Shu Kikuta

Neurons in the anterior olfactory nucleus pars externa detect right or left localization of odor sources

Rodents can localize odor sources by comparing odor inputs to the right and left nostrils. However, the neuronal circuits underlying such odor localization are not known. We recorded neurons in the anterior olfactory nucleus (AON) while administering odors to the ipsilateral or contralateral (ipsi- or contra-) nostril. Neurons in the AON pars externa (AONpE) showed respiration phase-locked excitatory spike responses to ipsinostril-only stimulation with a category of odorants, and inhibitory responses to contranostril-only stimulation with the same odorants. Simultaneous odor stimulation of the ipsi- and contranostrils elicited significantly smaller responses than ipsinostril-only stimulation, indicating that AONpE neurons subtract the contranostril odor inputs from ipsinostril odor inputs. An ipsilateral odor source induced larger responses than a centrally located source, whereas an odor source at the contralateral position elicited inhibitory responses. These results indicate that individual AONpE neurons can distinguish the right or left position of an odor source by referencing signals from the two nostrils.

Compensatory Rapid Switching of Binasal Inputs in the Olfactory Cortex

Odors are inhaled through the nostrils into two segregated nasal passages and detected by sensory neurons in the bilateral olfactory epithelia. Airflow through the two nasal passages is usually asymmetrical because of alternating changes in nasal mucosal congestion. Here we show that neurons in the anterior olfactory nucleus (AON) of the adult rat olfactory cortex are ordinarily dominated by ipsi-nasal inputs and that binasal neurons in the AON respond to ipsilateral and contralateral nasal inputs with nearly equivalent odorant category selectivity. Deprivation of ipsilateral nasal inputs by unilateral nostril obstruction greatly enhanced the response to contralateral odor stimulation, in a reversible manner, in ∼33% of AON neurons within only several minutes. In 27% of AON neurons that showed spike responses induced by the inspiration of room air, ipsilateral nasal obstruction initially suppressed respiration phase-locked spike discharges and, several minutes later, induced respiration phase-locked discharges with longer delays between inspiration and response. Recordings from AON neurons in rats with anterior commissure (AC) transection indicated that the resumed respiration phase-locked discharges with longer delays were mediated by the contralateral pathway via the AC. The ipsi-nasal occlusion-induced switching of nasal inputs to individual AON neurons shows that a subset of AON neurons in the adult rat has neuronal mechanisms for rapid nostril dominance plasticity, which may enable both right and left olfactory cortices to preserve their responsiveness to the external odor world, despite reciprocal changes in nasal airflow.

Sensory Deprivation Disrupts Homeostatic Regeneration of Newly Generated Olfactory Sensory Neurons after Injury in Adult Mice

Although it is well known that injury induces the generation of a substantial number of new olfactory sensory neurons (OSNs) in the adult olfactory epithelium (OE), it is not well understood whether olfactory sensory input influences the survival and maturation of these injury-induced OSNs in adults. Here, we investigated whether olfactory sensory deprivation affected the dynamic incorporation of newly generated OSNs 3, 7, 14, and 28 d after injury in adult mice. Mice were unilaterally deprived of olfactory sensory input by inserting a silicone tube into their nostrils. Methimazole, an olfactotoxic drug, was also injected intraperitoneally to bilaterally ablate OSNs. The OE was restored to its preinjury condition with new OSNs by day 28. No significant differences in the numbers of olfactory marker protein-positive mature OSNs or apoptotic OSNs were observed between the deprived and nondeprived sides 0–7 d after injury. However, between days 7 and 28, the sensory-deprived side showed markedly fewer OSNs and mature OSNs, but more apoptotic OSNs, than the nondeprived side. Intrinsic functional imaging of the dorsal surface of the olfactory bulb at day 28 revealed that responses to odor stimulation were weaker in the deprived side compared with those in the nondeprived side. Furthermore, prevention of cell death in new neurons 7–14 d after injury promoted the recovery of the OE. These results indicate that, in the adult OE, sensory deprivation disrupts compensatory OSN regeneration after injury and that newly generated OSNs have a critical time window for sensory-input-dependent survival 7–14 d after injury.

Cigarette Smoke Delays Regeneration of the Olfactory Epithelium in Mice

The olfactory system is a unique part of the mammalian nervous system due to its capacity for neurogenesis and the replacement of degenerating receptor neurons. Cigarette smoking is a major cause of olfactory dysfunction. However, the mechanisms by which cigarette smoke impairs the regenerative olfactory receptor neurons (ORNs) remain unclear. Here, we investigated the influence of cigarette smoke on ORN regeneration following methimazole-induced ORN injury. Administration of methimazole caused detachment of the olfactory epithelium from the basement membrane and induced olfactory dysfunction, thus enabling us to analyze the process of ORN regeneration. We found that intranasal administration of cigarette smoke solution (CSS) suppressed the recovery of ORNs and olfaction following ORN injury. Defective ORN recovery in CSS-treated mice was not associated with any change in the number of SOX2+ ORN progenitor cells in the basal layer of the OE, but was associated with impaired recovery of GAP43+ immature ORNs. In the nasal mucosa, mRNA expression levels of neurotrophic factors such as brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-5, glial cell-derived neurotrophic factor, and insulin-like growth factor-1 (IGF-1) were increased following OE injury, whereas CSS administration decreased the ORN injury-induced IGF-1 expression. Administration of recombinant human IGF-1 prevented the CSS-induced suppression of ORN recovery following injury. These results suggest that CSS impairs regeneration of ORNs by suppressing the development of immature ORNs from ORN progenitors, at least partly by reducing IGF-1 in the nasal mucosa.

Denervation of nasal mucosa induced by posterior nasal neurectomy suppresses nasal secretion, not hypersensitivity, in an allergic rhinitis rat model.

The posterior nasal nerve is the dominant source of the parasympathetic, sympathetic, and sensory fibers that innervate the nasal respiratory mucosa. Therefore, a posterior nasal neurectomy (PNN) is thought to induce denervation of the nasal mucosa and relieve the nasal symptoms of allergic rhinitis. However, the underlying mechanisms and therapeutic action of PNN remain unknown. To investigate the impact of PNN-induced denervation of the nasal mucosa on allergic rhinitis, we developed a rat model of PNN and examined the effects of PNN on allergic rhinitis in ovalbumin-sensitized rats. This rat model of PNN was characterized by the depletion of nerve fibers, choline acetyltransferase, and neuropeptides (eg, substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, and neuropeptide Y) in the nasal respiratory mucosa. These animals exhibited nasal gland and goblet cell hypertrophy in the septal mucosa and atrophy of the submucosal gland in the lateral nasal wall, as well as reduced nasal secretion due to deficient acetylcholine synthesis. In an ovalbumin-sensitized model of allergic rhinitis, PNN also induced the depletion of nerve fibers, choline acetyltransferase, and neuropeptides in the nasal mucosa and suppressed nasal secretion. However, PNN did not affect mucosal thickening, eosinophil and mast cell infiltration, interleukin-4 and interferon-γ mRNA expression, and allergic symptoms (ie, sneezing and nasal scratching). These results suggest that the peripheral nerves and corresponding neuropeptides regulate nasal secretion, but not hypersensitivity, in allergic rhinitis, and that allergic rhinitis-related mucosal reactions occur in a highly denervated mucosa after PNN. Posterior nasal neurectomy may be a therapeutic option for the treatment of hyperrhinorrhea, but not allergic rhinitis hypersensitivity.

Differences in Postoperative Hearing Outcomes and Vertigo in Patients with Otosclerosis Treated with Laser-Assisted Stapedotomy versus Stapedectomy.

Background: Otosclerosis is an abnormal bone growth in the otic capsule that can result in hearing loss. In this study, we compared postoperative hearing outcomes and vestibular symptoms between patients treated with laser-assisted stapedotomy versus stapedectomy. Methods: The medical charts of 99 ears treated with stapes surgery were retrospectively reviewed. Results: A stapedotomy, partial stapedectomy, or total stapedectomy was conducted in 77, 16, and 56 ears, respectively. The ears treated with partial- and total stapedectomies were unified into one stapedectomy group. The postoperative changes in the air-bone gap after stapedotomies were significantly larger than those after stapedectomies at 1, 2, and 4 kHz. The postoperative changes in the air conduction threshold after stapedotomies were significantly larger than those after stapedectomies at 1, 2, 4, and 8 kHz. The postoperative changes in the bone conduction threshold at 0.5, 1, 2, and 4 kHz did not differ between the groups. The postoperative vertigo duration after stapedotomies was significantly shorter than that after stapedectomies. Conclusions: Surgery-induced sensorineural hearing losses were similar for stapedotomies and stapedectomies. However, stapedotomies were more effective and atraumatic than stapedectomies because of the better postoperative hearing results at middle and high frequencies and the shorter postoperative vertigo.

Correlation of basophil infiltration in nasal polyps with the severity of chronic rhinosinusitis

Chronic rhinosinusitis (CRS) represents a heterogeneous disease group characterized by local inflammation of the sinonasal tissues.1 It has been defined as symptomatic inflammation of the sinonasal mucosa that lasts more than 12 weeks as confirmed by computed tomography (CT) and nasal endoscopy.2 Generally, CRS is divided into 2 subsets based on endoscopic findings: CRS with nasal polyps (CRSwNP) and CRS without nasal polyps (CRSsNP).3 In Europe and the United States, eosinophilia is evident in nasal polyps (NPs) from patients with CRSwNP.4 In contrast, heterogeneity of CRSwNP has been reported in East Asian countries, such as Japan, Korea, and China, where the presence and extent of eosinophilia are variable and a significant proportion of NPs do not manifest local eosinophilia.5 Although the pathogenesis of CRS remains controversial, eosinophilic inflammation is considered at least partly responsible. Eosinophilic NPs contain an environment enriched for TH2 cytokines, including interleukin (IL) 4, IL-5, and IL-13.6 TH2 cytokines are believed to contribute to the pathogenesis of eosinophilic CRSwNP, with IL-5 and IL-13 inducing eosinophil recruitment and promoting their activation and IL-4 promoting the switching of the immunoglobulin to the IgE isotype.7 Basophils are reportedly increased in the bronchial submucosa of asthmatic patients and the nasal submucosa of patients with allergic rhinitis.8,9 Research is increasingly addressing the role of basophils in inducing TH2-type responses.10 Although CRSwNP is a highly TH2-biased disease, making the involvement of basophils likely, there are few reports of the involvement of basophils in CRS.11

Factors associated with the presence of drug-resistant bacteria and recurrent acute otitis media in children – a study in a private clinic

Conclusions. The proportion of drug-resistant bacteria was lower than previous reports. In children with acute otitis media (AOM), lower age, presence of multiple bacteria, and otitis media with effusion (OME) represented significant factors for recurrent AOM and the presence of drug-resistant bacteria. Objective. Recently, the proportion of drug-resistant bacteria has been increasing in children with AOM. We studied the proportion of drug-resistant bacteria and background factors for detection of drug-resistant bacteria and recurrent AOM in a private clinic. Subjects and methods. Subjects comprised 170 patients <12 years old with AOM. Middle ear fluid was collected and pathogenic bacteria were identified. The following factors were considered: age, sex, use of antibiotics in the past 1 month, past history of recurrent AOM, presence of OME, and multiple bacteria of the three main strains (Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis). Results. A total of 169 strains were detected in 77% of children with AOM. Drug-resistant bacteria comprised 44 of the 169 strains (26%). Lower age (p=0.001) and presence of multiple bacteria (p<0.001) represented significant factors for the presence of drug-resistant bacteria. OME was a significant factor for recurrent AOM (p<0.001).

Reduction of Proliferating Olfactory Cells and Low Expression of Extracellular Matrix Genes Are Hallmarks of the Aged Olfactory Mucosa

Background: The incidence of olfactory impairment increases with age; however, the detailed molecular and cellular mechanisms underlying this increase are yet to be determined. Methods: We examined the influence of aging on olfactory receptor neurons (ORNs), which are maintained by a unique stem cell system, from olfactory progenitor cells to mature ORNs, by histological comparisons of the physiological status of the olfactory epithelium between young adult and aged mice. Furthermore, we clarified the expression of genes encoding inflammatory cytokines, neurotrophins, growth factors, and extracellular matrix proteins to reveal the molecular mechanisms underlying olfactory impairment caused by aging. Results: The numbers of mature and immature ORNs, but not olfactory progenitors, decreased in the aged olfactory epithelium, with a concurrent reduction in Ki-67-positive proliferating cells. Transcriptome analyses revealed an increase in Il6, encoding a component of senescence-associated secretary phenotypes (SASP), and a decrease in Igf1, encoding a growth factor for ORNs, in the aged nasal mucosa. Interestingly, expression levels of several extracellular matrix genes, including Col1a2, decreased in the aged nasal mucosa. Consistent with the transcriptional changes, the number of Col1a2-GFP-positive cells decreased in the aged lamina propria. Conclusions: Our data suggest that reduction in ORN number and cell proliferation, reduced extracellular matrix gene expression, and increased SASP contribute to olfactory impairment during aging.

Intravenous olfactory test latency correlates with improvement in post-infectious olfactory dysfunction

Abstract Conclusion: This cohort study showed that onset latency in the intravenous olfactory test (IVO) may help predict when olfaction in patients with post-infectious olfactory dysfunction (PIOD) improves. Objectives: To identify factors that predict the olfactory improvement period in patients with PIOD. Methodology/Principal: All consecutive patients presenting with PIOD in 1994–2014 who were followed up for 2 years were identified retrospectively. The ability of demographic/clinical factors (age, sex, body mass index, presence/absence of allergic rhinitis, treatment/non-treatment with herbal medicines, patient dependence on herbal medicine treatment, presence/absence of diabetes mellitus, and smoking status) and olfactory test factors (response/no response and onset latency and duration in the IVO test, and detection and recognition scores on the T&T olfactory test) to predict the olfactory improvement period (defined respectively as the time from PIOD onset or olfactory testing to the first self-report of olfaction improvement) was analyzed by univariate and multivariate regression. Results: Of the 187 PIOD patients, the prognostic ability of demographic/clinical factors was analyzed in 65. None predicted the olfactory improvement period. Of the 65 patients, 20 did not respond in the IVO test. In the remaining 45 patients, onset latency (but not the other olfactory test factors) was a significant prognosticator of olfactory improvement period (R2=0.24, p = 0.003).