal cavity.

Histochemical study of glycoconjugates in the nasal mucosa of the rat and guinea pig

A histochemical study was carried out on the glycoconjugates of the nasal mucosa of rat and guinea pig using conventional techniques and peroxidase-labelled lectins. Both the respiratory mucosa and neuroepithelium were studied. Sulphate and sialic acid groups were found in the mucous layer of the neuroepithelia, Bowman's glands and goblet cells. In contrast, the nasal glands did not possess these groups, and only a few showed neutral mucins. Carbohydrate residues were more numerous in the acini of the Jacobson glands. Thus, the nasal glands in the rat and guinea pig are probably of a serous type because of the scarcity of carbohydrate residues.

Autoradiographic analysis of muscarinic receptors in rat nasal glands

An in vitro method was developed for the biochemical and autoradiographic demonstration of low muscarinic receptor densities in peripheral tissue. Histological criteria point clearly to the necessity for fixation to preserve tissue quality. [3H]l-Quinuclidinylbenzilate bound specifically to a homogeneous class of binding sites in 0.5% glutardialdehyde-fixed cryostat sections (10 microns) of rat nasal glands with high affinity (Kd = 0.47 +/- 0.06 nM) and with a receptor density (Bmax) of 41 +/- 1 fmol/mg protein. This binding was linearly dependent on the thickness of the sections. Kinetic experiments resulted in a Kd value of 0.19 nM. Binding was stereoselectively inhibited by benzetimide enantiomers. Autoradiograms, generated after incubation with 0.6 nM [3H]l-quinuclidinylbenzilate and dipping in nuclear K2 emulsion, showed specific labelling of the glandular acini and excretory ducts. These in vitro observations provide conclusive evidence for the presence of acetylcholine receptors in the nasal glands of the rat.