Lectin histochemical localization of galactose, N-acetylgalactosamine, and N-acetylglucosamine in glycoconjugates of the rat vomeronasal organ, with comparison to the olfactory and septal mucosae

Glycoconjugate-Specific Developmental Changes in the Horse Vomeronasal Organ

The vomeronasal organ (VNO) is a tubular pheromone-sensing organ in which the lumen is covered with sensory and non-sensory epithelia. This study used immunohistochemistry and lectin histochemistry techniques to evaluate developmental changes, specifically of the glycoconjugate profile, in the horse VNO epithelium. Immunostaining analysis revealed PGP9.5 expression in some vomeronasal non-sensory epithelium (VNSE) cells and in the vomeronasal receptor cells of the vomeronasal sensory epithelium (VSE) in fetuses, young foals, and adult horses. Olfactory marker protein expression was exclusively localized in receptor cells of the VSE in fetuses, young foals, and adult horses and absent in VNSE. To identify the glycoconjugate type, lectin histochemistry was performed using 21 lectins. Semi-quantitative analysis revealed that the intensities of glycoconjugates labeled with WGA, DSL, LEL, and RCA120 were significantly higher in adult horse VSE than those in foal VSE, whereas the intensities of glycoconjugates labeled with LCA and PSA were significantly lower in adult horse VSE. The intensities of glycoconjugates labeled with s-WGA, WGA, BSL-II, DSL, LEL, STL, ConA, LCA, PSA, DBA, SBA, SJA, RCA120, jacalin, and ECL were significantly higher in adult horse VNSE than those in foal VNSE, whereas the intensity of glycoconjugates labeled with UEA-I was lower in adult horse VNSE. Histochemical analysis of each lectin revealed that various glycoconjugates in the VSE were present in the receptor, supporting, and basal cells of foals and adult horses. A similar pattern of lectin histochemistry was also observed in the VNSE of foals and adult horses. In conclusion, these results suggest that there is an increase in the level of N-acetylglucosamine (labeled by WGA, DSL, LEL) and galactose (labeled by RCA120) in horse VSE during postnatal development, implying that they may influence the function of VNO in adult horses.

Nanoparticle-Guided Brain Drug Delivery: Expanding the Therapeutic Approach to Neurodegenerative Diseases

Neurodegenerative diseases (NDs) represent a heterogeneous group of aging-related disorders featured by progressive impairment of motor and/or cognitive functions, often accompanied by psychiatric disorders. NDs are denoted as 'protein misfolding' diseases or proteinopathies, and are classified according to their known genetic mechanisms and/or the main protein involved in disease onset and progression. Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD) are included under this nosographic umbrella, sharing histopathologically salient features, including deposition of insoluble proteins, activation of glial cells, loss of neuronal cells and synaptic connectivity. To date, there are no effective cures or disease-modifying therapies for these NDs. Several compounds have not shown efficacy in clinical trials, since they generally fail to cross the blood-brain barrier (BBB), a tightly packed layer of endothelial cells that greatly limits the brain internalization of endogenous substances. By engineering materials of a size usually within 1-100 nm, nanotechnology offers an alternative approach for promising and innovative therapeutic solutions in NDs. Nanoparticles can cross the BBB and release active molecules at target sites in the brain, minimizing side effects. This review focuses on the state-of-the-art of nanoengineered delivery systems for brain targeting in the treatment of AD, PD and HD.

Regeneration of olfactory neuroepithelium in 3-methylindole-induced anosmic rats treated with intranasal chitosan

Olfactory dysfunction significantly impairs the life quality of patients but without effective treatments to date. The previous report has demonstrated that chitosan mediates the differentiation of olfactory receptor neurons (ORNs) through insulin-like growth factors and insulin-like growth factor binding protein-2 axis in an in vitro model. However, whether chitosan can further treat olfactory dysfunction in vivo remains unexplored. This study aims to evaluate the therapeutic effect of chitosan on a 3-methylindole-induced anosmic rat model. Intraperitoneal injection of 3-methylindole is performed to induce anosmia in rats. Experimental results demonstrate that the food-finding duration after chitosan treatment gradually decrease to around 80 s, and both the olfactory neuroepithelium (ON) thickness and mature ORNs (expressing olfactory marker protein) are significantly restored. Furthermore, proliferating cells (expressing bromodeoxyuridine) are mainly co-expressed with immature ORNs (expressing βIII tubulin) below the intermediate layer of the ON in the chitosan-treated group on day 28 following 3-methylindole treatment. Conversely, proliferating cells are scattered over the ON, and co-localized with immature ORNs and sustentacular cells (expressing keratin 18) in the sham group, and even immature ORNs go into apoptosis (expressing DNA fragmentation and cleaved caspase-3), possibly causing incomplete regeneration. Consequently, chitosan regenerates the ON by regulating olfactory neural homeostasis and reducing ORN apoptosis, and serves as a potential therapeutic intervention for olfactory dysfunction in the future.

The vomeronasal organ of wild canids: the fox (Vulpes vulpes) as a model

The vomeronasal system (VNS) has been extensively studied within specific animal families, such as Rodentia. However, the study of the VNS in other families, such as Canidae, has long been neglected. Among canids, the vomeronasal organ (VNO) has only been studied in detail in the dog, and no studies have examined the morphofunctional or immunohistochemical characteristics of the VNS in wild canids, which is surprising, given the well-known importance of chemical senses for the dog and fox and the likelihood that the VNS plays roles in the socio-reproductive physiology and behaviours of these species. In addition, characterising the fox VNS could contribute to a better understanding of the domestication process that occurred in the dog, as the fox would represent the first wild canid to be studied in depth. Therefore, the aim of this study was to analyze the morphological and immunohistochemical characteristics of the fox VNO. Tissue dissection and microdissection techniques were employed, followed by general and specific histological staining techniques, including with immunohistochemical and lectin-histochemical labelling strategies, using antibodies against olfactory marker protein (OMP), growth-associated protein 43 (GAP-43), calbindin (CB), calretinin (CR), α-tubulin, Gαo, and Gαi2 proteins, to highlight the specific features of the VNO in the fox. This study found significant differences in the VNS between the fox and the dog, particularly concerning the expression of Gαi2 and Gαo proteins, which were associated with the expression of the type 1 vomeronasal receptors (V1R) and type 2 vomeronasal receptors (V2R), respectively, in the vomeronasal epithelium. Both are immunopositive in foxes, as opposed to the dog, which only expresses Gαi2. This finding suggests that the fox possesses a well-developed VNO and supports the hypothesis that a profound transformation in the VNS is associated with domestication in the canid family. Furthermore, the unique features identified in the fox VNO confirm the necessity of studying the VNS system in different species to better comprehend specific phylogenetic aspects of the VNS.

The vomeronasal system of the newborn capybara: a morphological and immunohistochemical study

The vomeronasal system (VNS) is responsible for the perception mainly of pheromones and kairomones. Primarily studied in laboratory rodents, it plays a crucial role in their socio-sexual behaviour. As a wild rodent, the capybara offers a more objective and representative perspective to understand the significance of the system in the Rodentia, avoiding the risk of extrapolating from laboratory rodent strains, exposed to high levels of artificial selection pressure. We have studied the main morphological and immunohistochemical features of the capybara vomeronasal organ (VNO) and accessory olfactory bulb (AOB). The study was done in newborn individuals to investigate the maturity of the system at this early stage. We used techniques such as histological stains, lectins-labelling and immunohistochemical characterization of a range of proteins, including G proteins (Gαi2, Gαo) and olfactory marking protein. As a result, we conclude that the VNS of the capybara at birth is capable of establishing the same function as that of the adult, and that it presents unique features as the high degree of differentiation of the AOB and the active cellular migration in the vomeronasal epithelium. All together makes the capybara a promising model for the study of chemical communication in the first days of life.

Regulation of chitosan-mediated differentiation of human olfactory receptor neurons by insulin-like growth factor binding protein-2

Olfaction is normally taken for granted in our lives, not only assisting us to escape from dangers, but also increasing our quality of life. Although olfactory neuroepithelium (ON) can reconstitute its olfactory receptor neurons (ORNs) after injury, no adequate treatment for olfactory loss has yet emerged. The present study investigates the role of glycosaminoglycans (GAGs) in modulating olfactory neuronal homeostasis and elucidates the regulatory mechanism. This work isolates and cultures human olfactory neuroepithelial cells (HONCs) with various GAGs for 7 days, and find that chitosan promotes ORN maturation, expressing olfactory marker protein (OMP) and its functional components. Growth factor protein array, ELISA and western blot analysis reveal that insulin-like growth factor binding protein 2 (IGFBP2) shows a higher level in chitosan-treated HONCs than in controls. Biological activity of insulin-like growth factor-1 (IGF-1), IGF-2 and IGF-1 receptor (IGF1R) is further investigated. Experimental results indicate that IGF-1 and IGF-2 enhance the growth of immature ORNs, expressing βIII tubulin, but decrease mature ORNs. Instead, down-regulation of phosphorylated IGF1R lifts the OMP expression, and lowers the βIII tubulin expression, by incubation with the phosphorylated inhibitor of IGF1R, OSI-906. Finally, the effect of chitosan on ORN maturity is antagonized by concurrently adding IGFBP2 protease, matrix metallopeptidase-1. Overall, our data demonstrate that chitosan promotes ORN differentiation by raising the level of IGFBP2 to sequestrate the IGFs-IGF1R signaling. STATEMENT OF SIGNIFICANCE: Olfactory dysfunction serves as a crucial alarm in neurodegenerative diseases, and one of its causes is lacking of sufficient mature olfactory receptor neurons to detect odorants in the air. However, the clinical treatment for olfactory dysfunction is still controversial. Chitosan is the natural linear polysaccharide and exists in rat olfactory neuroepithelium. Previously, chitosan has been demonstrated to mediate the differentiation of olfactory receptor neurons in an in vitro rat model, but the mechanism is unknown. The study aims to evaluate the role and mechanism of chitosan in an in vitro human olfactory neurons model. Overall, these results reveal that chitosan is a potential agent for treating olfactory disorder by the maintenance of olfactory neural homeostasis. This is the first report to demonstrate that chitosan promotes differentiation of olfactory receptor neurons through increasing IGFBP2 to sequestrate the IGFs-IGF1R.

Lectin histochemical studies on the olfactory gland and two types of gland in vomeronasal organ of the brown bear

Olfaction is mediated by the vomeronasal and main olfactory systems, and the peripheral vomeronasal organ (VNO) processes species-specific chemicals that are associated with various behaviors in mammals. Sensory epithelial surfaces of the olfactory mucosa and VNO are covered by mucosal fluid that contains secretory products derived from associated glands, and glycoconjugates in the mucosal fluid are involved in odorant reception. The VNO of brown bears contains two types of glands; submucosal vomeronasal glands (VNG) and multicellular intraepithelial glands (MIG). The present study determined the labelling profiles of 21 lectins in the olfactory glands (OG), VNG and MIG of young male brown bears. The OG reacted with 12 lectins, and the VNG and MIG were positive for seven and eight lectins, respectively. Six lectins bound only to the OG, while four reacted with both or either of the VNG and MIG, but not the OG. The differences of lectin labelling pattern between the OG and glands in the VNO suggest that glycans in covering mucosal fluids differ between the olfactory mucosa and VNO. In addition, Bandeiraea simplicifolia lectin-I, Sophora japonica agglutinin and Jacalin reacted with the MIG but not the VNG, whereas Datura stramonium lectin and concanavalin A bound to the VNG, but not the MIG. These findings indicate that the properties of secretory substances differ between the two types of glands in the bear VNO, and that the various secretions from these two types of glands may function in the lumen of VNO together.

Morphological Analysis for Neuron-Like Cells in the Vomeronasal Organ of Human Fetuses at the Middle of Gestation

The vomeronasal organ (VNO) of 5-month-old fetuses was examined immunohistochemically by the use of an antiserum to protein gene product 9.5 (PGP). The purpose was to identify if the human fetal VNO is lined by neuroepithelium. The PGP antiserum labeled abundant cells within the vomeronasal epithelium (VE), nerve fiber bundles in its lamina propria, and cells associated with these bundles. PGP-immunoreactive (ir) vomeronasal epithelial cells were classified into three subtypes. Type I cells, about 44% of the total cells observed, did not have any processes and tended to be located in the basal layer of the VE. Type II cells, about 37% had a single apical process that projected toward the lumen, ending at the epithelial surface. Type III cells sent a prominent process mainly toward the basement membrane, and occupied about 19% of the total cells observed. In the lamina propria, a considerable number of PGP-ir cells was observed. Some of them were present in nerve fiber bundles and contained processes parallel to the bundles. In addition, PGP-ir nerve fiber bundles and cells associated with them were even present in the portion of the nasal septal mucosa that was very close to the brain. The present results strongly suggested that the VE in human fetuses at mid-gestation is a neuroepithelium and that the VE may produce migrating cells toward the brain.

Histological and ultrastructural characteristics of the primordial vomeronasal organ in lungfish

Many vertebrates have two anatomically distinct olfactory organs--the olfactory epithelium and the vomeronasal organ--to detect chemicals such as general odorants and pheromones in their environment. The vomeronasal organ is not present in fish but is present in vertebrates of a higher order than amphibians. Among all extant fishes, the lungfish is considered to be genetically and phylogenetically closest to tetrapods. In this study, we examined the olfactory organs of African lungfish, Protopterus annectens, by lectin histochemistry, immunohistochemistry, and transmission electron microscopy. Two types of sensory epithelia were identified in the olfactory organ--the olfactory epithelium covering the surface of lamellae and the sensory epithelium lining the recesses both at the base of lamellae and in the wall of the nasal sac--and designated here as the lamellar olfactory epithelium and the recess epithelium, respectively. Based on analysis of G-protein expression and ultrastructure, the lamellar olfactory epithelium resembled the olfactory epithelium of ordinary teleosts and the recess epithelium resembled the vomeronasal organ of tetrapods. Furthermore, lectin histochemistry demonstrated that the axons from the recess epithelium converge and project to the ventrolateral part of the olfactory bulb, suggesting that lungfish possess a region homologous to the accessory olfactory bulb of tetrapods. Based on these results, it seems appropriate to refer to the recess epithelium as "a primordium of the vomeronasal organ." This study may provide important clues to elucidate how the vomeronasal organ emerged during the evolution of vertebrates.

Nose-to-brain transport pathways of wheat germ agglutinin conjugated PEG-PLA nanoparticles

PURPOSE

To investigate the possible pathways for transport of wheat germ agglutinin conjugated PEG-PLA nanoparticles (WGA-NP) into the brain after nasal administration.

METHODS

The nose-to-brain pathways were investigated using WGA-NP containing 6-coumarin (as a fluorescent marker) and (125)I-labeled WGA-NP. Ex vivo imaging analysis was also employed to visualize the transport process.

RESULTS

Nasal administration of WGA-NP to rats resulted in transcellular absorption across the olfactory epithelium and transfer to the olfactory bulb within 5 min. After entering the lamina propria, a proportion of WGA-NP were transferred from the olfactory nerve bundles and their surrounding connective tissue to the olfactory bulb. The trigeminal nerves also contributed to WGA-NP brain transfer, especially to WGA-NP distribution in the caudal brain areas. However, cerebrospinal fluid pathway may have little contribution to the process of transferring WGA-NP into the central nervous system (CNS) after intranasal administration.

CONCLUSIONS

These results demonstrated that intranasally administered WGA-NP reach the CNS via olfactory pathway and trigeminal nerve pathway, and extracellular transport along these nerves is the most possible mechanism.

Lectin histochemical studies on the olfactory epithelium and vomeronasal organ in the Japanese striped snake, Elaphe quadrivirgata

The olfactory epithelium and the vomeronasal organ of the Japanese striped snake were examined by lectin histochemistry. Of the 21 lectins used in the study, all lectins except succinylated-wheat germ agglutinin (s-WGA) showed similar binding patterns in the vomeronasal receptor cells and the olfactory receptor cells with varying intensities. The binding patterns of s-WGA varied among individuals in the vomeronasal and olfactory receptor cells, respectively. Four lectins, Bandeiraea simplicifolia lectin-II (BSL-II), Dolichos biflorus agglutinin (DBA), Sophora japonica agglutinin (SJA), and Erythrina cristagalli lectin (ECL) stained secretory granules and the organelles in the olfactory supporting cells and did not stain them in the vomeronasal supporting cells. These results suggest that the glycoconjugate moieties are similar in the vomeronasal and olfactory receptor cells of the Japanese striped snake.

Histological properties of the nasal cavity and olfactory bulb of the Japanese jungle crow Corvus macrorhynchos

The nasal cavity and olfactory bulb (OB) of the Japanese jungle crow (Corvus macrorhynchos) were studied using computed tomography (CT) and histochemical staining. The nasal septum divided the nasal cavity in half. The anterior and maxillary conchae were present on both sides of the nasal cavity, but the posterior concha was indistinct. A small OB was present on the ventral surface of the periphery of the cerebrum. The OB-brain ratio--the ratio of the size of the OB to that of the cerebral hemisphere--was 6.13. The olfactory nerve bundles projected independently to the OB, which appeared fused on gross examination. Histochemical analysis confirmed the fusion of all OB layers. Using a neural tracer, we found that the olfactory nerve bundles independently projected to the olfactory nerve layer (ONL) and glomerular layer (GL) of the left and right halves of the fused OB. Only 4 of 21 lectins bound to the ONL and GL. Thus, compared with mammals and other birds, the jungle crow may have a poorly developed olfactory system and an inferior sense of olfaction. However, it has been contended recently that the olfactory abilities of birds cannot be judged from anatomical findings alone. Our results indicate that the olfactory system of the jungle crow is an interesting research model to evaluate the development and functions of vertebrate olfactory systems.

Brain delivery of vasoactive intestinal peptide enhanced with the nanoparticles conjugated with wheat germ agglutinin following intranasal administration

The development of biotech drugs such as peptides and proteins that act in the central nervous system has been significantly impeded by the difficulty of delivering them across the blood-brain barrier. The surface engineering of nanoparticles with lectins opened a novel pathway to the absorption of drugs loaded by biodegradable poly (ethylene glycol)-poly (lactic acid) nanoparticles in the brain following intranasal administration. In the present study, vasoactive intestinal peptide, a neuroprotective peptide, was efficiently incorporated into the poly (ethylene glycol)-poly (lactic acid) nanoparticles modified with wheat germ agglutinin and the biodistribution, brain uptake and neuroprotective effect of the formulation were assessed. The area under the concentration-time curve of intact 125I-vasoactive intestinal peptide in brain of mice following the intranasal administration of 125I-vasoactive intestinal peptide carried by nanoparticles and wheat germ agglutinin-conjugated ones was significantly enlarged by 3.5 approximately 4.7 folds and 5.6 approximately 7.7 folds, respectively, compared with that after intranasal application of 125I-vasoactive intestinal peptide solution. The same improvements in spatial memory in ethylcholine aziridium-treated rats were observed following intranasal administration of 25 microg/kg and 12.5 microg/kg of vasoactive intestinal peptide loaded by unmodified nanoparticles and wheat germ agglutinin-modified nanoparticles, respectively. Distribution profiles of wheat germ agglutinin-conjugated nanoparticles in the nasal cavity presented their higher affinity to the olfactory mucosa than to the respiratory one. Inhibition experiment with specific sugars suggested that the interaction between the nasal mucosa and the wheat germ agglutinin-functionalized nanoparticles were due to the immobilization of carbohydrate-binding pockets on the surface of the nanoparticles. The results clearly indicated wheat germ agglutinin-modified nanoparticles might serve as promising carriers especially for biotech drugs such as peptides and proteins.

Phenotypic characterization of taste cells of the mouse small intestine

Nutrient-evoked gastrointestinal reflexes are likely initiated by specialized epithelial cells located in the small intestine that detect luminal stimuli and release mediators that activate vagal endings. The G-protein alpha-gustducin, a key signal molecule in lingual taste detection, has been identified in mouse small intestine, where it may also subserve nutrient detection; however, the phenotype of alpha-gustducin cells is unknown. Immunohistochemistry was performed throughout the mouse small intestine for alpha-gustducin, enteroendocrine cell markers 5-HT and glucagon-like peptide-1 (GLP-1), and brush cell markers neuronal nitric oxide synthase and Ulex europaeus agglutinin-1 (UEA-1) lectin binding, singly, and in combination. alpha-Gustducin was expressed in solitary epithelial cells of the mid to upper villus, which were distributed in a regional manner with most occurring within the midjejunum. Here, 27% of alpha-gustducin cells colabeled for 5-HT and 15% for GLP-1; 57% of alpha-gustducin cells colabeled UEA-1, with no triple labeling. alpha-Gustducin cells that colabeled for 5-HT or GLP-1 were of distinct morphology and exhibited a different alpha-gustducin immunolabeling pattern to those colabeled with UEA-1. Neuronal nitric oxide synthase was absent from intestinal epithelium despite strong labeling in the myenteric plexus. We conclude that subsets of enteroendocrine cells in the midjejunum and brush cells (more generally distributed) are equipped to utilize alpha-gustducin signaling in mice. Intestinal taste modalities may be signaled by these enteroendocrine cells via the release of 5-HT, GLP-1, or coexpressed mediators or by brush cells via a nonnitrergic mediator in distinct regions of the intestine.

Lectin-conjugated PEG–PLA nanoparticles: Preparation and brain delivery after intranasal administration

In order to improve the absorption of nanoparticles in the brain following nasal administration, a novel protocol to conjugate biorecognitive ligands-lectins to the surface of poly (ethylene glycol)-poly (lactic acid) (PEG-PLA) nanoparticles was established in the study. Wheat germ agglutinin (WGA), specifically binding to N-acetyl-D-glucosamine and sialic acid, both of which were abundantly observed in the nasal cavity, was selected as a model lectin. The WGA-conjugated nanoparticles were prepared by incorporating maleimide in the PLA-PEG molecular and taking advantage of its thiol group binding reactivity to conjugate with 2-iminothialane thiolated WGA. Coupling of WGA with the PEG-PLA nanoparticles was confirmed by the existence of gold-labeled WGA-NP under TEM. The retention of biorecognitive activity of WGA after the covalent coupling procedure was confirmed by haemagglutination test. The resulting nanoparticles presented negligible nasal ciliatoxicity and the brain uptake of a fluorescent marker-coumarin carried by WGA functionized nanoparticles was about 2 folds in different brain tissues compared with that of coumarin incorporated in the unmodified ones. Thus, the technique offered a novel effective noninvasive system for brain drug delivery, especially for brain protein and gene delivery.

Ultrastructural localization of alpha-galactose-containing glycoconjugates in the rat vomeronasal organ

Binding sites of Griffonia simplicifolia I-B4 isolectin (GS-I-B4), which recognizes terminal alpha-galactose residues of glycoconjugates, were examined in the juxtaluminal region of the rat vomeronasal sensory epithelium and its associated glands of the vomeronasal organ, using a lectin cytochemical technique. Lowicryl K4M-embedded ultra-thin sections, which were treated successively with biotinylated GS-I-B4 and streptavidin-conjugated 10 nm colloidal gold particles, were observed under a transmission electron microscope. Colloidal gold particles, which reflect the presence of terminal alpha-galactose-containing glycoconjugates, were present in vomeronasal receptor neurons in the sensory epithelium and secretory granules of acinar cells of associated glands of the epithelium. Quantitative analysis demonstrated that the density of colloidal gold particles associated with sensory cell microvilli that projected from dendritic endings of vomeronasal neurons was considerably higher than that of microvilli that projected from neighboring sustentacular cells. The same was true for the apical cytoplasms of these cells just below the microvilli. These results suggest that of the sensory microvilli and dendritic endings contained a much larger amount of the alpha-galactose-containing glycoconjugates, compared with those in sustentacular microvilli. Further, biochemical analyses demonstrated several vomeronasal organ-specific glycoproteins with terminal alpha-galactose.

Development of the vomeronasal receptor epithelium and the accessory olfactory bulb in sheep

The morphological development of the vomeronasal organ (VNO) and accessory olfactory bulb (AOB) of the sheep from anlage to birth were studied by classical and histochemical methods using embryos and fetuses obtained from an abattoir with ages estimated from crown-to-rump length. Both VNO and AOB developed in a biologically logical sequence and completed their morphological development around day 98, at entry into the last third of the gestation period. A lectin with specificity for oligomeric N-acetylglucosamine labeled the sensory epithelium of the VNO, the vomeronasal nerves, and the nervous and glomerular layers of the AOB before birth. These results suggest that the vomeronasal system, which is well developed and functional in adult sheep, may be able to function at or even before birth in these animals (whereas in rodents, for example, this is precluded by the AOB not completing its development until after birth).

Lectin-induced apoptosis of mature olfactory receptor cells

Previous studies showed that uptake of the lectin conjugate, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) by olfactory receptor cells results in a thinning of the olfactory epithelium (OE) and increased turnover of globose basal cells. To ascertain the cell-type lost as well as the time course and mechanism of the loss, the current study measured changes in the number of dendritic knobs, olfactory marker protein (OMP) expression and assessed TUNEL labeling as an indicator of apoptosis. Electron microscopic analysis of the number of dendritic knobs showed that the largest reduction occurred at 1 week after intranasal irrigation with WGA-HRP. This data in conjunction with decreased OMP staining provided evidence for a loss of mature receptor neurons. TUNEL labeling, especially in more superficial aspects of the OE, peaked at 18 hr after WGA-HRP application suggesting that the lectin-conjugate produced a rapid induction of apoptotic cell death that was complete by 3 days. Measurement of tyrosine hydroxylase (TH) activity in the olfactory bulb, a sensitive measure of deafferentation, showed that innervation reached a nadir at about 1 week and that reinnervation was complete by 4 weeks. These findings demonstrate that internalization of WGA-HRP by some receptor cells results in their death by apoptosis and a subsequent deafferentation of the olfactory bulb.

Characterisation of glycoconjugate sugar residues in the vomeronasal organ of the armadillo Chaetophractus villosus (Mammalia, Xenarthra)

Conventional carbohydrate histochemistry and the binding patterns of 21 lectins were analysed to characterise the glycoconjugate content in the components of the vomeronasal organ of the armadillo Chaetophractus villosus. The mucomicrovillous complex of the sensory epithelium bound most of the lectins studied. No reaction was observed with Con A, PSA, S-Con A and SBA, and the sustentacular cells were-stained with UEA-I, DSL, LEL, STL and Con A. The vomeronasal receptor neurons were labelled with S-WGA, WGA, PNA, UEA-I, STL, Con A, S-Con A, ECL and RCA120. The basal cell layer reacted with S-WGA, WGA, LCA, UEA-I, DSL, LEL, STL, Con A, JAC and VVA. The nonsensory epithelium exhibited a differential staining in relation to the different components. The mucociliary complex stained with ECL, DBA, JAC, RCA120, STL, LCA, PHA-E, PHA-L, LEL, BSL-I and VVA. However, SJA and UEA-I stained the mucus complex lining a subpopulation of columnar cells. The cytoplasm and cell membranes of columnar cells was labelled with DBA, DSL and LCA. The apical region of these cells exhibited moderate reactivity with LEL and SJA. None of the lectins bound specifically to secretory granules of the nonsecretory cells. Basal cells of the nonsensory epithelium were labelled with DSL, LEL, LCA, BSL-I and STL. The vomeronasal glands showed a positive reaction with WGA, DSL, LEL, LCA, DBA, PNA, RCA120 and SBA. Subpopulations of acinar cells were observed with ECL, S-WGA, Con A, S-Con A and DBA. PNA and RCA120 stained the cells lining the glandular ducts. In comparison with previous results obtained in the olfactory mucosa of the same group of armadillos, the carbohydrate composition of the vomeronasal organ sensory epithelium differed from the olfactory sensory epithelium. This is probably related to the different nature of molecules involved in the perireceptor processes.

Vomeroglandin/CRP-Ductin is strongly expressed in the glands associated with the mouse vomeronasal organ: identification and characterization of mouse vomeroglandin

Vomeroglandin, a subform of mouse CRP-ductin, is a protein strongly expressed in the glands of mouse vomeronasal system. Both the proteins contain several of scavenger receptor cysteine-rich and CUB domains and one ZP domain. This domain arrangement is similar to those of rat Ebnerin, human DMBT1, and rabbit hensin. In situ hybridization analysis shows strong expression of vomeroglandin mRNA in the glands of vomeronasal system. Immunological analyses detect both membrane-bound and secreted forms of vomeroglandin. The secreted protein seems to be localized in the lumen of the vomeronasal organ, playing a certain role in the pheromone perception.

A descriptive and comparative lectin histochemical study of the vomeronasal system in pigs and sheep

The accessory olfactory bulb (AOB) is the primary target of the sensory epithelium of the vomeronasal organ (VNO), and thus constitutes a fundamental component of the accessory olfactory system, which is involved in responses to behaviour-related olfactory stimuli. In this study we investigated the characteristics of the AOB, VNO, vomeronasal nerves (VNNs) and caudal nasal nerve (CdNN) in pigs and sheep, species in which olfaction plays a key behavioural role both in the neonatal period and in adulthood. The patterns of staining of the AOB by the Bandeiraea simplicifolia and Lycopersicon esculentum lectins were the same in the 2 species, whereas the Ulex europeus and Dolichos biflorus lectins gave different patterns. In both species, lectin staining of the AOB was consistent with that of the VNNs, while the CdNN did not label any of the structures studied. The entire sensory epithelium of the pig was labelled by Ulex europeus and Lycopersicum esculentum lectins, and all 4 lectins used labelled the mucomicrovillar surface of the sensory epithelium in sheep.

Brush cells of the mouse intestine possess a specialized glycocalyx as revealed by quantitative lectin histochemistry. Further evidence for a sensory function

Brush cells occur in the epithelium of the small intestine and in various other epithelia of endodermal origin. Ultrastructural and histochemical characteristics suggest that they represent sensory cells. Because the apical membrane of brush cells might be involved in and specialized for (chemo-)receptive functions, we investigated the composition of the glycocalyx and compared it with that of enterocytes. Ultrathin sections of murine small intestine were labeled with a panel of eight lectins. Their binding sites in the brush border and on vesicles of the apical cytoplasm were detected by colloidal gold and quantified using image analysis. The glycocalyx of brush cells contained significantly higher amounts of l-fucose residues than that of enterocytes, as detected by the lectins UEA-I and LTA. In contrast, most of the other lectins bound more avidly to the glycocalyx of enterocytes. The cytoplasmic vesicles closely resembled the apical membrane in their labeling pattern. Quantitation of the brush cells' distribution revealed that the epithelia of the Peyer's patches contained 10-fold higher numbers of brush cells than the small intestinal mucosa distant from lymphoid tissue. We conclude that brush cells possess a glycocalyx with a specialized composition and differ significantly from enterocytes. Because similar peculiarities of the apical membrane have previously been described for sensory cells of the olfactory and gustatory organs, this study provides further evidence in favor of a sensory function of brush cells.

Lectin characterization of the olfactory system in brachiopterygian fish

Lectin binding was performed on the olfactory system of Polypterus and Erpetoichthys, the living genera of the subclass of Brachiopterygii. The lectin histochemical patterns and the Western-blot analysis indicate that the receptor cells of the olfactory mucosa are characterized by high density of specific glycoconjugate residues. The presence of glycoproteins, whose terminal sugars are detected by lectin binding, might be related to the reception of an odor stimulus and its transduction into a nervous signal or to the histogenesis of the olfactory system.

Epidermal growth factor receptor mRNA and protein are expressed in progenitor cells of the olfactory epithelium

Olfactory receptor neurons are continuously replaced postnatally through the initiation of the division and terminal differentiation of progenitor cells located in the basal layer of the olfactory epithelium. Although the factors that regulate this process in vivo are not known, recent in vitro studies demonstrated that members of the epidermal growth factor (EGF) family including transforming growth factor-alpha (TGF alpha) and EGF are highly potent in promoting the proliferation of progenitor cells, suggesting a role for the EGF receptor (EGFR), which is the molecular receptor for both mitogens. We have examined the expression of EGFR mRNA and protein in the olfactory epithelium by using reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis and have examined their cellular localization with in situ RT-PCR and immunocytochemistry. RT-PCR and Southern blot analysis demonstrated that EGFR mRNA is expressed in the olfactory mucosa and also in the positive control tissues, kidney and tongue. The 170-kDa EGFR protein was identified with Western blot analysis in the olfactory epithelium and control tissues. Our results using in situ RT-PCR localized EGFR mRNA-expressing cells more extensively in the basal cell layer of the epithelium than did the immunocytochemical methods. These results suggest that EGFR mediates the mitogenic effect of TGF alpha and/or EGF on the quiescent basal cells to initiate the cell cycle.

In-vitro cell culture models of the nasal epithelium: a comparative histochemical investigation of their suitability for drug transport studies

PURPOSE

To evaluate different in-vitro cell culture models for their suitability to study drug transport through cell monolayers.

METHODS

Bovine turbinate cells (BT; ATCC CRL 1390), human nasal septum tumor cells (RPMI, 2650; ATCC CCL 30), and primary cell cultures of human nasal epithelium were characterized morphologically and histochemically by their lectin binding properties. The development of tight junctions in culture was monitored by actin staining and transepithelial electrical resistance measurements.

RESULTS

The binding pattern of thin-sections of excised human nasal respiratory epithelium was characterized using a pannel of fluorescently-labelled lectins. Mucus in goblet cells was stained by PNA, WGA and SBA, demonstrating the presence of terminal N-acetylglucosamine, N-acetylgalactosamine and galactose residues respectively in the mucus of human nasal cells. Ciliated cells revealed binding sites for N-acetylglucosamine, stained by WGA, whereas Con A, characteristic for mannose moieties, labelled the apical cytoplasm of epithelial cells. Binding sites for DBA were not present in this tissue. Comparing three different cell culture models: BT, RPMI 2650, and human nasal cells in primary culture using three lectins (PNA, WGA, Con A) as well as intracellular actin staining and transepithelial electrical resistance measurements we found, that only human nasal epithelial cells in primary culture showed differentiated epithelial cells, ciliated nasal cells and mucus producing goblet cells, which developed confluent cell monolayers with tight junctions.

CONCLUSIONS

Of the in-vitro cell culture models studied, only human nasal cells in primary culture appears to be suitable for drug transport studies.

Identification of surface glycoconjugates in the olfactory system of turtle

Lectin binding histochemistry was performed on the olfactory system of Pseudemys scripta to investigate the distribution and density of defined carbohydrate terminals on the cell surface glycoproteins of the olfactory receptors and their terminals in the olfactory bulbs. The lectin staining patterns indicate that the receptor cells of the olfactory mucosa are characterized by glycoconjugates containing alpha-D-galactose and N-acetyl-D-glucosamine terminal residues. The vomeronasal receptor cells contain instead alpha-N-acetyl-D-galactosamine, N-acetyl-D-glucosamine and alpha-D-galactose residues. The results demonstrate that the vomeronasal receptor cells contain high density of alpha-N-acetyl-D-galactosamine sugar residues that are not expressed by receptor cells of the olfactory mucosa. The presence of specific glycoproteins, whose terminal sugars are detected by lectin binding, might be related to the chemoreception and transduction of the odorous message into a nervous signal or in the histogenesis of the olfactory system. In fact, the olfactory receptors are the only known neurons in the vertebrate nervous system that undergo a continual cycle of proliferation not only in developing animals but also in mature ones. Moreover the results show that BSA-I-B4, an alpha-D-galactosyl-specific isolectin, targets the terminal sugar residues in the ramified microglial cells.

Enhanced extrinsic innervation of nasal and oral chemosensory mucosae in keratin 14-NGF transgenic mice

The role of nerve growth factor (NGF) in neurotrophic support for the extrinsic innervation of the nasal and oral mucosae was investigated in keratin 14 (K14) - NGF transgenic mice in which NGF was overexpressed in K14-synthesizing cells. K14 immunoreactivity was localized in the epithelial basal cells of the whisker pad skin, the hard palate, the floor of the ventral meatus, and the anterior tongue that are stratified squamous epithelia, and also in basal cells of the vomeronasal, olfactory, and respiratory epithelia that are non-stratified epithelia. In transgenic mice, NGF expression was identified and confined primarily to the basal cells of stratified epithelia. The nasal mucosae including the vomeronasal, olfactory, and respiratory mucosae, and the glands associated with the vomeronasal organ received a greater innervation of protein gene product 9.5-immunoreactive extrinsic fibers in transgenic animals than nontransgenic controls. An increased density of calcitonin gene-related peptide-immunoreactive extrinsic fibers was observed in the nonsensory epithelia of the vomeronasal organ, the olfactory sensory and respiratory epithelia in transgenic animals. Our results indicated that the hyperinnervation of the nasal and oral mucosae by extrinsic neurons is due at least partially to target-derived NGF synthesis and release by K14-expressing basal cells.

Identification of the Ulex europaeus agglutinin-I-binding protein as a unique glycoform of the neural cell adhesion molecule in the olfactory sensory axons of adults rats

Histochemical localization of two lectins, Ulex europaeus agglutinin-I (UEA-I) and Tetragonolobus purpureus (TPA), was studied in the olfactory bulb of adult rats. In contrast to TPA, UEA-I detected a fucosylated glycoprotein that is only present in the surface membranes of olfactory sensory cells including the whole course of their neurites up to the final arborization in glomeruli. Immunoblotting revealed that UEA-I binds specifically to a protein of 205 kDa, while TPA stains several other glycoproteins. Affinity chromatography with the use of a UEA-I column identified the 205 kDa protein as a glycoform of neural cell adhesion molecule (N-CAM), specific for the rat olfactory sensory nerves.

Resolution of sensory and mucoid glycoconjugates with terminal alpha-galactose residues in the mucomicrovillar complex of the vomeronasal sensory epithelium by dual confocal laser scanning microscopy

The organization of the mucomicrovillar complex of the vomeronasal sensory epithelium of adult rats was examined using confocal laser scanning microscopy. In specimens labeled with the FITC-conjugated isolectin B4 of Bandeiraea simplicifolia, which recognizes terminal alpha-galactose sugar residues of glycoconjugates, we demonstrated that the mucomicrovillar complex was composed of islet-like structures with a high-density alpha-galactose core. The mucomicrovillar complex was further resolved into sensory and mucoid components in double-labeling and dual scanning experiments. The sensory component, which consists of the dendritic terminals of olfactory marker protein-immunoreactive vomeronasal receptor neurons, contained cytosolic glycoconjugates with terminal alpha-galactose sugar residues. The extracellular mucoid component consisted of glycoconjugates containing terminal alpha-galactose derived from the glands associated with the vomeronasal organ. These results demonstrated the complex microchemical organization of the sensory and mucoid components of the mucomicrovillar complex.

Differential expression of vomeromodulin and odorant-binding protein, putative pheromone and odorant transporters, in the developing rat nasal chemosensory mucosae

Expression of the putative pheromone and odorant transporter, vomeromodulin, was characterized in developing rat nasal mucosae using in situ hybridization and immunocytochemistry. Initial expression of vomeromodulin mRNA and protein was detected at embryonic day (E)16 in the maxillary sinus component of the lateral nasal glands. The abundance of mRNA and protein in the lateral nasal glands increased with age and reached a peak at postnatal day (P)27. Also at P27, vomeromodulin mRNA and protein expression was initiated in vomeronasal glands and posterior glands of the nasal septum. Comparison of the developmental expression of odorant-binding protein, another carrier protein synthesized in the lateral nasal glands, with that of vomeromodulin demonstrated major differences. In contrast to vomeromodulin, odorant-binding protein was not detected until postnatal day 2 in the ventral component of the lateral nasal glands and anterior glands of the nasal septum. These results suggest that the expression of vomeromodulin and odorant-binding protein is developmentally and differentially regulated and confirms the suggestion that vomeromodulin may function in olfactory and vomeronasal perireceptor processes as a transporter for pheromones and odorants. In addition, the embryonic expression of vomeromodulin suggests its involvement in olfactory perireceptor processes in utero.