[Show abstract][Hide abstract] ABSTRACT: Neural precursors in the developing olfactory epithelium (OE) give rise to three major neuronal classes - olfactory receptor (ORNs), vomeronasal (VRNs) and gonadotropin releasing hormone (GnRH) neurons. Nevertheless, the molecular and proliferative identities of these precursors are largely unknown. We characterized two precursor classes in the olfactory epithelium (OE) shortly after it becomes a distinct tissue at midgestation in the mouse: slowly dividing self-renewing precursors that express Meis1/2 at high levels, and rapidly dividing neurogenic precursors that express high levels of Sox2 and Ascl1. Precursors expressing high levels of Meis genes primarily reside in the lateral OE, whereas precursors expressing high levels of Sox2 and Ascl1 primarily reside in the medial OE. Fgf8 maintains these expression signatures and proliferative identities. Using electroporation in the wild-type embryonic OE in vitro as well as Fgf8, Sox2 and Ascl1 mutant mice in vivo, we found that Sox2 dose and Meis1 - independent of Pbx co-factors - regulate Ascl1 expression and the transition from lateral to medial precursor state. Thus, we have identified proliferative characteristics and a dose-dependent transcriptional network that define distinct OE precursors: medial precursors that are most probably transit amplifying neurogenic progenitors for ORNs, VRNs and GnRH neurons, and lateral precursors that include multi-potent self-renewing OE neural stem cells.
[Show abstract][Hide abstract] ABSTRACT: We asked whether specific mesenchymal/epithelial (M/E) induction generates olfactory receptor neurons (ORNs), vomeronasal neurons (VRNs), and gonadotropin-releasing hormone (GnRH) neurons, the major neuron classes associated with the olfactory epithelium (OE). To assess specificity of M/E-mediated neurogenesis, we compared the influence of frontonasal mesenchyme on frontonasal epithelium, which becomes the OE, with that of the forelimb bud. Despite differences in position, morphogenetic and cytogenic capacity, both mesenchymal tissues support neurogenesis, expression of several signaling molecules and neurogenic transcription factors in the frontonasal epithelium. Only frontonasal mesenchyme, however, supports OE-specific patterning and activity of a subset of signals and factors associated with OE differentiation. Moreover, only appropriate pairing of frontonasal epithelial and mesenchymal partners yields ORNs, VRNs, and GnRH neurons. Accordingly, the position and molecular identity of specialized frontonasal epithelia and mesenchyme early in gestation and subsequent inductive interactions specify the genesis and differentiation of peripheral chemosensory and neuroendocrine neurons.
Full-text · Article · Jun 2010 · Developmental Dynamics
[Show abstract][Hide abstract] ABSTRACT: Chronic rhinosinusitis (CRS) is a complex heterogeneous inflammatory disease that affects the nasal cavity, but the pathological examination of the olfactory mucosa (OM) in this disease has been limited.
Nasal biopsy specimens were obtained from 20 control subjects and 50 CRS patients in conjunction with clinical assessments. Histopathology of these nasal biopsy specimens was performed and immunohistochemistry was used to characterize nonneuronal, neuronal, and inflammatory cells in the OM. These OM characteristics were then evaluated to determine the degree to which pathological features may be related to smell loss in CRS.
Histopathological examination of control and CRS OM revealed changes in the normal pseudostratified olfactory epithelium (OE): intermixing of goblet cells, metaplasia to squamous-like cells, and erosion of the OE. Lower percentages of normal epithelium and olfactory sensory neurons were found in CRS OE compared with controls. Relative to other CRS patients, those with anosmia had the greatest amount of OE erosion, the highest density of eosinophils infiltrating the OE, and exhibited the most extensive abnormalities on CT and endoscopic examination, including being significantly more likely to exhibit nasal polyposis.
Our results suggest that OM pathology observed in nasal biopsy specimens can assist in understanding the degree of epithelial change and sensorineural damage in CRS and the potential for olfactory loss.
Full-text · Article · Dec 2009 · American Journal of Rhinology and Allergy
[Show abstract][Hide abstract] ABSTRACT: The olfactory epithelium constitutes the sole source of regenerating neural cells that can be obtained from a living human. As such, primary cultures derived from human olfactory epithelial biopsies can be utilized to study neurobiological characteristics of individuals under different conditions and disease states. Here, using such human cultures, we report in vitro generation of cells that exhibit a complex neuronal phenotype, encompassing receptors and signaling pathways pertinent to both olfaction and other aspects of CNS function. Using in situ hybridization, we demonstrate for the first time the native expression of olfactory receptors in cultured cells derived from human olfactory epithelial tissue. We further establish the presence and function of olfactory transduction molecules in these cells using immunocytochemistry, calcium imaging and molecular methods. Western blot analysis revealed the expression of neurotransmitter receptors for dopamine (D2R), 5-HT (5HT2C) and NMDA subtypes 1 and 2A/2B. Stimulation with dopamine or 5-HT enhanced receptor G protein activation in a subtype specific manner, based on 35S-guanosine triphosphate incorporation assay. Functional characteristics of the cultured cells are demonstrated through enhanced tyrosine phosphorylation of NMDAR 2A/2B and recruitment of signaling partners in response to NMDA stimulation. The array of neuronal characteristics observed here establishes that proliferating cells derived from the human olfactory epithelium differentiate in vitro to express functional and molecular attributes of mature olfactory neurons. These cultured neural cells exhibit neurotransmitter pathways important in a number of neuropsychiatric disorders. Their ready availability from living humans thus provides a new tool to link functional and molecular features of neural cells with clinical characteristics of individual living patients.
[Show abstract][Hide abstract] ABSTRACT: Primary and immortalized cultures of many cell types have facilitated efforts to understand the signals involved in proliferation, differentiation and senescence, and yielded tools to rapidly assay new molecules targeting specific receptor pathways. Surprisingly, few studies have reported successful primary culture protocols for taste cells, and those reported have had a limited life span and have not purported to generate new cells in vitro. Like other epithelial cells, taste cells are generated throughout life from a basal cell population, although the precise lineage and signaling molecules involved in this process are not well known. We have recently developed a primary taste cell culture method that supports the generation of new cells expressing key molecular and functional features of mature taste cells. These cultures can be maintained for functional assays for over two months. In this chapter we will present insights into the development of this protocol and discuss advantages and disadvantages of the approach. We will also discuss the potential use of these cultures as discovery tools to study the effects of neurotrophic factors on taste cell proliferation and differentiation and as an aid in the development and evaluation of new taste molecules.
No preview · Article · Mar 2008 · ACS Symposium Series
[Show abstract][Hide abstract] ABSTRACT: Circulating signals like the acidic derivative of vitamin A: retinoic acid (RA) may regulate resident stem cells in the adult nervous system, particularly in the olfactory pathway. RA is an essential factor for inducing neural stem or precursor cells that give rise to olfactory receptor neurons (ORNs) and olfactory bulb (OB) interneurons (OBINs) during embryonic development. Similar precursors in the adult brain constantly generate new ORNs and OBINs, and embryonic signaling pathways, like that via RA, may be retained or reactivated for this purpose. We have shown that RA regulates neural precursors in the embryonic and adult olfactory pathway. Moreover, RA administration after olfactory system damage stimulates an immune response and yields a more rapid recovery of olfactory-guided behavior. We suggest that olfactory integrity may be maintained by RA-mediated regulation of neurogenesis as well as local immune responses, and that aging compromises these mechanisms. The chemical senses, particularly olfaction, decline in aged individuals, and RA (via vitamin A) levels may also decline, perhaps due to changes in appetite and food intake. This synergy may result in a high prevalence of olfactory pathology in aged individuals.
No preview · Article · Jan 2007 · Experimental Gerontology
[Show abstract][Hide abstract] ABSTRACT: Retinoic acid (RA), a member of the steroid/thyroid superfamily of signaling molecules, is an essential regulator of morphogenesis, differentiation, and regeneration in the mammalian olfactory pathway. RA-mediated teratogenesis dramatically alters olfactory pathway development, presumably by disrupting retinoid-mediated inductive signaling that influences initial olfactory epithelium (OE) and bulb (OB) morphogenesis. Subsequently, RA modulates the genesis, growth, or stability of subsets of OE cells and OB interneurons. RA receptors, cofactors, and synthetic enzymes are expressed in the OE, OB, and anterior subventricular zone (SVZ), the site of neural precursors that generate new OB interneurons throughout adulthood. Their expression apparently accommodates RA signaling in OE cells, OB interneurons, and slowly dividing SVZ neural precursors. Deficiency of vitamin A, the dietary metabolic RA precursor, leads to cytological changes in the OE, as well as olfactory sensory deficits. Vitamin A therapy in animals with olfactory system damage can accelerate functional recovery. RA-related pathology as well as its potential therapeutic activity may reflect endogenous retinoid regulation of neuronal differentiation, stability, or regeneration in the olfactory pathway from embryogenesis through adulthood. These influences may be in register with retinoid effects on immune responses, metabolism, and modulation of food intake.
Preview · Article · Jun 2006 · Journal of Neurobiology
[Show abstract][Hide abstract] ABSTRACT: All-trans retinoic acid (ATRA), a metabolite of vitamin A, binds to retinoic acid receptors (RARs) to mediate gene transcription in target cells. We previously found that an ATRA supplement enhanced olfactory recovery rate in adult mice after olfactory bulb deafferentation. In this study, we examined the cellular localization of RARalpha, RARbeta, and RARgamma and the effects of surgery and ATRA treatment using immunocytochemistry. Mice received a left olfactory nerve transection with the right side serving as internal control. One day after surgery, the mice were given either ATRA mixed with sesame oil or just sesame oil. In the unoperated olfactory bulb, only RARalpha immunoreactivity (ir) was observed. In the unoperated right olfactory epithelium, RARalpha-ir was found in flask-shaped cells located in the supporting cell layer, in cell clusters above the basal cell layer, in cells in the lamina propria, in some respiratory cells and in the olfactory bulb. The flask-shaped cells did not immunostain for either neurons or sustentacular cells. RARbeta-ir was localized only in the respiratory cells while no RARgamma-ir was observed in the olfactory epithelium. The density of RARalpha-ir cells was higher in the operated left olfactory epithelium and highest after ATRA treatment. This study demonstrates the presence of RARs in the olfactory system, provides additional support that the ATRA-signaling pathway may be involved in the recovery of the olfactory epithelium after injury, and suggests a role for an unstudied cell type in that process.
[Show abstract][Hide abstract] ABSTRACT: Objectives 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.Study Design/Methods 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.Results 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.Conclusions 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.
No preview · Article · Jun 2002 · The Laryngoscope
[Show abstract][Hide abstract] ABSTRACT: Although rodents are nocturnal, their behavior is usually tested during the day. The authors present the results of a preliminary study, which suggest that altering the animals' day:night cycle might be the key to eliminating the need for food or water deprivation prior to testing.
[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Jan 2001 · Journal of Neuroscience Research
[Show abstract][Hide abstract] ABSTRACT: Evidence has accumulated to support a model for odorant detection in which individual olfactory receptor neurons (ORNs) express one of a large family of G protein-coupled receptor proteins that are activated by a small number of closely related volatile chemicals. However, the issue of whether an individual ORN expresses one or multiple types of receptor proteins has yet to be definitively addressed. Physiological data indicate that some individual ORNs can be activated by odorants differing substantially in structure and/or perceived quality, suggesting multiple receptors or one nonspecific receptor per cell. In contrast, molecular biological studies favor a scheme with a single, fairly selective receptor per cell. The present studies directly assessed whether individual rat ORNs can express multiple receptors using single-cell PCR techniques with degenerate primers designed to amplify a wide variety of receptor sequences. We found that whereas only a single OR sequence was obtained from most ORNs examined, one ORN produced two distinct receptor sequences that represented different receptor gene families. Double-label in situ hybridization studies indicated that a subset of ORNs co-express two distinct receptor mRNAs. A laminar segregation analysis of the cell nuclei of ORNs labeled with the two OR mRNA probes showed that for one probe, the histogram of the distribution of the cell nuclei along the depth of the epithelium was bimodal, with one peak overlapping the (unimodal) histogram for the other probe. These results are consistent with co-expression of two OR mRNAs in a population of single ORNs.
Preview · Article · Aug 2000 · Journal of Neurochemistry
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Human olfactory neuroepithelium (OE) is situated within the olfactory cleft of the nasal cavity and has the characteristic property of continually regenerating neurons during the lifetime of the individual. This regenerative ability of OE provides a unique model for neuronal differentiation, but little is known about the structure and biology of human olfactory mucosa. Thus, to better understand neurogenesis in human OE, we studied the expression of olfactory marker protein (OMP), TrkB and NeuroD in human nasal biopsies and autopsy specimens and compared these data with those obtained from normal and regenerating mouse OE. We show that NeuroD and TrkB are coordinately expressed in human OE. Thus, by using these markers we have been able to extend the known boundaries of the human OE to include the inferior middle turbinate. In normal mouse OE, TrkB and OMP expression overlap in cells closest to the superficial layer, but TrkB is expressed more strongly in the lower region of this layer. In contrast, NeuroD expression is more basally restricted in a region just above the globose basal cells. These characteristic expression patterns of OMP, TrkB and NeuroD were also observed in the regenerating mouse OE induced by axotomy. These results support a role of NeuroD and brain-derived neurotrophic actor (BDNF), the preferred ligand for TrkB, in the maintenance of the olfactory neuroepithelium in humans and mice.
No preview · Article · Jan 2000 · Cell and Tissue Research
[Show abstract][Hide abstract] ABSTRACT: Genetics, experience, environment, and health can all affect the anatomic and physiologic components of the olfactory system and thereby influence olfactory performance. Large individual differences exist among subjects with respect to olfactory sensitivity and identification ability, which may result in both qualitative and quantitative differences in perceptual ability.
No preview · Article · Jun 1999 · Quintessence international
[Show abstract][Hide abstract] ABSTRACT: A gradual loss of olfactory capability with age and in a number of neurodegenerative diseases is common, and mechanisms underlying these losses are not understood. We determined the feasibility of using ORNs obtained from olfactory epithelial biopsies to identify possible changes in ORN function that may contribute to olfactory impairment in these individuals. ORNs from nine healthy subjects (66-84 yr), three patients with Alzheimer's disease and one with multi-infarct dementia were studied with calcium imaging techniques and two odorant mixtures. Seventy-five viable ORNs were studied; 53% of these were odorant responsive, and twenty percent of these responded to both odorant mixtures. In contrast, 25% of 173 ORNs from younger subjects were odorant responsive, and none of these responded to both odorant mixtures. The proportion of cells responding to each of the odorant mixtures also differed between older and younger subjects. These studies demonstrate the feasibility of this approach to examine age or disease-associated changes in neuronal function. Further, age-related changes in ORN selectivity may contribute to changes in olfactory performance.
No preview · Article · Dec 1998 · Annals of the New York Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Select groups of neurons within the brain alter their firing rate when ambient glucose levels change. These glucose-responsive neurons are integrated into systems which control energy balance in the body. They contain an ATP-sensitive K+ channel (KATP) which mediates this response. KATP channels are composed of an inwardly rectifying pore-forming unit (Kir6.1 or Kir6.2) and a sulfonylurea binding site. Here, we examined the anatomical distribution and phenotype of cells containing Kir6.2 mRNA within the rat brain by combinations of in situ hybridization and immunocytochemistry. Cells containing Kir6.2 mRNA were widely distributed throughout the brain without apparent concentration in areas known to contain specific glucose-responsive neurons. Kir6.2 mRNA was present in neurons expressing neuron-specific enolase, tyrosine hydroxylase, neuropeptide Y (NPY) and the glutamic acid decarboxylase isoform, GAD65. No astrocytes expressing glial fibrillary acidic protein or oligodendrocytes expressing carbonic anhydrase II were found to co-express Kir6.2 mRNA. Virtually all of the NPY neurons in the hypothalamic arcuate n. and catecholamine neurons in the substantia nigra, pars compacta and locus coeruleus contained Kir6.2 mRNA. Epinephrine neurons in the C2 area also expressed high levels of Kir6.2, while noradrenergic neurons in A5 and A2 areas expressed lower levels. The widespread distribution of Kir6.2 mRNA suggests that the KATP channel may serve a neuroprotective role in neurons which are not directly involved in integrating signals related to the body's energy homeostasis.
[Show abstract][Hide abstract] ABSTRACT: Transduction mechanisms were investigated in human olfactory neurons by determining characteristics of odorant-induced changes in intracellular calcium concentration ([Ca2+]i). Olfactory neurons were freshly isolated from nasal biopsies, allowed to attach to coverslips, and loaded with the calcium-sensitive indicator fura-2. Changes in [Ca2+]i were studied in response to exposure to individual odors, or odorant mixtures composed to distinguish between transduction pathways mediated by adenosine 3'5'-monophosphate (cAMP; mix A) or inositol 1,4,5-trisphosphate (InsP3; mix B). Overall, 52% of biopsies produced one or more odorant-responsive olfactory neurons, whereas 24% of all olfactory neurons tested responded to odorant exposure with a change in [Ca2+]i. As in olfactory neurons from other species, the data suggest that odorant exposure elicited calcium influx via second-messenger pathways involving cAMP or InsP3. Unlike olfactory neurons from other species that have been tested, some human olfactory neurons responded to odorants with decreases in [Ca2+]i. Also in contrast with olfactory neurons from other species, human olfactory neurons were better able to discriminate between odorant mixtures in that no neuron responded to more than one type of odor or mixture. These results suggest the presence of a previously unreported type of olfactory transduction mechanism, and raise the possibility that coding of odor qualities in humans may be accomplished to some degree differently than in other vertebrates, with the olfactory neuron itself making a greater contribution to the discrimination process.
Full-text · Article · Apr 1997 · Journal of Neurophysiology
[Show abstract][Hide abstract] ABSTRACT: Olfactory neuroblastoma is a rare malignancy of the olfactory mucosa that may be derived from the olfactory epithelium. To characterize this tumor, we cultured olfactory neuroblastoma cells in the presence or absence of growth factors (transforming growth factor alpha and basic fibroblast growth factor) known to affect olfactory tissue and assessed their responsiveness to known odorants by measuring changes in intracellular calcium. Untreated cells did not respond to odorants. Basic fibroblast growth factor treatment had cytotoxic effects, and treated cells did not respond to odorants. Transforming growth factor alpha treatment resulted in the induction of odor responsiveness in these cells. Cells responded to odorants at 100 nM to 100 microM concentrations and responded with both increases and decreases in intracellular calcium. Increases in intracellular calcium were mediated by a calcium influx and were reversibly blocked by compounds known to inhibit second messenger pathways in olfactory receptor neurons. The calcium responses of the olfactory neuroblastoma cells were thus specific to the odorants and similar to those found in olfactory receptor neurons. The results support the notion that olfactory neuroblastoma cells may be of olfactory origin and thus they can be used as a model cell line to study human olfaction.