A new surgical technique to increase airflow in the olfactory cleft: superior turbinate lateralization procedure.

BACKGROUND: The olfactory cleft (OC) is the most important anatomical site for the maintenance of olfactory function. Obstruction of airflow in the OC by various conditions, such as inflammation, leads to poor olfactory function. Therefore, it is important to increase OC airflow while performing endoscopic sinus surgery (ESS). However, no technique to increase airflow has yet been established. METHODS: We designed a superior turbinate lateralization (STL) procedure that displaces the entire ST bone laterally by eliminating the connection between the posterior ST and the anterior wall of the sphenoid sinus. The effect of the STL procedure was investigated in terms of anatomy and olfactory function. RESULTS: ESS with the STL procedure was performed on seven patients with chronic rhinosinusitis and nasal polyps. The cross-sectional area of the OC at 3 months postoperatively was significantly larger than that before ESS. In addition, the Open Essence test and questionnaires revealed significantly improvements in sense of smell. Airflow in the OC was significantly higher in STL procedure group than in the non-STL procedure group. CONCLUSION: The STL procedure enlarges the bony framework of the OC, and by increasing OC airflow, facilitates the transport of odorants to the olfactory epithelium, thereby improving olfactory perception.

Structures and functions of the normal and injured human olfactory epithelium.

The olfactory epithelium (OE) is directly exposed to environmental agents entering the nasal cavity, leaving OSNs prone to injury and degeneration. The causes of olfactory dysfunction are diverse and include head trauma, neurodegenerative diseases, and aging, but the main causes are chronic rhinosinusitis (CRS) and viral infections. In CRS and viral infections, reduced airflow due to local inflammation, inflammatory cytokine production, release of degranulated proteins from eosinophils, and cell injury lead to decreased olfactory function. It is well known that injury-induced loss of mature OSNs in the adult OE causes massive regeneration of new OSNs within a few months through the proliferation and differentiation of progenitor basal cells that are subsequently incorporated into olfactory neural circuits. Although normal olfactory function returns after injury in most cases, prolonged olfactory impairment and lack of improvement in olfactory function in some cases poses a major clinical problem. Persistent inflammation or severe injury in the OE results in morphological changes in the OE and respiratory epithelium and decreases the number of mature OSNs, resulting in irreversible loss of olfactory function. In this review, we discuss the histological structure and distribution of the human OE, and the pathogenesis of olfactory dysfunction associated with CRS and viral infection.

Anesthetized animal experiments for neuroscience research.

Brain research has progressed with anesthetized animal experiments for a long time. Recent progress in research techniques allows us to measure neuronal activity in awake animals combined with behavioral tasks. The trends became more prominent in the last decade. This new research style triggers the paradigm shift in the research of brain science, and new insights into brain function have been revealed. It is reasonable to consider that awake animal experiments are more ideal for understanding naturalistic brain function than anesthetized ones. However, the anesthetized animal experiment still has advantages in some experiments. To take advantage of the anesthetized animal experiments, it is important to understand the mechanism of anesthesia and carefully handle the obtained data. In this minireview, we will shortly summarize the molecular mechanism of anesthesia in animal experiments, a recent understanding of the neuronal activities in a sensory system in the anesthetized animal brain, and consider the advantages and disadvantages of the anesthetized and awake animal experiments. This discussion will help us to use both research conditions in the proper manner.

Endoplasmic reticulum stress associated with lead (Pb)-induced olfactory epithelium toxicity in an olfactory dark basal cell line.

Lead (Pb) can damage organs and also have undesirable effects on neural development. To explore the effects of Pb on olfactory cells, we investigated Pb-induced cell toxicity in the DBC1.2 olfactory cell line, with a focus on endoplasmic reticulum (ER) stress, apoptosis, and necroptosis. Representative markers of ER stress, apoptosis, and necroptosis were analyzed by quantitative PCR. The mRNA expression levels of GRP94, GRP78, spliced XBP1, PERK, and ATF6 increased significantly after Pb exposure in a dose-dependent manner. The expression of Caspase 3 and Caspase 12 did not increase after Pb exposure, which suggested that apoptosis-induced cell death was not activated after Pb exposure. However, the mRNA of RIPK3 and MLKL showed increases in expression, which indicated that necroptosis-induced cell death was activated after Pb exposure. These results indicate that Pb exposure induced dose-dependent cytotoxicity through ER stress and necroptosis pathways in DBC1.2 cells, whereas the apoptosis pathway was not significantly stimulated. HEPES buffer showed a partial protective effect in terms of ER stress, apoptosis, and necroptosis. In summary, the necroptosis pathway plays a crucial rule in Pb exposure-induced cytotoxicity in olfactory cells.

Heterogeneous Damage to the Olfactory Epithelium in Patients with Post-Viral Olfactory Dysfunction.

OBJECTIVES: Post-viral olfactory dysfunction (PVOD) is a neurogenic disorder caused by a common cold virus. Based on the homology of deduced amino acid sequences, olfactory sensory neurons (OSNs) in both mice and humans express either class I or class II odorant receptor genes encoding class I and class II OSNs. The purpose of this study was to determine whether OSN damage in PVOD occurs uniformly in both neuron types. MATERIALS AND METHODS: The characteristics of PVOD patients were compared with those of patients with chronic rhinosinusitis (CRS) or post-traumatic olfactory dysfunction (PTOD). Briefly, subjects underwent orthonasal olfaction tests using five different odors (T&T odors) and a retronasal olfaction test using a single odor (IVO odor). The regions in the mouse olfactory bulb (OB) activated by the T&T and the IVO odors were also examined. RESULTS: Multivariate analysis of 307 cases of olfactory dysfunction (PVOD, 118 cases; CRS, 161 cases; and PTOD, 28 cases) revealed that a combination of responses to the IVO odor, but not to the T&T odors, is characteristic of PVOD, with high specificity (p < 0.001). Imaging analysis of GCaMP3 mice showed that the IVO odor selectively activated the OB region in which the axons of class I OSNs converged, whereas the T&T odors broadly activated the OB region in which axons of class I and class II OSNs converged. CONCLUSIONS: A response to T&T odors, but not IVO odor, in PVOD suggests that class I OSNs are injured preferentially, and that OSN damage in PVOD may occur heterogeneously in a neuron-type-dependent manner.

Long-term Outcomes of Non-vascularized Multilayer Fascial Closure Technique for Dural Repair in Endoscopic Transnasal Surgery: Efficacy, Durability, and Limitations.

OBJECTIVE: Non-vascularized multilayer fascial closure technique (NMFCT) can be used instead of nasoseptal flap reconstruction for dural repair in endoscopic transnasal surgery (ETS); however, due to the lack of blood supply, its long-term durability and possible limitations need to be clarified. METHODS: This was a retrospective study on patients who underwent ETS with intraoperative cerebrospinal fluid (CSF) leakage. We assessed the postoperative and delayed CSF leakage rates and the associated risk factors. RESULTS: Among 200 ETSs with intraoperative CSF leakage, 148 (74.0%) ETSs were performed for skull base pathologies other than pituitary neuroendocrine tumor. The mean follow-up period was 34.4 months. Esposito grade 3 leakage was confirmed in 148 (74.0%) cases. NMFCT was used either with (67 [33.5%]) or without (133 [66.5%]) lumbar drainage. There were 10 cases (5.0%) of postoperative CSF leakage that necessitated reoperation. In 4 other cases (2.0%), CSF leakage was suspected but lumbar drainage alone successfully restored the condition. Multivariate logistic regression analyses revealed that posterior skull base location (P < 0.01, odds ratio 11.5, 95% CI 1.99-2.17 × 102) and craniopharyngioma pathology (P = 0.03, odds ratio 9.4, 95% CI 1.25-1.92 × 102) were significantly associated with postoperative CSF leakage. No delayed leakage occurred during the observation period except for 2 patients who underwent multiple radiotherapies. CONCLUSIONS: NMFCT is a reasonable alternative with long-term durability, though vascularized flap may be a better choice for cases in which vascularity of the surrounding tissues is significantly impaired due to interventions including multiple radiotherapies.

Kashimé: A Novel Knotless Surgical Suture to Simplify Dural Stitches in Endoscopic Transnasal Surgery.

BACKGROUND: Dural suturing is an effective adjunct to skull base dural repair in endoscopic transnasal surgery, although it is technically cumbersome. Here, we presented a novel surgical suture "Kashimé" (Kono Seisakusho) that can be tightened without tying. OBJECTIVE: To examine the efficacy of Kashimé for skull base dural repair in endoscopic transnasal surgery. METHODS: Kashimé was used in 8 patients with skull base dural defects during nonpedicled flap-based multilayered skull base reconstruction to close or approximate the gaps between the dural edges or secure a free fascial graft. The time required for each dural stitch (passing a needle through the dura, pulling out the thread, and tightening it) and the incidence of postoperative cerebrospinal fluid leakage were the study end points. RESULTS: Based on our preliminary experiences with 12 stitches used, no postoperative cerebrospinal fluid leakage was observed. The learning curve was steep, and the mean (±SD) time was 127 (±44) seconds for a single stitching procedure, except for the first case. Regarding the metal artifact, although a beam hardening artifact was not observed on computed tomography, a 4- to 9-mm diameter image defect was observed on magnetic resonance imaging. CONCLUSION: Kashimé can help surgeons to complete a single dural stitch in endoscopic transnasal surgery for approximately 2 minutes. It may be an optimal tool for skull base reconstruction, but the efficacy and safety need to be investigated.

Sleep deprivation induces delayed regeneration of olfactory sensory neurons following injury.

The circadian system, which is essential for the alignment of sleep/wake cycles, modulates adult neurogenesis. The olfactory epithelium (OE) has the ability to generate new neurons throughout life. Loss of olfactory sensory neurons (OSNs) as a result of injury to the OE triggers the generation of new OSNs, which are incorporated into olfactory circuits to restore olfactory sensory perception. This regenerative potential means that it is likely that the OE is substantially affected by sleep deprivation (SD), although how this may occur remains unclear. The aim of this study is to address how SD affects the process of OSN regeneration following OE injury. Mice were subjected to SD for 2 weeks, which induced changes in circadian activity. This condition resulted in decreased activity during the night-time and increased activity during the daytime, and induced no histological changes in the OE. However, when subjected to SD during the regeneration process after OE injury, a significant decrease in the number of mature OSNs in the dorsomedial area of the OE, which is the only area containing neurons expressing NQO1 (quinone dehydrogenase 1), was observed compared to the NQO1-negative OE. Furthermore, a significant decrease in proliferating basal cells was observed in the NQO1-positive OE compared to the NQO1-negative OE, but no increase in apoptotic OSNs was observed. These results indicate that SD accompanied by disturbed circadian activity could induce structurally negative effects on OSN regeneration, preferentially in the dorsomedial area of the OE, and that this area-specific regeneration delay might involve the biological activity of NQO1.

High CT Attenuation Values Relative to the Brainstem Predict Fungal Hyphae Within the Sinus.

Objectives: There is currently no established objective diagnostic indicator for the differentiation of sinus fungal ball (SFB) from unilateral nonfungal chronic sinusitis (UCRS). This study evaluated whether computed tomography (CT) attenuation values relative to those of the brainstem (relative CT number) are useful for differentiating SFB from UCRS. Materials and Methods: Consecutive patients who were pathologically diagnosed with SFB or UCRS between 2013 and 2021 were retrospectively identified. The relative CT numbers of region of interest (ROIs) within the sinuses were compared between the two patient groups. Factors with predictive power for differentiating SFBs from UCRSs were identified by uni/multivariable logistic regression analyses. Results: One hundred and eighty-three patients with unilateral chronic sinusitis were finally analyzed (SFB, 86 cases; UCRS, 97 cases). Regardless of the presence or absence of calcified lesions, the relative CT numbers in SFB were significantly higher than those in UCRS. ROIs showing high relative CT numbers were those where fungal hyphae were present. In the uni/multivariable logistic regression analysis, age (p < 0.001), relative CT number (p < 0.001), and calcification (p = 0.002) had predictive value for distinguishing SFB from UCRS. Within those cases not showing calcification, age (p = 0.004) and relative CT number (p < 0.001) were predictive factors for differentiating SFB from UCRS. A relative CT number >1.5 was significantly associated with SFB (sensitivity, 70%; specificity, 91%), with a significantly larger area under the receiver operating characteristics curve than age. Conclusions: High relative CT numbers within the sinus are strongly associated with the presence of fungal hyphae, and measurement of relative CT number is a powerful adjunctive diagnostic method for distinguishing between SFB and UCRS.

Heterogeneous distribution of mature olfactory sensory neurons in human olfactory epithelium.

BACKGROUND: The olfactory cleft (OC) comprising the olfactory epithelium (OE) is the most important anatomical location for olfactory function. Endoscopic sinus surgery (ESS) is used to treat diseases related to the OC and improve olfactory dysfunction. However, iatrogenic OE injury occasionally occurs. Comprehensive knowledge of the olfactory region is required to avoid damage to the OE during endoscopic procedures. METHODS: Immunohistochemistry was performed on olfactory mucosa obtained from the unaffected side of olfactory neuroblastoma surgical specimens. The OE was defined as the epithelium containing mature olfactory sensory neurons (OSNs). The distribution and cell kinetics of the OE were examined. RESULTS: The OE was selectively localized to the anterior two-thirds of the superior turbinate (ST) and in the nasal septum (NS) just opposite to the ST; the OE was not detected within the mucosa of the superior meatus. The density of mature OSNs was high at the ethmoid tegmen but gradually decreased with distance from the ethmoid tegmen. The extent of cell death and proliferation was relatively even across the OE. Analysis of airflow profiles revealed that resection of inferior ST does not decrease airflow to the OC. CONCLUSION: The results indicate that the distribution and degree of differentiation of mature OSNs are heterogenous throughout the OE. Epithelial resection of the anterior or superior ST has the potential to damage olfactory function. Resection of the inferior or posterior ST or widening of the superior meatus is a safer alternative that does not damage mature OSNs or alter airflow to the OC.

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 ß 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.

High CT values relative to the brainstem differentiate inverted papillomas from nasal polyps.

OBJECTIVES: A diagnostic indicator for the differentiation of inverted papillomas (IPs) from inflammatory nasal polyps (NPs) has not been established. This study aimed to evaluate whether CT attenuation values relative to those of the brainstem (relative CT number) could be useful for differentiating IPs from NPs. MATERIAL AND METHODS: Consecutive patients who were pathologically diagnosed with IP or NP between 2005 and 2019 were retrospectively identified. Relative CT numbers were compared between the two patient groups. The factors with predictive power for differentiating IPs from NPs were identified by univariate and multivariate logistic regression analyses. RESULTS: One hundred and twenty-two sinonasal masses were finally analysed (IP, 51 cases; NP, 71 cases). Relative CT numbers were significantly higher in IP than in NP (P < 0.001). Univariate logistic regression analysis showed relative CT number, bone erosion and bone thickening to have predictive value for differentiating IPs from NPs (relative CT number, P < 0.001; bone erosion, p = 0.04; bone thickening, P < 0.001). In the multivariate logistic regression analysis, relative CT number and bone thickening had predictive value for distinguishing IP from NP (relative CT number, p < 0.001; bone thickening, p = 0.02). The optimum cut off value calculation from the area under the receiver operating characteristics curve indicated that a relative CT number >1.3 was significantly associated with IP (sensitivity, 72.6%; specificity, 87.3%). Within cases not showing bone thickening, only the relative CT number was a predictive factor for differentiating IPs from NPs in the univariate analysis. CONCLUSIONS: High relative CT numbers could potentially indicate IP, and their measurement could provide a basis for differentiating IPs from NPs.

Protective Effect of Insulin in Mouse Nasal Mucus Against Olfactory Epithelium Injury.

Insulin is present in nasal mucus and plays an important role in the survival and activity of individual olfactory sensory neurons (OSNs) via insulin receptor-mediated signaling. However, it is unclear whether insulin acts prophylactically against olfactotoxic drug-induced olfactory epithelium (OE) injury, and whether the degree of damage is affected by the concentration of insulin in the nasal mucus. The apoptosis-inducing drug methimazole was administered to the nasal mucus of diabetic and normal mice along with different concentrations of insulin. Immunohistochemical analysis was used to assess the relationship between damage to the OE and the mucus insulin concentration and the protective effect of insulin administration against eosinophilic cationic protein (ECP)-induced OE injury. Diabetic mice had lower concentrations of insulin in their nasal mucus than normal mice (diabetic vs. normal mice, p < 0.001). Methimazole administration reduced the number of OSNs in normal mice and had a more marked effect in diabetic mice. However, unilateral insulin administration prevented the methimazole-induced reduction in the number of OSNs on the ipsilateral side but not on the contralateral side (OSNs; Insulin vs. contralateral side, p < 0.001). Furthermore, intranasal ECP administration damaged the OE by inducing apoptosis (OSNs; ECP vs. contralateral side, p < 0.001), but this damage was largely prevented by insulin administration (OSNs; Insulin + ECP vs. contralateral side, p = 0.36), which maintained the number of mature OSNs. The severity of methimazole-induced damage to the OE is related to the insulin concentration in the nasal mucus (Correlation between the insulin concentration in nasal mucus and the numbers of OSNs, R2 = 0.91, p < 0.001), which may imply that nasal insulin protects OSNs and that insulin administration might lead to the development of new therapeutic agents for ECP-induced OE injury.

A murine model of eosinophilic chronic rhinosinusitis using the topical application of a vitamin D3 analog.

BACKGROUND: Eosinophilic chronic rhinosinusitis (ECRS) is a chronic inflammatory disease, characterized by eosinophilic infiltration, T-helper type 2 (Th2-type) response, and olfactory dysfunction. A master regulator of Th2-type inflammation, thymic stromal lymphopoietin (TSLP), is important for basophil activation. TSLP-elicited basophils are a key factor in the pathogenesis of ECRS. METHODS: In order to elucidate the mechanisms of ECRS in humans, we aimed to establish a murine model of ECRS based on TSLP production in response to the topical application of MC903 (a vitamin D3 analog) and the subsequent TSLP-induced basophil activation. Histological analyses were performed to assess immune cell infiltration into the nasal mucosa and to explore the impact of eosinophilic inflammation on the olfactory epithelium. The status of Th2-type inflammation was evaluated by quantitative real-time PCR and enzyme-linked immunosorbent assay (ELISA). RESULTS: Eosinophils, basophils, and M2 macrophages increased significantly in the nasal mucosa of the mice treated with MC903 and ovalbumin (OVA), compared to those treated with OVA alone or the controls. Quantitative real-time PCR and ELISA revealed elevated expression of interleukin (IL)-4, IL-5, IL-13, TSLP, the chemokine CCL11, and CCL24 in the nasal mucosa of the ECRS mice. In parallel, thinned olfactory epithelium and decreased mature olfactory sensory neurons were observed in the ECRS mice. CONCLUSIONS: Our model of ECRS displayed Th2-type inflammation in the sinonasal region, including both eosinophil infiltration and basophil infiltration. Additionally, olfactory epithelium turned out to be affected by eosinophilic inflammation. These features are consistent with the characteristics of the human ECRS.

Zone-specific damage of the olfactory epithelium under protein restriction.

Oxidative stress causes tissue damage, affecting age-related pathologies. Protein restriction (PR) provides a powerful intervention strategy for reducing oxidative stress, which may have a positive effect on individual organs. However, it is unknown whether PR intervention influences the olfactory system. Here, we investigated how 10 months of PR could affect the cell dynamics of the olfactory epithelium (OE) in mice. We found that PR reduced age-related loss of outer hair cells in the cochlea, providing preventive effects against age-related hearing loss. In contrast, PR resulted in reduced mature olfactory sensory neurons (OSNs), increased proliferative basal cells, and increased apoptotic OSNs in zone 1 (the only area containing neurons expressing NQO1 [quinone dehydrogenase 1]) of the OE in comparison with animals given a control diet. Substantial oxidative stress occurred in NQO1-positive cells and induced apoptotic OSNs in zone 1. These results indicate that in contrast to the positive effect on the auditory system, PR induces oxidative stress and structurally and functionally negative effects on OSNs in zone 1, which is probably involved in the bioactivation of NQO1.

Age-Related Olfactory Dysfunction: Epidemiology, Pathophysiology, and Clinical Management.

Like other sensory systems, olfactory function deteriorates with age. Epidemiological studies have revealed that the incidence of olfactory dysfunction increases at the age of 60 and older and males are more affected than females. Moreover, smoking, heavy alcohol use, sinonasal diseases, and Down's syndrome are associated with an increased incidence of olfactory dysfunction. Although the pathophysiology of olfactory dysfunction in humans remains largely unknown, studies in laboratory animals have demonstrated that both the peripheral and central olfactory nervous systems are affected by aging. Aged olfactory neuroepithelium in the nasal cavity shows the loss of mature olfactory neurons, replacement of olfactory neuroepithelium by respiratory epithelium, and a decrease in basal cell proliferation both in the normal state and after injury. In the central olfactory pathway, a decrease in the turnover of interneurons in the olfactory bulb (OB) and reduced activity in the olfactory cortex under olfactory stimulation is observed. Recently, the association between olfactory impairment and neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), has gained attention. Evidence-based pharmacotherapy to suppress or improve age-related olfactory dysfunction has not yet been established, but preliminary results suggest that olfactory training using odorants may be useful to improve some aspects of age-related olfactory impairment.

High CT attenuation values relative to the brainstem may predict squamous cell carcinoma arising from inverted papilloma.

Background: A diagnostic indicator for differentiating squamous cell carcinomas (SCCs) from inverted papillomas (IPs) has not been established. Objectives: This study aimed to evaluate whether CT attenuation values relative to those of the brainstem (relative CT number) could be useful in differentiating IPs from SCCs. Material and Methods: Consecutive patients who were pathologically diagnosed with IP or SCC between 2007 and 2017 were retrospectively identified. Relative CT numbers were compared between the two patient groups. The factors with predictive power for differentiating IPs from SCCs were identified by univariate and multivariate logistic regression analyses. Results: Fifty-four sinonasal tumour cases were finally analysed (IP, 25 cases; SCC, 29 cases). Relative CT numbers were significantly higher in SCC than in IP (p < .001). The univariate logistic regression analysis showed BMI, relative CT number, and disease duration to have predictive value for differentiating IPs from SCCs. In the multivariate logistic regression analysis, only the relative CT number had predictive value for distinguishing IP from SCC (odds ratio, 1.97), with a relative CT number of ≥1.4 being significantly associated with SCC. Conclusions: High relative CT numbers could potentially be used to identify SCCs, and their measurement could provide a basis for differentiating IPs from SCCs.

Caloric restriction reduces basal cell proliferation and results in the deterioration of neuroepithelial regeneration following olfactotoxic mucosal damage in mouse olfactory mucosa.

The effects of caloric restriction (CR) on cell dynamics and gene expression in the mouse olfactory neuroepithelium are evaluated. Eight-week-old male C57BL/6 mice were fed either control pellets (104 kcal/week) or CR pellets (67 kcal/week). The cytoarchitecture of the olfactory neuroepithelium in the uninjured condition and its regeneration after injury by an olfactotoxic chemical, methimazole, were compared between mice fed with the control and CR diets. In the uninjured condition, there were significantly fewer olfactory marker protein (OMP)-positive olfactory receptor neurons and Ki67-positive proliferating basal cells at 3 months in the CR group than in the control group. The number of Ki67-positive basal cells increased after methimazole-induced mucosal injury in both the control and the CR groups, but the increase was less robust in the CR group. The recovery of the neuroepithelium at 2 months after methimazole administration was less complete in the CR group than in the control group. These histological changes were region-specific. The decrease in the OMP-positive neurons was prominent in the anterior region of the olfactory mucosa. Gene expression analysis using a DNA microarray and quantitative real-time polymerase chain reaction demonstrated that the expression levels of two inflammatory cytokines, interleukin-6 and chemokine ligand 1, were elevated in the olfactory mucosa of the CR group compared with the control group. These findings suggest that CR may be disadvantageous to the maintenance of the olfactory neuroepithelium, especially when it is injured.

Dorsal-zone-specific reduction of sensory neuron density in the olfactory epithelium following long-term exercise or caloric restriction.

Exercise (Ex) and caloric restriction (CR) reduce oxidative stress and improve organ function. For instance, voluntary Ex or CR is known to reduce age-related cochlear damage in male C57BL/6J mice. However, the effect of Ex and CR on the olfactory system is unknown. In this study, we confirmed the positive effect of Ex and CR on age-related cochlear damage, but found that Ex and CR affected negatively cell dynamics in the olfactory epithelium (OE) by reducing the number of mature olfactory sensory neurons (OSNs) and increasing the number of proliferative basal cells and apoptotic OSNs in the dorsal zone of the olfactory epithelium (OE), which contains neurons expressing NADPH quinone oxido-reductase 1 (NQO1). In addition, these interventions resulted in lower odor-induced c-fos expression in areas of the olfactory bulb receiving projections from dorsal-zone OSNs than in areas receiving ventral-zone projections. Further, we observed substantial oxidative stress in NQO1-positive cells and apoptotic OSNs in the dorsal zone in Ex and CR animals. These results suggest that, in contrast to their positive effects in other organs, Ex and CR facilitate oxidative stress and negatively impact structure and function in dorsal-zone OSNs, probably in association with NQO1 bioactivation.

Cigarette Smoke-Induced Cell Death Causes Persistent Olfactory Dysfunction in Aged Mice.

Introduction: Exposure to cigarette smoke is a cause of olfactory dysfunction. We previously reported that in young mice, cigarette smoke damaged olfactory progenitors and decreased mature olfactory receptor neurons (ORNs), then, mature ORNs gradually recovered after smoking cessation. However, in aged populations, the target cells in ORNs by cigarette smoke, the underlying molecular mechanisms by which cigarette smoke impairs the regenerative ORNs, and the degree of ORN regeneration after smoking cessation remain unclear. Objectives: To explore the effects of cigarette smoke on the ORN cell system using an aged mouse model of smoking, and to investigate the extent to which smoke-induced damage to ORNs recovers following cessation of exposure to cigarette smoke in aged mice. Methods: We intranasally administered a cigarette smoke solution (CSS) to 16-month-old male mice over 24 days, then examined ORN existence, cell survival, changes of inflammatory cytokines in the olfactory epithelium (OE), and olfaction using histological analyses, gene analyses and olfactory habituation/dishabituation tests. Results: CSS administration reduced the number of mature ORNs in the OE and induced olfactory dysfunction. These changes coincided with an increase in the number of apoptotic cells and Tumor necrosis factor (TNF) expression and a decrease in Il6 expression. Notably, the reduction in mature ORNs did not recover even on day 28 after cessation of treatment with CSS, resulting in persistent olfactory dysfunction. Conclusion: In aged mice, by increasing ORN death, CSS exposure could eventually overwhelm the regenerative capacity of the OE, resulting in continued reduction in the number of mature ORNs and olfactory dysfunction.