Histological development of the vomeronasal complex in the pre- and postnatal rat

Morphology of cat vomeronasal organ non-sensory epithelium during postnatal development

The vomeronasal organ has an important role in mammal's social and sexual behaviours. In addition, it mediates defensive behavior through detection of protein pheromone homologues. In this work, a detailed morphological description of the postnatal development of the non-sensory epithelium (NSE) lining the vomeronasal duct (VND) of the female cat is provided using various histological techniques. The study focused on newborn, 2 weeks, 4 weeks, and 8 weeks of postnatal ages using four animals for each age. We report here for the first time that three types of NSE line the rostral segment of the VND; nonkeratinized stratified squamous epithelium, stratified cuboidal epithelium, and ciliated pseudo stratified columnar ciliated epithelium with goblet cells and that the VND undergoes 90° a change in its its axis from the vertical position caudally to the horizontal position rostral. The NSE which lines the lateral side of the VND middle segment is consists of cliated pseudostratified columnar epithelium without goblet cells. In addition to basal cells, the NSE contains ciliated and three types of nonciliated columnar epithelial cells (dark, light, and unstained). Mitotic figures were observed only in the basal cells layer during the first 2 weeks of postnatal development. Intraepithelial invading inflammatory cells were uncommon. Scanning electron microscopy revealed unevenly distributed long cilia intermingled with microvillar processes and intervening short microvillar processes. These projecting cilia and microvilli revealed a gradual increase in their height during development toward maturity.

Embryology of the VNO and associated structures in the grass snake Natrix natrix (Squamata: Naticinae): a 3D perspective

BACKGROUND

Snakes are considered to be vomerolfaction specialists. They are members of one of the most diverse groups of vertebrates, Squamata. The vomeronasal organ and the associated structures (such as the lacrimal duct, choanal groove, lamina transversalis anterior and cupola Jacobsoni) of adult lizards and snakes have received much anatomical, histological, physiological and behavioural attention. However, only limited embryological investigation into these structures, constrained to some anatomical or cellular studies and brief surveys, has been carried out thus far. The purpose of this study was, first, to examine the embryonic development of the vomeronasal organ and the associated structures in the grass snake (Natrix natrix), using three-dimensional reconstructions based on histological studies, and, second, to compare the obtained results with those presented in known publications on other snakes and lizards.

RESULTS

Five major developmental processes were taken into consideration in this study: separation of the vomeronasal organ from the nasal cavity and its specialization, development of the mushroom body, formation of the lacrimal duct, development of the cupola Jacobsoni and its relation to the vomeronasal nerve, and specialization of the sensory epithelium. Our visualizations showed the VNO in relation to the nasal cavity, choanal groove, lacrimal duct and cupola Jacobsoni at different embryonic stages. We confirmed that the choanal groove disappears gradually, which indicates that this structure is absent in adult grass snakes. On our histological sections, we observed a gradual growth in the height of the columns of the vomeronasal sensory epithelium and widening of the spaces between them.

CONCLUSIONS

The main ophidian taxa (Scolecophidia, Henophidia and Caenophidia), just like other squamate clades, seem to be evolutionarily conservative at some levels with respect to the VNO and associated structures morphology. Thus, it was possible to homologize certain embryonic levels of the anatomical and histological complexity, observed in the grass snake, with adult conditions of certain groups of Squamata. This may reflect evolutionary shift in Squamata from visually oriented predators to vomerolfaction specialists. Our descriptions offer material useful for future comparative studies of Squamata, both at their anatomical and histological levels.

Morphology of non-sensory epithelium during post-natal development of the rabbit vomeronasal organ

The vomeronasal organ (VNO), because of its ability to detect pheromones, has an important role in many social and sexual behaviours in mammals. It also mediates defensive behaviours through detection of protein pheromone homologues. A detailed morphological description of the post-natal development of the 'non-sensory' epithelium (NSE) of the female rabbit is recorded. Histological techniques were used to study the NSE of the VNO in post-natal development of female rabbits. The study focused on the following post-natal ages: newborn, 1 week, 2 weeks and 1 month (five animals each) beside to two adult animals. The rabbit VNO was surrounded externally by bony capsule and internally by cartilaginous capsule. NSE was pseudostratified columnar partially ciliated epithelium without goblet cells. In addition to basal cells, NSE contained ciliated and three types of non-ciliated columnar cells (dark, pale and light). At birth, dark cells may have primary cilia. By 1 month, the cytoplasm became lighter with less free ribosomes. The pale cells had electron-lucent cytoplasm, which contained a few organelles. Mitotic figures were observed in basal and columnar cells, particularly during the first 2 weeks of post-natal development. Light columnar cells were common during the first week. Numerous leucocytes and a few nerve endings were detected intra-epithelial. Scanning electron microscope revealed a gradual increase in height of microvilli of non-ciliated cells. Ciliated cells had cilia and microvilli. Cells were arranged singly, in clumps or in a dense population of cells. The rabbit VNO-NSE had a unique morphological structure.

The Bruce effect in Norway rats

Intrauterine implantation of fertilized ova can be blocked by exposing recently inseminated females with an unfamiliar male. This selective pregnancy failure, designated as the Bruce effect (Bruce, Nature 1959; 184:105), is well studied in laboratory mice and has been confirmed in several other rodent species. However, no clear information exists concerning this phenomenon in the laboratory rat. The present study was conducted to investigate whether or not the Bruce effect exists in the rat. Females of two F1 hybrid strains (n(total) = 354) with different MHC genotypes (F344BNF1, RT1(lv1/n), and LEWPVGF1, RT1(l/c)) were mated with males of their own strain and subsequently exposed during the first 4 days postcoitus either to a male of the other hybrid strain or to an unfamiliar male of the same strain as the stud. The litter rate of each treatment group was determined. As a control, mated females of both strains were reexposed to the stud male to determine baseline litter rates. Female rats of both F1 hybrid strains showed a significantly lower litter rate when exposed to males of a different strain than their stud male, compared to the expected values of birth rates observed in control females (F344BNF1: P = 0.017; LEWPVGF1: P = 0.019). In contrast, there was no difference between expected and observed litter rates in females of both F1 hybrid strains after exposure to an unfamiliar male of the same strain as their stud. Our results demonstrate for the first time that the Bruce effect, well documented in mice, occurs in the Norway rat.

Morphology of the non-sensory tissue components in rat aging vomeronasal organ

With 30 figures, 3 histograms and 3 tables

SUMMARY

The vomeronasal organ (VNO) is a chemosensory organ that detects environmental pheromones. The morphology of the 'non-sensory' epithelium (NSE) of the VNO and its lamina propria, as well as how it relates to ageing has received little attention. Histological, histochemical, morphometric and ultrastructural techniques were used to study the morphological structure of the rat NSE in five adult (3 months old) and five aged (2-2.5 years old) male albino rats. In adult rats, the NSE contained dark and light columnar cells with predominance of the latter. The surface of the epithelial cells was covered with microvilli and/or cilia. The lamina propria contained serous vomeronasal glands (VNGs), smooth muscles with numerous variable-sized mitochondria, vessels including lymphatic capillaries and nerve bundles. The following changes were detected in aged rats. The NSE exhibited an increase in number of dark columnar cells. Some cells revealed a prominent cell coat, dense aggregation of filaments in the luminal cytoplasm and appearance of multinucleated cells. Their surface revealed malformed configuration. Large mitochondria (2 μm), formed by fusion, were frequently observed in the smooth muscle cells of the lamina propria. Lipid droplets were frequently detected both in the VNGs acini and in the lymphatic endothelium. Ageing affected both the cells of the tissues and the extracellular matrix.

Immunohistochemical studies on the differential maturation of three types of olfactory organs in the rats

Differential maturation of three types of olfactory organs, the olfactory epithelium (OE), the vomeronasal organ (VNO) and the septal olfactory organ of Masera (MO), was examined immunohistochemically in embryonic and newborn rats by the use of antiprotein gene product 9.5 (PGP 9.5) serum. These olfactory organs were derived in common from the olfactory placode as neuroepithelia. In the OE, PGP 9.5-immunopositive olfactory cells first appeared at 13 days of gestation. The OE maturated completely, and showed the same cytological features as in the adult at 20 days of gestation. The MO first appeared as a dense mass of PGP 9.5-immunopositive sensory cells on the most ventrocaudal part of the nasal septum at 15 days of gestation and was evidently isolated from the OE by the decrease of immunopositive cells in the intercalated epithelium between the OE and the MO at 20 days of gestation. However, even at 7 days after birth, the MO did not complete its development and contained sensory cells aggregating in the mass. The VNO was separated from the nasal cavity at 13 days of gestation as a tubular structure of a neuroepithelium including PGP 9.5-immunopositive sensory cells. These cells gradually increased in number in the sensory epithelium of the VNO and extended their dendritic processes to the free surface at 7 days after birth. These findings clarified the differential maturation of these olfactory organs. That is, the OE completes its development before birth, while the MO and VNO after birth.

Comparative morphology and histochemistry of glands associated with the vomeronasal organ in humans, mouse lemurs, and voles

The vomeronasal organ (VNO) is a chemosensory structure of the vertebrate nasal septum that has been recently shown to exist in nearly all adult humans. Although its link to reproductive behaviors has been shown in some primates, its functionality in humans is still debated. Some authors have suggested that the human VNO has the capacity to detect pheromones, while others described it as little more than a glandular pit. However, no studies have utilized histochemical techniques that would reveal whether the human VNO functions as a generalized gland duct or a specialized chemosensory organ. Nasal septal tissue from 13 humans (2-86 years old) were compared to that of two adult lemurs (Microcebus murinus) and eight adult voles (four Microtus pennsylvanicus and four Microtus ochrogaster). Sections at selected intervals of the VNO were stained with periodic acid-Schiff (PAS), alcian blue (AB), AB-PAS, and PAS-hematoxylin procedures. Results revealed typical well-developed VNOs with tubuloacinar glands in Microtus and Microcebus. VNO glands were AB-negative and PAS-positive in voles and mouse lemurs. Homo differed from Microtus and Microcebus in having more branched, AB and PAS-positive glands that emptied into the VNO lumen. Furthermore, the human VNO epithelium had unicellular mucous glands (AB and PAS-positive) and cilia, similar to respiratory epithelia. These results demonstrate unique characteristics of the human VNO which at once differs from glandular ducts (e.g., cilia) and also from the VNOs of mammals possessing demonstrably functional VNO.

Proliferation in the vomeronasal organ of the rat during postnatal development

We investigated proliferation of sensory cell precursors in the rat vomeronasal organ (VNO) at various postnatal ages from birth (P1) to P666. In the rat, which continues to grow during most of its adult life, proliferation might be related to growth and/or replacement. Proliferating cells were labelled by BrdU injection, and histological sections of the VNO were evaluated after immunohistochemical detection of BrdU. Proliferation density (number of proliferating cells/section) decreased dramatically from 115 at P1 to 27.2 at P21, although the area increased. Adult values were reached at P66-P333 (10.3 cells/section); at P400-P666 the value was 8.6 cells/section. Distribution of labelled cells changed considerably with age: in neonates the cells were nearly equally distributed throughout the sensory epithelium, whereas from P21 onwards most proliferating cells were concentrated in clusters near the boundaries with non-sensory epithelium. Labelled cells in the sensory neuronal layer were adjacent to the undulating basement membrane-bordering capillaries that intrude into the sensory epithelium, indicating that they were true basal cells. The volume of the sensory epithelium increased between P1 and P66, and remained constant thereafter, although the length still increased. Length and volume of the sensory epithelium were related to body size, not to sex; males and females of the same body size had the same VNO size. The complex changes in proliferation pattern during postnatal development indicate differential growth and replacement. We suggest that in adults the labelled cell clusters near the boundaries are a pool for growth, whereas proliferation in the central parts represents a replacement pool.

Supporting tissue and vasculature of the mammalian vomeronasal organ: the rat as a model

The blood supply and osseocartilaginous support structures of the vomeronasal organ of the rat were studied. The study focused on adults, though 3- to 18-day-old animals were also examined. The techniques used included dissection and microdissection, injection of the vascular system with Araldite or with Indian ink in agar or gelatine, conventional histology, and scanning and transmission electron microscopy. The results indicated that blood reaches the vomeronasal organ via a branch of the sphenopalatine artery, and drains into an associated vein. Within the organ, one vein stood out by virtue of its size; this vein is accompanied by lesser veins, together with arterioles, capillaries, and lymphatic vessels. Connective tissue was readily apparent, though its distribution was heterogeneous. Analysis of series of transverse sections indicates that, in adults, the capsule that encases the vomeronasal organ is bony; in younger animals, the capsule is bony externally and cartilaginous internally; in very young animals, the capsule is entirely cartilaginous. However, it was noted that the change from cartilage to bone was due not to ossification of the existing cartilage, but to physical displacement of that cartilage by an extension of the vomer and incisive bones. Taken together, these results confirm the importance of considering the morphology of the vomeronasal organ as a whole, since there are major changes from rostral to caudal ends. Secondly, our findings regarding blood supply and the nature of the capsule support the view that the vomeronasal organ acts as a pump.

Prenatal development of the mammalian vomeronasal organ

The vomeronasal organ (VNO) originates from the medial wall of the olfactory pit shortly after the middle of the embryonic period in mammals. The Anlage stage consists of a cellular bud that grows dorsally, caudally, and towards the midline leaving a groove. The following stage, Early Morphogenesis, includes the closure of the vomeronasal groove to form a parasagittal blind-ended tube in the nasal septum, which opens into the nasal and/or oral cavities. The lumen adopts a crescent shape while the epithelial lining differentiates into an increasingly wider epithelium on the concave side and a gradually thinner epithelium on the convex side. The former goes on to occupy a medial position and develops neuroblasts among supporting and undifferentiated cells, with supporting cell nuclei tending to align in the upper rows. The lateral "non-sensory" epithelium furrows, giving a kidney-shaped appearance to the VNO cross section. The next stage, Late Morphogenesis is extended up to a difference in thickness between both epithelia becomes similar to the adult, generally by birth. An increasing number of ciliary generation complexes, larger and more abundant microvilli, and an evident glycocalyx are observed in the neuroepithelium at the luminal surface, while enzymatic activities become more intense. The non-sensory epithelium appears quite mature save for its luminal surface, which is still devoid of cilia. Blood capillaries penetrate the most basal region of the neuroepithelium and vomeronasal glands are very few and immature. At birth, some neurons appear well developed to support certain functionality; however, persistence of architectural, histochemical, and ultrastructural signs of immaturity, suggests that full performance of the VNO does not occur in newborn mammals, but in prepubertal ages.

CaBPs and other immunohistochemical markers of the human vomeronasal system: a comparison with other mammals

After more than two centuries of almost sporadic inquiry as to the existence and function of the human vomeronasal system (VNS), the last decade has seen a resurgent interest in it. The principal question vexing many laboratories is whether adult humans retain the VNS that clearly develops during fetal growth. Additional questions are whether the structurally defined fetal VNS has any function role, and if this structure and function extend into postnatal life. One research tool that has been successfully used to identify key components of the mammalian VNS has been immunohistochemistry (IHC). This technique has clearly defined the vomeronasal receptor neurons in the vomeronasal organ, the vomeronasal nerve that projects into the central nervous system, and the target of this nerve, the accessory olfactory bulb. This review will discuss immunohistochemical studies that have identified these features in the mammalian VNS, and relate them to structural and IHC studies of the fetal and adult human VNS. Suggestions as to future studies to clarify the status of the human VNO also are offered.

Searching for the vomeronasal organ of adult humans: preliminary findings on location, structure, and size

The adult human vomeronasal organ (VNO) has been the focus of numerous recent investigations, yet its developmental continuity from the human fetal VNO is poorly understood. The present study compared new data on the adult human "VNO" with previous findings on the fetal human VNO. Nasal septa were removed from twelve adult human cadavers and each specimen was histologically sectioned. Coronal sections were stained with hematoxylin-eosin and periodic acid-Schiff-hematoxylin. The sections were examined by light microscopy for the presence of VNOs and the anterior paraseptal cartilages (PC). VNOs were quantified using a computer reconstruction technique to obtain VNO length, volume, and vomeronasal epithelium (VNE) volume. Histologically, VNOs and PCs were identified in eleven specimens. VNOs had ciliated, pseudostratified columnar epithelium with goblet cells. Variations (e.g., multiple communications to the nasal cavity) were observed in several specimens. Quantification was possible for 16 right or left VNOs. Right or left VNOs ranged from 3.5 to 11.8 mm in length, from 1.8 to 33.8 x 10(-4)cc in volume, and from 2.7 to 18.1 x 10(-4)cc in VNE volume. Results indicated that the adult human VNO was similar in VNE morphology, lumen shape, and spatial relationships when compared to human fetal VNOs. By comparison with previous fetal VNO measures, mean VNO length, volume, and VNE volume were larger in adult humans. These results support previous suggestions that postnatal VNO growth occurs. Findings on location and spatial relationships of the adult VNO were similar to those seen in human fetuses, but critical questions remain regarding the ontogeny of the vomeronasal nerves and VNE.

Differential expression of manganese and copper-zinc superoxide dismutases in the olfactory and vomeronasal receptor neurons of rats during ontogeny

Superoxide dismutases (SODs) protect cells from damage by oxygen free radicals. Manganese (Mn) SOD is preferentially induced in terminally differentiating cells; induction of copper-zinc (CuZn) SOD is more closely associated with postnatal exposure to environmental sources of oxygen free radicals. The purpose of this study was to investigate ontogenetic changes in immunoreactivity for MnSOD and CuZnSOD relative to the expression of markers of neuronal and chemosensory differentiation in olfactory and vomeronasal receptor neurons (ORNs and VRNs, respectively), which mature with different time courses. Immunoreactivity for both SODs was detected in rat ORNs at embryonic day (E) 14, the earliest time point investigated, but not until E16 in vomeronasal neuroblasts. ORNs also expressed the neuronal marker protein gene product (PGP) 9.5 and the chemosensory cell marker olfactory marker protein (OMP) at E14; vomeronasal neuroblasts expressed PGP 9.5 at E16 but were not immunoreactive for OMP until postnatal day (P) 2. Immunoreactivity for MnSOD in ORNs and VRNs generally increased pre- and postnatally to a maximum at P11. Immunoreactivity for CuZnSOD did not increase markedly until after birth, reaching maximal levels at P11-P24. Within ORNs and VRNs, the most intense immunoreactivity was localized in the dendritic and supranuclear regions. The results indicate that in ORNs and VRNs, increases in MnSOD immunoreactivity during ontogeny parallel the ongoing differentiation and maturation of chemosensory receptor neurons; in contrast, the induction of immunoreactivity for CuZnSOD is associated with postnatal exposure to the ambient oxygen and xenobiotic environment.

The pheromonal restoration of cyclic activity in young estrogenized persistent estrus female rats is a vomeronasal effect

Eight sham-operated (SO) and six vomeronasalectomized (VMNX) young adult female rats were used to demonstrate the participation of the vomeronasal organ (VNO) in the pheromonal restoration of cyclic activity (PRCA). All rats were normal four-day cycling before and after surgery and they received a single subcutaneous injection of 2 mg of estradiol benzoate (EB) to induce an anovulatory persistent vaginal estrus. Fifteen days after EB injection, they were treated by spraying in the nostrils, every 10 min for one hour on only one day, 50 muL of urine from young fertile males. SO rats showed PRCA in the following days, while VMNX did not. These results support the VNO as the receptor of the male urinary pheromone (or pheromones) responsible for PRCA, demonstrating that it is possible to improve the function of aging ovaries acting with an exteroceptive stimulus.

Electrophysiological characterization of chemosensory neurons from the mouse vomeronasal organ

The mechanism of sensory transduction in chemosensory neurons of the vomeronasal organ (VNO) is not known. Based on molecular data, it is likely to be different from that mediating sensory transduction in the main olfactory system. To begin to understand this system, we have characterized the electrophysiological properties of dissociated mouse VNO neurons with patch-clamp recording. Sensory neurons were distinguished from nonsensory neurons by the presence of a dendrite, by immunoreactivity for olfactory marker protein, and by the firing of action potentials. The resting potential of VNO neurons was approximately -60 mV, and the average input resistance was 3 Gomega. Current injections as small as 1-2 pA elicited steady trains of action potentials that showed no sign of elicited steady trains of action potentials that showed no sign of adaptation during a 2 sec stimulus duration. The voltage-gated conductances in VNO neurons are distinct from those in olfactory neurons. The Na+ current is composed of two components; the major component was TTX-sensitive (Ki = 3.6 nM). The outward K+ current activates at -30 mV with kinetics 10 times slower than for K+ currents in olfactory neurons. The Ca2+ current is composed of at least two components: an L-type current and a T-type current that activates at -60 mV and is not found in olfactory neurons. We find no evidence for cyclic nucleotide-gated channels in VNO neurons under a variety of experimental conditions, including those that produced large responses in mouse olfactory neurons, which is further evidence for a novel transduction pathway.

Differential expression of odorant-binding protein genes in rat nasal glands: implications for odorant-binding proteinII as a possible pheromone transporter

We examined the distribution and ontogeny of two odorant-binding proteins in the rat at various stages of development from newborn to adult using northern blot and in situ hybridization methods. Our results demonstrated spatial segregation between odorant-binding protein and odorant-binding proteinII in nasal glandular tissues. Odorant-binding protein messenger RNA was expressed in the glandular system opening into the nasal vestibule, whereas odorant-binding proteinII messenger RNA was seen in the posterior glands of the nasal septum and in the vomeronasal glands. In addition, odorant-binding protein and odorant-binding proteinII messenger RNA levels increased during early postnatal stages with time courses that paralleled the anatomical development of the main olfactory system and the vomeronasal system, respectively. Our results suggest that odorant-binding proteinII functions as a pheromone transporter in the vomeronasal system.

Coculture of the vomeronasal organ and olfactory bulb of the fetal rat

The vomeronasal organ and the olfactory bulb of the rat were cocultured from 15-day embryo siblings on collagen-coated membrane in Dulbecco's modified Eagle's medium containing fetal calf serum, horse serum, and antibiotics. At 4 days in vitro (DIV), vomeronasal axons forming two to three large fascicles were seen originating from the explants of the vomeronasal organ. Differential axonal growth was observed. Some fascicles made connections with the explants of the olfactory bulb. Twenty percent of the cocultures studied here showed the formation of connections. At 6-10 DIV many fascicles that did not connect with the olfactory bulb had degenerated, and large fascicles that were connected with the olfactory bulb survived for more than 10 DIV. The formation of connections between the vomeronasal organ and the olfactory bulb in coculture favors the survival of large nerve fascicles, but it could not be determined whether or not the presence of the olfactory bulb affects the initial orientation of the fibers and fascicles from the explants of the vomeronasal organ.

Development of substance P immunoreactivity in the mouse vomeronasal organ

We investigated the development of substance P immunoreactivity in mouse vomeronasal organs in embryos, juveniles, and adults. In all stages, substance P fibers were found in the receptor-free epithelial area, but never in the neuroepithelium. Substance P fibers were found sparsely in the lamina propria of 15-day-old embryos. Although buds of the vomeronasal glands in the cavernous tissue were observed in 17-day-old embryos, and gradually grew in size and numbers, the substance P fibers around them decreased after about the 13th day. Thus, substance P may be a trophic factor for the development of the vomeronasal glands in the cavernous tissue. We first recognized substance P fibers reaching the surface of the receptor-free epithelium in 13-day-old pups. In 21-day-old mice, substance P fibers were as well developed as in adult mice. Considering the development of the substance P fibers in the receptor-free epithelium and the cavernous tissue, they probably cause the vasodilation of the cavernous tissue via local axon reflexes. These structures may then act as a defense system, eliminating noxious stimulus substances sucked into the vomeronasal organ.

Morphology of vomeronasal organ cultures from fetal rat

The vomeronasal organs (VNOs) of rats were cultured from embryonic 15-day littermates on collagen-coated membrane in Dulbecco's modified Eagle's medium containing serum. The explants were observed sequentially and fixed at 4, 6, 8, 10 and 14 days in vitro (DIV). Organogenesis of VNOs and cell differentiation took place in vitro. Patterns of organogenesis of the VNO in vitro were different from those in vivo. Both sensory and supporting cells in the sensory epithelium had microvilli on their surface. Epithelial cells in aggregates of non-sensory epithelial cells had cilia and microvilli on their surface. Vomeronasal axons forming two to three large fascicles were seen originating from the VNO at 4, 6, and 8 DIV, and degenerated at 10 or 14 DIV. Glial cells (ensheathing cells) were observed in the fascicles. These morphological characteristics of VNO cells in vitro were similar to those observed in vivo.

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.

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

The localization of alpha-D-galactose, N-acetyl-D-galactosamine, and N-acetyl-D-glucosamine sugar residues of glycoconjugates in the vomeronasal organ, olfactory mucosa, and septal organ in the nasal mucosae of rats was investigated using lectinohistochemical techniques combined with bright-field, epifluorescence, and confocal laser scanning microscopy. Glycoconjugates in the mucomicrovillar complex of the vomeronasal organ contained all the sugar residues investigated, whereas glycoconjugates in the mucociliary complex of the olfactory mucosa and septal organ contained only N-acetyl-D-glucosamine. Vomeronasal receptor neurons expressed glycoconjugates with terminal alpha-D-galactose and beta-N-acetyl-D-galactosamine, and N-acetyl-D-glucosamine residues, whereas olfactory and septal receptor neurons expressed glycoconjugates with only N-acetyl-D-glucosamine residues. Secretory granules of glands of the vomeronasal organ contained glycoconjugates with terminal alpha-D-galactose and N-acetyl-D-galactosamine, and N-acetyl-D-glucosamine, whereas those of the Bowman's glands and glands of septal organ contained glycoconjugates with only internal N-acetyl-D-glucosamine residues. The results demonstrate that the glycoconjugates expressed by vomeronasal receptor neurons and glands contain terminal alpha-D-galactose and beta-N-acetyl-D-galactosamine sugar residues that are not expressed by analogous cells in the olfactory mucosa and septal organ.

Protein gene product 9.5 in the developing and mature rat vomeronasal organ

Protein gene product 9.5 (PGP 9.5) was immunocytochemically identified in structures of the developing and mature rat vomeronasal organ (VNO). This study started with embryos at 17 days of gestation. By this stage, PGP 9.5 was immunolocalized within both the receptor cells of the neuroepithelium and cells of the receptor-free epithelium, located on the opposite side of the lumenal space. Nerve fibers surrounding the nascent vomeronasal vein also showed PGP 9.5 immunoreactivity. Labeling was retained in the neuroepithelium and nerve fibers around the vein during development and into adulthood. Within the pool of receptor cells of the adult neuroepithelium, labeling was observed within the cytoplasm of the somata and dendrites; some receptor cells also expressed nuclear labeling. The number of immunoreactive cells in the receptor-free epithelium appeared to increase postnatally but by adulthood immunoreactivity virtually was absent. These results suggest a role for PGP 9.5 in development and maturation of the VNO and a continuing role within the steadily renewing receptor cell population found in the mature neuroepithelium. The findings of this study also suggest that PGP 9.5 is localized within the nerve fibers surrounding the vomeronasal vein from early in development through adulthood.

Differential development of binding sites of two lectins in the vomeronasal axons of the rat accessory olfactory bulb

Binding of fluorochrome-conjugated lectins, Bandeiraea simplicifolia lectin-I (BSL-I) and Vicia villosa agglutinin (VVA), to the vomeronasal axons was investigated in the accessory olfactory bulb (AOB) of developing rats at embryonic day (E) 16, 18, and 20, and postnatal day (P) 0, 3, 7, 14, and 28. Intense fluorescence for VVA was first observed at E18, and the position-specific binding pattern observed in adults was established at P0; intense fluorescence for VVA was observed in the posterior 2/3 of the vomeronasal nerve layer (VNL) and glomerular layer (GL) and weak fluorescence was present in the anterior 1/3 of these layers. Fluorescence for BSL-I was observed in the posterior half of VNL and GL at P0; the area bound with BSL-I was expanded to the anterior area and intensity of the fluorescence increased as the development proceeded. At P28, binding of BSL-I was observed in the entire VNL and GL as identical to adults. These results indicate that the binding sites of BSL-I and VVA in the vomeronasal axons at the level of rat AOB develop differentially during ontogeny, suggesting that rat VN axons consist of two subpopulations expressing different glycoconjugates.

An immuno-electron microscopic comparison of olfactory marker protein localization in the supranuclear regions of the rat olfactory epithelium and vomeronasal organ neuroepithelium

Immuno-electron microscopy was used to examine olfactory marker protein (OMP) ultrastructural localization in the supranuclear regions of the rat olfactory epithelium (OE) and vomeronasal organ (VNO) neuroepithelium. In the OE, OMP immuno-reaction product was observed within the cytoplasm of olfactory chemoreceptor cell dendrites, vesicles and cilia. Reaction product was absent from olfactory microvillar cells and their unique microvillar projections. In the neuroepithelium of the VNO, immuno-reaction product was seen within the dendrites of the chemoreceptor cells, and in the bases of their attached microvilli; the remaining distal portions of these microvilli were unlabeled. These results demonstrate a difference in the distribution of OMP immunoreactivity over the surfaces of the rat OE and VNO. They also show that OMP immunoreactivity does not exist in the rat olfactory microvillar cells.

Calbindin-like immunoreactivity in two peripheral chemosensory tissues of the rat: taste buds and the vomeronasal organ

In the rat, calbindin-like immunoreactivity was observed at both the light and electron microscopic levels within the chemoreceptor neurons of the vomeronasal organ (VNO) and both intragemmal cells and associated nerve fibers of the circumvallate taste buds. All VNO neurons were immunoreactive. Only a subset of intragemmal taste cells was immunoreactive; associated immunoreactive nerve fibers were apposed to both labeled and unlabeled cells but no synaptic contacts were observed.

Ultrastructure of the human vomeronasal organ

Virtually all vertebrates have a vomeronasal system whose involvement in pheromone detection plays a crucial role in reproduction. In humans, the vomeronasal organ has been assumed to be vestigial or absent and without functional significance. In the present study involving over 400 subjects, vomeronasal pits were observed in all individuals except those with pathological conditions affecting the septum. Electron microscopy of the adult human vomeronasal organ indicates the presence of two potential receptor elements in the pseudostratified epithelial lining: microvillar cells, and unmyelinated, intraepithelial axons. In addition, unmyelinated axons are common in the lamina propria surrounding the organ. They appear to constitute the components essential for a functional chemosensory system, and may thus provide the basis for a pheromone detection system as in other animals.

Ontogenesis of the axonal circuitry associated with the olfactory system of the rat embryo

The prenatal development of axonal connections in the rat olfactory system was studied using DiI. On day 16 (E16), the olfactory and vomeronasal nerves extended from the olfactory epithelia to the olfactory bulb (OB), the terminal nerve to the telencephalic septum, while axons of mitral and tufted cells reached the anterior olfactory nucleus (AO). Axons from the AO were also seen in the anterior commissure. On day E16(8) (at 16 days, 8 h), axons were anterogradely followed from the dorsal OB through the lateral olfactory tract (lo) to the bed nucleus of the accessory olfactory tract. At E18(0), crystals implanted in the olfactory epithelium labeled the mitral cell layer and the lo.

Postnatal development of the vomeronasal epithelium in the rat: an ultrastructural study

Three basic types of cells are distinguished in the rat vomeronasal epithelium at birth: bipolar neurons, supporting cells, and basal cells. Neurons at this time include both immature and differentiated cells. By the end of the first postnatal week, all neurons show morphological signs of maturity in their cytoplasm, including abundant granular and smooth endoplasmic reticulum, neurotubules, dense lamellar bodies, apical centrioles, and tufts of microvilli. During the third week microvilli are more frequently encountered and appear to be longer and more branched. Supporting cells appear well-developed by the second day after birth. During the first ten days of life, supporting cells lose their centrioles and all of the complex associated with ciliary generation in the apical zone. Basal cells appear to be more numerous in newborns than in older animals. Protrusions projecting into the lumen are frequently observed in the epithelium of newborn animals, both on the dendrites of neurons and on supporting cells. After the third week, such protrusions are only observed in the transitional zone between the sensory and the non-sensory epithelia of the vomeronasal tubes. In this transitional zone, a fourth cell type showing apical protrusions with microvilli differentiates. Cytoplasm in this type resembles that of neighboring ciliated cells but has no cilia or centrioles. These transitional cells are considered to be cells in an intermediate state of differentiation, between that of the differentiated neurons and supporting cells of the sensory epithelium and that of the predominate ciliated cells of the non-sensory epithelium. The results suggest that by the end of the third week the vomeronasal epithelium is morphologically mature.

Incorporation of 3H-thymidine in the embryonic vomeronasal and olfactory epithelial of garter snakes

Previous studies have shown that the vomeronasal and olfactory epithelia of adult vertebrates provide good models for studying normal neuronal turnover and regeneration in response to axotomy. However, little is known about the cell dynamics in the embryonic vomeronasal and olfactory epithelia or the origins of different cell types in these structures. By using 3H-thymidine autoradiography, both in vivo and in vitro, the origins of receptor and supporting cells and the survival of labelled cells in the embryonic vomeronasal and olfactory epithelial of garter snakes were examined. The results of this study suggest that the receptor and supporting cells of both epithelial arise from separate stem cells and that two subpopulations of stem cells exist for receptor cells in the embryonic vomeronasal epithelium. One subpopulation generates cells that migrate through the receptor cell columns, while another subpopulation remains at the base of the epithelium for approximately 50 days. Although it is unclear how long receptor cells in the embryonic olfactory epithelium survive, the results of this study suggest that they survive at least 37 days and may survive over 56 days. In addition, the development of these sensory epithelia appears different in early versus late embryos, and regeneration in the vomeronasal and olfactory epithelia of adult garter snakes appears similar to development during late gestation. Cells in the developing receptor cell layer of the olfactory epithelium lose their ability to incorporate 3H-thymidine before those in the vomeronasal epithelium, suggesting that the onset of neuronal maturation occurs earlier in the olfactory epithelium than in the vomeronasal epithelium.

Identification of a new non-neuronal cell type in rat olfactory epithelium

We have examined adult and embryonic rat olfactory epithelia by immunohistochemical techniques using the monoclonal antibody 1A-6, which was raised against embryonic rat olfactory epithelia. A heretofore unidentified cell type, reactive with the monoclonal antibody 1A-6, was observed scattered within the epithelium. The 1A-6 reactivity of these cells is most intense on the microvilli projecting from the luminal cell surfaces. For several reasons, we believe these cells are not neurons but a distinct subpopulation of supporting cells or some other sort of non-neuronal cells. (1) They have no identifiable axonal process, are not reactive with an antibody against olfactory marker protein, and are not in juxtaposition with trigeminal axons. (2) They survive ablation of the olfactory bulb. (3) Their nuclei lie within the supporting cell layer, and they resemble supporting cells morphologically and in their [3H]thymidine birthdating and turnover characteristics. However, the 1A-6-positive cells fail to react with the general supporting cell-specific monoclonal antibody SUS-1 [see Hempstead J. L. and Morgan J. I. (1983) Brain Res. 188, 289-295] a finding which suggests that they are not typical supporting cells. Immunoreactivity to 1A-6 is developmentally regulated. Immunohistochemical preparations of almost all tissues we examined showed widespread reactivity in the embryo but a much more restricted pattern in the adult. In the olfactory epithelium of the fetus, the luminal surfaces of all cells, including supporting cells and olfactory receptor cells and cilia, are reactive, while in the adult only the non-neuronal cell subpopulation shows this reactivity. We also found that during the reconstitution of olfactory epithelium which occurs in response to olfactory bulbectomy-induced neuronal degeneration, fetal patterns of 1A-6 reactivity are not re-expressed, i.e. the only 1A-6-positive cells are the non-neuronal cells seen in unperturbed adult olfactory epithelium. Preliminary biochemical analyses of membrane fractions from E19 brain and from adult olfactory mucosa indicate that the 1A-6 reactivity is associated with two bands, having molecular weights of 42,000 and 46,000 on Western blots.

Embryonic and neonatal development of the vomeronasal and olfactory systems in garter snakes (Thamnophis spp.)

Newborn, unfed garter snakes (Thamnophis spp.) respond preferentially to aqueous extracts of natural prey items, and these responses are mediated by the vomeronasal system (VNS). Since the VNS, and possibly the olfactory system (OS), are functional at birth, we examined the ontogeny of VNS and OS structures in four embryonic stages and two postnatal ages in garter snakes. The results of this study show 1) significant changes in thickness of the receptor epithelia for both systems; 2) temporal differences in the innervation of the telencephalon for each system; and 3) concurrent development of primary and secondary projection sites in both systems. Possible interactions between different cell populations and their significance for morphogenesis are discussed.

Developmental studies on the rat vomeronasal organ: vascular pattern and neuroepithelial differentiation. I. Light microscopy

The origin and the developmental sequence of the rat vomeronasal organ and its vascular supply are followed by means of India ink injection in serial sections of celloidin-embedded embryos from the eleventh day of gestation up to birth. The anlage of the vomeronasal organ has been established by the twelfth day of gestation (E 12). It appears as a shallow longitudinal impression of the medial wall of the nasal pit. At day E 14, it separates from the epithelium of the primary nasal cavity, forming a tube. The lumen of the organ remains continuous with the nasal cavity frontally, but ends blindly at the edge of the primary palate dorsally. From day E 16 to E 18 the lateral surface of the tubular vomeronasal organ invaginates toward the lumen forming a wide longitudinal furrow. The lumen is bordered by the developing neuroepithelium and receptor-free epithelium by this time. The vomeronasal organ receives a separate arterial blood supply arising from septal tributaries of the olfactory artery, a branch of the anterior cerebral artery from the earliest stage of development. Blood from the vomeronasal complex is collected in the vomeronasal vein lying in the longitudinal furrow next to the receptor-free epithelium. The typical vascular pattern of the vomeronasal organ is established by the eighteenth day of gestation. At this time, the first capillary loops appear within the neuroepithelium and the vomeronasal vein can already be seen to extend along the long axis of the organ.

Developmental studies on the rat vomeronasal organ: vascular pattern and neuroepithelial differentiation. II. Electron microscopy

The present electron microscopical study demonstrates that the establishment of the typical vascular pattern of the rat vomeronasal organ by the eighteenth day of gestation is accompanied by neither complete maturation of the wall of the blood vessels nor of the vomeronasal neuroepithelium. In the newborn rat, however, the vasculature and the neuroepithelium of the vomeronasal organ present morphological elements suggesting functional capability at birth.