Human Olfactory Neurons Research Articles

Shedding light on human olfaction: Electrophysiological recordings from sensory neurons in acute slices of olfactory epithelium

The COVID-19 pandemic brought attention to our limited understanding of human olfactory physiology. While the cellular composition of the human olfactory epithelium is similar to that of other vertebrates, its functional properties are largely unknown. We prepared acute slices of human olfactory epithelium from nasal biopsies and used the whole-cell patch-clamp technique to record electrical properties of cells. We measured voltage-gated currents in human olfactory sensory neurons and supporting cells, and action potentials in neurons. Additionally, neuronal inward current and action potentials responses to a phosphodiesterase inhibitor suggested a transduction cascade involving cAMP as a second messenger. Furthermore, responses to odorant mixtures demonstrated that the transduction cascade was intact in this preparation. This study provides the first electrophysiological characterization of olfactory sensory neurons in acute slices of the human olfactory epithelium, paving the way for future research to expand our knowledge of human olfactory physiology.

Neurodegeneration-Associated Proteins in Human Olfactory Neurons Collected by Nasal Brushing.

The olfactory neuroepithelium is located in the upper vault of the nasal cavity, lying on the olfactory cleft and projecting into the dorsal portion of the superior and middle turbinates beyond the mid-portion of the nasal septum. It is composed of a variety of cell types including olfactory sensory neurons, supporting glial-like cells, microvillar cells, and basal stem cells. The cells of the neuroepithelium are often intermingled with respiratory and metaplastic epithelial cells. Olfactory neurons undergo a constant self-renewal in the timespan of 2–3 months; they are directly exposed to the external environment, and thus they are vulnerable to physical and chemical injuries. The latter might induce metabolic perturbations and ultimately be the cause of cell death. However, the lifespan of olfactory neurons is biologically programmed, and for this reason, these cells have an accelerated metabolic cycle leading to an irreversible apoptosis. These characteristics make these cells suitable for research related to nerve cell degeneration and aging. Recent studies have shown that a non-invasive and painless olfactory brushing procedure allows an efficient sampling from the olfactory neuroepithelium. This approach allows to detect the pathologic prion protein in patients with sporadic Creutzfeldt–Jakob disease, using the real-time quaking-induced conversion assay. Investigating the expression of all the proteins associated to neurodegeneration in the cells of the olfactory mucosa is a novel approach toward understanding the pathogenesis of human neurodegenerative diseases. Our aim was to investigate the expression of α-synuclein, β-amyloid, tau, and TDP-43 in the olfactory neurons of normal subjects. We showed that these proteins that are involved in neurodegenerative diseases are expressed in olfactory neurons. These findings raise the question on whether a relationship exists between the mechanisms of protein aggregation that occur in the olfactory bulb during the early stage of the neurodegenerative process and the protein misfolding occurring in the olfactory neuroepithelium.

Neuropeptide Y increases differentiation of human olfactory receptor neurons through the Y1 receptor

Olfactory dysfunction significantly impedes the life quality of patients. Neuropeptide Y (NPY) is not only a neurotrophic factor in the rodent olfactory system but also an orexigenic peptide that regulates feeding behavior. NPY increases the olfactory receptor neurons (ORNs) responsivity during starvation; however, whether NPY can promote differentiation of human ORNs remains unexplored. This study investigates the effect of NPY on the differentiation of human olfactory neuroepithelial cells in vitro. Human olfactory neuroepithelium explants were cultured on tissue culture polystyrene dishes for 21 days. Then, cells were cultured with or without NPY at the concentration of 0.5 ng/mℓ for 7 days. The effects of treatment were assessed by phase contrast microscopy, immunocytochemistry and western blot analysis. The further mechanism was evaluated with NPY Y1 receptor-selected antagonist BIBP3226. NPY-treated olfactory neuroepithelial cells exhibited thin bipolar shape, low circularity, low spread area, and long processes. The expression levels of Ascl1, βIII tubulin, GAP43 and OMP were significantly higher in NPY-treated cells than in controls (p < 0.05). NPY-treated olfactory neuroepithelial cells expressed more components of signal transduction apparatuses, Golf and ADCY3, than those without NPY treatment. Western blot analysis also further confirmed these findings (p < 0.05). Additionally, the expression levels of Ascl1, βIII2 tubulin, GAP43, OMP, ADCY3, and Golf in BIBP3226 + NPY and controls were comparable (p > 0.05). NPY not only increases expressions of protein markers of human olfactory neuronal progenitor cells, but also promotes differentiation of ORN and enhances formation of components of olfactory-specific signal transduction pathway through Y1 receptors.

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

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

Hendra and Nipah Virus Infection in Cultured Human Olfactory Epithelial Cells.

Henipaviruses are emerging zoonotic viruses and causative agents of encephalitis in humans. However, the mechanisms of entry into the central nervous system (CNS) in humans are not known. Here, we evaluated the possible role of olfactory epithelium in virus entry into the CNS. We characterized Hendra virus (HeV) and Nipah virus (NiV) infection of primary human olfactory epithelial cultures. We show that henipaviruses can infect mature olfactory sensory neurons. Henipaviruses replicated efficiently, resulting in cytopathic effect and limited induction of host responses. These results show that human olfactory epithelium is susceptible to infection with henipaviruses, suggesting that this could be a pathway for neuroinvasion in humans. IMPORTANCE Henipaviruses are emerging zoonotic pathogens that can cause acute and severe respiratory and neurological disease in humans. The pathways by which henipaviruses enter the central nervous system (CNS) in humans are still unknown. The observation that human olfactory neurons are highly susceptible to infection with henipaviruses demonstrates that the olfactory epithelium can serve as a site of Henipavirus entry into the CNS.

Age-associated loss of selectivity in human olfactory sensory neurons

We report a cross-sectional study of olfactory impairment with age based on both odorant-stimulated responses of human olfactory sensory neurons (OSNs) and tests of olfactory threshold sensitivity. A total of 621 OSNs from 440 subjects in 2 age groups of younger (≤ 45 years) and older (≥ 60 years) subjects were investigated using fluorescence intensity ratio fura-2 imaging. OSNs were tested for responses to 2 odorant mixtures, as well as to subsets of and individual odors in those mixtures. Whereas cells from younger donors were highly selective in the odorants to which they responded, cells from older donors were more likely to respond to multiple odor stimuli, despite a loss in these subjects' absolute olfactory sensitivity, suggesting a loss of specificity. This degradation in peripheral cellular specificity may impact odor discrimination and olfactory adaptation in the elderly. It is also possible that chronic adaptation as a result of reduced specificity contributes to observed declines in absolute sensitivity.

Olfactory system

The olfactory system has several unique features in terms of mechanisms of sensory transduction, relay, and central processing of information and provides a typical example of functional plasticity.1–5 Olfactory deficits are frequently found in neurodegenerative disorders, particularly Parkinson disease (PD) and Alzheimer disease (AD). The neuropathologic substrate of olfactory dysfunction in neurodegenerative disorders is incompletely elucidated and likely reflects degenerative changes at multiple levels of the olfactory system, including the olfactory epithelium, olfactory bulb, primary olfactory cortices, and their secondary targets.6,7 These issues have been extensively reviewed1–7 and only some salient points are emphasized here. ### Olfactory receptor cells and sensory transduction. The olfactory sensory neurons form clusters interposed among patches of respiratory neuroepithelium.1 These neurons are bipolar cells with a dendritic end containing 3–50 cilia that project into the overlying mucus; their unmyelinated axons form bundles that project through the cribriform plate and synapse in the olfactory bulb.1,2 Odorants bind to guanine nucleotide binding (G) protein–coupled receptors located in the cilia of the olfactory receptor neuron. There are about 400 types of receptors expressed in human olfactory neurons and an individual olfactory sensory neuron typically responds to more than one odorant type.1,5 The first step in olfactory signal transduction is the activation of the Gαolf, which stimulates adenylyl cyclase 3 and production of cyclic adenosyl monophosphate (figure). This triggers opening of a cyclic nucleotide–gated channel allowing calcium (Ca2+) influx and depolarization; subsequent opening of Ca2+ activated chloride (Cl−) channels elicits Cl− efflux that amplifies the depolarization of the sensory neuron.1 The olfactory receptor neurons have several unique features: they can regenerate; serve both as odorant-selective receptor cells and first-order neurons; and are directly exposed to the external environment, thus providing a primary route for invasion into the brain by viruses or toxins.5 …

Cellular Basis for the Olfactory Response to Nicotine

Smokers regulate their smoking behavior on the basis of sensory stimuli independently of the pharmacological effects of nicotine (Rose J. E., et al. (1993) Pharmacol., Biochem. Behav.44 (4), 891-900). A better understanding of sensory mechanisms underlying smoking behavior may help to develop more effective smoking alternatives. Olfactory stimulation by nicotine makes up a considerable part of the flavor of tobacco smoke, yet our understanding of the cellular mechanisms responsible for olfactory detection of nicotine remains incomplete. We used biophysical methods to characterize the nicotine sensitivity and response mechanisms of neurons from olfactory epithelium. In view of substantial differences in the olfactory receptor repertoire between rodent and human (Mombaerts P. (1999) Annu. Rev. Neurosci.22, 487-509), we studied biopsied human olfactory sensory neurons (OSNs), cultured human olfactory cells (Gomez G., et al. (2000) J. Neurosci. Res.62 (5), 737-749), and rat olfactory neurons. Rat and human OSNs responded to S(-)-nicotine with a concentration dependent influx of calcium and activation of adenylate cyclase. Some rat OSNs displayed some stereoselectivity, with neurons responding to either enantiomer alone or to both. Freshly biopsied and primary cultured human olfactory neurons were less stereoselective. Nicotinic cholinergic antagonists had no effect on the responses of rat or human OSNs to nicotine. Patch clamp recording of rat OSNs revealed a nicotine-activated, calcium-sensitive nonspecific cation channel. These results indicate that nicotine activates a canonical olfactory receptor pathway rather than nicotinic cholinergic receptors on OSNs. Further, because the nicotine-sensitive mechanisms of rodents appear generally similar to those of humans, this animal model is an appropriate one for studies of nicotine sensation.

Oxidative damage in cultured human olfactory neurons from Alzheimer's disease patients.

Oxidative abnormalities precede clinical and pathological manifestations of Alzheimer's disease and are the earliest pathological changes reported in the disease. The olfactory pathways and mucosa also display the pathological features associated with Alzheimer's disease in the brain. Olfactory neurons are unique because they can undergo neurogenesis and are able to be readily maintained in cell culture. In this study, we examined neuronal cell cultures derived from olfactory mucosa of Alzheimer's disease and control patients for oxidative stress responses. Levels of lipid peroxidation (hydroxynonenal), N(epsilon)-(carboxymethyl)lysine (glycoxidative and lipid peroxidation), and oxidative stress response (heme oxygenase-1) were measured immunocytochemically. We found increased levels for all the oxidative stress markers examined in Alzheimer's disease neurons as compared to controls. Interestingly, in one case of Alzheimer's disease, we found hydroxynonenal adducts accumulated in cytoplasmic lysosome-like structures in about 20% of neurons cultured, but not in neurons from control patients. These lysosome-like structures are found in about 100% of the vulnerable neurons in brains of cases of Alzheimer's disease. This study suggests that manifestations of oxidative imbalance in Alzheimer's disease extend to cultured olfactory neurons. Primary culture of human olfactory neurons will be useful in understanding the mechanism of oxidative damage in Alzheimer's disease and can even be utilized in developing therapeutic strategies.

Cell and molecular biology of human olfaction.

Progress in our understanding of olfactory receptor physiology has progressed greatly over the past 10 years. It has become clear that many anatomical and molecular features of the peripheral aspect of the olfactory system have remained highly conserved across diverse species. Yet, this structure is responsible for conveying a wide variety of information about the environment that is necessary to the successful location of food, mates, and avoidance of danger, and it is thus not surprising that specializations have also evolved to suit the differing needs of different species. While the basic anatomical features reflect those of other mammals, functional studies of human olfactory receptor neurons have revealed physiological features both similar to and differing from those of other mammalian species. This review presents an overview of both the anatomical and physiological data describing the cell and molecular biology of the peripheral human olfactory system and how it functions in health and disease.

The Superior Turbinate as a Source of Functional Human Olfactory Receptor Neurons

The function of human olfactory receptor neurons (ORNs) remains incompletely understood, in part because of the difficulty of obtaining viable olfactory tissue for study. During endoscopic sphenoidotomy, a portion of the superior turbinate is often removed to achieve wide and safe access to the sphenoid sinus. The purpose of this study was to determine whether functional olfactory mucosa could be obtained from such superior turbinate tissue. Superior turbinate tissue was resected from 4 patients undergoing transnasal endoscopic approaches to the sphenoid sinus. The gross appearance of the turbinate mucosa was normal at the time of surgery. The specimens were placed directly into cold cell culture media and transferred to the laboratory. A portion of the mucosa was fixed and embedded for histology and immunohistochemistry. The remaining tissue was enzymatically dissociated, and the resulting cell suspension was either prepared for immediate calcium imaging or placed into cell culture. Cultured ORNs underwent calcium imaging after several weeks to assess their ability to respond to odorants. Histologic analysis of superior turbinate tissue revealed the presence of patchy olfactory neuroepithelium staining positive for olfactory marker protein. Acutely dissociated ORNs were capable of generating calcium responses to odorant mixtures. ORNs could be maintained in mixed culture and retained their ability to respond to odorants. Superior turbinate tissue removed during endoscopic sphenoidotomy can provide a valuable source of human olfactory neuroepithelium for functional or histologic study. Superior turbinate tissue yields stem cells and immature neurons capable of differentiating into ORNs that retain many of their functional characteristics even after growth in culture.

Modulation of odor-induced increases in [Ca 2+] i by inhibitors of protein kinases A and C in rat and human olfactory receptor neurons

Protein kinases A and C have been postulated to exert multiple effects on different elements of signal transduction pathways in olfactory receptor neurons. However, little is known about the modulation of olfactory responses by protein kinases in intact olfactory receptor neurons. To further elucidate the details of the modulation of odorant responsiveness by these protein kinases, we investigated the action of two protein kinase inhibitors: H89, an inhibitor of protein kinase A, and N-myristoylated EGF receptor, an inhibitor of protein kinase C, on odorant responsiveness in intact olfactory neurons. We isolated individual olfactory neurons from the adult human and rat olfactory epithelium and measured responses of the isolated cells to odorants or biochemical activators that have been shown to initiate cyclic AMP or inositol 1,4,5-trisphospate production in biochemical preparations. We employed calcium imaging techniques to measure odor-elicited changes in intracellular calcium that occur over several seconds. In human olfactory receptor neurons, the protein kinase A and C inhibitors affected the responses to different sets of odorants. In rats, however, the protein kinase C inhibitor affected responses to all odorants, while the protein kinase A inhibitor had no effect. In both species, the effect of inhibition of protein kinases was to enhance the elevation and block termination of intracellular calcium levels elicited by odorants. Our results show that protein kinases A and C may modulate odorant responses of olfactory neurons by regulating calcium fluxes that occur several seconds after odorant stimulation. The effects of protein kinase C inhibition are different in rat and human olfactory neurons, indicating that species differences are an important consideration when applying data from animal studies to apply to humans.

Characteristics of odorant elicited calcium changes in cultured human olfactory neurons.

An important step in establishing and utilizing a cell culture system for the in vitro study of olfaction is assessing whether the cultured cells possess physiological properties similar to those of mature olfactory neurons. Various investigators have successfully established proliferating cell lines from olfactory tissue, but few have demonstrated the characteristics of odor sensitivity of these cells. We successfully established cultured cell lines from adult human olfactory tissue obtained using an olfactory biopsy procedure and measured their ability to respond to odor stimulation using calcium imaging techniques. A subset of the human olfactory cells in culture displayed a distinct morphology and specifically expressed immunocytochemical markers characteristic of mature human olfactory neurons such as OMP, G(olf), NCAM and NST. Under defined growth conditions, these cultured cells responded to odorant mixes that have been previously shown to elicit intracellular calcium changes in acutely-isolated human olfactory neurons. These odorant-elicited calcium responses displayed characteristics similar to those found in mature human olfactory neurons. First, cultured cells responded with either increases or decreases in intracellular calcium. Second, increases in calcium were abolished by removal of extracellular calcium. Third, inhibitors of the olfactory signal transduction cascades reversibly blocked these odorant-elicited intracellular calcium changes. Our results demonstrate that cultures of adult human olfactory cells established from olfactory biopsies retain some of the in vivo odorant response characteristics of acutely isolated cells from the adult olfactory epithelium. This work has important ramifications for investigation of olfactory function and dysfunction using biopsy procedures and in vitro assays of odor sensitivity.

New techniques for biopsy and culture of human olfactory epithelial neurons.

To improve the success of culturing olfactory neurons from human nasal mucosa by investigating the intranasal distribution of the olfactory epithelium and devising new techniques for growing human olfactory epithelium in vitro. Ninety-seven biopsy specimens were obtained from 33 individuals, aged 21 to 74 years, collected from 6 regions of the nasal cavity. Each biopsy specimen was bisected, and 1 piece was processed for immunohistochemistry or electron microscopy while the other piece was dissected further for explant culture. Four culture techniques were performed, including whole explants and explanted biopsy slices. Five days after plating, neuronal differentiation was induced by means of a medium that contained basic fibroblast growth factor. After another 5 days, cultures were processed for immunocytochemical analysis. The probability of finding olfactory epithelium in a biopsy specimen ranged from 30% to 76%, depending on its location. The dorsoposterior regions of the nasal septum and the superior turbinate provided the highest probability, but, surprisingly, olfactory epithelium was also found anteriorly and ventrally on both septum and turbinates. A new method of culturing the olfactory epithelium was devised. This slice culture technique improved the success rate for generating olfactory neurons from 10% to 90%. This study explains and overcomes most of the variability in the success in observing neurogenesis in cultures of adult human olfactory epithelium. The techniques presented here make the human olfactory epithelium a useful model for clinical research into certain olfactory dysfunctions and a model for the causes of neurodevelopmental and neurodegenerative diseases.

On the Origin and Diagnostic Criteria of Olfactory Neuroblastoma.

The origin and diagnostic criteria of olfactory neuroblastoma are still under dispute. Tosolve these problems, seven cases of olfactory neuroblastomas satisfying diagnostic criteria of Choi and Anderson were analyzed immunohistochemically by using antibodies to markers expressed in developing and mature human olfactory placode-derived neurons such as keratin, a 34 kDa epithelial membrane glycoprotein, luteinizing-hormone-releasing-hormone (LHRH) and to other neural tissue markers. Ultrastructural analysis was also carried out. Five cases were identified as neuroblastomas because neurites were disclosed in them. All of these five cases had widespread immunoreactivity to an antibody to a 34 kDa epithelial membrane glycoprotein (Ber-EP4) in the tumor cell bodies and/or neuritic processes. They also contained keratin positive cells. LHRH was demonstrated in two of these Ber-EP4 positive neuroblastomas. The spectrum of immunohistochemical findings of these five cases was identical to the normal neuroblasts arising from olfactory placode.Accordingly, it is concluded that neuroblastoma of true olfactory placodal origin does exist. The diagnostic criteria of this tumor is as follows: demonstration of neurites and immunoreactivity to Ber-EP4 and/or LHRH. Keratin is not necessary to regard as an evidence of epithelial differentiation in this tumor.

Cyclic nucleotide-gated channels in identified human olfactory receptor neurons.

Patch-clamp recordings revealed the presence of a non-desensitizing cyclic nucleotide-gated channel on human olfactory receptor neurons and a fast-desensitizing non-specific cation channel activated by nucleotides on human supporting cells. Cyclic nucleotide-gated channels on olfactory receptor neurons showed selective channel activation by cAMP (K1/2 = 5 microM) and cGMP (K1/2 = 2 microM), a unitary conductance of approximately 20 pS, a reversal potential of single-channel currents close to 0 mV, a linear current-voltage relationship over the range of -80 to 80 mV and a strong extracellular but a weaker intracellular blocking effect of Ca2+. The channel activity outlasted the cyclic nucleotide pulses for hundreds of milliseconds when higher agonist concentrations (> 50 microM cAMP) were applied. The duration of the response was longer than in cyclic nucleotide-gated channels from other species studied so far. The plateau duration and the decay remained constant for pulses with a length of 50-150 ms, whereas pulses shorter than 50 ms successively reduced the time required by shortening the plateau phase. A larger difference for the K1/2 values of cAMP (K1/2 = 22 microM) and cGMP (K1/2 = 2.5 microM) were found for a small group (n = 3) of cyclic nucleotide-gated channels, pointing to the selective expression of the alpha-subunit in a small subgroup of olfactory receptor neurons.

Human olfactory receptor neurons contain OMP mRNA in their dendritic and axonal processes.

The cellular expression of olfactory marker protein (OMP) mRNA and protein was investigated in the olfactory mucosa of humans ranging in age from 26 weeks of gestation to 85 years using in situ hybridization and immunocytochemistry. OMP mRNA and protein were most abundant in the somas of olfactory receptor neurons (ORNs). The hybridization signal over the ORN somal layer was greater in older subjects than in younger ones, reflecting either a higher neuronal density or more OMP mRNA per cell. In contrast, it was significantly lower in subjects with Alzheimer's disease when compared with an age-matched control. Characteristics of older subjects were patchiness in the distribution of OMP-expressing ORNs and the occurrence of subepithelial invaginations containing OMP-positive neurons. In addition, a significant hybridization signal was detected in the apical olfactory epithelium containing the dendrites, dendritic knobs, and cilia of ORNS, and over olfactory nerve bundles in the lamina propria, indicating the occurrence of OMP mRNA in dendritic and axonal domains.

Human and Rodent OMP Genes: Conservation of Structural and Regulatory Motifs and Cellular Localization

Immunocytochemical analysis has demonstrated that expression of the olfactory marker protein (OMP) is highly restricted to mature olfactory receptor neurons in virtually all vertebrate species from fish to man. We have now cloned the OMP gene from human and mouse and demonstrated conservation of gene structure, protein sequence, and Olf-1 and upstream binding region (UBE) regulatory domains. The OMP gene in all species studied lacks canonical TATA and CAAT motifs and introns. The deduced protein sequence is 88.4% identical between mouse and human, and most of the differences observed are conservative changes. The proximal Olf-1 binding sites differ by two purine-purine replacements and effectively cross-compete in mobility shift assays. The distal Olf- 1 binding site is also highly conserved in terms of both sequence and binding activity. The availability of sequence from multiple species has permitted us to determine that the UBE site has close similarity to motifs that bind members of the NF-1 family of transcription factors. Gel mobility shift assays confirm this prediction, providing additional insight into mechanisms that may participate in the stringent regulation of the expression of this neuronal-specific protein. Furthermore, we demonstrate the in situ localization of OMP mRNA in human olfactory neuroepithelium and its colocalization to immunocytochemically identified human olfactory receptor neurons.

Human olfactory neurons respond to odor stimuli with an increase in cytoplasmic Ca2+

The sense of smell allows terrestrial animals to collect information about the chemical nature of their environment through the detection of airborne molecules. In humans smell is believed to play an important role in protecting the organism from environmental hazards such as fire, gas leaks and spoiled food, in determining the flavor of foods, and perhaps in infant-parent bonding. In addition, the study of human olfaction is relevant to a number of medical problems that result in olfactory dysfunction, which can affect nutritional state, and to the study of the etiology of neurodegenerative diseases which manifest themselves in the olfactory epithelium. Although much is known about behavioral aspects of human olfaction, little is understood about the underlying cellular mechanisms in humans. Here we report that viable human olfactory neurons (HON) can be isolated from olfactory tissue biopsies, and we find that HON respond to odorants with an increase in intracellular calcium concentration ([Cai]).

Olfactory marker protein is present in olfactory receptor cells of human fetuses

Light microscopic observations indicated that cellular differentiation of the primary olfactory pathway in human fetuses was relatively advanced by the end of the first trimester. However, immunohistochemical staining showed that olfactory marker protein was present in the receptor cells only at about 28 weeks post-conception. At about 32 weeks, modest amounts of the protein could be found in the peripheral olfactory nerve layer and a few glomeruli, with increased staining observed in subsequent weeks. The results show conclusively that human fetal olfactory neurons synthesize olfactory marker protein during the later half of gestation.