Secretory characteristics of the rat nasal glands

Distribution of ion transport mRNAs throughout murine nose and lung

Evidence of absorptive or secretory ion transport in different respiratory regions of the mouse was sought by assessing the regional distribution of alpha-, beta-, and gamma-epithelial sodium channel (ENaC; Na(+) absorptive), cystic fibrosis transmembrane conductor regulator (CFTR), and Na(+)-K(+)-2Cl(-) cotransporter mRNAs. High levels of ENaC subunit expression were found in nasal surface epithelium and gland ducts. CFTR was expressed in both superficial nasal respiratory epithelium and glands. These results are consistent with basal amiloride-sensitive Na(+) absorption and cAMP-dependent Cl(-) secretion in murine nasal epithelia. Expression of all three ENaC subunits increased progressively from trachea to terminal bronchioles. Intermediate levels of CFTR and cotransporter expression in bronchial epithelium diminished in bronchioles. The low abundance of CFTR mRNA throughout murine pulmonary epithelium is consistent with functional data that attributes Cl(-) secretion predominantly to an alternative Cl(-) channel. alpha-ENaC as the only mRNA found in all regions of airway epithelia is consistent with the alpha-subunit as requisite for Na(+) absorption, and the increased expression of alpha-, beta-, and gamma-ENaC in distal airways suggests a greater absorptive capability in this region.

Nasal route for direct delivery of solutes to the central nervous system: fact or fiction?

During this century, several investigators reported that certain viruses, metals, drugs, and other solutes could bypass systemic circulation and enter the brain and/or cerebrospinal fluid directly following nasal administration. Although evidence clearly suggests that the olfactory epithelium and its olfactory cells play a major role, little is known about the mechanisms of direct transport of solutes into the brain. An overview of what is known about these mechanisms may aid in further research in this field, including studies of direct drug delivery to the central nervous system. This review, in addition to summarizing the literature to date, clearly describes the intricate association of the anatomical features involved in direct entry of solutes into the brain following nasal administration. To aid in the understanding of the possible routes a solute can take after nasal administration, the anatomy of the olfactory epithelium and surrounding tissues is described, and a detailed scheme delineating the emerging pathways is presented. Techniques used in delineating these pathways and studies supporting a particular pathway are discussed in greater detail. Finally, some factors influencing the direct transport of solutes to the cerebrospinal fluid and brain are summarized.

Immunocytochemical analysis of a novel carbohydrate differentiation antigen (CDA-3C2) associated with olfactory and otic systems during embryogenesis in the rat

Carbohydrate differentiation antigens are known to display specific patterns of expression during mammalian development and are thought to participate in significant morphogenetic events. In the present study, two monoclonal antibodies that react with a novel carbohydrate differentiation antigen (CDA-3C2) were used to analyze, by light microscopy, the spatiotemporal distribution of this unique high molecular weight antigen during embryogenesis in the rat. Correlative analysis of the development of peripheral neural structures, in which CDA-3C2 was expressed, was carried out with an anti-neurofilament antibody. Enzymatic digestion, combined with Western blots, reveal that the CDA-3C2 epitope is a carbohydrate which is carried on a high molecular weight glycoprotein with a mass of greater than 1 million Daltons. Characteristic of carbohydrate antigens, immunoreactivity was found in several distinct cellular patterns: only along the apical border of cells, along lateral and basal membranes of cells, and extracellular-like staining in the mesenchyme. During neurulation, CDA-3C2 showed differential staining in the ectoderm, distinguishing lateral from neural regions. Following closure of the neural tube, there was a striking specificity of expression of CDA-3C2 in the periphery, found almost exclusively in olfactory and otic epithelial structures. While CDA-3C2 is found in placode-derived tissues that subserve sensory transduction, it appears to be primarily associated with the supportive cells (and their secretions) in both otic and olfactory regions and less so with the sensory cells. The data suggest that a unique carbohydrate antigen on a large macromolecule may play a role in neurulation and/or morphogenesis of the placode-derived otic and olfactory structures.

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.

The mucosal lining of the Eustachian tube of the rat

This report deals with a microscopical study on the Eustachian tube of the rat. The tube consists of a small membranous part and a larger part which is supported by cartilage to a varying extent. The epithelial lining is composed of pseudostratified ciliated epithelium and squamous epithelium, both arranged in coherent fields, extending from nasopharynx to the middle ear cavity. The ciliated epithelium, which is continuous with the tracts of ciliated epithelium in the middle ear, provides morphological evidence for the existence of a mucociliary transport system. The part of the tube, that is lined by squamous epithelium is suggested to be involved in facilitating the passage of air. The observations made on the secretory elements refer to a different function of goblet cells and the subepithelial compound glands in Eustachian tube physiology.

Lateral nasal gland secretion in the anaesthetized dog

The effects of pharmacological and nervous stimuli on the flow of secretion from the dog lateral nasal gland following catheterization are described. Drugs were injected close-arterially into the arterial supply to the nose, or intravenously. Cholinergic agonists (pilocarpine, methacholine), given intravenously (I.V.) or intra-arterially (I.A.), and stimulation of the vidian nerve produced a copious flow of secretion which was blocked by atropine. The adrenoceptor agonists phenylephrine (alpha) and salbutamol (beta 2), given I.V. or I.A., and stimulation of the vagosympathetic nerve produced a small but consistent flow of secretion. Histamine (50 micrograms), substance P (0.1 micrograms) and prostaglandin E1 (1-5 micrograms), injected I.A., produced small flows of secretion. Bradykinin (25 ng-50 micrograms), 5-hydroxytryptamine (100 ng-50 micrograms) and vasoactive intestinal peptide (VIP) (10 ng-50 micrograms) did not cause secretion. The total protein content, the composition of secretions as revealed by sodium dodecyl sulphate-polyacrylamide agarose gel electrophoresis, and changes in [Na] and [K] in relation to flow of secretion are described. Differences in ion and protein concentrations, and in protein composition, are described for vidian nerve-induced and vagosympathetically induced secretions. Electron microscopy revealed that the gland contains serous cells in the secretory region, and ducts morphologically similar to the intercalated, striated and excretory ducts of salivary glands.

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

The secretory behaviour of rat nasal glands, under normal conditions and after the application of cholinergic drugs, has been studied using morphological and radiobiochemical techniques. Autoradiography and electrophoresis provide evidence for the selective incorporation of 3H-arginine into the glycoprotein-containing fraction of the nasal glandular secretion. Radiobiochemical experiments show that labelled arginine is rapidly incorporated into the acinar cells of unstimulated glands, although it takes approximately 4 h before the labelled secretory proteins leave the cells. The secretion of proteins is stimulated by the parasympathetic agonist pilocarpine, whose main action is to promote discharge. Histological sections show a depletion of secretory granules after pilocarpine treatment. The cholinergic antagonist atropine inhibits the secretion; the acinar cells are completely filled with secretory granules following this treatment. The time course of the events following atropine administration suggests that there is no feed-back system controlling glycoprotein synthesis. The techniques employed here therefore appear to be useful for studying the effects of drugs that interfere with the secretory activity of the nasal glands.

The mucoperiosteum of the middle ear in experimentally induced sterile otitis media

The effect of Eustachian tube obstruction has been studied in germ-free rats. This model proved to be a reliable approach by which to study the isolated effect of tubal occlusion without the interference of infection. The effects on the middle ear structures are characterized mainly by stratification and hyperplasia of the epithelium, a transient increase in the periosteal activity, tympanosclerotic-like changes and accumulation of cholesterol in the middle ear fluid. No increase in the number of secretory elements could be registered during an observation period of 2 years.