Calbindin-like immunoreactivity in epithelial cells of the newborn and adult human vomeronasal organ

Primary and secondary olfactory centres in human ontogeny

The olfactory centres are the evolutionary oldest and most conservative area of the telencephalon. Olfactory deficiencies are involved in a large spectrum of neurologic disorders and neurodegenerative diseases. The growing interest in human olfaction has been also been driven by COVID-19-induced transitional anosmia. Nevertheless, recent data on the human olfactory centres concerning normal histology and morphogenesis are rare. Published data in the field are mainly restricted to classic studies with non-uniform nomenclature and varied definitions of certain olfactory areas. While the olfactory system in model animals (rats, mice, and more rarely non-human primates) has been extensively investigated, the developmental timetable of olfactory centres in both human prenatal and postnatal ontogeny are poorly understood and unsystemised, which complicates the process of analysing human material, including medical researches. The main purpose of this review is to provide and discuss relevant morphological data on the normal ontogeny of the human olfactory centres, with a focus on the timetable of maturation and developmental cytoarchitecture, and with special reference to the definitions and terminology of certain olfactory areas.

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.

Anatomical evidence for an endocrine activity of the vomeronasal organ in humans

The mammalian vomeronasal organ (VNO) is a well-adjusted chemosensory structure that facilitates social and reproductive behavior in mammals. The existence, locality, and function of this organ in human adults remain a matter of discussion. Most authors now agree that a neuroreceptive function of the adult human VNO can be excluded due to the absence of both neural receptive cells associated with the VNO in other mammals despite the enigmatic reports on the effects of pheromones on human behavior. Adult cadavers form European (Caucasoid) descent were used in this article and parasagittal dissection of the heads allowed access to the nasal septa, which were grossly examined for the VNO openings. Tissue samples were collected, embedded in gelatin and serially sectioned through cryomicrotomy. Nissl staining was performed as well as immunohistochemically stained with an antibody against calcium-binding protein. The findings presented here confirm the bilateral presence of the VNO in adult cadavers and demonstrate morphological connections of VNO receptor cells with the underlying capillaries. In addition, possible endocrine activity associated with the epithelium of this chemosensory structure has been demonstrated by the expression of calcium-binding protein in a part of these receptor cells.

Olfactory structures in staged human embryos

The olfactory region was investigated in 303 serially sectioned human embryos, 23 of which were controlled by precise graphic reconstructions. The following findings in the embryonic period are new for the human. (1) The nasal plates arise at the neurosomatic junction, as do also the otic placodes. (2) Crest comes from the nasal plates later (stage 13) than the maximum production in the neural folds (stage 10). (3) The crest arises and migrates during a much longer time (at least until the end of the embryonic period) than the neural crest of the head, where origin and migration end at stage 12. (4) Olfactory nerve fibres enter the brain at stage 17, the vomeronasal fibres and those of the nervus terminalis at stages 17 and 18. (5) Fibre connections between the olfactory tubercle and the olfactory bulb, as well as those to the amygdaloid nuclei, forebrain septum, and hippocampus, develop during and after stage 17. (6) Mitral cells appear late in the embryonic period. (7) Localized, although incomplete, lamination of the olfactory bulb is detectable at the embryonic/fetal transition. (8) Tangential migratory streams of neurons, from stage 22 to the early fetal period, proceed from the subventricular zone of the olfactory bulb towards the future claustrum; they remain within the insular region but are separated from the cortical plate. (9) In future cebocephaly morphological indications may be visible as early as stage 13. The various findings are integrated by means of staging, and current information for the fetal period is tabulated from the literature.

The existence of the vomeronasal organ in human beings

The frequency, location, and function of the vomeronasal organ, also known as the Jacopson organ, in human beings remains poorly understood. In this study, a search for the frequency of the vomeronasal organ was performed by nasal examinations of 346 adult patients and 21 cadaver heads by anterior rhinoscopy and videotaped rigid 30 degrees endoscopy. The vomeronasal organ was identified in 112 patients (32%) and in 8 cadaver heads (38%). The location, shape, type, and relation to sex of the vomeronasal organ were described. Ten specimens were examined histologically and histochemically for neuron-specific enolase (anti-neuron-specific enolase), high-molecular-weight cytokeratin (anti-high-molecular-weight cytokeratin), and low-molecular-weight cytokeratin (anti-low-molecular-weight cytokeratin). Considering its variability in shape and the lack of immunohistochemical characteristics of nerve tissue, the present results are not suited to argue for functional significance of the vomeronasal organ in human beings.

The human vomeronasal organ. Part II: prenatal development

During the 20th century, the human vomeronasal organ (VNO) has been controversial regarding its structure, function, and even identity. Despite reports that provide evidence for its presence throughout prenatal and postnatal ontogeny, some studies and numerous textbooks declare its absence in late fetal and postnatal humans. To that end, the present study was designed to establish firmly whether the human VNO is homologous with that of other mammals and whether it degenerates (partially or completely) or persists throughout prenatal development. Fifty human embryos and fetuses (33 d to 32 wk fertilisation age) and 2 neonates were examined by light microscopy. Four embryonic primates (mouse lemurs) were examined for a comparison of VNO embryogenesis. The presence or absence and structural characteristics of the VNO and supporting tissues are described. The first appearance of the VNO was in the form of bilateral epithelial thickenings of the nasal septum, the vomeronasal primordium. The primordia invaginated between 37 and 43 d of age and formed the tubular VNO. The tubular VNO was located dorsally at a variable distance from, but was always spatially separated from the paraseptal cartilages. The mouse lemurs examined in this study and other reports from the literature indicate that the human VNO resembles that of primates having functional VNOs until just after a tubular VNO is formed. Examination of the VNO and adjacent tissues suggested that the VNO may lose receptor cells and corresponding vomeronasal nerves and become a ciliated, pseudostratified epithelium between approximately 12 and 14 wk of age. Our findings indicate the prenatal human VNO goes through 3 successive stages: early morphogenesis, transformation (of the epithelium), and growth. These observations indicated that (1) all embryonic humans develop a vomeronasal organ which is homologous with the VNOs of other mammals, but which has become displaced and highly variable in relative location during embryogenesis; (2) the human vomeronasal organ does not degenerate prenatally, but very likely loses the functional components of the vomeronasal complex of other mammals; and (3) the remnant of the human VNO persists until birth and beyond.

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.

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.

Protein gene product 9.5-like and calbindin-like immunoreactivity in the nasal respiratory mucosa of perinatal humans

BACKGROUND

Protein gene product 9.5 (PGP) and calbindin-D28k (calbindin) are neuroendocrine markers that have been localized to neuroendocrine cells in the developing tracheobronchial epithelium. Neuroendocrine cells may play some role in the development of the tracheobronchial epithelium. Little is known about the development of the nasal respiratory epithelium (RE).

METHODS

Nasal respiratory mucosa from fetal and newborn humans was examined to determine immunoreactivity for PGP and calbindin.

RESULTS

At all stages studied, cells of different morphologies displayed PGP-like immunoreactivity (-LI) and calbindin-LI. Columnar immunoreactive cells for both markers predominated, but labeled cells of different shapes were also observed. Most labeled columnar cells were in the RE at its border with olfactory epithelium (OE); a few similarly labeled columnar cells also appeared in this OE. In the lamina propria, PGP-LI was also seen in numerous thin branching fibers. Some of these branches penetrated into the epithelium, where fiber varicosities appeared to contact cells, some of which also exhibited PGP-LI.

CONCLUSION

This study demonstrates that during development the human nasal RE contains different cell types, as illustrated by the assortment of epithelial cells displaying PGP-LI and calbindin-LI among unlabeled cells. Because PGP and calbindin immunoreactivities were found within neuroendocrine cells in previous studies, the present results indicate that the developing human nasal RE also may support a number of neuroendocrine cells. Furthermore, at least some of these cells may form synaptic contacts with nerve fibers from outside the epithelium.

Neurocalcin-immunoreactive receptor cells in the rat olfactory epithelium and vomeronasal organ

Occurrence of neurocalcin, a calcium-binding protein with three EF hand motifs, was examined immunohistochemically in the rat olfactory epithelium and vomeronasal organ epithelium. Immunoreactivity was detected in receptor cells in these epithelia. Immunoreactions were distributed in cytoplasm associated with outer mitochondrial membrane, endoplasmic reticulum and microtubules. Olfactory and vomeronasal nerve fibers in the lamina propria exhibited immunoreactivity. Neurocalcin may participate in calcium signalling and cytoskeletal arrangement in receptor cells.