Mouse Olfactory Epithelium Research Articles

Constitutive and evoked release of ATP in adult mouse olfactory epithelium.

In adult olfactory epithelium (OE), ATP plays a role in constant cell turnover and post-injury neuroregeneration. We previously demonstrated that constitutive and ATP-evoked ATP release are present in neonatal mouse OE and underlie continuous cell turn-over and post-injury neuroregeneration, and that activation of purinergic P2X7 receptors is involved in the evoked release. We hypothesized that both releases are present in adult mouse OE. To study the putative contribution of olfactory sensory neurons to ATP release, we used olfactory sensory neuronal-like OP6 cells derived from the embryonic olfactory placode cells. Calcium imaging showed that OP6 cells and primary adult OE cell cultures express functional purinergic receptors. We monitored ATP release from OP6 cells and whole adult OE turbinates using HEK cells as biosensors and luciferin-luciferase assays. Constitutive ATP release occurs in OP6 cells and whole adult mouse OE turbinates, and P2X7 receptors mediated evoked ATP release occurs only in turbinates. The mechanisms of ATP release described in the present study might underlie the constant cell turn-over and post-injury neuroregeneration present in adult OE and thus, further studies of these mechanisms are warranted as it will improve our knowledge of OE tissue homeostasis and post-injury regeneration.

Outbreak of tauopathy in the olfactory system of PS19 mice: an early marker for Alzheimer’s disease diagnosis?

AbstractBackgroundClinical data indicate that impairment of olfactory function is an early indicator of neurodegenerative diseases, including Alzheimer’s disease (AD)(Attems et al., 2014). Our hypothesis is that typical AD lesions could appear in olfactory neurons from the olfactory epithelium (OE). The olfactory epithelium can be easily collected in human individuals (e.g., by nasal brushing), which provides an important tool to investigate the pathology in patients. Here, we address the question of the occurrence of tauopathy in the OE of transgenic mice and its correlation with pathology in the central nervous system (CNS). We use Tau P301S mice (PS19 mice), a tauopathy mouse model. These mice express human tau protein (1N4R) carrying the P301S mutation. They develop neurofibrillary tangle‐like inclusions in the cortex and hippocampus, leading to progressive neurodegeneration at eight months (Yoshiyama et al., 2007).MethodMouse samples were collected from heterozygous PS19 and wild‐type (WT) mice. Immunohistochemical staining (DAB) was used to demonstrate the presence of hyperphosphorylated human tau protein (hTau). We investigated regions of the olfactory system to correlate with data obtained in CNS regions (e.g., hippocampal formation, entorhinal cortex). Mouse heads decalcification was also implemented to preserve the olfactory epithelium structure. Western blots were performed to monitor tau levels and tau phosphorylation pattern.ResultThe hyperphosphorylated human tau protein (Ser202, Thr205) is only detected in PS19 mice sections while the endogenous murine tau protein is expressed both in WT and PS19 mice. The localization and expression of these proteins vary according to the region (OE or CNS subregions), the age (3, 6 or 9 months), and the genotype of the mice (WT or heterozygous PS19). It also seems that tau lesions may spread between brain regions that are directly connected, notably through the olfactory pathway.ConclusionIn PS19 mice, a pathological phosphorylation pattern peaked in the OE prior to vulnerable CNS regions or olfactory bulbs. We hypothesize that tau lesions appearing early in the OE may spread in the olfactory bulb and finally reach the entorhinal cortex and piriform cortex, highlighting the significance of the olfactory system investigation as an early diagnosis tool.

The Effects of the Levels of Hypoxia in the Olfactory Nervous System in Mouse Model.

Intermittent hypoxia (IH) results in low-grade inflammation, sympathetic overactivity, and oxidative stress. However, the specific effects of IH on olfaction have not yet been directly assessed and remain unclear. Therefore, the purpose of this study was to investigate the cytotoxic effects of IH exposure on the mouse olfactory epithelium and the relationship between the concentration of hypoxia and the degree of destruction of the olfactory system. Thirty mice were randomly divided into six groups: control (room air for 4weeks), recovery control (room air for 5weeks), IH 5% oxygen concentration, IH 7% oxygen concentration, recovery 5% hypoxia, and recovery 7% hypoxia groups. Mice in the two hypoxia groups were exposed to 5% and 7% oxygen for 4weeks. Mice in the two recovery groups were exposed to room air for 1week after 4weeks of hypoxia period. Based on, the olfactory marker protein (OMP), Olfr1507, ADCY3, and GNAL were lower, whereas S100b and NGFRAP1 messenger RNA (mRNA) levels were higher in the 5% hypoxia group than those in the control group in the olfactory neuroepithelium. In the brain tissue, the changes in RNA analysis for Olfr 1507, OMP, ADCY, and GNAL mRNA were not typical. However, NeuN and GFAP levels were decreased under 5% hypoxia in the brain tissue. In the recovery state, CNPase, S100b and NeuN levels were increased significantly in both the olfactory neuroepithelium and brain tissue in the 5% hypoxia group. The change in RNA activity in PCR was much higher in the 5% hypoxia group than in the 7% hypoxia group. Our findings suggest that IH damages the olfactory neuroepithelium and brain tissue in mouse model. The activity of olfactory marker genes and neurogenesis in the olfactory neuroepithelium were decreased. The levels of oxygen may be affect changes in the olfactory neuroepithelium. The olfactory ensheathing cell may be a major factor in the recovery of the olfactory neuroepithelium.

Diversity within olfactory sensory derivatives revealed by the contribution of Dbx1 lineages.

In vertebrates, the embryonic olfactory epithelium contains progenitors that will give rise to distinct classes of neurons, including olfactory sensory neurons (OSNs; involved in odor detection), vomeronasal sensory neurons (VSNs; responsible for pheromone sensing), and gonadotropin-releasing hormone (GnRH) neurons that control the hypothalamic-pituitary-gonadal axis. Currently, these three neuronal lineages are usually believed to emerge from uniform pools of progenitors. Here, we found that the homeodomain transcription factor Dbx1 is expressed by neurogenic progenitors in the developing and adult mouse olfactory epithelium. We demonstrate that Dbx1 itself is dispensable for neuronal fate specification and global organization of the olfactory sensory system. Using lineage tracing, we characterize the contribution of Dbx1 lineages to OSN, VSN, and GnRH neuron populations and reveal an unexpected degree of diversity. Furthermore, we demonstrate that Dbx1-expressing progenitors remain neurogenic in the absence of the proneural gene Ascl1. Our work therefore points to the existence of distinct neurogenic programs in Dbx1-derived and other olfactory lineages.

Expression patterns of prosaposin and its receptors, G protein-coupled receptor (GPR) 37 and GPR37L1, in the mouse olfactory organ

Prosaposin is a glycoprotein conserved widely in vertebrates, because it is a precursor for saposins that are required for normal lysosomal function and thus for autophagy, and acts as a neurotrophic factor. Most tetrapods possess two kinds of olfactory neuroepithelia, namely, the olfactory epithelium (OE) and the vomeronasal epithelium (VNE). This study examined the expression patterns of prosaposin and its candidate receptors, G protein-coupled receptor (GPR) 37 and GPR37L1, in mouse OE and VNE by immunofluorescence and in situ hybridization. Prosaposin immunoreactivity was observed in the olfactory receptor neurons, vomeronasal receptor neurons, Bowman’s gland (BG), and Jacobson’s gland (JG). Prosaposin expression was mainly observed in mature neurons. Prosaposin mRNA expression was observed not only in these cells but also in the apical region of the VNE. GPR37 and GPR37L1 immunoreactivities were found only in the BG and/or the JG. Prosaposin was suggested to secrete and facilitate the autophagic activities of the neurons and modulate the mucus secretion in mouse olfactory organ.

Effects of zinc deficiency on the regeneration of olfactory epithelium in mice.

The olfactory epithelium can regenerate after damage; however, the regeneration process is affected by various factors, such as viral infections, head trauma, and medications. Zinc is an essential trace element that has important roles in organ development, growth, and maturation. Zinc also helps regulate neurotransmission in the brain; nevertheless, its relationship with olfactory epithelium regeneration remains unclear. Therefore, we used a severe zinc deficiency mouse model to investigate the effects of zinc deficiency on olfactory epithelium regeneration. Male wild-type C57BL/6 mice were divided into zinc-deficient and control diet groups at the age of 4 weeks, and methimazole was administered at the age of 8 weeks to induce severe olfactory epithelium damage. We evaluated the olfactory epithelium before and 7, 14, and 28 d after methimazole administration by histologically analyzing paraffin sections. RNA sequencing was also performed at the age of 8 weeks before methimazole administration to examine changes in gene expression caused by zinc deficiency. In the zinc-deficient group, the regenerated olfactory epithelium thickness was decreased at all time points, and the numbers of Ki-67-positive, GAP43-positive, and olfactory marker protein-positive cells (i.e., proliferating cells, immature olfactory neurons, and mature olfactory neurons, respectively) failed to increase at some time points. Additionally, RNA sequencing revealed several changes in gene expression, such as a decrease in the expression of extracellular matrix-related genes and an increase in that of inflammatory response-related genes, in the zinc-deficient group. Therefore, zinc deficiency delays olfactory epithelium regeneration after damage in mice.

Rapid presynaptic maturation in naturally regenerating axons of the adult mouse olfactory nerve.

Successful neuronal regeneration requires the reestablishment of synaptic connectivity. This process requires the reconstitution of presynaptic neurotransmitter release, which we investigate here in a model of entirely natural regeneration. After toxin-induced injury, olfactory sensory neurons in the adult mouse olfactory epithelium can regenerate fully, sending axons via the olfactory nerve to reestablish synaptic contact with postsynaptic partners in the olfactory bulb. Using electrophysiological recordings in acute slices, we find that, after initial recontact, functional connectivity in this system is rapidly established. Reconnecting presynaptic terminals have almost mature functional properties, including high release probability and strong capacity for presynaptic inhibition. Release probability then matures quickly, rendering reestablished terminals functionally indistinguishable from controls just 1week after initial contact. These data show that successful synaptic regeneration in the adult mammalian brain is almost a "plug-and-play" process, with presynaptic terminals undergoing a rapid phase of functional maturation as they reintegrate into target networks.

Chronic intermittent hypoxia impacts the olfactory nervous system in an age-dependent manner: pilot study.

Obstructive sleep apnea (OSA) is characterized by repetitive upper airway collapse during sleep, which induces chronic intermittent hypoxia (CIH). CIH results in low-grade inflammation, sympathetic overactivity, and oxidative stress. Nevertheless, it remains unclear how exposure to CIH affects olfaction. The purpose of this study was, therefore, to investigate the cytotoxic effects of CIH exposure on mouse olfactory epithelium and the underlying pathophysiology involved. Mice were randomly divided into four groups: Youth mouse (You) + room air (RA), You + intermittent hypoxia (IH), Elderly mouse (Eld) + RA, and Eld + IH (n = 6 mice/group). Mice in the two hypoxia groups were exposed to CIH. The control condition involved exposure to room air (RA) for 4weeks. Olfactory neuroepithelium was harvested for histologic examination, gene ontology analysis, quantitative real-time polymerase chain reaction (qRT-PCR), and western blotting. Based on qRT-PCR analysis, olfactory marker protein (OMP), Olfr1507, ADCY3, and GNAL mRNA levels were lower, whereas NGFR, CNPase, NGFRAP1, NeuN, and MAP-2 mRNA levels were higher in the You + IH group than in the You + RA group. Olfactory receptor-regulated genes, neurogenesis-related genes and immunohistochemical results were altered in nasal neuroepithelium under CIH exposure. Based on genetic and cytologic analysis, CIH impacted the olfactory neuroepithelium in an age-dependent manner. Our findings suggest that CIH-induced damage to the olfactory neuroepithelium may induce more severe change in the youth than in the elderly.

Lifespan of mature olfactory sensory neurons varies with location in the mouse olfactory epithelium and age of the animal.

The olfactory sensory neurons (OSNs) of the olfactory epithelium (OE) exhibit a remarkable regenerative capability, which protects the population against environmental insult and enables adjustment to new odors. The lifespan of OSNs is still open to question, with estimates ranging from 1 month to at least 1 year. However, the estimates come with some caveats, including low labeling efficiency and a focus solely on newborn neurons. We revisited the issue via the use of OMP-tTA; TetO-Cre; Rosa26-fl(stop)-Tdtomato (OMP-tTA;TdT) mice, which allowed us to selectively label ∼95% of the OMP(+) OSN population that reach maturity by a given time and, by switching to doxycycline chow, to "chase" this preexisting OSN population. Two loading protocols were used: conception to 2 months old and conception to 4.5 months old. Surviving OSNs were common up to 6 months chase time in both groups, but more neurons survived when loading for 4.5 months as compared with 2 months. A spatial difference was evident: higher percentages of OSNs survived in the dorsomedial OE as compared with ventrolateral and in posterior versus anterior OE regions. Finally, proliferation rates anticorrelated with the spatial differences in OSN survival; higher proliferation rates were observed ventrally. Together, these results demonstrate spatial and temporal differences in OSN survival, highlighting it as a dynamic system that can be studied for factors affecting neuronal survival.

Long-range migration of centrioles to the apical surface of the olfactory epithelium.

Olfactory sensory neurons (OSNs) in vertebrates detect odorants using multiple cilia, which protrude from the end of the dendrite and require centrioles for their formation. In mouse olfactory epithelium, the centrioles originate in progenitor cells near the basal lamina, often 50-100 μm from the apical surface. It is unknown how centrioles traverse this distance or mature to form cilia. Using high-resolution expansion microscopy, we found that centrioles migrate together, with multiple centrioles per group and multiple groups per OSN, during dendrite outgrowth. Centrioles were found by live imaging to migrate slowly, with a maximum rate of 0.18 µm/minute. Centrioles in migrating groups were associated with microtubule nucleation factors, but acquired rootletin and appendages only in mature OSNs. The parental centriole had preexisting appendages, formed a single cilium before other centrioles, and retained its unique appendage configuration in the mature OSN. We developed an air-liquid interface explant culture system for OSNs and used it to show that centriole migration can be perturbed ex vivo by stabilizing microtubules. We consider these results in the context of a comprehensive model for centriole formation, migration, and maturation in this important sensory cell type.

Human APOE ɛ3 and APOE ɛ4 Alleles Have Differential Effects on Mouse Olfactory Epithelium.

Alzheimer's disease (AD) is a progressive age-dependent disorder whose risk is affected by genetic factors. Better models for investigating early effects of risk factors such as apolipoprotein E (APOE) genotype are needed. To determine whether APOE genotype produces neuropathologies in an AD-susceptible neural system, we compared effects of human APOE ɛ3 (E3) and APOE ɛ4 (E4) alleles on the mouse olfactory epithelium. RNA-Seq using the STAR aligner and DESeq2, immunohistochemistry for activated caspase-3 and phosphorylated histone H3, glucose uptake after oral gavage of 2-[1,2-3H (N)]-deoxy-D-glucose, and Seahorse Mito Stress tests on dissociated olfactory mucosal cells. E3 and E4 olfactory mucosae show 121 differentially abundant mRNAs at age 6 months. These do not indicate differences in cell type proportions, but effects on 17 odorant receptor mRNAs suggest small differences in tissue development. Ten oxidoreductases mRNAs important for cellular metabolism and mitochondria are less abundant in E4 olfactory mucosae but this does not translate into differences in cellular respiration. E4 olfactory mucosae show lower glucose uptake, characteristic of AD susceptibility and consistent with greater expression of the glucose-sensitive gene, Asns. Olfactory sensory neuron apoptosis is unaffected at age 6 months but is greater in E4 mice at 10 months. Effects of human APOE alleles on mouse olfactory epithelium phenotype are apparent in early adulthood, and neuronal loss begins to increase by middle age (10 months). The olfactory epithelium is an appropriate model for the ability of human APOE alleles to modulate age-dependent effects associated with the progression of AD.

Involvement of aldehyde oxidase in the metabolism of aromatic and aliphatic aldehyde-odorants in the mouse olfactory epithelium

Xenobiotic-metabolizing enzymes (XMEs) expressed in the olfactory epithelium (OE) are known to metabolize odorants. Aldehyde oxidase (AOX) recognizes a wide range of substrates among which are substrates with aldehyde groups. Some of these AOX substrates are odorants, such as benzaldehyde and n-octanal. One of the mouse AOX isoforms, namely AOX2 (mAOX2), was shown to be specifically expressed in mouse OE but its role to metabolize odorants in this tissue remains unexplored. In this study, we investigated the involvement of mouse AOX isoforms in the oxidative metabolism of aldehyde-odorants in the OE. Mouse OE extracts effectively metabolized aromatic and aliphatic aldehyde-odorants. Gene expression analysis revealed that not only mAOX2 but also the mAOX3 isoform is expressed in the OE. Furthermore, evaluation of inhibitory effects using the purified recombinant enzymes led us to identify specific inhibitors of each isoform, namely chlorpromazine, 17β-estradiol, menadione, norharmane, and raloxifene. Using these specific inhibitors, we defined the contribution of mAOX2 and mAOX3 to the metabolism of aldehyde-odorants in the mouse OE. Taken together, these findings demonstrate that mAOX2 and mAOX3 are responsible for the oxidation of aromatic and aliphatic aldehyde-odorants in the mouse OE, implying their involvement in odor perception.

Spatiotemporal expression of IgLON family members in the developing mouse nervous system

Differential expression of cell adhesion molecules in neuronal populations is one of the many mechanisms promoting the formation of functional neural circuits in the developing nervous system. The IgLON family consists of five cell surface immunoglobulin proteins that have been associated with various developmental disorders, such as autism spectrum disorder, schizophrenia, and major depressive disorder. However, there is still limited and fragmented information about their patterns of expression in certain regions of the developing nervous system and how their expression contributes to their function. Utilizing an in situ hybridization approach, we have analyzed the spatiotemporal expression of all IgLON family members in the developing mouse brain, spinal cord, eye, olfactory epithelium, and vomeronasal organ. At one prenatal (E16) and two postnatal (P0 and P15) ages, we show that each IgLON displays distinct expression patterns in the olfactory system, cerebral cortex, midbrain, cerebellum, spinal cord, and eye, indicating that they likely contribute to the wiring of specific neuronal circuitry. These analyses will inform future functional studies aimed at identifying additional roles for these proteins in nervous system development.

Effects of Urban Particulate Matter on the Olfactory System in a Mouse Model.

Exposure to urban particulate matter (UPM) is linked to the aggravation of various health problems. Although the nasal cavity is the first barrier to encounter UPM, there is a lack of studies on the impact of UPM on the olfactory area. The purpose of this study was to investigate the cytotoxic effects of UPM on mouse olfactory epithelium, the underlying pathophysiology involved, and changes in cytokine levels. Mice were divided into 4 groups: control, 400UPM (administered 400 µg UPM daily; standard reference material 1649b; average particle diameter 10.5 μm) 1week, 400UPM 2weeks, and recovery 1week after 400UPM 2weeks (n = 10, 6, 6, and 6, respectively). Olfactory function was evaluated by conducting a food-finding test once a week. The olfactory neuroepithelium was harvested for histologic examination, gene ontology, quantitative real-time polymerase chain reaction, and western blotting. Compared to those in the control group, olfactory marker protein, olfactory receptor 1507, adenylyl cyclase 3, and GNAL mRNA levels were lower and S-100, 2',3'-cyclic nucleotide 30-phosphodiesterase, nerve growth factor receptor-associated protein, brain-derived neurotrophic factor, and tachykinin receptor mRNA levels were higher in the 400UPM group olfactory neuroepithelium. There were no significant differences in neuroepithelial inflammatory marker levels between the 400UPM and saline group. UPM decreased olfactory function and might have cytotoxic effects on the olfactory epithelium. Olfactory ensheathing cells and trigeminal nerve might be related to the regeneration of the olfactory epithelium after olfactory destruction associated with UPM.

Insulin-Dependent Maturation of Newly Generated Olfactory Sensory Neurons after Injury.

Loss of olfactory sensory neurons (OSNs) after injury to the olfactory epithelium (OE) triggers the generation of OSNs that are incorporated into olfactory circuits to restore olfactory sensory perception. This study addresses how insulin receptor-mediated signaling affects the functional recovery of OSNs after OE injury. Insulin levels were reduced in mice by ablating the pancreatic β cells via streptozotocin (STZ) injections. These STZ-induced diabetic and control mice were then intraperitoneally injected with the olfactotoxic drug methimazole to selectively ablate OSNs. The OE of diabetic and control mice regenerated similarly until day 14 after injury. Thereafter, the OE of diabetic mice contained fewer mature and more apoptotic OSNs than control mice. Functionally, diabetic mice showed reduced electro-olfactogram (EOG) responses and their olfactory bulbs (OBs) had fewer c-Fos-active cells following odor stimulation, as well as performed worse in an odor-guided task compared with control mice. Insulin administered intranasally during days 8-13 after injury was sufficient to rescue recovery of OSNs in diabetic mice compared with control levels, while insulin administration between days 1 and 6 did not. During this critical time window on days 8-13 after injury, insulin receptors are highly expressed and intranasal application of an insulin receptor antagonist inhibits regeneration. Furthermore, an insulin-enriched environment could facilitate regeneration even in non-diabetic mice. These results indicate that insulin facilitates the regeneration of OSNs after injury and suggest a critical stage during recovery (8-13 d after injury) during which the maturation of newly generated OSNs is highly dependent on and promoted by insulin.

In vivo Optical Access to Olfactory Sensory Neuronsin the Mouse Olfactory Epithelium.

In neuroscience, it is fundamental to understand how sensory stimuli are translated into neural activity at the entry point of sensory systems. In the olfactory system, odorants inhaled into the nasal cavity are detected by ~1,000 types of odorant receptors (ORs) that are expressed by olfactory sensory neurons (OSNs). Since each OSN expresses only one type of odorant receptor, the odor-evoked responses reflect the interaction between odorants and the expressed OR. The responses of OSN somata are often measured by calcium imaging and electrophysiological techniques; however, previous techniques require tissue dissection or cell dissociation, rendering it difficult to investigate physiological responses. Here, we describe a protocol that allows us to observe odor-evoked responses of individual OSN somata in the mouse olfactory epithelium in vivo. Two-photon excitation through the thinned skull enables highly-sensitive calcium imaging using a genetically encoded calcium indicator, GCaMP. Recording of odor-evoked responses in OSN somata in freely breathing mice will be fundamental to understanding how odor information is processed at the periphery and higher circuits in the brain.

Single or Repeated Ablation of Mouse Olfactory Epithelium by Methimazole

Odor-detecting olfactory sensory neurons residing in the nasal olfactory epithelium (OE) are the only neurons in direct contact with the external environment. As a result, these neurons are subjected to chemical, physical, and infectious insults, which may be the underlying reason why neurogenesis occurs in the OE of adult mammals. This feature makes the OE a useful model for studying neurogenesis and neuronal differentiation, with the possibility for systemic as well as local administration of various compounds and infectious agents that may interfere with these cellular processes. Several different chemical compounds have been shown to cause toxic injury to the OE, which can be used for OE ablation. We, and others, have found that the systemic administration of the hyperthyroid drug, methimazole, reliably causes olfactotoxicity as a side effect. Here, we outline an OE lesioning protocol for single or repeated ablation by methimazole. A single methimazole administration can be used to study neuroepithelial regeneration and stem cell activation, while repeated ablation and regeneration of OE enable the study of tissue stem cell exhaustion and generation of tissue metaplasia.

Age-Dependent Activation and Neuronal Differentiation of Lgr5+ Basal Cells in Injured Olfactory Epithelium via Notch Signaling Pathway.

Aging is an important factor affecting function of smell, leading to the degeneration of mature olfactory sensory neurons and inducing the occurrence of smell loss. The mammalian olfactory epithelium (OE) can regenerate when subjected to chemical assaults. However, this capacity is not limitless. Inactivation of globose basal cells and failure to generate sensory neurons are the main obstacles to prevent the OE regeneration. Here, we found the significant attenuation in mature sensory neuronal generation and apparent transcriptional alternation in the OE from aged mice compared with young ones. The recruitment of leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5)-positive cells in injured OE was weakened in aged mice, and more Lgr5+ cells remained quiescence in aged OE postinjury. Lineage-traced progenies from Lgr5+ cells were significantly fewer in the OE with aging. Moreover, Notch activation enhanced the neuronal regeneration in aged OE, making the regenerative capacity of aged OE comparable with that of young animals after injury. The growth and morphology of three-dimensional (3D)-cultured organoids from the OE of young and aged mice varied and was modulated by small molecules regulating the Notch signaling pathway. Thus, we concluded that activation of Lgr5+ cells in injured OE was age dependent and Notch activation could enhance the capacity of neuronal generation from Lgr5+ cells in aged OE after injury.

Endogenous zinc nanoparticles in the rat olfactory epithelium are functionally significant

The role of zinc in neurobiology is rapidly expanding. Zinc is especially essential in olfactory neurobiology. Naturally occurring zinc nanoparticles were detected in olfactory and nasal respiratory epithelia and cilia in animals. The addition of these nanoparticles to a mixture of odorants, including ethyl butyrate, eugenol, and carvone, considerably increased the electrical responses of the olfactory sensory receptors. Studies of these nanoparticles by ransmission electron microscopy (TEM) and selected area electron diffraction revealed metal elemental crystalline zinc nanoparticles 2–4 nm in diameter. These particles did not contain oxidized zinc. The enhancement of the odorant responses induced by the endogenous zinc nanoparticles appears to be similar to the amplification produced by engineered zinc nanoparticles. Zinc nanoparticles produce no odor response but increase odor response if mixed with an odorant. These effects are dose-dependent and reversible. Some other metal nanoparticles, such as copper, silver, gold, and platinum, do not have the effects observed in the case of zinc nanoparticles. The olfactory enhancement was observed in young and mature mouse olfactory epithelium cultures, in the dissected olfactory epithelium of rodents, and in live conscious dogs. The physiological significance of the detected endogenous metal nanoparticles in an animal tissue has been demonstrated for the first time. Overall, our results may advance the understanding of the initial events in olfaction.

Inhibition of focal adhesion kinase increases adult olfactory stem cell self-renewal and neuroregeneration through ciliary neurotrophic factor.

Constant neuroregeneration in adult olfactory epithelium maintains olfactory function by basal stem cell proliferation and differentiation to replace lost olfactory sensory neurons (OSNs). Understanding the mechanisms regulating this process could reveal potential therapeutic targets for stimulating adult olfactory neurogenesis under pathological conditions and aging. Ciliary neurotrophic factor (CNTF) in astrocytes promotes forebrain neurogenesis but its function in the olfactory system is unknown. Here, we show in mouse olfactory epithelium that CNTF is expressed in horizontal basal cells, olfactory ensheathing cells (OECs) and a small subpopulation of OSNs. CNTF receptor alpha was expressed in Mash1-positive globose basal cells (GBCs) and OECs. Thus, CNTF may affect GBCs in a paracrine manner. CNTF−/− mice did not display altered GBC proliferation or olfactory function, suggesting that CNTF is not involved in basal olfactory renewal or that they developed compensatory mechanisms. Therefore, we tested the effect of increased CNTF in wild type mice. Intranasal instillation of a focal adhesion kinase (FAK) inhibitor, FAK14, upregulated CNTF expression. FAK14 also promoted GBC proliferation, neuronal differentiation and basal stem cell self-renewal but had no effective in CNTF−/− mice, suggesting that FAK inhibition promotes olfactory neuroregeneration through CNTF, making them potential targets to treat sensorineural anosmia due to OSN loss.