CNS glial cells support in vitro survival, division, and differentiation of dissociated olfactory neuronal progenitor cells

N,N-dimethyltryptamine compound found in the hallucinogenic tea ayahuasca, regulates adult neurogenesis in vitro and in vivo

N,N-dimethyltryptamine (DMT) is a component of the ayahuasca brew traditionally used for ritual and therapeutic purposes across several South American countries. Here, we have examined, in vitro and vivo, the potential neurogenic effect of DMT. Our results demonstrate that DMT administration activates the main adult neurogenic niche, the subgranular zone of the dentate gyrus of the hippocampus, promoting newly generated neurons in the granular zone. Moreover, these mice performed better, compared to control non-treated animals, in memory tests, which suggest a functional relevance for the DMT-induced new production of neurons in the hippocampus. Interestingly, the neurogenic effect of DMT appears to involve signaling via sigma-1 receptor (S1R) activation since S1R antagonist blocked the neurogenic effect. Taken together, our results demonstrate that DMT treatment activates the subgranular neurogenic niche regulating the proliferation of neural stem cells, the migration of neuroblasts, and promoting the generation of new neurons in the hippocampus, therefore enhancing adult neurogenesis and improving spatial learning and memory tasks.

Primary Cultures of Olfactory Neurons from the Avian Olfactory Epithelium

The culture of the olfactory epithelium has been a useful model for the study of neurogenesis since olfactory neurons regenerate continuously throughout the adult lifespan. Structurally and functionally mature olfactory neurons are generated in vitro from non-neuronal precursors in a process that resembles the in vivo counterparts. This chapter describes a technique for culture of olfactory neurons from the avian olfactory epithelium of embryonic chickens; this enables the controlled laboratory study of a critical sensory system that is unstudied in this major vertebrate class. The techniques described here are broadly applicable to other endothermic vertebrate species.

Intranasal Borna Disease Virus (BoDV-1) Infection: Insights into Initial Steps and Potential Contagiosity

Mammalian Bornavirus (BoDV-1) typically causes a fatal neurologic disorder in horses and sheep, and was recently shown to cause fatal encephalitis in humans with and without transplant reception. It has been suggested that BoDV-1 enters the central nervous system (CNS) via the olfactory pathway. However, (I) susceptible cell types that replicate the virus for successful spread, and (II) the role of olfactory ensheathing cells (OECs), remained unclear. To address this, we studied the intranasal infection of adult rats with BoDV-1 in vivo and in vitro, using olfactory mucosal (OM) cell cultures and the cultures of purified OECs. Strikingly, in vitro and in vivo, viral antigen and mRNA were present from four days post infection (dpi) onwards in the olfactory receptor neurons (ORNs), but also in all other cell types of the OM, and constantly in the OECs. In contrast, in vivo, BoDV-1 genomic RNA was only detectable in adult and juvenile ORNs, nerve fibers, and in OECs from 7 dpi on. In vitro, the rate of infection of OECs was significantly higher than that of the OM cells, pointing to a crucial role of OECs for infection via the olfactory pathway. Thus, this study provides important insights into the transmission of neurotropic viral infections with a zoonotic potential.

Role of Astrocytes in the Neurogenic Niches

In the mammalian brain, highly specialized astrocytes serve as neural stem cells (NSCs) that divide and give rise to new neurons, in a process called neurogenesis. During embryonic development NSCs generate almost all neurons of the brain. Soon after birth the neurogenic potential of NSCs is highly reduced, and neurogenesis occurs only in two specialized brain regions called the neurogenic niches. Niche cells are essential to stem cells as they provide structural and nutritional support, and control fundamental stem cell decisions. Astrocytes, major components of the adult neurogenic niches, are evolving as important regulators of neurogenesis, by controlling NSC proliferation, fate choice, and differentiation of the progeny. Therefore, astrocytes contribute to neurogenesis in two ways: as NSCs and as niche cells. This review highlights the role of astrocyte-like NSCs during development and adulthood, and summarizes how niche astrocytes control the process of adult neurogenesis.

Neuronal Homeostasis in Mammalian Olfactory Epithelium: A Review

The neuronal lineage of the olfactory epithelium (OE) is a cell lineage that includes the neuronal stem cell and its progeny (ultimately the mature olfactory receptor neuron [ORN]). Recent studies, including further characterization of the neuronal lineage of the OE, and of factors that influence proliferation, survival, and death of cells of this lineage, have contributed significantly to understanding of neuronal homeostasis, i.e., normal maintenance of neuronal number, in mammalian OE. Our recent studies indicate that in adult mice, all cell types of the neuronal lineage of the OE—neuronal precursors, immature ORNs and mature ORNs—undergo constitutive death, i.e., a normal, basal level of cell death, that is characteristic of programmed cell death or apoptosis. To some extent, constitutive cell death in this lineage may reflect random environmental insults; however, this may also be the result of an ongoing developmental program that acts to control both numbers and phenotypic organization of olfactory neurons. Although a variety of extrinsic and intrinsic factors are likely to contribute to cell death in the neuronal lineage of the OE, most have not been thoroughly studied. Detailed analysis of one of these factors, effects of target deprivation, suggests that survival of individual cell types of the neuronal lineage of the OE may be differentially regulated with mature ORNs, but not immature ORNs or neuronal precursors, dependent upon the olfactory bulb for their survival. Factors normally provided to cells of the ORN lineage, as in other neuronal systems, are likely to promote survival by inhibiting an endogenous genetic program of cell death. Whether candidate polypeptide growth factors, e.g., the neurotrophins, or other pharmacological inhibitors of apoptosis will eventually play a role in the treatment of specific anosmias remains to be determined.

Transcriptional and Epigenetic Control of Mammalian Olfactory Epithelium Development

The postnatal mammalian olfactory epithelium (OE) represents a major aspect of the peripheral olfactory system. It is a pseudostratified tissue that originates from the olfactory placode and is composed of diverse cells, some of which are specialized receptor neurons capable of transducing odorant stimuli to afford the perception of smell (olfaction). The OE is known to offer a tractable miniature model for studying the systematic generation of neurons and glia that typify neural tissue development. During OE development, stem/progenitor cells that will become olfactory sensory neurons and/or non-neuronal cell types display fine spatiotemporal expression of neuronal and non-neuronal genes that ensures their proper proliferation, differentiation, survival, and regeneration. Many factors, including transcription and epigenetic factors, have been identified as key regulators of the expression of such requisite genes to permit normal OE morphogenesis. Typically, specific interactive regulatory networks established between transcription and epigenetic factors/cofactors orchestrate histogenesis in the embryonic and adult OE. Hence, investigation of these regulatory networks critical for OE development promises to disclose strategies that may be employed in manipulating the stepwise transition of olfactory precursor cells to become fully differentiated and functional neuronal and non-neuronal cell types. Such strategies potentially offer formidable means of replacing injured or degenerated neural cells as therapeutics for nervous system perturbations. This review recapitulates the developmental cellular diversity of the olfactory neuroepithelium and discusses findings on how the precise and cooperative molecular control by transcriptional and epigenetic machinery is indispensable for OE ontogeny.

Globose basal cells for spinal cord regeneration

Spinal cord injury (SCI) is a devastating condition with loss of motor and sensory functions below the injury level. Cell based therapies are experimented in pre-clinical studies around the world. Neural stem cells are located intra-cranially in subventricular zone and hippocampus which are highly invasive sources. The olfactory epithelium is a neurogenic tissue where neurogenesis takes place throughout the adult life by a population of stem/progenitor cells. Easily accessible olfactory neuroepithelial stem/progenitor cells are an attractive cell source for transplantation in SCI. Globose basal cells (GBCs) were isolated from rat olfactory epithelium, characterized by flow cytometry and immunohistochemically. These cells were further studied for neurosphere formation and neuronal induction. T10 laminectomy was done to create drop-weight SCI in rats. On the 9^th day following SCI, 5 × 10⁵ cells were transplanted into injured rat spinal cord. The outcome of transplantation was assessed by the Basso, Beattie and Bresnahan (BBB) locomotor rating scale, motor evoked potential and histological observation. GBCs expressed neural stem cell markers nestin, SOX2, NCAM and also mesenchymal stem cell markers (CD29, CD54, CD90, CD73, CD105). These cells formed neurosphere, a culture characteristics of NSCs and on induction, differentiated cells expressed neuronal markers βIII tubulin, microtubule-associated protein 2, neuronal nuclei, and neurofilament. GBCs transplanted rats exhibited hindlimb motor recovery as confirmed by BBB score and gastrocnemius muscle electromyography amplitude was increased compared to controls. Green fluorescent protein labelled GBCs survived around the injury epicenter and differentiated into βIII tubulin-immunoreactive neuron-like cells. GBCs could be an alternative to NSCs from an accessible source for autologous neurotransplantation after SCI without ethical issues.

N-acetyl cysteine mitigates the acute effects of cocaine-induced toxicity in astroglia-like cells

Cocaine has a short half-life of only about an hour but its effects, predominantly on the central nervous system (CNS), are fairly long-lasting. Of all cells within the CNS, astrocytes may be the first to display cocaine toxicity owing to their relative abundance in the brain. Cocaine entry could trigger several early response changes that adversely affect their survival, and inhibiting these changes could conversely increase their rate of survival. In order to identify these changes and the minimal concentrations of cocaine that can elicit them in vitro, rat C6 astroglia-like cells were treated with cocaine (2–4 mM for 1h) and assayed for alterations in gross cell morphology, cytoplasmic vacuolation, viability, reactive oxygen species (ROS) generation, glutathione (GSH) levels, cell membrane integrity, F-actin cytoskeleton, and histone methylation. We report here that all of the above identified features are significantly altered by cocaine, and may collectively represent the key pathology underlying acute toxicity-mediated death of astroglia-like cells. Pretreatment of the cells with the clinically available antioxidant N-acetyl cysteine (NAC, 5 mM for 30 min) inhibited these changes during subsequent application of cocaine and mitigated cocaine-induced toxicity. Despite repeated cocaine exposure, NAC pretreated cells remained highly viable and post NAC treatment also increased viability of cocaine treated cells to a smaller yet significant level. We show further that this alleviation by NAC is mediated through an increase in GSH levels in the cells. These findings, coupled with the fact that astrocytes maintain neuronal integrity, suggest that compounds which target and mitigate these early toxic changes in astrocytes could have a potentially broad therapeutic role in cocaine-induced CNS damage.

Anatomy and cellular constituents of the human olfactory mucosa: a review

Studies using animal models have recently suggested that the olfactory mucosa may be a source of cells capable of stimulating and contributing to complex neurologic regeneration. Several groups have already transplanted cell derivatives from the olfactory mucosa into injury models, and the results so far have been promising. To fully appreciate the meaning of these experiments, a better understanding of the cellular biology and physiology of the olfactory system is necessary. It is therefore of utmost importance for us to first identify and understand its constituents.

Primary culture of embryonic rat olfactory receptor neurons

Embryonic cells are very robust in surviving dissection and culturing protocols and easily adapt to their in vitro environment. Despite these advantages, research in the olfactory field on cultured embryonic olfactory neurons is sparse. In this study, two primary rat olfactory explant cultures of different embryonic d (E17 and E20) were established, comprising epithelium and bulb. The functionality of these neurons was tested by measuring intracellular calcium responses to cAMP-inducing agents forskolin (FSK) and 3-isobutyl-1-methylxanthine (IBMX) with fluorescence microscopy. For E17, the responsive cell fraction increased over time, from an initial 3% at the 1 d in vitro (DIV) to a maximum of 19% at 11 DIV. The response of E20 neurons fluctuated over time around a more or less stable 13%. A logistic regression analysis indicated a significant difference between both embryonic d in the response to FSK + IBMX. In addition, of these functional neurons, 23.3% of E17 and 54.3% of E20 cultures were responsive to the odorant isoamyl acetate.

CARBON NANOTUBE RIBBON AND THREAD SUPPORT ATTACHMENT AND DIFFERENTIATION OF NEURAL STEM CELLS

Carbon nanotubes (CNTs) have properties that promise an exciting role in nervous tissue repair. CNTs are strong, extremely light weight, biocompatible and electrically conductive. A relatively novel form of CNT material, multiple strands of CNTs spun into thread, accentuates the linear geometry of CNTs while retaining electrical conductivity. We propose that CNT thread, which is strong, pliable and readily manipulated, has the potential to support longitudinal growth of nerves after injury, in nervous system prostheses. Towards understanding how CNT materials support nervous tissue regeneration, we examined the in vitro interactions between CNT materials and neural stem cell-containing neurospheres, prepared from newborn mouse cortices. Intact neurospheres attached to pieces of as-grown arrays of CNTs, CNT "ribbon" material pulled from the arrays, and CNT thread. Stem cells differentiated into both neurons and glia under these conditions. Processes and cells aligned with the longitudinal axis of the CNT materials, both with and without coatings. For comparisons, dissociated neurosphere cells were plated on CNT thread, polypropylene surgical suture thread and commercial carbon fibers. Initial cell attachment (within seconds) and attachment at 24 h was greater on CNT thread than on the other fiber types. Stem cells on CNT threads differentiated into neurons and astrocytes over several days, on all fibers. The presence of serum greatly aided the health and spreading of both neurons and astrocytes. These findings demonstrate that CNT materials, in particular the thread form, are viable preparations for neural cell attachment, outgrowth and differentiation.

Neurons growing from neonatal murine olfactory explant culture responded to forskolin

CONCLUSION

Olfactory epithelium explant culture represents a model that will be useful in studying the calcium signal transduction of olfactory sensory neurons (OSNs).

OBJECTIVES

The aim of this study was to test the feasibility and efficacy of olfactory epithelium explant culture in the study of calcium signal transduction.

MATERIALS AND METHODS

Using explant culture, devoid of any enzyme use, a mixed cell type culture system from newborn murine olfactory epithelium was achieved. Morphological and immunochemical criteria were employed to identify the cultured cells. Calcium imaging, using the fluorescent calcium indicator fura-2, was used to monitor changes in the intracellular calcium concentration of candidate OSNs following exposure to forskolin, a cAMP pathway stimulant.

RESULTS

The putative OSNs synthesized both neuronal proteins and olfactory-specific markers. The cultured neurons originated from the 'precursors' present in the olfactory epithelium explants, became fully developed, and could survive for at least 9 days in vitro. Upon stimulation, the intracellular calcium concentration of the OSNs increased from 58.5+/-12.8 nM (n=20) to 577.2+/-57.6 nM (n=10).

Ventral mesencephalon astrocytes are more efficient than those of other regions in inducing dopaminergic neurons through higher expression level of TGF-beta3

Being supportive cells for neurons in the central nervous system, astrocytes have recently found to be associated with neurogenesis. Ventral mesencephalon (VM) astrocytes were also detected being instructive for VM dopaminergic (DA) neurogenesis, but the underling mechanisms are still unclear. This research is to figure out whether VM astrocytes are more efficient than those from other brain regions in inducing VM DA neurons from their precursors and whether transforming growth factor-betas (TGF-betas) are the underlying molecules. We found that, compared with astrocytes preparations from striatum and hippocampus, VM astrocytes preparations displayed markedly higher efficacy in inducing DA neurogenesis. Besides, they also expressed higher level of TGF-beta3 than those of two other regions. When TGF-beta3 gene expression in astrocytes preparations was inhibited by its antisense oligonucleotide, the induction of DA neurons decreased to a similar level among these three astrocytes preparations. Thus, our experiment indicates that VM astrocytes preparations which contained highly purified astrocytes are more efficient in inducing DA neurogenesis than those from other regions. Furthermore, it also suggests that the regional differences are regulated by different expression levels of TGF-beta3 in those astrocytes preparations from different derivations.

Induction of neurogenesis in nonconventional neurogenic regions of the adult central nervous system by niche astrocyte-produced signals

The central nervous system (CNS) of adult mammals regenerates poorly; in vivo, neurogenesis occurs only in two restricted areas, the hippocampal subgranular zone (SGZ) and the subventricular zone (SVZ). Neurogenic potential depends on both the intrinsic properties of neural progenitors and the environment, or niche, in which progenitor cells reside. Isolation of multipotent progenitor cells from broad CNS regions suggests that the neurogenic potential of the adult CNS is dictated by local environmental cues. Here, we report that astrocytes in the neurogenic brain regions, the SGZ and SVZ, of adult mice release molecular signals, such as sonic hedgehog (Shh), that stimulate adult neural progenitors to reenter the cell cycle and generate new neurons in vitro and in vivo. Transplantation of SGZ astrocytes or application of Shh caused de novo neurogenesis from the non-neurogenic neocortex of adult mice. These findings identify a molecular target that can activate the dormant neurogenic potential from nonconventional neurogenic regions of the adult CNS and suggest a novel mechanism of neural replacement therapy for treating neurodegenerative disease and injury without transplanting exogenous cells.

Brain micro-ecologies: neural stem cell niches in the adult mammalian brain

Neurogenesis persists in two germinal regions in the adult mammalian brain, the subventricular zone of the lateral ventricles and the subgranular zone in the hippocampal formation. Within these two neurogenic niches, specialized astrocytes are neural stem cells, capable of self-renewing and generating neurons and glia. Cues within the niche, from cell-cell interactions to diffusible factors, are spatially and temporally coordinated to regulate proliferation and neurogenesis, ultimately affecting stem cell fate choices. Here, we review the components of adult neural stem cell niches and how they act to regulate neurogenesis in these regions.

Primitive and committed human hematopoietic progenitor cells interact with primary murine neural cells and are induced to undergo self-renewing cell divisions

OBJECTIVE

Studies in animal models have indicated that hematopoietic progenitor cells (HPC) migrate and home to the central nervous system and might acquire neural features under specific circumstances. The interaction between HPC and the neural environment and the functional effect on hematopoiesis have not yet been defined.

METHODS

CD34(+)133(+) cells from mobilized peripheral blood were cocultured with primary murine neurons or astrocytes. Chemotaxis and adhesive interactions were studied by applying beta(1)- and beta(2)-integrin function-blocking anibodies. The impact of neural feeder layers on integrin expression of HPC and the presence of appropriate adhesion ligands on neural cells were determined by immunostaining and flow cytometry. The hematopoietic long-term fate was monitored by time-lapse microscopy of individual cell-division history followed by long-term culture-initiating cell (LTC-IC) and colony-forming cell (CFC) assays. Neural differentiation was assessed by immunostaining against specific neuronal and glial antigens.

RESULTS

The 23.0% +/- 4.9% of HPC showed stromal cell-derived factor-1-induced migration toward neural cells, and 20.2% +/- 1.6% displayed firm beta(1)-integrin-mediated adhesion to astrocytes. The latter expressed appropriate adhesion ligands, stabilized beta(1)-integrin expression, and increased beta(2)-integrin expression of HPC. Neural differentiation of HPC could not be identified but astrocytes were able to induce limited self-renewing cell divisions of HPC and thus maintain 25.8% +/- 3.4% of the initial LTC-IC and 80.7% +/- 1.9% of the initial CFC.

CONCLUSION

Human HPC are able to interact with neural cells and interaction maintains, albeit to a limited extent, the self-renewal capability of HPC.

Cell cycle alterations in biopsied olfactory neuroepithelium in schizophrenia and bipolar I disorder using cell culture and gene expression analyses

We previously demonstrated that olfactory cultures from individuals with schizophrenia had increased cell proliferation compared to cultures from healthy controls. The aims of this study were to (a) replicate this observation in a new group of individuals with schizophrenia, (b) examine the specificity of these findings by including individuals with bipolar I disorder and (c) explore gene expression differences that may underlie cell cycle differences in these diseases. Compared to controls (n = 10), there was significantly more mitosis in schizophrenia patient cultures (n = 8) and significantly more cell death in the bipolar I disorder patient cultures (n = 8). Microarray data showed alterations to the cell cycle and phosphatidylinositol signalling pathways in schizophrenia and bipolar I disorder, respectively. Whilst caution is required in the interpretation of the array results, the study provides evidence indicating that cell proliferation and cell death in olfactory neuroepithelial cultures is differentially altered in schizophrenia and bipolar disorder.

Implication of “Down syndrome cell adhesion molecule” in the hippocampal neurogenesis of ischemic monkeys

Molecular signals regulating adult neurogenesis in primates are largely unknown. Here the authors used differential display to analyze gene expression changes that occur in dentate gyrus of adult monkeys after transient global cerebral ischemia. Among 14 genes upregulated, the authors focused on Down syndrome cell adhesion molecule (DSCAM) known to play crucial role during neuronal development, and characterized its expression pattern at the protein level. In contrast with approximately threefold upregulation of Dscam gene on days 5 and 7, immunoblotting and immunofluorescence analyses using specific antibodies showed a gradual decrease of DSCAM after ischemia until day 9 followed by recovery on day 15. In the control, immunofluorescence reactivity of DSCAM was detected in dentate gyrus granule cells and CA4 neurons but decreased after ischemia, being compatible with the immunoblotting data. However, in the subgranular zone, cerebral ischemia led to a marked increase of DSCAM-positive cells on days 9 and 15. DSCAM upregulation was seen in two cell types: one is immature neurons positive for polysialylated neural cell adhesion molecule or betaIII-tubulin, while another is astrocytes positive for S100beta. Young astrocytes were in intimate contact with newly generated neurons in the subgranular zone. These data suggest implication of DSCAM in the adult neurogenesis of primate hippocampus upregulated after ischemia.

Transplantation de cellules gliales olfactives après traumatisme médullaire

Ensheathing olfactory glial cells (OEC) can be considered, with stem cells, as the other most important cell type for developing therapeutic cellular transplantation strategies following lesion of the central nervous system (CNS) and particularly in the case of spinal cord injury. OECs are macroglial cells whose precursors are located in the olfactory mucosa. OEC ensheath the axons of the sensory olfactory neurons, from the peripheral mucosa to the central olfactory bulbs. These glial cells constitute one of the rare macroglial cells which, after removal in the adult mammal, can survive in culture and multiply. After post-traumatic transplantation in the CNS, these cells have induced several instances of functional recovery after injury of different neural systems. The "OEC transplantation effect" consists in modifying the central inhibitory environment to make it more propitious for axonal regrowth and cell survival (reduction of the glial scar; releasing of numerous survival and neurotrophic factors, and of surface, extracellular matrix and adhesion molecules). In addition to the fact that OEC can ensheath and/or myelinate central axons, migrate in the CNS and accompany the growing axons over a relatively long distance, they also can be obtained from olfactory mucosa. OEC thus constitute a preferential candidate for autologous transplantation for the purposes of repair.

Multipotent stem cells from adult olfactory mucosa

Multipotent stem cells are thought to be responsible for the generation of new neurons in the adult brain. Neurogenesis also occurs in an accessible part of the nervous system, the olfactory mucosa. We show here that cells from human olfactory mucosa generate neurospheres that are multipotent in vitro and when transplanted into the chicken embryo. Cloned neurosphere cells show this multipotency. Multipotency was evident without prior culture in vitro: cells dissociated from adult rat olfactory mucosa generate leukocytes when transplanted into bone marrow-irradiated hosts, and cells dissociated from adult mouse olfactory epithelium generated numerous cell types when transplanted into the chicken embryo. It is unlikely that these results can be attributed to hematopoietic precursor contamination or cell fusion. These results demonstrate the existence of a multipotent stem-like cell in the olfactory mucosa useful for autologous transplantation therapies and for cellular studies of disease.

Identification and molecular regulation of neural stem cells in the olfactory epithelium

The sensory neurons that subserve olfaction, olfactory receptor neurons (ORNs), are regenerated throughout life, making the neuroepithelium in which they reside [the olfactory epithelium (OE)] an excellent model for studying how intrinsic and extrinsic factors regulate stem cell dynamics and neurogenesis during development and regeneration. Numerous studies indicate that transcription factors and signaling molecules together regulate generation of ORNs from stem and progenitor cells during development, and work on regenerative neurogenesis indicates that these same factors may operate at postnatal ages as well. This review describes our current knowledge of the identity of the OE neural stem cell; the different cell types that are thought to be the progeny (directly or indirectly) of this stem cell; and the factors that influence cell differentiation in the OE neuronal lineage. We review data suggesting that (1) the ORN lineage contains three distinct proliferating cell types--a stem cell and two populations of transit amplifying cells; (2) in established OE, these three cell types are present within the basal cell compartment of the epithelium; and (3) the stem cell that gives rise ultimately to ORNs may also generate two glial cell types of the primary olfactory pathway: sustentacular cells (SUS), which lie within OE proper; and olfactory ensheathing cells (OEC), which envelope the olfactory nerve. In addition, we describe factors that are both made by and found within the microenvironment of OE stem and progenitor cells, and which exert crucial growth regulatory effects on these cells. Thus, as with other regenerating tissues, the basis of regeneration in the OE appears be a population of stem cells, which resides within a microenvironment (niche) consisting of factors crucial for maintenance of its capacity for proliferation and differentiation.

Culture of neural cells on polymers coated surfaces for biosensor applications

We focused our study on the olfactory cells growth on biocompatible polymer films electrodeposited on a silicon microsystem. Several substrates such as polyethyleneimine (PEI), polypropyleneimine (PPI), and polypyrrole (PPy), acting as potentially good candidates for cell culture, were tested in order to allow cells to adhere and proliferate. During their growth, the evolution of their morphology was monitored using both confocal microscope and immunohistochemistry, leading to the conclusion of a normal development. An estimation of the adhesion and proliferation rates of rat neuronal cell cultures indicated that PEI and PPI were the best substrates for cultivating olfactory cells.

EGF-responsive rat neural stem cells: molecular follow-up of neuron and astrocyte differentiation in vitro

Neural stem cells (NSCs) could be very useful for the "cell therapy" treatment of neurological disorders. For this reason basic studies aiming to well characterize the biology of NSCs are of great interest. We carried out a molecular and immunocytochemical analysis of EGF-responsive NSCs obtained from rat pups. After the initial growth of NSCs as floating neurospheres in EGF-containing medium, cells were plated on poly-L-ornithine-coated dishes either in the presence or absence of EGF. We followed cell differentiation and apoptosis for 21 days in vitro and analyzed the expression levels of some genes having a major role in these processes, such as pRB, pRB2/p130, p27, and p53. We observed that EGF impairs neuronal differentiation. Furthermore, in the absence of mitogens, apoptosis, which appeared to proceed through the "p53 network," was significantly lower than in the presence of EGF. The cyclin kinase inhibitor p27, while important for cell cycle exit, seemed dispensable for cell survival and differentiation.

Astroglia induce neurogenesis from adult neural stem cells

During an investigation of the mechanisms through which the local environment controls the fate specification of adult neural stem cells, we discovered that adult astrocytes from hippocampus are capable of regulating neurogenesis by instructing the stem cells to adopt a neuronal fate. This role in fate specification was unexpected because, during development, neurons are generated before most of the astrocytes. Our findings, together with recent reports that astrocytes regulate synapse formation and synaptic transmission, reinforce the emerging view that astrocytes have an active regulatory role--rather than merely supportive roles traditionally assigned to them--in the mature central nervous system.

Hair cell development in vivo and in vitro: analysis by using a monoclonal antibody specific to hair cells in the chick inner ear

The purpose of this study was to establish a hair cell-specific marker and a convenient explant culture system for developing chick otocysts to facilitate in vivo and in vitro studies focusing on hair cell genesis in the inner ear. To achieve this, a hair cell-specific monoclonal antibody, 2A7, was generated by immunizing chick inner ear tissues to a mouse. Through the use of immunofluorescence and immunoelectron microscopy, it was shown that 2A7 immunoreactivity (2A7-IR) was primarily restricted to the apical region of inner ear hair cells, including stereocilia, kinocilia, apical membrane amongst the extending cilia, and superficial layer of the cuticular plate. Although the 2A7 antibody immunolabeled basically all of the hair cells in the posthatch chick inner ear, two different patterns of 2A7-IR were observed; hair cells located in the striolar region of the utricular macula, which consist of two distinct cell types identifiable on the basis of the type of nerve ending, Type I and II hair cells, showed labeling restricted to the basal end of the hair bundles. On the other hand, hair cells in the extrastriolar region, which are exclusively of Type II, showed labeling extending over virtually the entire length of the bundles. These findings raised the possibility that chick vestibular Type II hair cells, characterized by their bouton-type afferent nerve endings, can be divided into two subpopulations. Analysis of developing inner ear by using the 2A7 antibody revealed that this antibody also recognizes newly differentiated immature hair cells. Thus, the 2A7 antibody is able to recognize both immature and mature hair cells in vivo. The developmental potential of embryonic otocysts in vitro was then assessed by using explant cultures as a model. In this study, conventional otocyst explant cultures were modified by placing the tissues on floating polycarbonate filters on culture media, thereby allowing the easy manipulation of explants. In these cultures, 2A7-positive hair cells were differentiated from dividing precursor cells in vitro on the same schedule as in vivo. Furthermore, it was found that hair cells with both types of 2A7-IR were generated in culture as in vivo, indicating that a maturational process of hair cells also occurred. All these results as presented here suggest that the 2A7 monoclonal antibody as a hair cell-specific marker together with the culture system could be a potential tool in analysis of mechanisms underlying hair cell development.

Intranasal inoculation with the olfactory bulb line variant of mouse hepatitis virus causes extensive destruction of the olfactory bulb and accelerated turnover of neurons in the olfactory epithelium of mice

Viral upper respiratory infections are the most common cause of clinical olfactory dysfunction, but the pathogenesis of dysosmia after viral infection is poorly understood. Biopsies of the olfactory mucosa in patients that complain of dysosmia after viral infection fall into two categories: one in which no olfactory epithelium is seen and another in which the epithelium is disordered and populated mainly by immature neurons. We have used intranasal inoculation with an olfactory bulb line variant of MHV to study the consequences of viral infection on peripheral olfactory structures. MHV OBLV has little direct effect on the olfactory epithelium, but causes extensive spongiotic degeneration and destruction of mitral cells and interneurons in the olfactory bulb such that the axonal projection from the bulb via the lateral olfactory tract is markedly reduced. Moreover, surviving mitral cells apparently remain disconnected from the sensory neuron input to the glomerular layer, judging from retrograde labeling studies using Dil. The damage to the bulb indirectly causes a persistent, long-term increase in the turnover of sensory neurons in the epithelium, i.e. the relative proportion of immature to mature sensory neurons and the rate of basal cell proliferation both increase. The changes that develop after inoculation with MHV OBLV closely resemble the disordering of the olfactory epithelium in some patient biopsies. Thus, damage to the olfactory nerve or bulb may contribute to a form of post-viral olfactory dysfunction and MHV OBLV is a useful model for studying the pathogenesis of this form of dysosmia.

Adult human olfactory stem cells

The location of stem cells within the adult CNS makes them impractical for surgical removal and autologous transplantation. Their limited availability and histocompatibility issues further restrict their use. In contrast, olfactory neuroepithelium (ONe) located in the nasal passageways has a continuous regenerative capability and can be biopsied readily. To investigate the potential of human ONe to provide viable populations of pluripotent cells, ONe was harvested from cadavers 6-18 h postmortem, dissociated, plated and fed every 3-4 days. Heterogeneous populations of neurons, glia, and epithelia were identified with lineage-specific markers. After several weeks, 5-10% of the cultures produced a population of rapidly dividing cells, which in turn, produced neurospheres containing at least two subpopulations based on neuronal and glial specific antigens. Most contained one or more neuronal markers; a few were positive for A2B5 and/or GFAP. To determine if growth modulators would affect the neurosphere forming cells, they were exposed to dibutyryl-cAMP. The nucleotide reduced cell division and increased process formation. Although the cells had been passaged more than 70 times, their viability remained constant as shown by the MTT viability index. Donor age or sex were not limiting factors, because neurospheres have been established from cadavers of both sexes from 50 to 95 years old at time of death. The ex vivo expansion of these cells will provide a patient-specific population of cells for immunological, genetic and pharmacological evaluation. Our long-term goal is to determine the utility of these cells to facilitate CNS repair.

Nerve growth factor applied onto the olfactory epithelium alleviates degenerative changes of the olfactory receptor neurons following axotomy

The olfactory neuroepithelium of the mammalian nervous system manifests continuous neurogenesis throughout life. Recent studies suggest that neurotrophic factors and their receptors may play a role in the regulation of development and regeneration in the olfactory system. However, there have been very few in vivo studies investigating the effect of exogenous neurotrophic factors in the olfactory system. In the present study, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) were administered into the rat olfactory mucosa for 5 days just after the transection of the olfactory nerve. We then examined the effect of exogenous neurotrophic factors on the degenerative changes in axotomized olfactory receptor neurons (ORNs). Further, we examined the location of their receptors, Trk A and Trk B. We found that both mature and immature ORNs expressed more intense signals for olfactory marker protein and beta-tubulin mRNAs, respectively, when NGF was applied to the axotomized olfactory neuroepithelium for 5 days, compared to the ORNs of saline-treated controls. BDNF at a 10 microg total dose did not show this effect. The effect of NGF applied onto the olfactory epithelium is consistent with the immunohistochemical finding that Trk A was present in the dendrites and axon bundles in normal and axotomized ORNs. These results suggest that NGF may protect the degenerative changes in mature and immature ORNs following axotomy through the binding to the Trk A receptor located on the surface of the olfactory epithelium.

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.

Growth factor regulation of neurogenesis in adult olfactory epithelium

Neurogenesis continues throughout adult life in the mammalian olfactory epithelium. This process is a dynamic state of proliferation, differentiation and cell death, probably regulated by autocrine and paracrine signals such as peptide growth factors. Previous investigations have demonstrated roles for some growth factors in olfactory neurogenesis in vitro, but the assay systems used make it difficult to be certain of their effects (proliferation, differentiation, enhanced survival) or their target cells. The present study investigated the effects of growth factors in cultures of purified olfactory epithelium comprising only basal cells and supporting cells in serum-free media. The advantage of this culture system is that proliferation, differentiation and survival of the basal cells and neurons can be examined separately. Under these conditions, three growth factors exerted well-defined effects: (i) fibroblast growth factor-2 stimulated proliferation of the globose basal cells; (ii) transforming growth factor-beta2 induced these cells to differentiate into neurons; and (iii) platelet-derived growth factor promoted survival of the differentiated neurons. We conclude that fibroblast growth factor-2, transforming growth factor-beta2 and platelet-derived growth factor act sequentially on precursor cells and immature neurons during neurogenesis in the adult olfactory epithelium.

Reconstructing smell

Odorant signal transduction and neurogenesis are fundamental properties of the olfactory epithelium. Many preparations have been used to elucidate some of the mechanisms underlying these properties. In this article, we briefly review these research areas and describe some of the techniques used to obtain the data. We focus specifically on the cell-culture paradigm and the data obtained from various immortal cell lines in their attempts to reconstruct the olfactory epithelium in vitro.

An olfactory sensory neuron line, odora, properly targets olfactory proteins and responds to odorants

The site for interactions between the nervous system and much of the chemical world is in the olfactory sensory neuron (OSN). Odorant receptor proteins (ORPs) are postulated to mediate these interactions. However, the function of most ORPs has not been demonstrated in vivo or in vitro. For this and other reasons, we created a conditionally immortalized cell line derived from the OSN lineage, which we term odora. Odora cells, under control conditions, are phenotypically similar to the OSN progenitor, the globose basal cell. After differentiation, odora cells more closely resemble OSNs. Differentiated odora cells express neuronal and olfactory markers, including components of the olfactory signal transduction pathway. Unlike other cell lines, they also efficiently target exogenous ORPs to their surface. Strikingly, differentiated odora cells expressing ORPs respond to odorants, as measured by an influx of calcium. In particular, cells expressing one ORP demonstrate a specific response to only one type of tested odorant. Odora cells, therefore, are ideal models to examine the genesis and function of olfactory sensory neurons.

Olfactory receptor neurons exist as distinct subclasses of immature and mature cells in primary culture

The processes of neuronal differentiation and survival are key questions in neurobiology. The olfactory system possesses unique regenerative capacity, as its neurons are continually replaced throughout adulthood from a maintained population of precursor cells. Primary cultures of olfactory epithelium enriched in olfactory neurons would provide a useful model to study the processes of neurogenesis, differentiation and senescence. To determine whether immature olfactory neurons could be isolated in primary culture and to investigate the mechanisms underlying these processes, culture conditions which selectively favored the presence of immature olfactory neurons were optimized. Using low plating densities, a population of cells was identified which, by reverse transcription-polymerase chain reaction, demonstrated messages for olfactory neuronal markers, including Golf, olfactory cyclic nucleotide-gated channel and olfactory marker protein, as well as the p75 low-affinity nerve growth factor receptor. Immunocytochemical analysis showed that these putative immature olfactory neurons possessed immunoreactivity to G(olf), neuron-specific tubulin, neural cell adhesion molecule, synaptophysin and neurofilament. These neurons were defined as olfactory receptor neuron-1 cells. Under these conditions, a separate class of rarely occurring cells with different morphology demonstrated immunoreactivity to mature markers, such as adenylyl cyclase III and olfactory marker protein. Electrophysiologically, these cells displayed properties consistent with those of acutely dissociated olfactory receptor neurons. Another class of rarer cells which represented less than 2% of cells in culture demonstrated immunoreactivity to glial fibrillary acidic protein. These cultures can serve as a model for in vitro analysis of olfactory receptor neuronal development and maintenance, and provide a potential substrate for the development of cell lines.

Interaction between astrocytes and adult subventricular zone precursors stimulates neurogenesis

Neurogenesis continues in the mammalian subventricular zone (SVZ) throughout life. However, the signaling and cell-cell interactions required for adult SVZ neurogenesis are not known. In vivo, migratory neuroblasts (type A cells) and putative precursors (type C cells) are in intimate contact with astrocytes (type B cells). Type B cells also contact each other. We reconstituted SVZ cell-cell interactions in a culture system free of serum or exogenous growth factors. Culturing dissociated postnatal or adult SVZ cells on astrocyte monolayers-but not other substrates-supported extensive neurogenesis similar to that observed in vivo. SVZ precursors proliferated rapidly on astrocytes to form colonies containing up to 100 type A neuroblasts. By fractionating the SVZ cell dissociates with differential adhesion to immobilized polylysine, we show that neuronal colony-forming precursors were concentrated in a fraction enriched for type B and C cells. Pure type A cells could migrate in chains but did not give rise to neuronal colonies. Because astrocyte-conditioned medium alone was not sufficient to support SVZ neurogenesis, direct cell-cell contact between astrocytes and SVZ neuronal precursors may be necessary for the production of type A cells.

BMPs inhibit neurogenesis by a mechanism involving degradation of a transcription factor

Bone morphogenetic proteins (BMPs), negative regulators of neural determination in the early embryo, were found to be potent inhibitors of neurogenesis in olfactory epithelium (OE) cultures. BMPs 2, 4 or 7 decreased the number of proliferating progenitor cells and blocked production of olfactory receptor neurons (ORNs). Experiments suggested that this effect was due to an action of BMPs on an early-stage progenitor in the ORN lineage. Further analysis revealed that progenitors exposed to BMPs rapidly (< 2 h) lost MASH1, a transcription factor known to be required for the production of ORNs. This disappearance was due to proteolysis of existing MASH1 protein, but new gene expression was required to trigger it. The data suggest a novel mechanism of BMP action, whereby the induced degradation of an essential transcription factor results in premature termination of a neuronal lineage.

Stress induces neurogenesis in non-neuronal cell cultures of adult olfactory epithelium

Among the basal cells of the olfactory epithelium is a stem cell which divides and whose progeny differentiate into new sensory neurons throughout adult life. Olfactory neurogenesis is highly regulated, for example it is stimulated by epithelial damage. Previous reports implicate several growth factors in progenitor cell proliferation and neuronal differentiation in vitro but these studies differ in growth conditions and age of donors making it difficult to determine precisely the roles of neurogenic stimuli and their sites of action. The aims of the present study were to develop purified basal cell cultures from adult olfactory epithelium and to stimulate neurogenesis in defined growth conditions in order to elucidate the cellular mechanisms by which neurogenesis is stimulated after epithelial damage. We show here that differentiated olfactory sensory neurons arise after biochemical or mechanical stress of rat and mouse olfactory epithelial cell cultures in the absence of growth factors, complex media (e.g., serum, conditioned media, pituitary and hypothalamic extracts), or other cells (e.g., explants, feeder layers of glia, or other non-epithelial cells). Prior to the stress, these cultures contained basal cells and supporting cells but not neurons. After the stress, some cells differentiated into bipolar neurons expressing a number of neuronal proteins including olfactory marker protein. Bromodeoxyuridine experiments show that the differentiated neurons arose from recently divided cells which did not divide again before differentiating. We conclude that stress disrupts cell surface contacts to induce the immediate neuronal precursors to undergo final differentiation into olfactory sensory neurons. This may be a mechanism for enhanced neurogenesis after epithelial damage.

The effect of extracellular matrix on the growth of mouse olfactory tissue in vitro

The aim of this study was to compare the capacity of extracellular matrix (ECM) components to support the growth and differentiation of olfactory tissue in vitro. Reconstituted basement membrane matrix (RBM) supported profuse neurite outgrowth from explants of olfactory bulb (OB), with no non-neuronal cell migration. In contrast, nasal tissue (NT) explants cultured on RBM produced profuse fibroblastic outgrowth, but no neurite outgrowth from olfactory sensory neurones (OSN). Three-dimensional collagen gels, on the other hand, supported extensive outgrowth of both non-neuronal and neurite outgrowth from OB and NT explants, mature OSNs in the latter being identified using antibodies against olfactory marker protein (OMP). These culture systems represent useful tools for investigating potential tropic influences of target tissue.

Effects of insulin-like growth factor 1 on olfactory neurogenesis in vivo and in vitro

The rate of neurogenesis in the peripheral olfactory neuroepithelium is regulated by unknown mechanisms. The members of the insulin-like growth factor (IGF) family can influence neuronal generation, survival and/or differentiation. Several members of this family, in particular IGF-1, are expressed at high levels in the olfactory bulb and epithelium, where they could influence the generation and/or survival of olfactory receptor neurons (ORNs). To explore the role of IGF-1 in the olfactory epithelium (OE), we asked which cells expressed IGF-1 receptors (IGF-1Rs), using olfactory cell cultures and cryostat-cut tissue sections of neonatal (postnatal day four) and adult rat OE. An antibody specific for the alpha subunit of the IGF-1R densely labeled a subset of ORNs but not other cell types in sections and cultures. These ORNs were primarily immature, as determined by double labeling with neuronal markers. The number of IGF-1R-labeled cells as well as the levels of IGF-1R protein (determined by immunoprecipitation and Western blotting) decreased with age, which is consistent with normal developmental changes. To study IGF-1 effects in the intact animal, we infused IGF-1 and related growth factors into the noses of newborn Sprague-Dawley rats, i.e., when the epithelium is still developing. Growth factors or carrier solution (0.9% NaCl with 0.25% bovine serum albumin to prevent nonspecific binding) were applied (10 microliters) to the left nostril once per day starting shortly after birth on postnatal day 1 (P1), P2 and P3, and the animals were sacrificed on P4 by decapitation. After paraformaldehyde immersion fixation, cryostat sections of the olfactory area of the nose were immunostained for the proliferating cell nuclear antigen (PCNA). Sections were position-matched by turbinate structure and then epithelial height and area of PCNA staining at the base of the epithelium (which represents division of primarily neuronal precursors) were measured by image analysis. Both were significantly increased by rat IGF-1 (20 ng/ml, 2.6 nM), but not insulin (20 ng/ml, 2.6 nM) or an IGF-1 derivative, LongR3 IGF-1 (200 ng/ml, 22 nM), that does not bind to the IGF-1 binding proteins (IGFBPs). Thus IGF-1 appears to influence the rate of olfactory neurogenesis, and its actions are not modified by the IGFBPs. These data suggest an important role for IGF-1 in the OE.

Basic fibroblast growth factor supports human olfactory neurogenesis by autocrine/paracrine mechanisms

Throughout life, olfactory sensory neurons are renewed from a population of dividing stem cells. Little is known about the molecular mechanisms that regulate the activation, self-renewal and differentiation of olfactory neuronal precursors; however, evidence indicates that soluble mediators may play a central role in olfactory neurogenesis. To identify molecules that regulate olfactory self-renewal and differentiation, we have recently established, cloned and propagated in vitro primary long-term cell cultures from the human fetal olfactory neuroepithelium. Here we show that primary human olfactory neuroblasts synthesize and release biologically active basic fibroblast growth factor which, in turn, supports neuroblast growth by autocrine/paracrine mechanisms. The growth-promoting activity of basic fibroblast growth factor is dose dependent and is accompanied by morphological changes of the cells and by an increase in the expression of neuronal-related genes. These observations indicate that endogenous basic fibroblast growth factor participates in controlling olfactory self-renewal and suggest that this cytokine represents a key regulatory element of olfactory neurogenesis.

A new factor derived from 1321N1 human astrocytoma cells causes differentiation of PC-12 cells mediated through mitogen-activated protein kinase cascade

Glial cells play an important role in maintaining neural function. In the present study, we examined the effects of a factor derived from human astrocytoma cells (1321N1) on differentiation of rat pheochromocytoma cells (PC-12). The conditioned medium which had been used for culture of 1321N1 cells caused the differentiation of PC-12 cells, suggesting that 1321N1 cells release a neurotrophic factor. The factor was apparently distinct from well-known neurotrophic factors, such as nerve growth factor (NGF), since it was resistant to boiling and trypsin treatment. The molecular size of the factor was assumed to be below 1000 through dialysis and ultrafiltration experiments. Furthermore, PC-12 cells were differentiated synergistically by the combined addition of NGF and the conditioned medium of 1321N1 cells. Partially purified fraction of the factor by Sephadex G-15 gel filtration column caused the prolonged activation of mitogen-activated protein kinase (MAPK). The differentiation of PC-12 cells induced by the fraction or NGF disappeared after the treatment with PD98059, a specific inhibitor of MAPK kinase (MEK), suggesting the involvement of MAPK in the differentiation. These results suggest that the new low-molecular factor derived from glial cells causes differentiation of PC-12 cells mediated through an activation of MAPK.

Olfactory ensheathing glia: properties and function

The failure of regenerating axons to grow within the adult mammalian central nervous system (CNS) does not apply to the olfactory bulb (OB). In this structure, normal and transected olfactory axons are able to enter, regenerate, and reestablish lost synaptic contacts with their targets, throughout the lifetime of the organism. A remarkable difference between an axonal growth-permissive structure such as the OB and the remaining CNS resides in the presence of ensheathing glia in the former. These cells exhibit phenotypic and functional properties known to be involved in the process of axonal elongation that may explain the permissibility of the OB to axonal growth. In addition, transplants of ensheathing glia were successfully used to promote axonal regeneration within the injured adult CNS. The axonal growth-promoting properties of ensheathing glia make the study of this cell type interesting to provide an insight into the mechanisms underlying the process of axonal regeneration. Therefore, in this article we review the developmental, morphologic, immunocytochemical, and functional properties presented by this unique glial cell type, and correlate them with the axonal growth-promoting ability of ensheathing glia. In addition, we provide some evidence of the potentiality that ensheathing glia might have as a promoter of axonal regeneration within the injured nervous system.

Isolation of lineage-restricted neuronal precursors from multipotent neuroepithelial stem cells

We have identified a neuronal-restricted precursor (NRP) cell that expresses E-NCAM (high polysialic-acid NCAM) and is morphologically distinct from multipotent neuroepithelial (NEP) cells (Kalyani et al., 1997) and spinal glial progenitors (Rao and Mayer-Proschel, 1997). NRP cells self renew over multiple passages in the presence of fibroblast growth factor (FGF) and neurotrophin-3 (NT-3) and differentiate in the presence of retinoic acid and the absence of FGF into postmitotic neurons. NRP cells can also be generated from multipotent E10.5 NEP cells. Clonal analysis shows that NRP cells arise from a NEP progenitor that generates other restricted CNS precursors. The NEP-derived NRPs undergo self renewal and can differentiate into multiple neuronal phenotypes. Thus, a direct lineal relationship exists between multipotential NEP cells and more restricted neuronal precursor cells present in vivo at E13.5 in the spinal cord.

Monoclonal antibody marker for olfactory sustentacular cell microvilli

BACKGROUND

The olfactory epithelial sustentacular cells may support the survival and function of olfactory receptor neurons, but few reagents are available to mark and manipulate such cells.

METHODS

Novel nasal cell-specific monoclonal antibodies were generated using whole cultured rat olfactory mucosal cells as the antigenic stimuli. They were characterized by immunostaining at the light level in rat tissues and newborn rat olfactory cell cultures, and at the electron microscopic level in adult tissues using freeze-substitution, post-embedding staining.

RESULTS

An IgMkappa monoclonal antibody designated 1F4 selectively labeled apical surfaces of the rat olfactory and respiratory epithelia in tissue sections and what appeared to be sustentacular cells in olfactory cell cultures. Using electron microscopy, 1F4 bound selectively to the microvilli of sustentacular cells and ductal cells of Bowman's glands in the olfactory epithelium, and to the microvilli and cilia of ciliated but not secretory cells in the respiratory epithelium. No staining was detected in olfactory receptor neurons, basal cells, or two types of microvilli-bearing cells that differed from sustentacular cells. A contrasting antibody, 2H4, bound to granules of secretory respiratory cells. Developmental expression of 1F4 binding began at E17 and increased at and after E18/E19. Bulbectomy did not alter 1F4 immunoreactivity. Cell culture studies found that the 1F4 epitope was external and insensitive to trypsin treatment, and that both 1F4 and 2H4 positive cells required contact with aggregated cells for survival up to fifteen days in vitro.

CONCLUSIONS

The antibody 1F4 is a useful marker and potential manipulation reagent specific for sustentacular cells and their microvilli.

Neurons are generated in confluent astroglial cultures of rat neonatal neocortex

Cells of the telencephalon are generated in specific proliferative zones from which neuronal and glial precursors migrate to their destinations. Recent evidence indicates that some precursors do not turn into differentiated cells but keep their ability to proliferate. Here, we report that neurons can originate in primary cultures of astroglial cells prepared from neocortex of newborn rats. The first neuronal cells appeared shortly before confluence, when a glial monolayer was being formed. After confluence, these still undifferentiated cells increased in number. Later, they became immunohistochemically positive for the neuron-specific marker microtubule-associated protein 2a,b. They also contained neurofilament-L protein as well as the specific messenger RNA coding for neurofilament-H. The observation that they took up bromo-deoxyuridine indicated that they synthesized DNA, i.e. they proliferated. When Dulbecco's modified essential medium was substituted with fetal calf serum, the appearance of neurons depended on the seeding density of the dispersed cells. This was no longer the case, when the cultures were maintained in Dulbecco's modified essential medium/F12 medium to which transferrin, insulin and selenium chloride had been added. It is concluded that neuronal precursors can survive in primary astroglial cultures. After confluence of the astroglial cells the precursors proliferate if appropriate conditions are present. Our observation provides a new model for the investigation of cultured neurons and neuronal-glial interactions.

In vitro generation of adult rat olfactory sensory neurons and regulation of maturation by coculture with CNS tissues

Olfactory sensory neurons (OSNs) are continually generated throughout life. Although previous studies have examined neurogenesis in olfactory cell cultures derived from embryonic or newborn rodents, we demonstrate neurogenesis in cell cultures derived from adult rat tissues. Dissociated cells taken from adult rat nasal mucosal tissues (ANM cells) were plated onto a feeder layer of newborn rat cortical glia (astrocytes) in serum-free conditions. Immature OSNs (stained for neuron-specific tubulin, NST) increased in number between 1 and 5 d in vitro (DIV) and in mass thereafter. Mature OSN (stained for olfactory marker protein, OMP) numbers decreased between 1 and 5 DIV, then increased over 5 DIV values by 12 and 15 DIV. Pulse labeling with [3H]thymidine confirmed in vitro neurogenesis. To determine whether the target cells for OSNs, olfactory bulb (OB) neurons, provide trophic support, dissociated newborn rat OB cells were cocultured with ANM cells on glia. This resulted in greater numbers of OMP-positive (OMP+) neurons after 9 DIV than ANM-alone cultures. This neurotrophic effect was not OB specific. Addition of newborn rat cerebellar and embryonic rat ventral mesencephalic cells to ANM cells also increased OMP+ neurons, whereas addition of newborn rat cortical cells or controls (purified glia or fibroblasts) did not. Changes in numbers of dopaminergic neurons (stained for tyrosine hydroxylase), present in OB and VM cultures, did not correlate with OMP+ neuronal increases. Thus, cultures of adult rat OSNs demonstrate neurogenesis, and trophic/maturation support is variably provided by CNS neurons (and not glia).

Promotion of neurogenesis in mouse olfactory neuronal progenitor cells by leukemia inhibitory factor in vitro

Olfactory neuronal progenitor cells were partially purified from the olfactory epithelia of 14.5-day-old mouse embryos by an immuno-killing method with an antibody against neural adhesion molecule (N-CAM). Immunostaining study showed that about 60% of the population after immunokilling, was class-III beta-tubulin-/keratin-neuronal progenitor cells and that they differentiated into N-CAM+/class-III beta-tubulin+ neurons in a chemically-defined medium within 1 day in culture. A part of them proliferated prior to their neuronal differentiation as determined by the incorporation of bromodeoxyuridine (BrdU) into neuronal nuclei. Leukemia inhibitory factor (LIF), but not ciliary neurotrophic factor or interleukin-6, increased the proportion of the BrdU-labeled neurons in vitro. These results suggest LIF promotes the neurogenesis in the olfactory neuronal progenitor cells.