Foxg1 regulates the development of microvillous cells in the olfactory epithelium.

Late prenatal development of the olfactory and vomeronasal systems in a wild rodent: The fossorial water vole.

Although SARS-CoV-2, the virus that causes COVID-19 has been responsible for pneumonia, recent studies indicate that it also affects the kidneys, heart, and brain, among other vital organs. Evidence suggests that this virus may travel retrogradely from the olfactory epithelium to brain stem sections, causing neurological impairments in a significant number of individuals. Individuals with severe COVID-19 frequently have elevated cytokines that promote inflammation and acute respiratory failure and require frequent supportive ventilation. These factors are believed to contribute to cognitive deterioration. Severe neurological outcomes in COVID-19 patients include- paralysis, stroke, cranial nerve deficits, delirium, encephalopathy, seizures, and meningitis. The virus, with its unique structure, and a high binding affinity for the human enzyme ACE2 (used as an entry point by the virus), contributes significantly to its deadly nature. Furthermore, to address the outbreak effectively, researchers worldwide must develop precise treatment strategies. Advancing new diagnostic and treatment methods to mitigate the long-term effects of COVID-19 on cognition requires further epidemiological research and clinical experience. Additionally, by understanding the virus's impact on cognitive functions, healthcare professionals can develop targeted treatments to alleviate these severe neurological consequences.

Amoebic infections of the brain can cause brain abscesses and meningoencephalitis. Brain abscess is a rare form of extraintestinal amoebiasis caused by hematogenous spread from intestinal infection with Entamoeba histolytica, which occurs through oral intake of contaminated water and food or fecal-oral transmission. It is mostly associated with amoebic liver abscesses and can be effectively treated with metronidazole. Meningoencephalitis caused by pathogenic free-living amoebae is extremely rare. Primary amoebic meningoencephalitis (PAM), caused by Naegleria fowleri infection of the olfactory epithelium with direct intracranial spread via the fila olfactoriae, primarily affects healthy young individuals through exposure to freshwater or brackish water in swimming pools, rivers, ponds, lakes, and estuaries. Granulomatous amoebic meningoencephalitis (GAM) results from the hematogenous spread of extracranial infectious foci caused by Acanthamoeba species or Balamuthia mandrillaris. Acanthamoeba-related GAM is more common in immunocompromised individuals, and waterborne transmission is relatively frequent. Balamuthia mandrillaris-related GAM can affect both immunocompromised and immunocompetent individuals, often affecting people in their 50s to 70s with underlying conditions, such as malignancies, diabetes, and chronic kidney disease, with soil-borne transmission being more common. Both PAM and GAM have high mortality rates, and effective treatments are yet to be established.

A spatial code governs olfactory receptor choice and aligns sensory maps in the nose and brain

Spatial Organization and Detection of Social Odors in Mouse Primary Olfactory System

The human nasal region arises from neural crest and placodal lineages, yet its early development remains poorly understood owing to limited fetal tissue access and structural complexity. Here we present an integrated single-nucleus and spatial transcriptomic atlas of the human fetal nasal region, generated from male and female fetuses between 7 and 12 post-conceptional weeks. Single-nucleus RNA sequencing [snRNA-seq] resolved 32 distinct cell types, while integration with multiplexed error-robust fluorescence in situ hybridization (MERFISH) enabled spatial and temporal mapping of gene expression dynamics across the olfactory epithelium (OE) and adjacent tissues. We identify markers of olfactory sensory neuron differentiation and pathways governing epithelial patterning and OE morphogenesis. Notably, spatially resolved snRNA-seq profiles of 169 olfactory receptor genes reveal molecular support for the "one neuron-one receptor" principle already in the first trimester. Together, this work establishes a molecular and spatial framework of early human olfactory development and provides a resource for studies of sensory neurogenesis and congenital disorders.

Headache disorders, specifically migraine headaches, are highly debilitating neurological disorders, with the potential to incapacitate an individual for several hours. Cannabinoid receptors are present in both peripheral and central nervous tissue, which serve as a potential target for the treatment of migraine. Cannabis sativa is a medicinal plant that has been used as self-medication for the treatment of headaches, but insufficient scientific information is currently available regarding their interactions with receptors, as well as intranasal delivery. The intranasal route of administration offers the potential for systemic delivery, as well as delivery into the brain. Nose-to-brain delivery offers a pathway directly to the brain via olfactory epithelium and trigeminal nerves and bypasses both the first-pass metabolism and the blood-brain-barrier (BBB). Known phytochemicals of C. sativa were docked in silico into the active site of the 6KPC crystal structure of the cannabinoid type 2 (CB2) receptor to screen for receptor affinity. Ex vivo permeation studies were done on these four selected cannabinoid compounds across excised sheep nasal epithelial tissue. Four cannabinoid compounds were identified with affinity for the CB2 receptor that may provide activity against migraine, namely cannabicyclol, cannabidiolic acid, cannabicitran and cannabielsoin. The ex vivo membrane permeation results revealed that some of the cannabinoids can be delivered to a similar extent than moderately permeable model drugs across nasal epithelium for systemic delivery and potentially also for direct nose-to-brain delivery. Through affinity for the CB2 receptor, the identified compounds have shown potential in migraine treatment. There is also potential for nose-to-brain delivery.

The main olfactory epithelium initiates the process of odor encoding. Recent studies have demonstrated intergenerationally inherited changes in the olfactory system in response to fear conditioning, resulting in increases in olfactory sensory neuron frequencies and altered responses to odors. We investigated changes in the cellular composition of the olfactory epithelium in response to an aversive stimulus. Here, we achieve volumetric cellular resolution to demonstrate that olfactory fear conditioning increases the number of odor-encoding neurons in mice that experience odor-shock conditioning (F0), as well as their unconditioned offspring (F1). We demonstrate that the increase in F0 is due, in part, to the biasing of the stem cell layer of the main olfactory epithelium. A detailed analysis of F1 behavior revealed subtle odor-specific differences between the offspring of unconditioned and conditioned parents, despite the absence of an active aversion to the conditioned odor. Thus, we reveal intergenerational regulation of olfactory epithelium composition in response to olfactory fear conditioning, providing insight into the heritability of acquired phenotypes.

The main olfactory epithelium initiates the process of odor encoding. Recent studies have demonstrated intergenerationally inherited changes in the olfactory system in response to fear conditioning, resulting in increases in olfactory sensory neuron frequencies and altered responses to odors. We investigated changes in the cellular composition of the olfactory epithelium in response to an aversive stimulus. Here, we achieve volumetric cellular resolution to demonstrate that olfactory fear conditioning increases the number of odor-encoding neurons in mice that experience odor-shock conditioning (F0), as well as their unconditioned offspring (F1). We demonstrate that the increase in F0 is due, in part, to the biasing of the stem cell layer of the main olfactory epithelium. A detailed analysis of F1 behavior revealed subtle odor-specific differences between the offspring of unconditioned and conditioned parents, despite the absence of an active aversion to the conditioned odor. Thus, we reveal intergenerational regulation of olfactory epithelium composition in response to olfactory fear conditioning, providing insight into the heritability of acquired phenotypes.

The main olfactory epithelium initiates the process of odor encoding. Recent studies have demonstrated intergenerationally inherited changes in the olfactory system in response to fear conditioning, resulting in increases in olfactory sensory neuron frequencies and altered responses to odors. We investigated changes in the cellular composition of the olfactory epithelium in response to an aversive stimulus. Here, we achieve volumetric cellular resolution to demonstrate that olfactory fear conditioning increases the number of odor-encoding neurons in mice that experience odor-shock conditioning (F0), as well as their unconditioned offspring (F1). We demonstrate that the increase in F0 is due, in part, to the biasing of the stem cell layer of the main olfactory epithelium. A detailed analysis of F1 behavior revealed subtle odor-specific differences between the offspring of unconditioned and conditioned parents, despite the absence of an active aversion to the conditioned odor. Thus, we reveal intergenerational regulation of olfactory epithelium composition in response to olfactory fear conditioning, providing insight into the heritability of acquired phenotypes.

Exposure to kerosene and diesel, which are environmental contaminants, is mainly via inhalation. Adverse effects of kerosene and diesel on parts of the respiratory system have been reported. There is, however, limited data on their effects on the olfactory epithelium. This study aimed to determine and compare the effect of short-term inhalation of kerosene and diesel on the olfactory epithelium of Wistar rats. Fifteen (15) Wistar rats weighing 120-150g were divided into three (3) groups (n=5). Group 1 (control) was not exposed. Groups 2 and 3 were placed in different inhalation chambers with a beaker containing 500mls of kerosene (group 2) and 500 mls of diesel (group 3). Groups 2 and 3 were exposed for 1hour daily for 21 days. Histopathological examination of the olfactory epithelium was conducted and blood samples were analyzed to determine the levels of SOD, MDA, and CAT. Thinning of the olfactory epithelium in group 2 and loss of the olfactory epithelial lining in group 3 was observed after exposure. A decrease in SOD (p>0.05) was observed in group 2 (0.39±0.04) and group 3 (0.31±0.06), while an increase in MDA (p>0.05) was observed in group 2 (0.58±0.26) and group 3 (0.67±0.44). A decrease in CAT (p>0.05) was observed in group 2 (2.87±0.49) and group 3 (2.50±0.16) after exposure. Short-term exposure to kerosene and diesel adversely affects the structure of the olfactory epithelium in Wistar rats.

Olfactory neuroblastoma (ONB) is a rare malignant tumor originating from the nasal olfactory sensory epithelium. It accounts for 3%-5% of all sinonasal malignancies. We evaluated patients with ONB who underwent en bloc resection using an endoscopic endonasal transcribriform approach. This study included 65 patients. The median follow-up period was 30.6 months. The 2- and 5-year overall survival (OS) rates were both 96.7%, the 2- and 5-year disease-specific survival (DSS) rates were both 98.3%, and the 2- and 5-year disease-free survival (DFS) rates were 81.7% and 59.1%, respectively. OS and DFS of en bloc resection were comparable to those reported in previous studies, with minimal operation-related complications. Recurrence can occur even in patients with low Kadish and Hyams grades, making it unclear which patients would benefit most from postoperative radiation therapy.

The olfactory system plays a crucial role in mediating fish behaviour, including reproduction. Senegalese sole (Solea senegalensis) is an important aquaculture flatfish species in Europe, in which reproductive dysfunction in captive males has been linked to potential alterations in chemical communication. Despite the expanded repertoire of olfactory receptor genes described for this species, detailed information on the cellular organization of its olfactory organs remains limited. This study provides a comprehensive histological, immunohistochemical, lectin-histochemical, and ultrastructural characterization of the olfactory rosettes of S. senegalensis across multiple life stages, including premetamorphic larvae, fry, juveniles and adults. Although the olfactory organs undergo substantial structural changes following metamorphosis, differentiated and functionally active olfactory sensory neurons (OSNs) are already present in premetamorphic larvae. Subsequently, two epithelial regions were distinguished along the olfactory lamellae: a sensory epithelium containing abundant OSNs and supporting cells, and a nonsensory epithelium dominated by goblet and other secretory cells. Ciliated and microvillous OSNs were distinguished from 60 dph onward based on morphological and ultrastructural features and supported by immunoreactivity with CR, CB, Gγ8 and PGP. Crypt cells showed immunolabelling with S100, NSE and CYK8. Furthermore, lectin histochemistry revealed ontogenetic changes in epithelial glycoconjugates, with early diffuse binding patterns evolving into stratified and region-specific distributions. Overall, these results demonstrate the structural and functional complexity of the olfactory epithelium in S. senegalensis, significantly enriching the limited available morphological and neurochemical information on the species.

The human olfactory epithelium possesses remarkable neurogenic capacity, sustained by a resident population of basal stem cells; however, establishing a dynamic in vitro model that faithfully recapitulates this regenerative process has been proven challenging. Here, we present an established protocol for generating olfactory organoids from progenitor cells isolated from adult human superior turbinate tissue. These organoids maintain stemness, as evidenced by SOX2 expression, and display a spatially organized differentiation pattern, characterized by uniform expression of the immature neuronal marker GAP43 and peripheral localization of the mature olfactory sensory neuron marker OMP. Subsequent targeted differentiation with the Notch inhibitor LY411575, the Wnt activator CHIR-99021, and retinoic acid generated marker-positive olfactory sensory neuron-like cells that co-expressed OMP and the neuronal marker Tuj1 (class III β-tubulin). This human-derived model circumvents the limitations of murine systems and provides a robust in vitro platform for studying olfactory neurogenesis, COVID-19-associated anosmia, and other olfactory-related neurodegenerative disorders.

Background Reliable access to the olfactory epithelium is important for clinical and translational research; however, data on bilateral biopsy performed in an outpatient setting are limited. Objectives To evaluate the feasibility and procedural outcomes of endoscopy-guided bilateral olfactory epithelium biopsy performed under local anaesthesia in an outpatient setting following controlled exposure sessions. Methods Healthy adults participated in a randomized, double-blind, crossover exposure study. Endoscopy-guided biopsies were obtained in an outpatient setting. Primary outcomes included bilateral biopsy success, tolerability, adverse events, and nucleic acid yield. Results Twenty-nine subjects were enrolled; 26 completed the study. Bilateral biopsies were obtained more frequently after implementation of pre-endoscopic screening than without screening (75.0% vs 30.0%; odds ratio 7.0, 95% CI 1.20–40.83). No serious procedural complications were observed. One self-limiting episode of delayed epistaxis. No participant reported postoperative olfactory dysfunction. All samples yielded RNA and DNA of sufficient quantity and purity for downstream analyses. Conclusion Endoscopy-guided bilateral olfactory epithelium biopsy appears feasible in a carefully screened outpatient cohort. Pre-endoscopic anatomical assessment was associated with improved procedural success. Although objective olfactory testing was not performed, and subtle functional changes cannot be excluded, this technique provides a reproducible methodological framework for future studies involving the olfactory cleft.

The sense of smell is maintained by regenerating olfactory sensory neurons (OSNs) from basal stem cells in the olfactory epithelium (OE). Acute inflammation destroys OSNs, causing hyposmia and anosmia, but activates basal cells. Manipulation of signaling pathways to promote basal cell proliferation and neuroregeneration would reveal novel therapeutic targets for smell deficits. We found that ciliary neurotrophic factor (CNTF) from horizontal basal cells (HBCs, quiescent stem cells) promotes neuroregeneration and functional recovery following methimazole-induced acute injury. Moreover, inhibition of focal adhesion kinase (FAK) upregulates CNTF in naïve OE. Here, we show that the small molecule FAK inhibitor increased CNTF expression in cultured primary HBCs isolated from methimazole-treated mice. Although methimazole-induced CNTF did not seem to be through FAK signaling, inducible cre-lox knockout of FAK in HBCs in mice further increased CNTF expression, as well as Mash1, a marker for globose basal cells (GBCs, neuronal progenitors), and GBC proliferation. Moreover, intranasal aspiration, but not systemic treatment, of a water-soluble pharmacological FAK inhibitor (FAK14) 3 days following methimazole, dose-dependently increased CNTF and Mash1 expression, and GBC proliferation. Intranasal FAK14 also enhanced methimazole-induced regeneration of new OSNs in CNTF+/+, but not in CNTF-/-, mice, demonstrating that FAK14 boosts neuroregeneration through additional CNTF following acute inflammation. Finally, intranasal FAK14 instillation following methimazole improved the functional recovery of smell. This study identifies the therapeutic potential of intranasal application of FAK inhibitors to enhance olfactory neuroregeneration and function following injury.

The nasal epithelium is a complex tissue composed of both respiratory and olfactory tissue, and is constantly exposed to environmental insults, including toxins and pathogens. The main olfactory epithelium (MOE) serves as the critical site for olfaction, or sense of smell. Dysfunction at this critical barrier tissue can result in partial or total loss of olfactory function, resulting in significant impact to quality of life. The MOE is heterogeneous, comprised of many cell types including olfactory sensory neurons, support cells, and immune cells. It is not well understood how these diverse cell types in the MOE interact to regulate this tissue during homeostasis, and during times of injury and inflammation. We investigated how environmental olfactory exposures impact cell type specific transcriptional responses in the mouse MOE. We performed single-cell RNA sequencing (scRNA-seq) of the MOE following controlled environmental exposure to both well-known odorants and allergens. We identified major cell types and subtypes within the MOE, and identified transcriptional changes in response to the olfactory exposures. We identified transcriptional changes in OSNs, sustentacular cells, and resident immune cells to each condition. This indicated that environmental olfactory exposures drive changes to multiple cell types in the MOE. To our knowledge, this is the first study to identify effects of environmental olfactory exposures on cell-type specific transcription at homeostasis. These findings highlight the potential importance of multi-cellular interactions and communication in regulation of the olfactory epithelium.

Diverse epigenetic regulatory mechanisms ensure and modulate cellular diversity. The histone 3 lysine 9 me3 (H3K9me3) post-translational modification participates in silencing lineage-inappropriate genes by restricting access of transcription factors and other regulatory proteins to genes that control cell fate. Mouse olfactory sensory neurons (OSNs) select one olfactory receptor (OR) gene out of 2600 possibilities. This monoallelic and stochastic OR choice occurs as OSNs differentiate and undergo dramatic changes in nuclear architecture. OR genes from different chromosomes converge into specialized nuclear bodies and chromatin compartments, as H3K9me3 and chromatin binding proteins including heterochromatin protein 1 (HP1) are incorporated. In this work, we have uncovered an unexpected role for HP1β in OR choice and neuronal identity that cannot be rescued by HP1α in vivo. With the use of a conditional knock-in mouse model, that after CRE expression replaces HP1β with HP1α, we observe changes in H3K9me3 levels and DNA accessibility over OR gene clusters. These changes alter the expression patterns that partition the mouse olfactory epithelium into five OR expression zones, which results in a reduced OR repertoire that leads to a loss of olfactory sensory neuron diversity. We propose that HP1β modulates the competition of OR promoters for enhancers to promote receptor diversity by establishing repression gradients in a zonal fashion.

2-Ethyl-1-hexanol (2EH) is a volatile organic compound that can cause sick building syndrome and can be released from flooring materials for more than 10years through the hydrolysis of compounds with 2-ethylhexyl moieties. Previous studies using mice have raised concerns about tissue-damaging effects on the olfactory epithelium (OE), olfactory bulb (OB), brain, lungs, and skin. A subchronic mouse study observed degeneration of OE at concentrations as low as 20ppm. However, the effects of long-term exposure to 2EH remain unclear. This study aimed to elucidate the histopathological effects of chronic exposure to 2EH relative to its airborne concentration. Ten-week-old male ICR mice were exposed to 0, 0.5, 10, or 100ppm 2EH by inhalation for 8h/d, 5 d/wk, for 6months. Subsequently, histopathological analysis was conducted. At 0.5ppm, acute and chronic inflammation were observed in the OE and alveoli, with tissue repair in the OE, and thickening of the epithelium and smooth muscle in the bronchi. Metaplasia of OE in the respiratory epithelium was induced at 10 and 100ppm. At all concentrations, the number of mature neurons in the OE and immature neurons in the OB decreased, suggesting that olfactory nerve activity was suppressed. Fibroblasts increased in the dorsal skin. Microglia in the hippocampus and amygdala increased in number. Chronic inhalation exposure at as low as 0.5ppm caused inflammation in the OE, OB, segmental bronchi, and alveoli, and affected the target area of OB neurons.