Differential development of binding sites for four lectins in the vomeronasal system of juvenile mouse: from the sensory transduction site to the first relay stage

Do fossorial water voles have a functional vomeronasal organ? A histological and immunohistochemical study

The fossorial water vole, Arvicola scherman, is an herbivorous rodent that causes significant agricultural damages. The application of cairomones and alarm pheromones emerges as a promising sustainable method to improve its integrated management. These chemical signals would induce stress responses that could interfere with the species regular reproductive cycles and induce aversive reactions, steering them away from farmlands and meadows. However, there is a paucity of information regarding the water vole vomeronasal system, both in its morphological foundations and its functionality, making it imperative to understand the same for the application of chemical communication in pest control. This study fills the existing gaps in knowledge through a morphological and immunohistochemical analysis of the fossorial water vole vomeronasal organ. The study is primarily microscopic, employing two approaches: histological, using serial sections stained with various dyes (hematoxylin-eosin, Periodic acid-Schiff, Alcian blue, Nissl), and immunohistochemical, applying various markers that provide morphofunctional and structural information. These procedures have confirmed the presence of a functional vomeronasal system in fossorial water voles, characterized by a high degree of differentiation and a significant expression of cellular markers indicative of active chemical communication in this species.

Comparative lectin histochemistry on the murine respiratory tract and primary olfactory pathway using a fully automated staining procedure

Lectins are naturally occurring molecules which bind to specific carbohydrates of glycoconjugates. The binding specificity of lectins can therefore be used to specifically elucidate the glycosylation pattern in various tissues. While lectin histochemistry is usually carried out manually on single slides, a fully automated immunostaining system offers an easy, standardized, and high throughput system. In this study lectin histochemistry was implemented and optimized on a fully automated immunostaining system to investigate glycosylation patterns in the murine respiratory tract and the primary olfactory pathway. We tested 22 commercially available biotinylated lectins for their labelling-profiles to specifically identify morphologic structures. The results showed that lectin staining profiles using the implemented protocol on the automated system were constant and suitable for high throughput morphological studies. Further, the morphological evaluation of the stained slides revealed a complete characterization of the murine respiratory tract and primary olfactory pathway including the lectin binding profiles for the olfactory bulb, the vomeronasal organ and the nasal-associated lymphoid tissue.

Neuroanatomical and Immunohistological Study of the Main and Accessory Olfactory Bulbs of the Meerkat (Suricata suricatta)

Simple Summary

In wild mammals, chemical senses are crucial to survival, but sensory system information is lacking for many species, including the meerkat (Suricata suricatta), an iconic mammal with a marked social hierarchy that has been ambiguously classified in both canid and felid families. We studied the neuroanatomical basis of the meerkat olfactory and accessory olfactory bulbs, aiming to provide information on the relevance of both systems to the behaviors of this species and contributing to improving its taxonomic classification. The accessory olfactory bulb serves as the integration center of vomeronasal information. When examined microscopically, the accessory olfactory bulb of the meerkat presents a lamination pattern more defined than observed in dogs and approaching the pattern described in cats. The degree of lamination and development in the meerkat main olfactory bulb is comparable to the general pattern observed in mammals but with numerous specific features. Our study supports the functionality of the olfactory and vomeronasal integrative centers in meerkats and places this species within the suborder Feliformia. Our study also confirms the importance of chemical signals in mediating the social behaviors of this species and provides essential neuroanatomical information for understanding the functioning of their chemical senses.

Abstract

We approached the study of the main (MOB) and accessory olfactory bulbs (AOB) of the meerkat (Suricata suricatta) aiming to fill important gaps in knowledge regarding the neuroanatomical basis of olfactory and pheromonal signal processing in this iconic species. Microdissection techniques were used to extract the olfactory bulbs. The samples were subjected to hematoxylin-eosin and Nissl stains, histochemical (Ulex europaeus agglutinin, Lycopersicon esculentum agglutinin) and immunohistochemical labelling (Gαo, Gαi2, calretinin, calbindin, olfactory marker protein, glial fibrillary acidic protein, microtubule-associated protein 2, SMI-32, growth-associated protein 43). Microscopically, the meerkat AOB lamination pattern is more defined than the dog’s, approaching that described in cats, with well-defined glomeruli and a wide mitral-plexiform layer, with scattered main cells and granular cells organized in clusters. The degree of lamination and development of the meerkat MOB suggests a macrosmatic mammalian species. Calcium-binding proteins allow for the discrimination of atypical glomerular subpopulations in the olfactory limbus between the MOB and AOB. Our observations support AOB functionality in the meerkat, indicating chemosensory specialization for the detection of pheromones, as identified by the characterization of the V1R vomeronasal receptor family and the apparent deterioration of the V2R receptor family.

Does a third intermediate model for the vomeronasal processing of information exist? Insights from the macropodid neuroanatomy

The study of the α-subunit of Gi2 and Go proteins in the accessory olfactory bulb (AOB) was crucial for the identification of the two main families of vomeronasal receptors, V1R and V2R. Both families are expressed in the rodent and lagomorph AOBs, according to a segregated model characterized by topographical anteroposterior zonation. Many mammal species have suffered from the deterioration of the Gαo pathway and are categorized as belonging to the uniform model. This scenario has been complicated by characterization of the AOB in the tammar wallaby, Notamacropus eugenii, which appears to follow a third model of vomeronasal organization featuring exclusive Gαo protein expression, referred to as the intermediate model, which has not yet been replicated in any other species. Our morphofunctional study of the vomeronasal system (VNS) in Bennett’s wallaby, Notamacropus rufogriseus, provides further information regarding this third model of vomeronasal transduction. A comprehensive histological, lectin, and immunohistochemical study of the Bennett’s wallaby VNS was performed. Anti-Gαo and anti-Gαi2 antibodies were particularly useful because they labeled the transduction cascade of V2R and V1R receptors, respectively. Both G proteins showed canonical immunohistochemical labeling in the vomeronasal organ and the AOB, consistent with the anterior–posterior zonation of the segregated model. The lectin Ulex europaeus agglutinin selectively labeled the anterior AOB, providing additional evidence for the segregation of vomeronasal information in the wallaby. Overall, the VNS of the Bennett’s wallaby shows a degree of differentiation and histochemical and neurochemical diversity comparable to species with greater VNS development. The existence of the third intermediate type in vomeronasal information processing reported in Notamacropus eugenii is not supported by our lectin-histochemical and immunohistochemical findings in Notamacropus rufogriseus.

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.

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.

Anatomy of the olfactory mucosa

The classic notion that humans are microsmatic animals was born from comparative anatomy studies showing the reduction in the size of both the olfactory bulbs and the limbic brain relative to the whole brain. However, the human olfactory system contains a number of neurons comparable to that of most other mammals, and humans have exquisite olfactory abilities. Major advances in molecular and genetic research have resulted in the identification of extremely large gene families that express receptors for sensing odors. Such advances have led to a renaissance of studies focused on both human and nonhuman aspects of olfactory physiology and function. Evidence that olfactory dysfunction is among the earliest signs of a number of neurodegenerative and neuropsychiatric disorders has led to considerable interest in the use of olfactory epithelial biopsies for potentially identifying such disorders. Moreover, the unique features of the olfactory ensheathing cells have made the olfactory mucosa a promising and unexpected source of cells for treating spinal cord injuries and other neural injuries in which cell guidance is critical. The olfactory system of humans and other primates differs in many ways from that of other species. In this chapter we provide an overview of the anatomy of not only the human olfactory mucosa but of mucosae from a range of mammals from which more detailed information is available. Basic information regarding the general organization of the olfactory mucosa, including its receptor cells and the large number of other cell types critical for their maintenance and function, is provided. Cross-species comparisons are made when appropriate. The polemic issue of the human vomeronasal organ in both the adult and fetus is discussed, along with recent findings regarding olfactory subsystems within the nose of a number of mammals (e.g., the septal organ and Grüneberg ganglion).

Age-dependent decrease in glomeruli and receptor cells containing α1-2 fucose glycan in the mouse main olfactory system but not in the vomeronasal system

Receptor cells of the olfactory epithelium (OE) and vomeronasal organ (VNO) project axons to glomeruli in the main olfactory bulb (MOB) and accessory olfactory bulb (AOB), respectively and undergo continuous turnover throughout life. Alpha1-2 fucose (α1-2Fuc) glycan mediates neurite outgrowth and synaptic plasticity and plays important roles in the formation of the olfactory system during development. We previously confirmed the localization of α1-2Fuc glycan in the olfactory system of 3- to 4-month-old mice but whether such localization persists throughout life remains unknown. Here, the MOB, AOB, OE and VNO of 1-, 3- and 8-month-old mice were histochemically examined using Ulex europaeus agglutinin-I (UEA-I) that specifically binds to α1-2Fuc glycan. Binding sites for UEA-I in the MOB were similar among all age groups but the ratio of UEA-I-positive glomeruli significantly decreased with aging. The frequency of UEA-I-positive receptor cells in the OE of the two older groups was also significantly lower than that of 1-month-old mice. On the other hand, UEA-I binding in the AOB and VNO did not significantly differ among all three groups. These findings suggest that the primary pathway of the main olfactory system requires the role of α1-2Fuc glycan in young mice rather than old mice, while the vomeronasal pathway equally requires this glycan in both young and old mice.

Histological and lectin histochemical studies of the vomeronasal organ of horses

The morphological characteristics and glycoconjugate composition of the vomeronasal organ (VNO) of the horse was investigated using histological, immunohistochemical, and lectin histochemical methods. The VNO is bilaterally located at the base of the nasal septum, has a tubular structure surrounded by cartilage, and consists of sensory and non-sensory epithelia. Immunohistochemical examination showed that the vomeronasal sensory epithelium (VSE) consisted of receptor cells positive for both olfactory marker protein (OMP) and protein gene product 9.5 (PGP 9.5), supporting cells, and basal cells. VNO receptor cells were positive for G protein Gαi2 (vomeronasal receptor type 1 marker), but not Gαo (vomeronasal receptor type 2 marker). Lectin histochemical studies using 21 biotinylated lectins showed that the free border of the VSE was positive for 20 lectins. The receptor and supporting cells reacted with 16 lectins while the basal cells reacted with 15 lectins, with varying intensities. In the vomeronasal non-sensory epithelium, the free border was positive for 19 lectins. The cilated cells were positive for 17 lectins and the basal cells were positive for 15 lectins. The vomeronasal glands, positioned in the lamina propria, were stained with both periodic acid Schiff (PAS) and alcian blue (pH 2.5). Eighteen lectins stained the acinar cells of the vomeronasal glands with various binding patterns. These findings suggest that horse VNO receptor cells express vomeronasal receptor type 1, and the VNO glands have mucous to seromucous characteristics. Moreover, each lectin differentially binds each cell type in both the VNO sensory and non-sensory epithelia.

Molecular clock regulates daily α1-2-fucosylation of the neural cell adhesion molecule (NCAM) within mouse secondary olfactory neurons

The circadian clock regulates various behavioral and physiological rhythms in mammals. Circadian changes in olfactory functions such as neuronal firing in the olfactory bulb (OB) and olfactory sensitivity have recently been identified, although the underlying molecular mechanisms remain unknown. We analyzed the temporal profiles of glycan structures in the mouse OB using a high-density microarray that includes 96 lectins, because glycoconjugates play important roles in the nervous system such as neurite outgrowth and synaptogenesis. Sixteen lectin signals significantly fluctuated in the OB, and the intensity of all three that had high affinity for α1-2-fucose (α1-2Fuc) glycan in the microarray was higher during the nighttime. Histochemical analysis revealed that α1-2Fuc glycan is located in a diurnal manner in the lateral olfactory tract that comprises axon bundles of secondary olfactory neurons. The amount of α1-2Fuc glycan associated with the major target glycoprotein neural cell adhesion molecule (NCAM) varied in a diurnal fashion, although the mRNA and protein expression of Ncam1 did not. The mRNA and protein expression of Fut1, a α1-2-specific fucosyltransferase gene, was diurnal in the OB. Daily fluctuation of the α1-2Fuc glycan was obviously damped in homozygous Clock mutant mice with disrupted diurnal Fut1 expression, suggesting that the molecular clock governs rhythmic α1-2-fucosylation in secondary olfactory neurons. These findings suggest the possibility that the molecular clock is involved in the diurnal regulation of olfaction via α1-2-fucosylation in the olfactory system.

Anatomy, histochemistry, and immunohistochemistry of the olfactory subsystems in mice

The four regions of the murine nasal cavity featuring olfactory neurons were studied anatomically and by labeling with lectins and relevant antibodies with a view to establishing criteria for the identification of olfactory subsystems that are readily applicable to other mammals. In the main olfactory epithelium and the septal organ the olfactory sensory neurons (OSNs) are embedded in quasi-stratified columnar epithelium; vomeronasal OSNs are embedded in epithelium lining the medial interior wall of the vomeronasal duct and do not make contact with the mucosa of the main nasal cavity; and in Grüneberg's ganglion a small isolated population of OSNs lies adjacent to, but not within, the epithelium. With the exception of Grüneberg's ganglion, all the tissues expressing olfactory marker protein (OMP) (the above four nasal territories, the vomeronasal and main olfactory nerves, and the main and accessory olfactory bulbs) are also labeled by Lycopersicum esculentum agglutinin, while Ulex europaeus agglutinin I labels all and only tissues expressing G_αi2 (the apical sensory neurons of the vomeronasal organ, their axons, and their glomerular destinations in the anterior accessory olfactory bulb). These staining patterns of UEA-I and LEA may facilitate the characterization of olfactory anatomy in other species. A 710-section atlas of the anatomy of the murine nasal cavity has been made available on line.

A morphological study of the vomeronasal organ and the accessory olfactory bulb in the Korean roe deer, Capreolus pygargus

The vomeronasal organ (VNO) and accessory olfactory bulb (AOB) of the Korean roe deer (Capreolus pygargus) were studied histologically to evaluate their morphological characteristics. Grossly, the VNO, encased by cartilage, has a paired tubular structure with a caudal blind end and a rostral connection through incisive ducts on the hard palate. In the VNO, the vomeronasal sensory epithelium (VSE) consists of galectin-3-positive supporting cells, protein gene product (PGP) 9.5-positive receptor cells, and basal cells. The vomeronasal respiratory epithelium (VRE) consists of a pseudostratified epithelium. The AOB strata included a vomeronasal nerve layer (VNL), a glomerular layer (GL), a mitral/tufted cell layer, and a granular cell layer. All lectins used in this study, including Bandeiraea simplicifolia agglutinin isolectin B4 (BSI-B4), soybean agglutinin (SBA), Ulex europaeus agglutinin I (UEA-I), and Triticum vulgaris wheat germ agglutinin (WGA), labeled the VSE with varying intensity. In the AOB, both the VNL and the GL reacted with BSI-B4, SBA, and WGA with varying intensity, but not with UEA-I. This is the first morphological study of the VNO and AOB of the Korean roe deer, which are similar to those of goats.

β3GnT2 null mice exhibit defective accessory olfactory bulb innervation

Vomeronasal sensory neurons (VSNs) extend axons to the accessory olfactory bulb (AOB) where they form synaptic connections that relay pheromone signals to the brain. The projections of apical and basal VSNs segregate in the AOB into anterior (aAOB) and posterior (pAOB) compartments. Although some aspects of this organization exhibit fundamental similarities with the main olfactory system, the mechanisms that regulate mammalian vomeronasal targeting are not as well understood. In the olfactory epithelium (OE), the glycosyltransferase β3GnT2 maintains expression of axon guidance cues required for proper glomerular positioning and neuronal survival. We show here that β3GnT2 also regulates guidance and adhesion molecule expression in the vomeronasal system in ways that are partially distinct from the OE. In wildtype mice, ephrinA5(+) axons project to stereotypic subdomains in both the aAOB and pAOB compartments. This pattern is dramatically altered in β3GnT2(-/-) mice, where ephrinA5 is upregulated exclusively on aAOB axons. Despite this, apical and basal VSN projections remain strictly segregated in the null AOB, although some V2r1b axons that normally project to the pAOB inappropriately innervate the anterior compartment. These fibers appear to arise from ectopic expression of V2r1b receptors in a subset of apical VSNs. The homotypic adhesion molecules Kirrel2 and OCAM that facilitate axon segregation and glomerular compartmentalization in the main olfactory bulb are ablated in the β3GnT2(-/-) aAOB. This loss is accompanied by a two-fold increase in the total number of V2r1b glomeruli and a failure to form morphologically distinct glomeruli in the anterior compartment. These results identify a novel function for β3GnT2 glycosylation in maintaining expression of layer-specific vomeronasal receptors, as well as adhesion molecules required for proper AOB glomerular formation.

Developmental changes affecting lectin binding in the vomeronasal organ of domestic pigs, Sus scrofa

This study investigated the developmental changes of glycoconjugate patterns in the porcine vomeronasal organs (VNOs) and associated glands (Jacobson's glands) from prenatal (9 weeks of gestation) and postnatal (2 days after birth) to the sexually mature stage (6 months old). The VNO of pigs (Sus scrofa) was examined using the following: Dolichos biflorus agglutinin (DBA), Bandeiraea simplicifolia agglutinin isolectin B4 (BSI-B4), Triticum vulgaris agglutinin (WGA), Ulex europaeus agglutinin I (UEA-I), and soybean agglutinin (SBA). At the fetal stage, all lectins examined were detected mainly in the free border of the vomeronasal epithelium, but few (WGA and UEA-I) and or absent in the VNO cell bodies. At the postnatal and sexually mature stages, the reactivity of some lectins, including WGA, UEA-I, DBA and SBA, were shown to increase in the VNO sensory epithelium as well as the free border. The increased reactivity of lectins as development progressed was also observed in Jacobson's gland acini. These findings suggest that binding sites of lectins, including those of WGA, UEA-I, DBA, and SBA, increase during development from fetal to postnatal growth, possibly contributing to the increased ability of chemoreception in the pig.

Lectin histochemical study on the olfactory bulb of the newt, Cynops pyrrhogaster

The function and/or morphological features of the vomeronasal olfactory system remain unclear in aquatic animals, although the system appeared first in urodeles based on phylogenic data. We examined the lectin binding patterns in the olfactory bulb of a semi-aquatic urodele, the Japanese red-bellied newt, Cynops pyrrhogaster, using 22 different lectins. Eleven of the lectins showed specific binding to the nerve fibres and glomeruli in the olfactory bulb. Among these, Wheat germ agglutinin, pokeweed and peanut agglutinin preferentially bound the main olfactory bulb, reflecting variation in the expression of glycoconjugates between the main and accessory olfactory bulbs. By contrast, the types of lectins bound to the Cynops olfactory bulb were considerably different from those reported in other urodele families. These results suggest a histochemical distinction between the main and accessory olfactory bulbs, and that glycoconjugate expression may differ significantly among urodele families.

The risk of extrapolation in neuroanatomy: the case of the Mammalian vomeronasal system

The sense of smell plays a crucial role in mammalian social and sexual behaviour, identification of food, and detection of predators. Nevertheless, mammals vary in their olfactory ability. One reason for this concerns the degree of development of their pars basalis rhinencephali, an anatomical feature that has been considered in classifying this group of animals as macrosmatic, microsmatic or anosmatic. In mammals, different structures are involved in detecting odours: the main olfactory system, the vomeronasal system (VNS), and two subsystems, namely the ganglion of Grüneberg and the septal organ. Here, we review and summarise some aspects of the comparative anatomy of the VNS and its putative relationship to other olfactory structures. Even in the macrosmatic group, morphological diversity is an important characteristic of the VNS, specifically of the vomeronasal organ and the accessory olfactory bulb. We conclude that it is a big mistake to extrapolate anatomical data of the VNS from species to species, even in the case of relatively close evolutionary proximity between them. We propose to study other mammalian VNS than those of rodents in depth as a way to clarify its exact role in olfaction. Our experience in this field leads us to hypothesise that the VNS, considered for all mammalian species, could be a system undergoing involution or regression, and could serve as one more integrated olfactory subsystem.

Identification of the plasticity-relevant fucose-alpha(1-2)-galactose proteome from the mouse olfactory bulb

Fucose-alpha(1-2)-galactose [Fucalpha(1-2)Gal] sugars have been implicated in the molecular mechanisms that underlie neuronal development, learning, and memory. However, an understanding of their precise roles has been hampered by a lack of information regarding Fucalpha(1-2)Gal glycoproteins. Here, we report the first proteomic studies of this plasticity-relevant epitope. We identify five classes of putative Fucalpha(1-2)Gal glycoproteins: cell adhesion molecules, ion channels and solute carriers/transporters, ATP-binding proteins, synaptic vesicle-associated proteins, and mitochondrial proteins. In addition, we show that Fucalpha(1-2)Gal glycoproteins are enriched in the developing mouse olfactory bulb (OB) and exhibit a distinct spatiotemporal expression that is consistent with the presence of a "glycocode" to help direct olfactory sensory neuron (OSN) axonal pathfinding. We find that expression of Fucalpha(1-2)Gal sugars in the OB is regulated by the alpha(1-2)fucosyltransferase FUT1. FUT1-deficient mice exhibit developmental defects, including fewer and smaller glomeruli and a thinner olfactory nerve layer, suggesting that fucosylation contributes to OB development. Our findings significantly expand the number of Fucalpha(1-2)Gal glycoproteins and provide new insights into the molecular mechanisms by which fucosyl sugars contribute to neuronal processes.

Loss of short dystrophin isoform Dp71 in olfactory ensheathing cells causes vomeronasal nerve defasciculation in mouse olfactory system

The Duchenne muscular dystrophy (DMD) gene encodes dystrophin, which is a protein defective in DMD patients, as well as a number of shorter isoforms, which have been shown to be expressed in various non-muscle, primarily neural, tissues. As of yet, the physiological function of the various dystrophin isoforms is not fully understood. In the present study, we investigated the neurological phenotype that arises in the DMD-null mice, where expression of all dystrophin isoforms had been disrupted. We demonstrate that vomeronasal axons in the DMD-null mice are defasciculated, and some of the defasciculated vomeronasal axons aberrantly entered into the main olfactory bulb, which indicates that the product(s) of the DMD gene plays an important role in vomeronasal nerve organization. Through western blot and immunofluorescence analyses, we determined that the dystrophin isoform Dp71 was exclusively expressed in the mouse olfactory system: mainly in the olfactory ensheathing cells (OECs), an olfactory system-specific glia cell that ensheaths fascicles of the olfactory nerve. In the OECs, Dp71 was co-localized with beta-dystroglycan, utrophin, laminin, and perlecan. Since beta-dystroglycan and perlecan expression was decreased in the OECs of DMD-null mice, we hypothesize that Dp71 expressed in the OECs participates in fasciculation of the vomeronasal nerve, most likely through interactions with extracellular matrix.

The cell surface carbohydrate blood group A regulates the selective fasciculation of regenerating accessory olfactory axons

Cell surface carbohydrates are differentially expressed by discrete subpopulations of primary sensory axons in the mammalian main and accessory olfactory systems. It has been proposed that these carbohydrates provide a glycocode which mediates the sorting of these sensory axons as they project from the olfactory neuroepithelium to their central targets in the main and accessory olfactory bulbs during development. As the differential expression of cell surface carbohydrates on olfactory axons persists in the adult we have now investigated their role during regeneration. We have recently generated a line of transgenic mice, BGAT-Tg, that mis-express the blood group A (BGA) carbohydrate on all primary olfactory axons rather than just on accessory olfactory axons as in wild-type mice. Following unilateral bulbectomy, accessory and main olfactory axons regenerate and grow into the frontal cortex where they fill the cavity which remains after the olfactory bulb ablation. In wild-type mice, the regenerating BGA-expressing accessory olfactory axons selectively aggregated with each other in large bundles but clearly separated from the BGA-negative main olfactory axons. In contrast, in the BGAT-Tg transgenic mice in which all main and accessory axons express the BGA carbohydrate, the accessory olfactory axons failed to correctly separate from the main olfactory axons. Instead, these axons formed numerous small bundles interspersed with main olfactory axons. These data provide strong evidence that the restricted expression of BGA is in part responsible for the selective segregation of accessory olfactory axons.

Perinatal size and maturation of the olfactory and vomeronasal neuroepithelia in lorisoids and lemuroids

Explanations for the chemosensory abilities of newborn mammals focus primarily on food (milk) acquisition and communication (e.g., maternal-infant bonding). However, the relative importance of the main and accessory (vomeronasal) olfactory systems is hypothesized to differ at birth between altricial and precocial mammals. Strepsirrhines (lemurs and lorises) possess main and accessory olfactory systems, and vary in life-history traits related to infant dependency and maturation. Accordingly, this study examines the size and maturational characteristics of vomeronasal (VNNE) and olfactory (OE) neuroepithelia in strepsirrhines. Serially sectioned heads of 18 infant cadavers were examined microscopically for neuroepithelial distribution. Measurements were taken on the length of the nasal fossa on one side that was occupied by VNNE and OE. The data were corrected for body size using the cranial length or body mass, and were then examined for correlation with several life-history variables, as well as activity pattern. In addition, immunohistochemistry was used to identify cells in the VNNE and OE that express olfactory marker protein (OMP), a marker of mature olfactory neurons. Relative OE extent was not significantly correlated with any of the life-history variables. Relative VNNE length was negatively correlated with relative gestation length and relative neonatal mass (P<0.05). However, when we corrected for phylogenetic relationships, we found no significant correlations between either of the neuroepithelial measurements and life-history variables. Immunohistochemical findings suggest that OE has more OMP-reactive cells than VNNE in all species. OMP-reactive cells appear to be less numerous in diurnal species compared to most nocturnal species. These results indicate that the VNNE may be relatively longer at birth in altricial species. However, it remains uncertain how phylogeny and/or ontogeny may explain these findings.

Genetic manipulation of blood group carbohydrates alters development and pathfinding of primary sensory axons of the olfactory systems

Primary sensory neurons in the vertebrate olfactory systems are characterised by the differential expression of distinct cell surface carbohydrates. We show here that the histo-blood group H carbohydrate is expressed by primary sensory neurons in both the main and accessory olfactory systems while the blood group A carbohydrate is expressed by a subset of vomeronasal neurons in the developing accessory olfactory system. We have used both loss-of-function and gain-of-function approaches to manipulate expression of these carbohydrates in the olfactory system. In null mutant mice lacking the alpha(1,2)fucosyltransferase FUT1, the absence of blood group H carbohydrate resulted in the delayed maturation of the glomerular layer of the main olfactory bulb. In addition, ubiquitous expression of blood group A on olfactory axons in gain-of-function transgenic mice caused mis-routing of axons in the glomerular layer of the main olfactory bulb and led to exuberant growth of vomeronasal axons in the accessory olfactory bulb. These results provide in vivo evidence for a role of specific cell surface carbohydrates during development of the olfactory nerve pathways.

Subdivision of the accessory olfactory bulb in the Japanese common toad, Bufo japonicus, revealed by lectin histochemical analysis

Lectin binding patterns in the olfactory bulb of the Japanese common toad, Bufo japonicus, were examined using 21 types of lectin. Ten out of 21 lectins, WGA, s-WGA, LEL, STL, DBA, VVA, SJA, RCA-I, PNA, and PHA-L, stained the olfactory nerve, the glomeruli in the main olfactory bulb (MOB), the vomeronasal nerve, and the glomeruli in the accessory olfactory bulb (AOB). The binding patterns of LEL, STL, DBA, and PHA-L subdivided AOB glomeruli into rostral and caudal regions, where LEL, STL, and DBA stained the rostral region more intensely than the caudal region, and PHA-L had the opposite effect. Another lectin, BSL-I, stained both AOB glomeruli and the vomeronasal nerve, but not MOB glomeruli or the olfactory nerve. This is the first report of histological subdivision in the AOB of an amphibian, which suggests that the AOB development in Bufo may be unique.

The sorting behaviour of olfactory and vomeronasal axons during regeneration

In order to begin to understand how primary olfactory and vomeronasal organ (VNO) axons target specific regions of the olfactory bulb, we examined the sorting behaviour of these axons following neonatal unilateral olfactory bulbectomy. Bulbectomy induced widespread ipsilateral death of the primary olfactory and VNO neurons. After 4 weeks, many new sensory axons had re-grown into the cranial cavity and established a prominent plexus with evidence of dense tufts that were similar in gross appearance to glomeruli. Axons expressing the cell adhesion molecule OCAM, which normally innervate the ventrolateral and rostral halves of the main and accessory olfactory bulbs, respectively, sorted out and segregated from those axons not expressing this molecule within the plexus. In addition, VNO axons formed large discrete bundles that segregated from main olfactory axons within the plexus. Thus, VNO and primary olfactory axons as well as discrete subpopulations of both are able to sort out and remain segregated in the absence of the olfactory bulb. Sorting and convergence of axons therefore occur independently of the olfactory bulb and are probably attributable either to inherent properties of the axons themselves or to interactions between the axons and accompanying glial ensheathing cells.

General organization of the perinatal and adult accessory olfactory bulb in mice

The vomeronasal system is currently a topical issue since the dual functional specificity, vomeronasal system-pheromones, has recently been questioned. Irrespective of the tools used to put such specificity in doubt, the diversity of the anatomy of the system itself in the animal kingdom is probably of more importance than has previously been considered. It has to be pointed out that a true vomeronasal system is integrated by the vomeronasal organ, the accessory olfactory bulb, and the so-called vomeronasal amygdala. Therefore, it seems reasonable to establish the corresponding differences between a well-developed vomeronasal system and other areas of the nasal cavity in which putative olfactory receptors, perhaps present in other kinds of mammals, may be able to detect pheromones and to process them. In consequence, a solid pattern for one such system in one particular species needs to be chosen. Here we report on an analysis of the general morphological characteristics of the accessory olfactory bulb in mice, a species commonly used in the study of the vomeronasal system, during growth and in adults. Our results indicate that the critical period for the formation of this structure comprises the stages between the first and the fifth day after birth, when the stratification of the bulb, the peculiarities of each type of cell, and the final building of glomeruli are completed. In addition, our data suggest that the conventional plexiform layers of the main olfactory bulb are not present in the accessory bulb.

Comparative study of lectin reactivity in the vomeronasal organ of human and nonhuman primates

The main and accessory olfactory systems of certain mammals (e.g., rodents, ungulates, and carnivores) have been investigated using lectin histochemistry to probe for sugar residues that may reflect physiological aspects of signal transduction or development. Morphologically, the vomeronasal organs (VNOs) of strepsirrhine primates (lemurs and lorises) are typical of functional VNOs in other mammals, whereas in humans and chimpanzees the VNOs appear vestigial. However, the human VNO is considered functional by some authors. To elucidate the cellular nature of the VNO in human and chimpanzees, a panel of six lectins (Con-A, ECL, PNA, RCA, s-WGA, and UEA-1) was applied to the VNO in eight species of primates, including humans and chimpanzees. The results indicated that there were few, if any, lectin-reactive cells in the human or chimpanzee VNO that resembled those seen in the vomeronasal neuroepithelium in other primates. The overall pattern of lectin reactivity in the human and chimpanzee VNO is unlike that seen in mammals with chemosensory VNOs, suggesting that the VNO of these hominoids does not function similarly to that of other primates.

Fetal development of vomeronasal system in the goat

Our previous study morphologically revealed that the adult goat vomeronasal (VN) system was different from the rodent and opossum one, and at least two types of VN systems exist in mammals. However, it remains unknown whether the developments in both types of VN systems are ontogenetically distinct and when the goat VN system is established. In this study, we morphologically observed the fetal development of the goat accessory olfactory bulb (AOB) and VN neuron. In the fetus, Gi2-expressing VN terminals terminated at glomeruli throughout the AOB, and no immunoreactivities for Go were detected in the nerve terminals reaching into AOB. The layer structure of AOB rapidly developed in the latter half of gestation. In the VN organ (VNO), at the middle stage of gestation, the dendritic processes of VN neuron were exposed in the VN lumen, and scattered and thin microvilli existed on the protrusion of the VN neuron. In the apical part of dendritic processes, no clear vesicle existed. However, the immunohistochemistry of an olfactory marker protein (OMP) revealed that a few VN neurons with OMP exist in VN sensory epithelium (VSE) before birth, although marked immunoreactivities were detected in adult VSE. Fetal VN neurons appeared to be underdeveloped. These results suggest that the goat VN system is ontogenetically distinct from the rodent and opossum VN systems, and is underdeveloped before birth. The goat VN system will develop and mature during the early postnatal period similar to the rodent and opossum VN systems.